Internet-Draft Header Protection S/MIME May 2021
Gillmor, et al. Expires 28 November 2021 [Page]
Workgroup:
LAMPS Working Group
Internet-Draft:
draft-ietf-lamps-header-protection-05
Published:
Intended Status:
Standards Track
Expires:
Authors:
D.K. Gillmor
American Civil Liberties Union
B. Hoeneisen
pEp Foundation
A. Melnikov
Isode Ltd

Header Protection for S/MIME

Abstract

S/MIME version 3.1 has introduced a feasible standardized option to accomplish Header Protection. However, few implementations generate messages using this structure, and several legacy and non-legacy implementations have revealed rendering issues at the receiving side. Clearer specifications regarding message processing, particularly with respect to header sections, are needed in order to resolve these rendering issues. Some mail user agents are also sending and receiving cryptographically-protected message headers using a different structure.

In order to help implementers to correctly compose and render email messages with Header Protection, this document updates S/MIME Header Protection specifications with additional guidance on MIME format, sender and receiver processing.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 28 November 2021.

Table of Contents

1. Introduction

Privacy and security issues regarding email Header Protection in S/MIME have been identified for some time. Most current implementations of cryptographically-protected electronic mail protect only the body of the message, which leaves significant room for attacks against otherwise-protected messages. For example, lack of header protection allows an attacker to substitute the message subject and/or author.

This document describes two different structures for how message headers can be cryptographically protected, and provides guidance for implementers of MUAs that generate and interpret such messages. It takes particular care to ensure that messages interact reasonably well with legacy MUAs.

1.1. Two Schemes of Protected Headers

Unfortunately, there are two different schemes for cryptographically-protected email headers that may be in use on the Internet today. This document addresses them both and provides guidance to implementers.

One scheme is the form specified in S/MIME 3.1 and later, which involves wrapping a message/rfc822 MIME object with a Cryptographic Envelope. This document calls this scheme "Wrapped Message", and it is documented in more detail in [RFC8551]. Experience has shown that this form does not interact well with some legacy MUAs (see Section 1.2).

Consequently, another form of header protection is produced and consumed by some MUAs, where the protected headers are placed directly on the Cryptographic Payload, without using an intervening message/* MIME object. This document calls this scheme "Injected Headers", and it is documented in more detail in [I-D.autocrypt-lamps-protected-headers].

1.2. Problems with Wrapped Messages

Several legacy MUAs have revealed rendering issues when dealing with a message with headers protected by the Wrapped Message scheme. In some cases the user sees an attachment suggesting a forwarded email message, which -- in fact -- contains the protected email message that should be rendered directly. For these cases, the user can click on the attachment to view the protected message. However, there have also been reports of email clients displaying garbled text, or sometimes nothing at all. In those cases the email clients on the receiving side are (most likely) not fully MIME-capable.

The following shortcomings have been identified to cause these issues:

  • Broken or incomplete implementations
  • Lack of a simple means to distinguish "forwarded message" and "wrapped message" (for the sake of Header Protection)
  • Not enough guidance with respect to handling of Header Fields on both the sending and the receiving side

1.3. Problems with Injected Headers

A legacy MUA dealing with an encrypted message that has some header fields obscured using the Injected Headers scheme will not render the obscured header fields to the user at all. A workaround "legacy display" mechanism is provided in this document, which some legacy MUAs will render to the user, albeit not in the same location that the header fields would normally be rendered. However, some legacy MUAs also fail to render the "legacy display" part, leaving the obscured header fields hidden from users of those MUAs.

1.4. Motivation

Furthermore, the need (technical) Data Minimization, which includes data sparseness and hiding all technically concealable information, has grown in importance over the past several years. In addition, backwards compatibility must be considered when it is possible to do so without compromising privacy and security.

No mechanism for Header Protection has been standardized for PGP/MIME (Pretty Good Privacy) [RFC3156] yet. PGP/MIME developers have implemented ad-hoc header-protection, and would like to see a specification that is applicable to both S/MIME and PGP/MIME.

This document describes the problem statement (Section 2), generic use cases (Section 3) and the specification for Header Protection (Section 4) with guidance on MIME format, sender and receiver processing .

[I-D.ietf-lamps-header-protection-requirements] defines the requirements that this specification is based on.

This document is in an early draft state and contains a proposal on which to base future discussions of this topic. In any case, the final mechanism is to be determined by the IETF LAMPS WG.

1.5. Other Protocols to Protect Email Headers

A range of protocols for the protection of electronic mail (email) exists, which allows one to assess the authenticity and integrity of the email headers section or selected Header Fields from the domain-level perspective, specifically DomainKeys Identified Mail (DKIM) [RFC6376], as used by Domain-based Message Authentication, Reporting, and Conformance (DMARC) [RFC7489]. These protocols provide a domain-based reputation mechanism that can be used to mitigate some forms of unsolicited email (spam). At the same time, these protocols can provide a level of cryptographic integrity and authenticity for some headers, depending on how they are used. However, integrity protection and proof of authenticity are both tied to the domain name of the sending e-mail address, not the sending address itself, so these protocols do not provide end-to-end protection, and are incapable of providing any form of confidentiality.

1.6. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

1.7. Terms

The following terms are defined for the scope of this document:

  • Man-in-the-middle (MITM) attack: cf. [RFC4949], which states: "A form of active wiretapping attack in which the attacker intercepts and selectively modifies communicated data to masquerade as one or more of the entities involved in a communication association."

    Note: Historically, MITM has stood for 'Man-in-the-middle'. However, to indicate that the entity in the middle is not always a human attacker, MITM can also stand for 'Machine-in-the-middle' or 'Meddler-in-the-middle'.

  • S/MIME: Secure/Multipurpose Internet Mail Extensions (cf. [RFC8551])
  • PGP/MIME: MIME Security with OpenPGP (cf. [RFC3156])
  • Message: An Email Message consisting of Header Fields (collectively called "the Header Section of the message") followed, optionally, by a Body; cf. [RFC5322].

    Note: To avoid ambiguity, this document does not use the terms "Header" or "Headers" in isolation, but instead always uses "Header Field" to refer to the individual field and "Header Section" to refer to the entire collection; cf. [RFC5322].

  • Header Field (HF): cf. [RFC5322] Header Fields are lines beginning with a field name, followed by a colon (":"), followed by a field body (value), and terminated by CRLF.
  • Header Section (HS): The Header Section is a sequence of lines of characters with special syntax as defined in [RFC5322]. It is the (top) section of a Message containing the Header Fields.
  • Body: The Body is simply a sequence of bytes that follows the Header Section and is separated from the Header Section by an empty line (i.e., a line with nothing preceding the CRLF); cf [RFC5322]. It is the (bottom) section of Message containing the payload of a Message. Typically, the Body consists of a (possibly multipart) MIME [RFC2045] construct.
  • MIME Header Fields: Header Fields describing content of a MIME entity [RFC2045], in particular the MIME structure. Each MIME Header Field name starts with "Content-" prefix.
  • MIME Header Section (part): The collection of MIME Header Fields. "MIME Header Section" refers to a Header Sections that contains only MIME Header Fields, whereas "MIME Header Section part" refers to the MIME Header Fields of a Header Section that - in addition to MIME Header Fields - also contains non-MIME Header Fields.
  • Essential Header Fields (EHF): The minimum set of Header Fields an Outer Message Header Section SHOULD contain; cf. Appendix C.1.2.5.
  • Header Protection (HP): cryptographic protection of email Header Sections (or parts of it) for signatures and/or encryption
  • Protection Levels (PL): The level of protection applied to a Message, e.g. 'signature and encryption' or 'signature only' (cf. Section 3.2).
  • Protected: Portions of a message that have had any Protection Levels applied.
  • Protected Message: A Message that has had any Protection Levels applied.
  • Unprotected: Portions of a Message that has had no Protection Levels applied.
  • Unprotected Message: A Message that has had no Protection Levels applied.
  • Submission Entity: The entity which executes further processing of the Message (incl. transport towards the receiver), after protection measures have been applied to the Message.

    Note: The Submission Entity varies among implementations, mainly depending on the stage where protection measures are applied: E.g. a Message Submission Agent (MSA) [RFC6409] or another (proprietary) solution. The latter is particularly relevant, if protection is implemented as a plugin solution. Some implementations may determine the destination recipients by reading the To, Cc and Bcc Header Fields of the Outer Message.

  • Original Message (OrigM): The Message to be protected before any protection-related processing has been applied on the sending side. If the source is not a "message/rfc822" Message, OrigM is defined as the "virtual" Message that would be constructed for sending it as unprotected email.
  • Inner Message (InnerM): The Message to be protected which has had wrapping and protection measures applied on the sending side OR the resulting Message once decryption and unwrapping on the receiving side has been performed. Typically, the Inner Message is in clear text. The Inner Message is a subset of (or the same as) the Original Message. The Inner Message must be the same on the sending and the receiving side.
  • Outer Message (OuterM): The Message as provided to the Submission Entity or received from the last hop respectively. The Outer Message normally differs on the sending and the receiving side (e.g. new Header Fields are added by intermediary nodes).
  • Receiving User Facing Message (RUFM): The Message used for rendering at the receiving side. Typically this is the same as the Inner Message.
  • Data Minimization: Data sparseness and hiding of all technically concealable information whenever possible.
  • Cryptographic Layer, Cryptographic Payload, Cryptographic Envelope, Structural Headers, and MUA are all used as defined in [I-D.dkg-lamps-e2e-mail-guidance]
  • User-Facing Headers are defined in [I-D.autocrypt-lamps-protected-headers].
  • Legacy MUA: a MUA that does not understand protected headers as described in this document. A Legacy Non-Crypto MUA is incapable of doing any end-to-end cryptographic operations. A Legacy Crypto MUA is capable of doing cryptographic operations, but does not understand or generate protected headers.
  • Wrapped Message: The protected headers scheme that uses the mechanism described in [RFC8551], where the Cryptographic Payload is a message/rfc822 or message/global MIME object.
  • Injected Headers: The protected headers scheme that uses the mechanism described in [I-D.autocrypt-lamps-protected-headers], where the protected headers are inserted on the Cryptographic Payload directly.
  • Header Confidentiality Policy: documented in Section 4.1.2.2

2. Problem Statement

The LAMPS charter contains the following Work Item:

In the following a set of challenges to be addressed:

[[ TODO: Enhance this section, add more items to the following. ]]

2.1. Privacy

  • (Technical) Data Minimization, which includes data sparseness and hiding all technically concealable information whenever possible

2.2. Security

2.3. Usability

  • Improved User interaction / User experience, in particular at the receiving side

2.4. Interoperability

  • Interoperability with [RFC8551] implementations

3. Use Cases

In the following, the reader can find a list of the generic use cases that need to be addressed for Messages with Header Protection (HP). These use cases apply regardless of technology (S/MIME, PGP/MIME, etc.) used to achieve HP.

3.1. Interactions

The following use cases assume that at least the sending side supports Header Protection as specified in this document. Receiving sides that support this specification are expected to be able to distinguish between Messages that use Header Protection as specified in this document, and (legacy) Mail User Agents (MUAs) which do not implement this specification.

[[ TODO: Verify once solution is stable and update last sentence. ]]

3.1.1. Main Use Case

Both the sending and receiving side (fully) support Header Protection as specified in this document.

The main use case is specified in Section 4.1.

3.1.2. Backward Compatibility Use Cases

Regarding backward compatibility, the main distinction is based on whether or not the receiving side conforms to MIME according to [RFC2046], ff., which in particular also includes Section 2 of [RFC2049] on "MIME Conformance". The following excerpt is contextually relevant:

  A mail user agent that is MIME-conformant MUST:

  [...]

       -- Recognize and display at least the RFC822 message
       encapsulation (message/rfc822) in such a way as to
       preserve any recursive structure, that is, displaying
       or offering to display the encapsulated data in
       accordance with its media type.

       -- Treat any unrecognized subtypes as if they were
       "application/octet-stream".

  [...]

  An MUA that meets the above conditions is said to be MIME-
  conformant.  A MIME-conformant MUA is assumed to be "safe" to
  send virtually any kind of properly-marked data to users of
  such mail systems, because these systems are, at a minimum,
  capable of treating the data as undifferentiated binary, and
  will not simply splash it onto the screen of unsuspecting
  users.

[[ TODO: The compatibility of legacy HP systems with this new solution, and how to handle issues surrounding future maintenance for these legacy systems, will be decided by the LAMPS WG. ]]

3.1.2.1. Receiving Side MIME-Conformant

The sending side (fully) supports Header Protection as specified in this document, while the receiving side does not support this specification. However, the receiving side is MIME-conformant according to [RFC2045], ff. (cf. Section 3.1.2).

This use case is specified in Section 4.2.1.

Note: This case should perform as expected if the sending side applies this specification as outlined in Section 4.1.

[[ TODO: Verify once solution is stable and update last sentence. ]]

3.1.2.2. Receiving Side Not MIME-Conformant

The sending side (fully) supports Header Protection as specified in this document, while the receiving side does not support this specification. Furthermore, the receiving side is not MIME-conformant according to [RFC2045], ff. (cf. Section 3.1.2).

This use case is specified in Section 4.2.2.

3.2. Protection Levels

3.2.1. In-Scope

The following Protection Levels are in scope for this document:

a) Signature and encryption

Messages containing a cryptographic signature, which are also
encrypted.

b) Signature only

Messages containing a cryptographic signature, but which are not
encrypted.

3.2.2. Out-of-Scope

Legacy implementations, implementations not (fully) compliant with this document or corner-cases may lead to further Protection Levels to appear on the receiving side, such as (list not exhaustive):

  • Triple wrap
  • Encryption only
  • Encryption before signature
  • Signature and encryption, but:

    • Signature fails to validate
    • Signature validates but the signing certificate revoked
  • Signature only, but:

    • with multiple valid signatures, layered atop each other

These Protection Levels, as well as any further Protection Levels not listed in Section 3.2.1 are beyond the scope of this document.

4. Specification

This section contains the specification for Header Protection in S/MIME to update and clarify Section 3.1 of [RFC8551] (S/MIME 4.0).

Note: It is likely that PGP/MIME [RFC3156] will also incorporate this specification or parts of it.

This specification applies to the Protection Levels "signature & encryption" and "signature only" (cf. Section 3.2):

Sending and receiving sides MUST implement the "signature and encryption" Protection Level, which SHOULD be used as default on the sending side.

Certain implementations may decide to send "signature only" Messages, depending on the circumstances and customer requirements. Sending sides MAY and receiving sides MUST implement "signature only" Protection Level.

It generally is NOT RECOMMENDED to send a Message with any other Protection Level. On the other hand, the receiving side must be prepared to receive Messages with other Protection Levels.

[[ TODO: Further study is necessary to determine whether - and if yes to what extent - additional guidance for handling messages with other Protection Levels, e.g. "encryption only" at the receiving side should be included in this document. ]]

4.1. Main Use Case

This section applies to the main use case, where the sending and receiving side (fully) support Header Protection as specified herein (cf. Section 3.1.1).

Note: The sending side specification of the main use case is also applicable to the cases where the sending side (fully) supports Header Protection as specified herein, while the receiving side does not, but is MIME-conformant according to [RFC2045], ff. (cf. Section 3.1.2 and Section 3.1.2.1).

Further backward compatibility cases are defined in Section 4.2.

4.1.1. MIME Format

4.1.1.1. Introduction

As per S/MIME version 3.1 and later (cf. [RFC8551]), the sending client MAY wrap a full MIME message in a message/RFC822 wrapper in order to apply S/MIME security services to these header fields.

To help the receiving side to distinguish between a forwarded and a wrapped message, the Content-Type header field parameter "forwarded" is added as defined in [I-D.melnikov-iana-reg-forwarded].

The simplified (cryptographic overhead not shown) MIME structure of such an Email Message looks as follows:

  <Outer Message Header Section (unprotected)>

  <Outer Message Body (protected)>

    <MIME Header Section (wrapper)>

      <Inner Message Header Section>

      <Inner Message Body>

The following example demonstrates how an Original Message might be protected, i.e., the Original Message is contained as Inner Message in the Protected Body of an Outer Message. It illustrates the first Body part (of the Outer Message) as a "multipart/signed" (application/pkcs7-signature) media type:

Lines are prepended as follows:

  • "O: " Outer Message Header Section
  • "I: " Message Header Section
  • "W: " Wrapper (MIME Header Section)
  O: Date: Mon, 25 Sep 2017 17:31:42 +0100 (GMT Daylight Time)
  O: Message-ID: <e4a483cb-1dfb-481d-903b-298c92c21f5e@m.example.net>
  O: Subject: Meeting at my place
  O: From: "Alexey Melnikov" <alexey.melnikov@example.net>
  O: To: somebody@example.net
  O: MIME-Version: 1.0
  O: Content-Type: multipart/signed; charset=us-ascii; micalg=sha1;
  O:  protocol="application/pkcs7-signature";
  O:  boundary=boundary-AM

     This is a multipart message in MIME format.
     --boundary-AM
  W: Content-Type: message/RFC822; forwarded=no
  W:
  I: Date: Mon, 25 Sep 2017 17:31:42 +0100 (GMT Daylight Time)
  I: From: "Alexey Melnikov" <alexey.melnikov@example.net>
  I: Message-ID: <e4a483cb-1dfb-481d-903b-298c92c21f5e@m.example.net>
  I: MIME-Version: 1.0
  I: MMHS-Primary-Precedence: 3
  I: Subject: Meeting at my place
  I: To: somebody@example.net
  I: X-Mailer: Isode Harrier Web Server
  I: Content-Type: text/plain; charset=us-ascii

     This is an important message that I don't want to be modified.

     --boundary-AM
     Content-Transfer-Encoding: base64
     Content-Type: application/pkcs7-signature

     [[base-64 encoded signature]]

     --boundary-AM--

The Outer Message Header Section is unprotected, while the remainder (Outer Message Body) is protected. The Outer Message Body consists of the wrapper (MIME Header Section) and the Inner Message (Header Section and Body).

The wrapper is a simple MIME Header Section with media type "message/rfc822" containing a Content-Type header field parameter "forwarded=no" followed by an empty line.

If the source is an Original (message/rfc822) Message, the Inner Message Header Section is typically the same as (or a subset of) the Original Message Header Section, and the Inner Message Body is typically the same as the Original Message Body.

The Inner Message itself may contain any MIME structure.

Note: It is still to be decided by the LAMPS WG whether or not to recommend an alternative MIME format as described in Appendix C.1.1.1 (instead of the currently standardized and above defined format).

4.1.2. Sending Side

This section describes the process an MUA should use to apply cryptographic protection to an e-mail message with header protection. We start by describing the legacy message composition process as a baseline.

4.1.2.1. Composing a Cryptographically-Protected Message Without Header Protection

[I-D.dkg-lamps-e2e-mail-guidance] describes the typical process for a legacy crypto MUA to apply cryptographic protections to an e-mail message. That guidance and terminology is replicated here for reference:

  • origbody: the traditional unprotected message body as a well-formed MIME tree (possibly just a single MIME leaf part). As a well-formed MIME tree, origbody already has structural headers (Content-*) present.
  • origheaders: the intended non-structural headers for the message, represented here as a list of (h,v) pairs, where h is a header field name and v is the associated value. Note that these are header fields that the MUA intends to be visible to the recipient of the message. In particular, if the MUA uses the Bcc header during composition, but plans to omit it from the message (see section 3.6.3 of [RFC5322]), it will not be in origheaders.
  • crypto: The series of cryptographic protections to apply (for example, "sign with the secret key corresponding to X.509 certificate X, then encrypt to X.509 certificates X and Y"). This is a routine that accepts a MIME tree as input (the Cryptographic Payload), wraps the input in the appropriate Cryptographic Envelope, and returns the resultant MIME tree as output.

The algorithm returns a MIME object that is ready to be injected into the mail system:

  • Apply crypto to origbody, yielding MIME tree output
  • For each header name and value (h,v) in origheaders:

    • Add header h of output with value v
  • Return output
4.1.2.2. Header Confidentiality Policy

When composing an encrypted message with protected headers, the composing MUA needs a Header Confidentialiy Policy. In this document, we represent that Header Confidentiality Policy as a function hcp:

  • hcp(name, val_in) --> val_out: this function takes a header field name name and initial value val_in as arguments, and returns a replacement header value val_out. If val_out is the special value null, it mean that the header in question should be omitted from the set of headers visible outside the Cryptographic Envelope.

For example, an MUA that only obscures the Subject header field by replacing it with the literal string [...] and does not offer confidentiality to any other header fields would be represented as (in pseudocode):

hcp(name, val_in) --> val_out: if name is 'Subject': return '[...]' else: return val_in

Note that such a policy is only needed when the end-to-end protections include encryption (confidentiality). No comparable policy is needed for other end-to-end cryptographic protections (integrity and authenticity), as they are simply uniformly applied so that all header fields known by the sender have these protections.

This asymmetry is an unfortunate consequence of complexities in message delivery systems, some of which may reject, drop, or delay messages where all headers are removed from the top-level MIME object.

This document does not mandate any particular Header Confidentiality Policy, though it offers guidance for MUA implementers in selecting one in Section 4.1.3. Future documents may recommend or mandate such a policy for an MUA with specific needs. Such a recommendation might be motivated by descriptions of metadata-derived attacks, or stem from research about message deliverability, or describe new signalling mechanisms, but these topics are out of scope for this document.

4.1.2.3. Composing with "Wrapped Message" Header Protection

To compose a message using "Wrapped Message" header protection, we use those inputs described in Section 4.1.2.1 plus the Header Confidentiality Policy hcp defined in Section 4.1.2.2. The new algorithm is:

  • For header name and value (h,v) in origheaders:

    • Add header h of origbody with value v
  • If any of the header fields in origbody, including headers in the nested internal MIME structure, contain any 8-bit UTF-8 characters (see section section 3.7 of [RFC6532]):

    • Let payload be a new MIME part with one header: Content-Type: message/global; forwarded=no, and whose body is origbody.
  • Else:

    • Let payload be a new MIME part with one header: Content-Type: message/rfc822; forwarded=no, and whose body is origbody.
  • Apply crypto to payload, yielding MIME tree output
  • If crypto contains encryption:

    • Create new empty list of header field names and values newh
    • For header name and value (h,v) in origheaders:

      • Let newval be hcp(h, v)
      • If newval is not null:

        • Append (h,newval) to newh
    • Set origheaders to newh
  • For header name and value (h,v) in origheaders:

    • Add header h of output with value v
  • Return output

Note that the Header Confidentiality Policy hcp is ignored if crypto does not contain encryption. This is by design.

4.1.2.4. Composing with "Injected Headers" Header Protection

To compose a message using "Injected Headers" header protection, the composing MUA needs one additional input in addition to the Header Confidentiality Policy hcp defined in Section 4.1.2.2.

  • legacy: a boolean value, indicating whether any recipient of the message is believed to have a legacy client. If all recipients are known to implement this draft, legacy should be set to false. (How a MUA determines the value of legacy is out of scope for this document; an initial implementation can simply set it to true)

The revised algorithm for applying cryptographic protection to a message is as follows:

  • Create a new MIME leaf part legacydisplay with header Content-Type: text/plain; protected-headers="v1" and an empty body.
  • if crypto contains encryption, and legacy is true:

    • For each header name and value (h,v) in origheaders:

      • If h is user-facing (see [I-D.autocrypt-lamps-protected-headers]):

        • If hcp(h,v) is not v:

          • Add h: v to the body of legacydisplay. For example, if h is Subject, and v is lunch plans?, then add the line Subject: lunch plans? to the body of legacydisplay
  • If the body of legacydisplay is empty:

    • Let payload be MIME part origbody, discarding legacydisplay
  • Else: (body of legacydisplay is not empty)

    • Construct a new MIME part wrapper with Content-Type: multipart/mixed
    • Give wrapper exactly two subparts: legacydisplay and origbody, in that order.
    • Let payload be MIME part wrapper
  • For each header name and value (h,v) in origheaders:

    • Add header h of MIME part payload with value v
  • Set the protected-headers parameter on the Content-Type of payload to v1
  • Apply crypto to payload, producing MIME tree output
  • If crypto contains encryption:

    • Create new empty list of header field names and values newh
    • For header name and value (h,v) in origheaders:

      • Let newval be hcp(h, v)
      • If newval is not null:

        • Add newh[h] to newval
    • Set origheaders to newh
  • For each header name and value (h,v) in origheaders:

    • Add header h of output with value v
  • Return output

Note that both new parameters (hcp and legacy) are effectively ignored if crypto does not contain encryption. This is by design, because they are irrelevant for signed-only cryptographic protections.

4.1.2.5. Choosing Between Wrapped Message and Injected Headers

When composing a message with end-to-end cryptographic protections, an MUA SHOULD protect the headers of that message as well as the body.

An MUA MAY protect the headers of any outbound message using either the "Wrapped Message" or the "Injected Headers" style of protection. See Section 4.2 for more discussion about reasons to choose one mechanism or another.

[[ TODO: this document should recommend generation of one particular scheme by default for new implementers ]]

4.1.3. Default Header Confidentiality Policy

An MUA SHOULD have a sensible default Header Confidentiality Policy, and SHOULD NOT require the user to select one.

The default Header Confidentiality Policy SHOULD provide confidentiality for the Subject header field by replacing it with the literal string [...]. Most users treat the Subject of a message the same way that they treat the body, and they are surprised to find that the Subject of an encrypted message is visible.

[[ TODO: select one of the two policies below the recommended default ]]

4.1.3.1. Minimalist Header Confidentiality Policy

Accordingly, the most conservative recommended Header Confidentiality Policy only protects the Subject:

hcp_minimal(name, val_in) --> val_out: if name is 'Subject': return '[...]' else: return val_in

4.1.3.2. Strong Header Confidentiality Policy

Alternately, a more aggressive (and therefore more privacy-preserving) Header Confidentiality Policy only leaks a handful of fields whose absence is known to increase rates of delivery failure, and simultaneously obscures the Message-ID behind a random new one:

hcp_strong(name, val_in) --> val_out: if name in ['From', 'To', 'Cc', 'Date']: return val_in else if name is 'Subject': return '[...]' else if name is 'Message-ID': return generate_new_message_id() else: return null

The function generate_new_message_id() represents whatever process the MUA typically uses to generate a Message-ID for a new outbound message.

4.1.3.3. Offering Stronger Header Confidentiality

A MUA MAY offer even stronger confidentiality for headers of an encrypted message than described in Section 4.1.3.2. For example, it might implement an HCP that obfuscates the From field, or omits the Cc field, or ensures Date is represented in UTC (obscuring the local timezone).

The authors of this document hope that implementers with deployment experience will document their chosen Header Confidentiality Policy and the rationale behind their choice.

4.1.4. Receiving Side

An MUA that receives a cryptographically-protected e-mail will render it for the user.

The receiving MUA will render the message body, a selected subset of header fields, and (as described in [I-D.dkg-lamps-e2e-mail-guidance]) provide a summary of the cryptographic properties of the message.

Most MUAs only render a subset of header fields by default. For example, few MUAs typically render Message-Id or Received header fields for the user, but most do render From, To, Cc, Date, and Subject.

A MUA that knows how to handle a message with protected headers makes the following two changes to its behavior when rendering a message:

  • If it detects that an incoming message had protected headers, it renders header fields for the message from the protected headers, ignoring the external (unprotected) headers.
  • It includes information in the message's cryptographic summary to indicate the types of protection that applied to each rendered header field (if any).

A MUA that handles protected headers does not need to render any new header fields that it did not render before.

4.1.4.1. Identifying that a Message has Protected Headers

An incoming message can be identified as having protected headers based on one of two signals:

  • The Cryptographic Payload has Content-Type: message/rfc822 or Content-Type: message/global and the parameter forwarded has a value of no. See Section 4.1.4.3 for rendering guidance.
  • The Cryptographic Payload has some other Content-Type and it has parameter protected-headers set to v1. See Section 4.1.4.4 for rendering guidance.

Messages of both types exist in the wild, and a sensible MUA should be able to handle them both. They provide the same semantics and the same meaning.

4.1.4.2. Updating the Cryptographic Summary

Regardless of whether a cryptographically-protected message has protected headers, the cryptographic summary of the message should be modified to indicate what protections the headers have.

Each header individually has exactly one the following protections:

  • unprotected (this is the case for all headers in messages that have no protected headers)
  • signed-only (bound into the same validated signature as the enclosing message, but also visible in transit)
  • encrypted-only (only appears within the cryptographic payload; the corresponding external header was either omitted or obfuscated)
  • encrypted-and-signed (same as encrypted, but additionally is under a validatd signature)

Note that while the message itself may be encrypted-and-signed, some headers may be replicated on the outside of the message (e.g. Date) Those headers would be signed-only, despite the message itself being encrypted-and-signed.

Rendering this information is likely to be complex and messy --- users may not understand it. It is beyond the scope of this document to suggest any specific graphical affordances or user experience. Future work should include examples of successful rendering of this information.

4.1.4.3. Rendering a Wrapped Message

When the Cryptographic Payload has Content-Type of message/rfc822 or message/global, and the parameter forwarded is set to no, the values of the protected headers are drawn from the headers of the Cryptographic Payload, and the body that is rendered is the body of the Cryptographic Payload.

4.1.4.3.1. Example Signed-Only Wrapped Message

Consider a message with this structure, where the MUA is able to validate the cryptographic signature:

A └─╴application/pkcs7-mime; smime-type="signed-data"
   ⇩ (unwraps to)
B  └┬╴message/rfc822 [Cryptographic Payload]
C   └┬╴multipart/alternative [Rendered Body]
D    ├─╴text/plain
E    └─╴text/html

The message body should be rendered the same way as this message:

C └┬╴multipart/alternative
D  ├─╴text/plain
E  └─╴text/html

It should render header fields taken from part C.

Its cryptographic summary should indicates that the message was signed and all rendered header fields were included in the signature.

The MUA SHOULD ignore header fields from part A for the purposes of rendering.

4.1.4.3.2. Example Encrypted-and-Signed Wrapped Message

Consider a message with this structure, where the MUA is able to validate the cryptographic signature:

F └─╴application/pkcs7-mime; smime-type="enveloped-data"
   ↧ (decrypts to)
G  └─╴application/pkcs7-mime; smime-type="signed-data"
    ⇩ (unwraps to)
H   └┬╴message/rfc822 [Cryptographic Payload]
I    └┬╴multipart/alternative [Rendered Body]
J     ├─╴text/plain
K     └─╴text/html

The message body should be rendered the same way as this message:

I └┬╴multipart/alternative
J  ├─╴text/plain
K  └─╴text/html

It should render headers taken from part I.

Its cryptographic summary should indicates that the message was signed and encrypted. Each rendered header field found in I should be compared against the header field of the same name from F. If the value found in F matches the value found in I, the header field should be marked as signed-only. If no matching header field was found in F, or the value found did not match the value from I, the header field should be marked as signed-and-encrypted.

4.1.4.4. Rendering a Message with Injected Headers

When the Cryptographic Payload does not have a Content-Type of message/rfc822 or message/global, and the parameter protected-headers is set to v1, the values of the protected headers are drawn from the headers of the Cryptographic Payload, and the body that is rendered is the Cryptographic Payload itself.

4.1.4.4.1. Example Signed-only Message with Injected Headers
L └─╴application/pkcs7-mime; smime-type="signed-data"
   ⇩ (unwraps to)
M  └┬╴multipart/alternative [Cryptographic Payload + Rendered Body]
N   ├─╴text/plain
O   └─╴text/html

The message body should be rendered the same way as this message:

M └┬╴multipart/alternative
N  ├─╴text/plain
O  └─╴text/html

It should render header fieldss taken from part M.

Its cryptographic summary should indicates that the message was signed and all rendered header fields were included in the signature.

The MUA SHOULD ignore header fields from part L for the purposes of rendering.

4.1.4.4.2. Example Signed-and-Encrypted Message with Injected Headers

Consider a message with this structure, where the MUA is able to validate the cryptographic signature:

P └─╴application/pkcs7-mime; smime-type="enveloped-data"
   ↧ (decrypts to)
Q  └─╴application/pkcs7-mime; smime-type="signed-data"
    ⇩ (unwraps to)
R   └┬╴multipart/alternative [Cryptographic Payload + Rendered Body]
S    ├─╴text/plain
T    └─╴text/html

The message body should be rendered the same way as this message:

R └┬╴multipart/alternative
S  ├─╴text/plain
T  └─╴text/html

It should render headers taken from part R.

Its cryptographic summary should indicates that the message was signed and encrypted. As in Section 4.1.4.3.2, each rendered header field found in R should be compared against the header field of the same name from P. If the value found in P matches the value found in R, the header field should be marked as signed-only. If no matching header field was found in P, or the value found did not match the value from R, the header field should be marked as signed-and-encrypted.

4.1.4.4.3. Do Not Render Legacy Display Part

As described [I-D.autocrypt-lamps-protected-headers], a message with cryptographic confidentiality protection MAY include a "Legacy Display" part for backward-compatibility with legacy MUAs

The receiving MUA SHOULD avoid rendering the Legacy Display part to the user at all, since it is aware of and can render the actual Protected Headers.

If a Legacy Display part is detected, it and its enclosing multipart/mixed wrapper should be discarded before rendering.

4.1.4.4.3.1. Legacy Display Detection Algorithm

A receiving MUA acting on a message SHOULD detect the presence of a Legacy Display part and the corresponding "original body" with the following simple algorithm:

  • Check that all of the following are true for the message:
  • The Cryptographic Envelope must contain an encrypting Cryptographic Layer
  • The Cryptographic Payload must have a Content-Type of multipart/mixed
  • The Cryptographic Payload must have exactly two subparts
  • The first subpart of the Cryptographic Payload must have a Content-Type of text/plain or text/rfc822-headers
  • The first subpart of the Cryptographic Payload's Content-Type must contain a property of protected-headers, and its value must be v1.
  • If all of the above are true, then the first subpart is the Legacy Display part, and the second subpart is the "original body". Otherwise, the message does not have a Legacy Display part.
4.1.4.4.3.2. Legacy Display Example

Consider a message with this structure, where the MUA is able to validate the cryptographic signature:

U └─╴application/pkcs7-mime; smime-type="enveloped-data"
   ↧ (decrypts to)
V  └─╴application/pkcs7-mime; smime-type="signed-data"
    ⇩ (unwraps to)
W   └┬╴multipart/mixed [Cryptographic Payload]
X    ├─╴text/plain [Legacy Display]
Y    └┬╴multipart/alternative [Rendered Body]
Z     ├─╴text/plain
A'    └─╴text/html

The message body should be rendered the same way as this message, effectively hiding the Legacy Display part (X) and its wrapper:

Y └┬╴multipart/alternative
Z  ├─╴text/plain
A' └─╴text/html

It should render headers taken from part W, following the same guidance as in Section 4.1.4.4.2 and Section 4.1.4.3.2 about the cryptographic status of each rendered header field.

4.1.4.5. Affordances for Debugging and Troubleshooting

Note that advanced users of an MUA may need access to the original message, for example to troubleshoot problems with the MUA itself, or problems with the SMTP transport path taken by the message.

A MUA that applies these rendering guidelines SHOULD ensure that the full original source of the message as it was received remains available to such a user for debugging and troubleshooting.

4.1.4.6. Composing a Reply to an Encrypted Message with Protected Headers

When composing a reply to an encrypted message with protected headers, the MUA is acting both as a receiving MUA and as a sending MUA. Special guidance applies here, as things can go wrong in at least two ways: leaking previously-confidential information, and replying to the wrong party.

4.1.4.6.1. Avoid Leaking Encrypted Headers in Reply

As noted in [I-D.dkg-lamps-e2e-mail-guidance], an MUA in this position MUST NOT leak previously-encrypted content in the clear in a followup message. The same is true for protected headers.

Values from any header field that was identified as either encrypted or signed-and-encrypted based on the steps outlined above MUST NOT be placed in cleartext output when generating a message.

In particular, if Subject was encrypted, and it is copied into the draft encrypted reply, the replying MUA MUST obfuscate the Subject field in the cleartext header as described above.

[[ TODO: formally describe how a replying MUA should generate a message-specific Header Protection policy based on the cryptographic status of the headers of the incoming message ]]

4.1.4.6.2. Avoid Misdirected Replies to Encrypted Messages with Protected Headers

When replying to a message, the Composing MUA typically decides who to send the reply to based on:

  • the Reply-To, Mail-Followup-To, or From headers
  • optionally, the other To or Cc headers (if the user chose to "reply all")

When a message has protected headers, the replying MUA MUST populate the destination fields of the draft message using the protected headers, and ignore any unprotected headers.

This mitigates against an attack where Mallory gets a copy of an encrypted message from Alice to Bob, and then replays the message to Bob with an additional Cc to Mallory's own e-mail address in the message's outer header.

If Bob knows Mallory's certificate already, and he replies to such a message without following the guidance in this section, it's likely that his MUA will encrypt the cleartext of the message directly to Mallory.

4.1.4.7. Implicitly-rendered Header Fields

While From and To and Cc and Subject and Date are often explicitly rendered to the user, some header fields do affect message display, without being explicitly rendered.

For example, Message-Id, References, and In-Reply-To header fields may collectively be used to place a message in a "thread" or series of messages.

In another example, Section 4.1.4.6.2 observes that the value of the Reply-To field can influence the draft reply message. So while the user may never see the Reply-To header directly, it is implicitly "rendered" when the user interacts with the message by replying to it.

An MUA that depends on any implicitly-rendered header field in a message with protected headers SHOULD use the value from the protected header, and SHOULD NOT use any value found outside the cryptographic protection.

4.1.4.8. Unprotected Headers Added in Transit

Some headers are legitimately added in transit, and could not have been known to the sender at message composition time.

The most common of these headers are Received and DKIM-Signature, neither of which are typically rendered, either explicitly or implicitly.

If a receiving MUA has specific knowledge about a given header field, including that:

  • the header field would not have been known to the original sender, and
  • the header field might be rendered explicitly or implicitly,

then the MUA MAY decide to operate on the value of that header field from the unprotected header section, even though the message has protected headers.

The MUA MAY prefer to verify that the headers in question have additional transit-derived cryptographic protections (e.g., to test whether they are covered by a valid DKIM-Signature) before rendering or acting on them.

Specific examples appear below.

4.1.4.8.1. Mailing list headers: List-* and Archived-At

If the message arrives through a mailing list, the list manager itself may inject headers (most of which start with List-) in the message:

  • List-Archive
  • List-Subscribe
  • List-Unsubscribe
  • List-Id
  • List-Help
  • List-Post
  • Archived-At

For some MUAs, these headers are implicitly rendered, by providing buttons for actions like "Subscribe", "View Archived Version", "Reply List", "List Info", etc.

An MUA that receives a message with protected headers that contains these header fields in the unprotected section, and that has reason to believe the message is coming through a mailing list MAY decide to render them to the user (explicitly or implicitly) even though they are not protected.

FIXME: other examples of unprotected transit headers?

4.2. Backward Compatibility Use Cases

4.2.1. Receiving Side MIME-Conformant

This section applies to the case where the sending side (fully) supports Header Protection as specified in this document, while the receiving side does not support this specification, but is MIME-conformant according to [RFC2045], ff. (cf. Section 3.1.2 and Section 3.1.2.1)

The sending side specification of the main use case (cf. Section 4.1) MUST ensure that receiving sides can still recognize and display or offer to display the encapsulated data in accordance with its media type (cf. [RFC2049], Section 2). In particular, receiving sides that do not support this specification, but are MIME-conformant according to [RFC2045], ff. can still recognize and display the Message intended for the user.

[[ TODO: Verify once solution is stable and update last sentence. ]]

4.2.2. Receiving Side Not MIME-Conformant

This section applies to cases where the sending side (fully) supports Header Protection as specified in this document, while the receiving side neither supports this specification nor is MIME-conformant according to [RFC2045], ff. (cf. Section 3.1.2 and Section 3.1.2.2).

[I-D.autocrypt-lamps-protected-headers] describes a possible way to achieve backward compatibility with existing S/MIME (and PGP/MIME) implementations that predate this specification and are not MIME-conformant (Legacy Display) either. It mainly focuses on email clients that do not render emails which utilize header protection in a user friendly manner, which may confuse the user. While this has been observed occasionally in PGP/MIME (cf. [RFC3156]), the extent of this problem with S/MIME implementations is still unclear. (Note: At this time, none of the samples in [I-D.autocrypt-lamps-protected-headers] apply header protection as specified in Section 3.1 of [RFC8551], which is wrapping as Media Type "message/RFC822".)

Should serious backward compatibility issues with rendering at the receiving side be discovered, the Legacy Display format described in [I-D.autocrypt-lamps-protected-headers] may serve as a basis to mitigate those issues (cf. Section 4.2).

Another variant of backward compatibility has been implemented by pEp [I-D.pep-email], i.e. pEp Email Format 1.0. At this time pEp has implemented this for PGP/MIME, but not yet S/MIME.

5. Usability Considerations

This section describes concerns for MUAs that are interested in easy adoption of header protection by normal users.

While they are not protocol-level artifacts, these concerns motivate the protocol features described in this document.

See also the Usability section in [I-D.dkg-lamps-e2e-mail-guidance].

6. Security Considerations

[[ TODO ]]

7. Privacy Considerations

[[ TODO ]]

8. IANA Considerations

This document requests no action from IANA.

[[ RFC Editor: This section may be removed before publication. ]]

9. Acknowledgments

The authors would like to thank the following people who have provided helpful comments and suggestions for this document: Berna Alp, Bernhard E. Reiter, Claudio Luck, David Wilson, Hernani Marques, juga, Krista Bennett, Kelly Bristol, Lars Rohwedder, Robert Williams, Russ Housley, Sofia Balicka, Steve Kille, Volker Birk, and Wei Chuang.

10. References

10.1. Normative References

[I-D.dkg-lamps-e2e-mail-guidance]
Gillmor, D. K., "Guidance on End-to-End E-mail Security", Work in Progress, Internet-Draft, draft-dkg-lamps-e2e-mail-guidance-01, , <https://www.ietf.org/archive/id/draft-dkg-lamps-e2e-mail-guidance-01.txt>.
[I-D.ietf-lamps-header-protection-requirements]
Melnikov, A. and B. Hoeneisen, "Problem Statement and Requirements for Header Protection", Work in Progress, Internet-Draft, draft-ietf-lamps-header-protection-requirements-01, , <https://www.ietf.org/archive/id/draft-ietf-lamps-header-protection-requirements-01.txt>.
[RFC2045]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, DOI 10.17487/RFC2045, , <https://www.rfc-editor.org/info/rfc2045>.
[RFC2046]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, DOI 10.17487/RFC2046, , <https://www.rfc-editor.org/info/rfc2046>.
[RFC2049]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC 2049, DOI 10.17487/RFC2049, , <https://www.rfc-editor.org/info/rfc2049>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC5322]
Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, , <https://www.rfc-editor.org/info/rfc5322>.
[RFC8551]
Schaad, J., Ramsdell, B., and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification", RFC 8551, DOI 10.17487/RFC8551, , <https://www.rfc-editor.org/info/rfc8551>.

10.2. Informative References

[I-D.autocrypt-lamps-protected-headers]
Einarsson, B. R., juga, and D. K. Gillmor, "Protected Headers for Cryptographic E-mail", Work in Progress, Internet-Draft, draft-autocrypt-lamps-protected-headers-02, , <https://www.ietf.org/archive/id/draft-autocrypt-lamps-protected-headers-02.txt>.
[I-D.ietf-lamps-samples]
Gillmor, D. K., "S/MIME Example Keys and Certificates", Work in Progress, Internet-Draft, draft-ietf-lamps-samples-04, , <https://www.ietf.org/archive/id/draft-ietf-lamps-samples-04.txt>.
[I-D.melnikov-iana-reg-forwarded]
Melnikov, A. and B. Hoeneisen, "IANA Registration of Content-Type Header Field Parameter 'forwarded'", Work in Progress, Internet-Draft, draft-melnikov-iana-reg-forwarded-00, , <https://www.ietf.org/archive/id/draft-melnikov-iana-reg-forwarded-00.txt>.
[I-D.pep-email]
Marques, H., "pretty Easy privacy (pEp): Email Formats and Protocols", Work in Progress, Internet-Draft, draft-pep-email-01, , <https://www.ietf.org/archive/id/draft-pep-email-01.txt>.
[pEp.mixnet]
pEp Foundation, "Mixnet", , <https://dev.pep.foundation/Mixnet>.
[RFC3156]
Elkins, M., Del Torto, D., Levien, R., and T. Roessler, "MIME Security with OpenPGP", RFC 3156, DOI 10.17487/RFC3156, , <https://www.rfc-editor.org/info/rfc3156>.
[RFC4949]
Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, , <https://www.rfc-editor.org/info/rfc4949>.
[RFC6376]
Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., "DomainKeys Identified Mail (DKIM) Signatures", STD 76, RFC 6376, DOI 10.17487/RFC6376, , <https://www.rfc-editor.org/info/rfc6376>.
[RFC6409]
Gellens, R. and J. Klensin, "Message Submission for Mail", STD 72, RFC 6409, DOI 10.17487/RFC6409, , <https://www.rfc-editor.org/info/rfc6409>.
[RFC6532]
Yang, A., Steele, S., and N. Freed, "Internationalized Email Headers", RFC 6532, DOI 10.17487/RFC6532, , <https://www.rfc-editor.org/info/rfc6532>.
[RFC7489]
Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", RFC 7489, DOI 10.17487/RFC7489, , <https://www.rfc-editor.org/info/rfc7489>.

Appendix A. Test Vectors

This section contains sample messages using the different schemes described in this document. Each sample contains a MIME object, a textual and diagrammatic view of its structure, and examples of how an MUA might render it.

The cryptographic protections used in this document use the S/MIME standard, and keying material and certificates come from [I-D.ietf-lamps-samples].

These messages should be accessible to any IMAP client at imap://bob@header-protection.cmrg.net/ (any password should authenticate to this read-only IMAP mailbox).

You can also download copies of these test vectors separately at https://header-protection.cmrg.net.

If any of the messages downloaded differ from those offered here, this document is the canonical source.

A.1. Baseline Messages

These messages offer no header protection at all, and can be used as a baseline. They are provided in this document as a counterexample. An MUA implementer can use these messages to verify that the reported cryptographic summary of the message indicates no header protection.

A.1.1. No cryptographic protections over a simple message

This message uses no cryptographic protection at all. Its body is a text/plain message.

It has the following structure:

└─╴text/plain 152 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Subject: no-crypto
Message-ID: <no-crypto@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:00:02 -0500

This is the no-crypto message.

This message uses no cryptographic protection at all.  Its body is a
text/plain message.

--
Alice
alice@smime.example

A.1.2. S/MIME signed-only signedData over a simple message, No Header Protection

This is a signed-only S/MIME message via PKCS#7 signedData. The payload is a text/plain message. It uses no header protection.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 3852 bytes
 ⇩ (unwraps to)
 └─╴text/plain 204 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="signed-data"
Subject: smime-one-part
Message-ID: <smime-one-part@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:01:02 -0500
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OA7IizkBD+GDEu8uKveERRXZncxGwy2MfbH1Ib3U8QzTjqB8+dz2AwYeMxODWq9o
pwtA/lTOkRg8uuivZfg/m5fFo/QshlHNaaTDVEXsU4Ps98Hm/3gznbvhdjFbZbi4
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ETAPBgNVBAsTCExBTVBTIFdHMRcwFQYDVQQDEw5BbGljZSBMb3ZlbGFjZTCCASIw
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dg0VQQ6Wz+CRQ/YbHPKaw7aRphZO63dKvIKp4cQVtkWQHi6syTjGsgkLcLNau5LZ
DQUdsGV+SAo3nBdWCRYV+I65x8Kf4hCxqqmjV3d/2NKRu0BXnDe/N+iDz3X0zEoj
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AaOBrzCBrDAMBgNVHRMBAf8EAjAAMBcGA1UdIAQQMA4wDAYKYIZIAWUDAgEwATAe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A.1.3. S/MIME signed-only multipart/signed over a simple message, No Header Protection

This is a signed-only S/MIME message via PKCS#7 detached signature (multipart/signed). The payload is a text/plain message. It uses no header protection.

It has the following structure:

└┬╴multipart/signed 4156 bytes
 ├─╴text/plain 224 bytes
 └─╴application/pkcs7-signature [smime.p7s] 3429 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/signed;
 protocol="application/pkcs7-signature"; boundary="76c";
 micalg="sha-256"
Subject: smime-multipart
Message-ID: <smime-multipart@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:02:02 -0500

--76c
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit

This is the smime-multipart message.

This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a text/plain message. It uses no
header protection.

--
Alice
alice@smime.example

--76c
Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-signature; name="smime.p7s"

MIIJ4AYJKoZIhvcNAQcCoIIJ0TCCCc0CAQExDTALBglghkgBZQMEAgEwCwYJKoZI
hvcNAQcBoIIHpjCCA88wggK3oAMCAQICEw8tJb0ROZdKzkJUh6HuPTQGirQwDQYJ
KoZIhvcNAQENBQAwVTENMAsGA1UEChMESUVURjERMA8GA1UECxMITEFNUFMgV0cx
MTAvBgNVBAMTKFNhbXBsZSBMQU1QUyBSU0EgQ2VydGlmaWNhdGlvbiBBdXRob3Jp
dHkwIBcNMTkxMTIwMDY1NDE4WhgPMjA1MjA5MjcwNjU0MThaMDsxDTALBgNVBAoT
BElFVEYxETAPBgNVBAsTCExBTVBTIFdHMRcwFQYDVQQDEw5BbGljZSBMb3ZlbGFj
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acKTg8cc2OtJ9ZSed6U3jUoiZVpMLcP3MUKtLeLg9r1mAfIDlB/wlbdmadXPmrsz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bKZa1oPTUNlm6QpivtqDIdqGJdGf8L1zLfXBuo2zL3HR+M9CDr4Opq2JCkzP0Qhp
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OKypyQ3eoZ6EPazXqMyHAVcsm0GI364IOA0b8PSrJNtjh+AqJ5QfH+0e7NSzNnEm
MYICADCCAfwCAQEwbDBVMQ0wCwYDVQQKEwRJRVRGMREwDwYDVQQLEwhMQU1QUyBX
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cml0eQITN0EFee11f0Kpolw69Phqzpqp1zALBglghkgBZQMEAgGgaTAYBgkqhkiG
9w0BCQMxCwYJKoZIhvcNAQcBMBwGCSqGSIb3DQEJBTEPFw0yMTAyMjAxNTAyMDJa
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e+F++YX8mXokgQpY26mZ+15Mv8pYYhptn6zdkRU1+QOwwlDCc6ykkCZeXyc+Hf7c
xqM6SqPMQ+G7wIF6P2jHCId8Xyl7sdbL0i6PjotesHU+7nQsCjgI/iVR/ubWUdFX
CTg8HVy4p683V3Y9DoRNP4MlUdmon8JasHDvA0240JcXxhJn1zEYa4gOnwgu3kh9
3Y+NeucYCT0bXCBq2RLVQSpdNZfScXKL9QvZ3FtB0r6Bmtky

--76c--

A.1.4. S/MIME encrypted and signed over a simple message, No Header Protection

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses no header protection.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 6720 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 3960 bytes
  ⇩ (unwraps to)
  └─╴text/plain 239 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: smime-enc-signed
Message-ID: <smime-enc-signed@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:03:02 -0500

MIITXAYJKoZIhvcNAQcDoIITTTCCE0kCAQAxggMQMIIBhAIBADBsMFUxDTALBgNV
BAoTBElFVEYxETAPBgNVBAsTCExBTVBTIFdHMTEwLwYDVQQDEyhTYW1wbGUgTEFN
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STC7LY11zMhZL+RvhwbWqjkKeKN3hQM4/45BHGFVgg6k5iobcv78lZHWO28SWila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A.1.5. No cryptographic protections over a complex message

This message uses no cryptographic protection at all. Its body is a multipart/alternative message with an inline image/png attachment.

It has the following structure:

└┬╴multipart/mixed 1357 bytes
 ├┬╴multipart/alternative 780 bytes
 │├─╴text/plain 206 bytes
 │└─╴text/html 290 bytes
 └─╴image/png inline 232 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="0f4"
Subject: no-crypto-complex
Message-ID: <no-crypto-complex@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:00:02 -0500

--0f4
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="384"

--384
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This is the no-crypto-complex message.

This message uses no cryptographic protection at all.  Its body is a
multipart/alternative message with an inline image/png attachment.

--
Alice
alice@smime.example
--384
Content-Type: text/html; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

<html><head><title></title></head><body>
<p>This is the <b>no-crypto-complex</b> message.</p>
<p>This message uses no cryptographic protection at all.  Its body is a
multipart/alternative message with an inline image/png attachment.</p>
<p><tt>-- <br/>Alice<br/>alice@smime.example</tt></p>
--384--

--0f4
Content-Type: image/png
Content-Transfer-Encoding: base64
Content-Disposition: inline

iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAcElEQVR42uVTOxbA
MAgS739nO3TpRw20dqpbfARQEjOywiwYnCtkDKnbcLk66sqlT+zt9cidkE+6KwkZ
sgrzfcqVMpL2jo0447gYDpeArk+OnJHkIhAfTPRicihAf5YJrw7vjv0ZWRWM/uli
vdPf1QZ2kDD9xppd8wAAAABJRU5ErkJggg==

--0f4--

A.1.6. S/MIME signed-only signedData over a complex message, No Header Protection

This is a signed-only S/MIME message via PKCS#7 signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses no header protection.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 5229 bytes
 ⇩ (unwraps to)
 └┬╴multipart/mixed 1274 bytes
  ├┬╴multipart/alternative 868 bytes
  │├─╴text/plain 258 bytes
  │└─╴text/html 339 bytes
  └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="signed-data"
Subject: smime-one-part-complex
Message-ID: <smime-one-part-complex@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:01:02 -0500

MIIPEQYJKoZIhvcNAQcCoIIPAjCCDv4CAQExDTALBglghkgBZQMEAgEwggU6Bgkq
hkiG9w0BBwGgggUrBIIFJ01JTUUtVmVyc2lvbjogMS4wDQpDb250ZW50LVR5cGU6
IG11bHRpcGFydC9taXhlZDsgYm91bmRhcnk9ImM4YiINCg0KLS1jOGINCk1JTUUt
VmVyc2lvbjogMS4wDQpDb250ZW50LVR5cGU6IG11bHRpcGFydC9hbHRlcm5hdGl2
ZTsgYm91bmRhcnk9ImM4MSINCg0KLS1jODENCkNvbnRlbnQtVHlwZTogdGV4dC9w
bGFpbjsgY2hhcnNldD0idXMtYXNjaWkiDQpNSU1FLVZlcnNpb246IDEuMA0KQ29u
dGVudC1UcmFuc2Zlci1FbmNvZGluZzogN2JpdA0KDQpUaGlzIGlzIHRoZSBzbWlt
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b25seSBTL01JTUUgbWVzc2FnZSB2aWEgUEtDUyM3IHNpZ25lZERhdGEuICBUaGUN
CnBheWxvYWQgaXMgYSBtdWx0aXBhcnQvYWx0ZXJuYXRpdmUgbWVzc2FnZSB3aXRo
IGFuIGlubGluZSBpbWFnZS9wbmcNCmF0dGFjaG1lbnQuIEl0IHVzZXMgbm8gaGVh
ZGVyIHByb3RlY3Rpb24uDQoNCi0tIA0KQWxpY2UNCmFsaWNlQHNtaW1lLmV4YW1w
bGUNCi0tYzgxDQpDb250ZW50LVR5cGU6IHRleHQvaHRtbDsgY2hhcnNldD0idXMt
YXNjaWkiDQpNSU1FLVZlcnNpb246IDEuMA0KQ29udGVudC1UcmFuc2Zlci1FbmNv
ZGluZzogN2JpdA0KDQo8aHRtbD48aGVhZD48dGl0bGU+PC90aXRsZT48L2hlYWQ+
PGJvZHk+DQo8cD5UaGlzIGlzIHRoZSA8Yj5zbWltZS1vbmUtcGFydC1jb21wbGV4
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ZSBpbWFnZS9wbmcNCmF0dGFjaG1lbnQuIEl0IHVzZXMgbm8gaGVhZGVyIHByb3Rl
Y3Rpb24uPC9wPg0KPHA+PHR0Pi0tIDxici8+QWxpY2U8YnIvPmFsaWNlQHNtaW1l
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Yy3iOx7YOqzXrl6udP07k0sV+UdSNRFxrfKeoQEFXgOaGdmnx4OG/e3p1fIKM0dP
zZLoOAJF5m5O0xzXPL74zFCWp2f1ZkuE4A6l41koaZXCN5XL7wWTLMLeNf9Byb5k
sKqUuqEHAMd1nmoNMgjY9VfVfcrv9w43GG8FtpSX+TWzB2zNS2OF+XIVnzRG5Deo
ULq8v88Z5bLpIJ/nx26r8A4SSwIBaVv4wPxAf1iPsIVKarUCAwEAAaOBrzCBrDAM
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DwEB/wQEAwIFIDAdBgNVHQ4EFgQUolNB1UQ8gCkVfAEj8OeOr83zdw8wHwYDVR0j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onX2doizcGMk53riugAocCn5zbzhW/JVdYn30UxfyrZlRAzEf7GHqgB/NyjOad3p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A.1.7. S/MIME signed-only multipart/signed over a complex message, No Header Protection

This is a signed-only S/MIME message via PKCS#7 detached signature (multipart/signed). The payload is a multipart/alternative message with an inline image/png attachment. It uses no header protection.

It has the following structure:

└┬╴multipart/signed 5185 bytes
 ├┬╴multipart/mixed 1330 bytes
 │├┬╴multipart/alternative 924 bytes
 ││├─╴text/plain 278 bytes
 ││└─╴text/html 362 bytes
 │└─╴image/png inline 232 bytes
 └─╴application/pkcs7-signature [smime.p7s] 3429 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/signed;
 protocol="application/pkcs7-signature"; boundary="d66";
 micalg="sha-256"
Subject: smime-multipart-complex
Message-ID: <smime-multipart-complex@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:02:02 -0500

--d66
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="7fe"

--7fe
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="848"

--848
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This is the smime-multipart-complex message.

This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a multipart/alternative message
with an inline image/png attachment. It uses no header protection.

--
Alice
alice@smime.example
--848
Content-Type: text/html; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

<html><head><title></title></head><body>
<p>This is the <b>smime-multipart-complex</b> message.</p>
<p>This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a multipart/alternative message
with an inline image/png attachment. It uses no header protection.</p>
<p><tt>-- <br/>Alice<br/>alice@smime.example</tt></p>
--848--

--7fe
Content-Type: image/png
Content-Transfer-Encoding: base64
Content-Disposition: inline

iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAcElEQVR42uVTOxbA
MAgS739nO3TpRw20dqpbfARQEjOywiwYnCtkDKnbcLk66sqlT+zt9cidkE+6KwkZ
sgrzfcqVMpL2jo0447gYDpeArk+OnJHkIhAfTPRicihAf5YJrw7vjv0ZWRWM/uli
vdPf1QZ2kDD9xppd8wAAAABJRU5ErkJggg==

--7fe--

--d66
Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-signature; name="smime.p7s"

MIIJ4AYJKoZIhvcNAQcCoIIJ0TCCCc0CAQExDTALBglghkgBZQMEAgEwCwYJKoZI
hvcNAQcBoIIHpjCCA88wggK3oAMCAQICEw8tJb0ROZdKzkJUh6HuPTQGirQwDQYJ
KoZIhvcNAQENBQAwVTENMAsGA1UEChMESUVURjERMA8GA1UECxMITEFNUFMgV0cx
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--d66--

A.1.8. S/MIME encrypted and signed over a complex message, No Header Protection

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses no header protection.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 8670 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 5408 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1342 bytes
   ├┬╴multipart/alternative 936 bytes
   │├─╴text/plain 293 bytes
   │└─╴text/html 374 bytes
   └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: smime-enc-signed-complex
Message-ID: <smime-enc-signed-complex@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:03:02 -0500

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gi0d7rnqWYuse+UrzUrbp5z/UpJQp/PyY6rdDlScWQp3WJYSNgEe62EmnMShGf+q
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/yXCBPWOnMCR+MVWVXUpf3wfXlHO4nZfNtyVb/v7e4lRCylyayXo7g2rkmR+LrH3
dEnczDF/LZLbDnkizNpzlgLU5BAlk9rDW6uwyMywrLIYlttVnRrHwjAol6US+mjF
sZib126lo8EIeHyccGZIqfyTHld03m32IzMnDnl6dVeX5TAuBmDuNGbXHP4h2OSG
m6tUHSFI9fMxO2pBT1Tts1kjYBU+jMenqI8GxpP6DD/Y8PUbxBNoPoP8aVR3rkBk
GONb4ksn6zWoRxT4XyaPvmImvFX5nkHHnvkThvL0DaWcwuIOrjtqOJwmPBTOywjA
KYPPCK7qVCwVAssJxx7adE1W+F15UoTyyyjpe6pVtgO90lGRcprYQnBasw03kATd
k8GFN7Ej37OiXIvrmsJ1toHzlhungW5uYedaTMBNmw8iU63r36sMhj46i9nML2jP
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5NRz07fwamd09k3N3dIeAB0I+YJyeElO69772qnqpiGnx10uq5lnhEyvtJCyH1tS
vWUvX0tyAFfuIBkdyCKMFP6zhHVxZCCa+r3W/qrfON6GH/tJ3aLdilvjwC2zQy29
iuNYYJoyAS3PCjC7CL41U0kAOBNJPka6Vqn6PwxpnxGaZZyFCSU2fpAvNyT2auOh
CmLz/P0tNE7z7l1JXqao62CoPa1dOQJ27NbEjsoR3GobhcGQQkYb3Zsss/y1QZaa
9lkTdk02ZDXfPPyaIUY46+VA3VcHlmWxChZiiFpqOdV21aAt+f4PJLtspE2/OTEG
GqHngtafmMV75z+MO8ExXvy5YrI5N+S2eArIteQxBjNs5DjXnsPjE3CGwb7GPx8T
XMsEmWDQ7TDtqFSUzHAIb8EieTziP0LL2LOd9dpE8xDH1X0gDC82whSxUrZOa15Z
iJ1sZkS1VRI/iq9/5zc8BX+218FfdN+rbHWZZAM02ge1IMyOsLF9qaaiR1K9ZQPJ
lYDLcCmnS6Q1oKA2JvDOiB8sbrpKLsLk31lcqCrVJ9eOIqnA4yAijsCNiUjI1DSC
TefQo1PVS8qAGhfkcA/4nw==

A.2. Signed-only Messages

These messages are signed-only, using different schemes of header protection and different S/MIME structure. The use no Header Confidentiality Policy because the hcp is only relevant when a message is encrypted.

A.2.1. S/MIME signed-only signedData over a simple message, Wrapped Message

This is a signed-only S/MIME message via PKCS#7 signedData. The payload is a text/plain message. It uses the Wrapped Message header protection scheme.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 4213 bytes
 ⇩ (unwraps to)
 └┬╴message/rfc822 566 bytes
  └─╴text/plain 228 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="signed-data"
Subject: smime-one-part-wrapped
Message-ID: <smime-one-part-wrapped@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:04:02 -0500

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aZXCN5XL7wWTLMLeNf9Byb5ksKqUuqEHAMd1nmoNMgjY9VfVfcrv9w43GG8FtpSX
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sIVKarUCAwEAAaOBrzCBrDAMBgNVHRMBAf8EAjAAMBcGA1UdIAQQMA4wDAYKYIZI
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hkiG9w0BCQMxCwYJKoZIhvcNAQcBMBwGCSqGSIb3DQEJBTEPFw0yMTAyMjAxNTA0
MDJaMC8GCSqGSIb3DQEJBDEiBCCt+Ik56mZTd2mpSgOXM38dS7jM5alU2FDX9/58
cga1szANBgkqhkiG9w0BAQEFAASCAQCxKLkx5li14OIOcH2tcWqcsQilPLgQ30ck
qhJL2X9/Cl22ibOGNwL8w3qSEBeG1a+WtHw3bSqJx1ciRYcLs16ms23no5QoZ0pU
fRLmQuTEgObCf+syiTGnWLj8e+2aRVP1L9yEIbin6+hFyp4s393zYhdMOPAP2ruI
lg+BxoWXUjXso+8lPgqLawA+9KMI6tQZMnwI9LpGJmZfoSXdHWqWtjdotzZpqsKm
Ihr8DBKtUetqgZ2zqDO3zo3W2L6EmNM05BJUmqwAt/cN+X9kws5dAqtHDQhPNTa1
WUX0oTTkMzn1RAlOxfowEStSnfDOOzIqg+L7LgiMw9jhIgP4/uB2

A.2.2. S/MIME signed-only multipart/signed over a simple message, Wrapped Message

This is a signed-only S/MIME message via PKCS#7 detached signature (multipart/signed). The payload is a text/plain message. It uses the Wrapped Message header protection scheme.

It has the following structure:

└┬╴multipart/signed 4451 bytes
 ├┬╴message/rfc822 596 bytes
 │└─╴text/plain 256 bytes
 └─╴application/pkcs7-signature [smime.p7s] 3429 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/signed;
 protocol="application/pkcs7-signature"; boundary="20c";
 micalg="sha-256"
Subject: smime-multipart-wrapped
Message-ID: <smime-multipart-wrapped@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:05:02 -0500

--20c
MIME-Version: 1.0
Content-Type: message/rfc822; forwarded="no"

MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Subject: smime-multipart-wrapped
Message-ID: <smime-multipart-wrapped@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:05:02 -0500

This is the smime-multipart-wrapped message.

This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a text/plain message. It uses the
Wrapped Message header protection scheme.

--
Alice
alice@smime.example

--20c
Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-signature; name="smime.p7s"

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KoZIhvcNAQENBQAwVTENMAsGA1UEChMESUVURjERMA8GA1UECxMITEFNUFMgV0cx
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acKTg8cc2OtJ9ZSed6U3jUoiZVpMLcP3MUKtLeLg9r1mAfIDlB/wlbdmadXPmrsz
yidmbuZmOpB5voVQfiLYYy3iOx7YOqzXrl6udP07k0sV+UdSNRFxrfKeoQEFXgOa
Gdmnx4OG/e3p1fIKM0dPzZLoOAJF5m5O0xzXPL74zFCWp2f1ZkuE4A6l41koaZXC
N5XL7wWTLMLeNf9Byb5ksKqUuqEHAMd1nmoNMgjY9VfVfcrv9w43GG8FtpSX+TWz
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arUCAwEAAaOBrzCBrDAMBgNVHRMBAf8EAjAAMBcGA1UdIAQQMA4wDAYKYIZIAWUD
AgEwATAeBgNVHREEFzAVgRNhbGljZUBzbWltZS5leGFtcGxlMBMGA1UdJQQMMAoG
CCsGAQUFBwMEMA4GA1UdDwEB/wQEAwIFIDAdBgNVHQ4EFgQUolNB1UQ8gCkVfAEj
8OeOr83zdw8wHwYDVR0jBBgwFoAUkTCOfAcXDKfxCShlNhpnHGh29FkwDQYJKoZI
hvcNAQENBQADggEBAIFJeKCcsTKcFqQMpTryujRGzJdYA+R9eBAuDLsatbtKtl4F
zkgRyOg31/+Cw7H8e30iLrPIFlWN1qjHrjgOyIs5AQ/hgxLvLir3hEUV2Z3MRsMt
jH2x9SG91PEM046gfPnc9gMGHjMTg1qvaKcLQP5UzpEYPLror2X4P5uXxaP0LIZR
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fjKYJFb9UhwtufZK9/WyVtytLsFJMYHZgUSWU3VbHk1L/cO0469Rbqo6CqlLRJPK
uN2Eul2UCa+3ovMIQ8g0NBflXrdfR0OVRqvfO91hLFkTxLfCDUG8ziRWOLWucgZg
zkVXqEzvFyOtsSbr3GAY817wWgl1+PTFchO4XF+rg7cNysKqGLtjxP9lN3PcURYv
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Rgd+NZNQD+VYDIOU1FI5ZjyjHpRmcFpywjvHNbTBGlYhv3q4

--20c--

A.2.3. S/MIME signed-only signedData over a simple message, Injected Headers

This is a signed-only S/MIME message via PKCS#7 signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 4185 bytes
 ⇩ (unwraps to)
 └─╴text/plain 239 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="signed-data"
Subject: smime-one-part-injected
Message-ID: <smime-one-part-injected@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:06:02 -0500

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A.2.4. S/MIME signed-only multipart/signed over a simple message, Injected Headers

This is a signed-only S/MIME message via PKCS#7 detached signature (multipart/signed). The payload is a text/plain message. It uses the Injected Headers header protection scheme.

It has the following structure:

└┬╴multipart/signed 4417 bytes
 ├─╴text/plain 258 bytes
 └─╴application/pkcs7-signature [smime.p7s] 3429 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/signed;
 protocol="application/pkcs7-signature"; boundary="12b";
 micalg="sha-256"
Subject: smime-multipart-injected
Message-ID: <smime-multipart-injected@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:07:02 -0500

--12b
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: smime-multipart-injected
Message-ID: <smime-multipart-injected@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:07:02 -0500
Content-Type: text/plain; charset="utf-8"; protected-headers="v1"

This is the smime-multipart-injected message.

This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a text/plain message. It uses the
Injected Headers header protection scheme.

--
Alice
alice@smime.example

--12b
Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-signature; name="smime.p7s"

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aqbbPK7xip5c/YZEaZWYAs8w+dif68J8Eo7QO/kkr45Tt5pf

--12b--

A.2.5. S/MIME signed-only signedData over a complex message, Wrapped Message

This is a signed-only S/MIME message via PKCS#7 signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Wrapped Message header protection scheme.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 5615 bytes
 ⇩ (unwraps to)
 └┬╴message/rfc822 1599 bytes
  └┬╴multipart/mixed 1535 bytes
   ├┬╴multipart/alternative 932 bytes
   │├─╴text/plain 282 bytes
   │└─╴text/html 366 bytes
   └─╴image/png inline 232 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="signed-data"
Subject: smime-one-part-complex-wrapped
Message-ID: <smime-one-part-complex-wrapped@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:04:02 -0500

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BAoTBElFVEYxETAPBgNVBAsTCExBTVBTIFdHMTEwLwYDVQQDEyhTYW1wbGUgTEFN
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TC3D9zFCrS3i4Pa9ZgHyA5Qf8JW3ZmnVz5q7M8onZm7mZjqQeb6FUH4i2GMt4jse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A.2.6. S/MIME signed-only multipart/signed over a complex message, Wrapped Message

This is a signed-only S/MIME message via PKCS#7 detached signature (multipart/signed). The payload is a multipart/alternative message with an inline image/png attachment. It uses the Wrapped Message header protection scheme.

It has the following structure:

└┬╴multipart/signed 5528 bytes
 ├┬╴message/rfc822 1657 bytes
 │└┬╴multipart/mixed 1593 bytes
 │ ├┬╴multipart/alternative 988 bytes
 │ │├─╴text/plain 310 bytes
 │ │└─╴text/html 394 bytes
 │ └─╴image/png inline 232 bytes
 └─╴application/pkcs7-signature [smime.p7s] 3429 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/signed;
 protocol="application/pkcs7-signature"; boundary="932";
 micalg="sha-256"
Subject: smime-multipart-complex-wrapped
Message-ID: <smime-multipart-complex-wrapped@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:05:02 -0500

--932
MIME-Version: 1.0
Content-Type: message/rfc822; forwarded="no"

MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="c35"
Subject: smime-multipart-complex-wrapped
Message-ID: <smime-multipart-complex-wrapped@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:05:02 -0500

--c35
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="645"

--645
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This is the smime-multipart-complex-wrapped message.

This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a multipart/alternative message
with an inline image/png attachment. It uses the Wrapped Message
header protection scheme.

--
Alice
alice@smime.example
--645
Content-Type: text/html; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

<html><head><title></title></head><body>
<p>This is the <b>smime-multipart-complex-wrapped</b> message.</p>
<p>This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a multipart/alternative message
with an inline image/png attachment. It uses the Wrapped Message
header protection scheme.</p>
<p><tt>-- <br/>Alice<br/>alice@smime.example</tt></p>
--645--

--c35
Content-Type: image/png
Content-Transfer-Encoding: base64
Content-Disposition: inline

iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAcElEQVR42uVTOxbA
MAgS739nO3TpRw20dqpbfARQEjOywiwYnCtkDKnbcLk66sqlT+zt9cidkE+6KwkZ
sgrzfcqVMpL2jo0447gYDpeArk+OnJHkIhAfTPRicihAf5YJrw7vjv0ZWRWM/uli
vdPf1QZ2kDD9xppd8wAAAABJRU5ErkJggg==

--c35--

--932
Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-signature; name="smime.p7s"
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--932--

A.2.7. S/MIME signed-only signedData over a complex message, Injected Headers

This is a signed-only S/MIME message via PKCS#7 signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 5631 bytes
 ⇩ (unwraps to)
 └┬╴multipart/mixed 1565 bytes
  ├┬╴multipart/alternative 936 bytes
  │├─╴text/plain 292 bytes
  │└─╴text/html 373 bytes
  └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="signed-data"
Subject: smime-one-part-complex-injected
Message-ID: <smime-one-part-complex-injected@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:06:02 -0500

MIIQOQYJKoZIhvcNAQcCoIIQKjCCECYCAQExDTALBglghkgBZQMEAgEwggZiBgkq
hkiG9w0BBwGgggZTBIIGT01JTUUtVmVyc2lvbjogMS4wDQpTdWJqZWN0OiBzbWlt
ZS1vbmUtcGFydC1jb21wbGV4LWluamVjdGVkDQpNZXNzYWdlLUlEOiA8c21pbWUt
b25lLXBhcnQtY29tcGxleC1pbmplY3RlZEBsaHAuZXhhbXBsZT4NCkZyb206IEFs
aWNlIDxhbGljZUBzbWltZS5leGFtcGxlPg0KVG86IEJvYiA8Ym9iQHNtaW1lLmV4
YW1wbGU+DQpEYXRlOiBTYXQsIDIwIEZlYiAyMDIxIDEyOjA2OjAyIC0wNTAwDQpD
b250ZW50LVR5cGU6IG11bHRpcGFydC9taXhlZDsgYm91bmRhcnk9ImNmZiI7IHBy
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IjdiZSINCg0KLS03YmUNCkNvbnRlbnQtVHlwZTogdGV4dC9wbGFpbjsgY2hhcnNl
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ci1FbmNvZGluZzogN2JpdA0KDQpUaGlzIGlzIHRoZSBzbWltZS1vbmUtcGFydC1j
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eSBTL01JTUUgbWVzc2FnZSB2aWEgUEtDUyM3IHNpZ25lZERhdGEuICBUaGUNCnBh
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PHRpdGxlPjwvdGl0bGU+PC9oZWFkPjxib2R5Pg0KPHA+VGhpcyBpcyB0aGUgPGI+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ggemMIIDzzCCAregAwIBAgITDy0lvRE5l0rOQlSHoe49NAaKtDANBgkqhkiG9w0B
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MA8GA1UECxMITEFNUFMgV0cxFzAVBgNVBAMTDkFsaWNlIExvdmVsYWNlMIIBIjAN
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kHm+hVB+IthjLeI7Htg6rNeuXq50/TuTSxX5R1I1EXGt8p6hAQVeA5oZ2afHg4b9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A.2.8. S/MIME signed-only multipart/signed over a complex message, Injected Headers

This is a signed-only S/MIME message via PKCS#7 detached signature (multipart/signed). The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme.

It has the following structure:

└┬╴multipart/signed 5496 bytes
 ├┬╴multipart/mixed 1623 bytes
 │├┬╴multipart/alternative 992 bytes
 ││├─╴text/plain 312 bytes
 ││└─╴text/html 396 bytes
 │└─╴image/png inline 232 bytes
 └─╴application/pkcs7-signature [smime.p7s] 3429 bytes

Its contents are:

MIME-Version: 1.0
Content-Type: multipart/signed;
 protocol="application/pkcs7-signature"; boundary="a23";
 micalg="sha-256"
Subject: smime-multipart-complex-injected
Message-ID: <smime-multipart-complex-injected@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:07:02 -0500

--a23
MIME-Version: 1.0
Subject: smime-multipart-complex-injected
Message-ID: <smime-multipart-complex-injected@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:07:02 -0500
Content-Type: multipart/mixed; boundary="d03"; protected-headers="v1"

--d03
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="8d8"

--8d8
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This is the smime-multipart-complex-injected message.

This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a multipart/alternative message
with an inline image/png attachment. It uses the Injected Headers
header protection scheme.

--
Alice
alice@smime.example
--8d8
Content-Type: text/html; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

<html><head><title></title></head><body>
<p>This is the <b>smime-multipart-complex-injected</b> message.</p>
<p>This is a signed-only S/MIME message via PKCS#7 detached signature
(multipart/signed).  The payload is a multipart/alternative message
with an inline image/png attachment. It uses the Injected Headers
header protection scheme.</p>
<p><tt>-- <br/>Alice<br/>alice@smime.example</tt></p>
--8d8--

--d03
Content-Type: image/png
Content-Transfer-Encoding: base64
Content-Disposition: inline

iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAcElEQVR42uVTOxbA
MAgS739nO3TpRw20dqpbfARQEjOywiwYnCtkDKnbcLk66sqlT+zt9cidkE+6KwkZ
sgrzfcqVMpL2jo0447gYDpeArk+OnJHkIhAfTPRicihAf5YJrw7vjv0ZWRWM/uli
vdPf1QZ2kDD9xppd8wAAAABJRU5ErkJggg==

--d03--

--a23
Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-signature; name="smime.p7s"
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--a23--

A.3. Encrypted-and-signed Messages

These messages are encrypted and signed. They use PKCS#7 signedData inside envelopedData, with different header protection schemes and different Header Confidentiality Policies.

A.3.1. S/MIME encrypted and signed over a simple message, Wrapped Message with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Wrapped Message header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7345 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4436 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 679 bytes
   └─╴text/plain 321 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <smime-enc-signed-wrapped-minimal@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:08:02 -0500
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pD0GWAM1ScYPggh4t5OFmSjFtyiqawhMcQhoRsAkGV387oXupYXH/lkaD7nIdZW+
pZK1/RZUU0txvlsRIpJduXcWm/Dsu0lQtQSfcg5FaslSMjBpMI41BD2KC9M5meDP
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55gQuo1k040YMqYRwdsJGETr/r/JaEPwNekogAfuXBkNE3JQB7aVgePp8mIZNIIU
0nP6eXp95UwLsoA/zwbOv9XSYgQDCcQ0MWycXmmn4ysbeWi1p7P+6CLwgx/TNTCC
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e+cJ4z++pLB0vQeq1JlbuqY8SkSX9FyDZegnUD+zCB3qv7YSZEwD+EjifauMcrl5
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ltigpNDSlfbskC4ZUKNLmwMTed03kH2leAZGK9afAC+nNwKvSlhWovXXujmTwGao
8fQPc9cKfRS3tx5dOnEY5A6ZPbAx3SkcdHpUc/Z6Z9at0NnN80ppl55sichJeP+Q
yoWX/IMhZwNksoiP1Wqa2KYGk89l3EvBOOKMH3G/IOcilg75VxjfKQ/IrB6xrhb7
wY3YCV14MtJ4T9gi0rtkXxq6YfJ6LQVXP3BWpmlf3xwxQn3HUsQNFO/dESQMikOy
PgNT/wkwX0+v0XY59maI2tF9sMFiheLeRRjPDbwaXNCX4ghzpOA0KQ1+0/upcXPd
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A.3.2. S/MIME encrypted and signed over a simple message, Injected Headers with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7305 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4406 bytes
  ⇩ (unwraps to)
  └─╴text/plain 333 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <smime-enc-signed-injected-minimal@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:09:02 -0500

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V+LiVvvQxHGpGiZEaV7onQ==

A.3.3. S/MIME encrypted and signed over a simple message, Injected Headers with hcp_minimal (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7865 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4810 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 923 bytes
   ├─╴text/plain 51 bytes
   └─╴text/plain 370 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-injected-minimal-legacy@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:10:02 -0500

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d/X6IOqUgQyas/1WakdhSpRiHZC6MXI5WUA1Fj7DqwlckxWDar3Poy9VsvtmP47w
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A.3.4. S/MIME encrypted and signed over a simple message, Wrapped Message with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Wrapped Message header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7345 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4432 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 675 bytes
   └─╴text/plain 319 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <73a42f8e-8f5a-5c62-b982-82ace766fd32@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:11:02 -0500

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A.3.5. S/MIME encrypted and signed over a simple message, Injected Headers with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7305 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4402 bytes
  ⇩ (unwraps to)
  └─╴text/plain 331 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <27139e00-e05f-581d-a339-d2bd43bd0f42@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:12:02 -0500

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A.3.6. S/MIME encrypted and signed over a simple message, Injected Headers with hcp_strong (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7845 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4802 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 918 bytes
   ├─╴text/plain 50 bytes
   └─╴text/plain 367 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <73a42f8e-8f5a-5c62-b982-82ace766fd32@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:13:02 -0500

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A.3.7. S/MIME encrypted and signed reply over a simple message, Wrapped Message with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Wrapped Message header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7605 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4626 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 816 bytes
   └─╴text/plain 327 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <smime-enc-signed-wrapped-minimal-reply@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:14:02 -0500
In-Reply-To: <smime-enc-signed-wrapped-minimal@lhp.example>
References: <smime-enc-signed-wrapped-minimal@lhp.example>

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A.3.8. S/MIME encrypted and signed reply over a simple message, Injected Headers with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7585 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4600 bytes
  ⇩ (unwraps to)
  └─╴text/plain 339 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-injected-minimal-reply@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:15:02 -0500
In-Reply-To: <smime-enc-signed-injected-minimal@lhp.example>
References: <smime-enc-signed-injected-minimal@lhp.example>

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A.3.9. S/MIME encrypted and signed reply over a simple message, Injected Headers with hcp_minimal (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 8170 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 5034 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1082 bytes
   ├─╴text/plain 57 bytes
   └─╴text/plain 376 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-injected-minimal-legacy-reply@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:16:02 -0500
In-Reply-To:
 <smime-enc-signed-injected-minimal-legacy@lhp.example>
References:
 <smime-enc-signed-injected-minimal-legacy@lhp.example>

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A.3.10. S/MIME encrypted and signed reply over a simple message, Wrapped Message with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Wrapped Message header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7605 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4616 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 810 bytes
   └─╴text/plain 325 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <fdccb76a-49ed-50c5-9030-e4aeb83d7f04@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:17:02 -0500

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A.3.11. S/MIME encrypted and signed reply over a simple message, Injected Headers with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 7565 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 4592 bytes
  ⇩ (unwraps to)
  └─╴text/plain 337 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <0e210732-9184-5855-9a95-2a635560d3a6@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:18:02 -0500

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w7LgVMRJKMMDllquSaKDrQ==

A.3.12. S/MIME encrypted and signed reply over a simple message, Injected Headers with hcp_strong (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a text/plain message. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 8150 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 5022 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1075 bytes
   ├─╴text/plain 56 bytes
   └─╴text/plain 373 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <27139e00-e05f-581d-a339-d2bd43bd0f42@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 10:19:02 -0500

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x8UuwNnS1G6MeJGd5oXIzA==

A.3.13. S/MIME encrypted and signed over a complex message, Wrapped Message with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Wrapped Message header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9450 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 5982 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 1805 bytes
   └┬╴multipart/mixed 1741 bytes
    ├┬╴multipart/alternative 1118 bytes
    │├─╴text/plain 375 bytes
    │└─╴text/html 459 bytes
    └─╴image/png inline 232 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-complex-wrapped-minimal@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:08:02 -0500

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A.3.14. S/MIME encrypted and signed over a complex message, Injected Headers with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9470 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6006 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1771 bytes
   ├┬╴multipart/alternative 1122 bytes
   │├─╴text/plain 387 bytes
   │└─╴text/html 468 bytes
   └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-complex-injected-minimal@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:09:02 -0500

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A.3.15. S/MIME encrypted and signed over a complex message, Injected Headers with hcp_minimal (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 10120 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6474 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 2095 bytes
   ├─╴text/plain 59 bytes
   └┬╴multipart/mixed 1600 bytes
    ├┬╴multipart/alternative 1194 bytes
    │├─╴text/plain 424 bytes
    │└─╴text/html 505 bytes
    └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-complex-injected-minimal-legacy@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:10:02 -0500

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A.3.16. S/MIME encrypted and signed over a complex message, Wrapped Message with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Wrapped Message header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9425 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 5974 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 1799 bytes
   └┬╴multipart/mixed 1735 bytes
    ├┬╴multipart/alternative 1114 bytes
    │├─╴text/plain 373 bytes
    │└─╴text/html 457 bytes
    └─╴image/png inline 232 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <0b3ea6dd-0e91-5a91-9bc0-3d553f892983@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:11:02 -0500

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A.3.17. S/MIME encrypted and signed over a complex message, Injected Headers with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9470 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 5998 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1765 bytes
   ├┬╴multipart/alternative 1118 bytes
   │├─╴text/plain 385 bytes
   │└─╴text/html 466 bytes
   └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <b10dcc75-cf43-5fd7-9e48-f932a9d68fb5@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:12:02 -0500

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A.3.18. S/MIME encrypted and signed over a complex message, Injected Headers with hcp_strong (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 10100 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6460 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 2088 bytes
   ├─╴text/plain 58 bytes
   └┬╴multipart/mixed 1596 bytes
    ├┬╴multipart/alternative 1190 bytes
    │├─╴text/plain 421 bytes
    │└─╴text/html 502 bytes
    └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <fdccb76a-49ed-50c5-9030-e4aeb83d7f04@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:13:02 -0500

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Gd0+hXYLrw1ooZzXU7ujig==

A.3.19. S/MIME encrypted and signed reply over a complex message, Wrapped Message with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Wrapped Message header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9750 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6200 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 1964 bytes
   └┬╴multipart/mixed 1900 bytes
    ├┬╴multipart/alternative 1130 bytes
    │├─╴text/plain 381 bytes
    │└─╴text/html 465 bytes
    └─╴image/png inline 232 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-complex-wrapped-minimal-reply@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:14:02 -0500
In-Reply-To:
 <smime-enc-signed-complex-wrapped-minimal@lhp.example>
References:
 <smime-enc-signed-complex-wrapped-minimal@lhp.example>

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A.3.20. S/MIME encrypted and signed reply over a complex message, Injected Headers with hcp_minimal

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9775 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6230 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1932 bytes
   ├┬╴multipart/alternative 1134 bytes
   │├─╴text/plain 393 bytes
   │└─╴text/html 474 bytes
   └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID:
 <smime-enc-signed-complex-injected-minimal-reply@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:15:02 -0500
In-Reply-To:
 <smime-enc-signed-complex-injected-minimal@lhp.example>
References:
 <smime-enc-signed-complex-injected-minimal@lhp.example>

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A.3.21. S/MIME encrypted and signed reply over a complex message, Injected Headers with hcp_minimal (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_minimal Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 10465 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6728 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 2278 bytes
   ├─╴text/plain 65 bytes
   └┬╴multipart/mixed 1612 bytes
    ├┬╴multipart/alternative 1206 bytes
    │├─╴text/plain 430 bytes
    │└─╴text/html 511 bytes
    └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <smime-enc-signed-complex-injected-minimal-legacy-reply@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:16:02 -0500
In-Reply-To:
 <smime-enc-signed-complex-injected-minimal-legacy@lhp.example>
References:
 <smime-enc-signed-complex-injected-minimal-legacy@lhp.example>

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A.3.22. S/MIME encrypted and signed reply over a complex message, Wrapped Message with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Wrapped Message header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9730 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6192 bytes
  ⇩ (unwraps to)
  └┬╴message/rfc822 1956 bytes
   └┬╴multipart/mixed 1892 bytes
    ├┬╴multipart/alternative 1126 bytes
    │├─╴text/plain 379 bytes
    │└─╴text/html 463 bytes
    └─╴image/png inline 232 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <95b9bb39-c028-5ff4-99b1-f179cb5d7585@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:17:02 -0500

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A.3.23. S/MIME encrypted and signed reply over a complex message, Injected Headers with hcp_strong

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 9775 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6222 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 1924 bytes
   ├┬╴multipart/alternative 1130 bytes
   │├─╴text/plain 391 bytes
   │└─╴text/html 472 bytes
   └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <23abef5f-8781-5c95-a46c-61e3a4464d58@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:18:02 -0500

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dTYlFvjuVh2TudqGzxeP9g==

A.3.24. S/MIME encrypted and signed reply over a complex message, Injected Headers with hcp_strong (+ Legacy Display)

This is a encrypted and signed S/MIME message using PKCS#7 envelopedData around signedData. The payload is a multipart/alternative message with an inline image/png attachment. It uses the Injected Headers header protection scheme with the hcp_strong Header Confidentiality Policy with a "Legacy Display" part.

It has the following structure:

└─╴application/pkcs7-mime [smime.p7m] 10445 bytes
 ↧ (decrypts to)
 └─╴application/pkcs7-mime [smime.p7m] 6712 bytes
  ⇩ (unwraps to)
  └┬╴multipart/mixed 2269 bytes
   ├─╴text/plain 64 bytes
   └┬╴multipart/mixed 1608 bytes
    ├┬╴multipart/alternative 1202 bytes
    │├─╴text/plain 427 bytes
    │└─╴text/html 508 bytes
    └─╴image/png inline 236 bytes

Its contents are:

Content-Transfer-Encoding: base64
Content-Type: application/pkcs7-mime; name="smime.p7m";
 smime-type="enveloped-data"
Subject: [...]
Message-ID: <0e210732-9184-5855-9a95-2a635560d3a6@lhp.example>
From: Alice <alice@smime.example>
To: Bob <bob@smime.example>
Date: Sat, 20 Feb 2021 12:19:02 -0500

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Appendix B. Additional information

B.1. Stored Variants of Messages with Bcc

Messages containing at least one recipient address in the Bcc header field may appear in up to three different variants:

  1. The Message for the recipient addresses listed in To or Cc header fields, which must not include the Bcc header field neither for signature calculation nor for encryption.
  2. The Message(s) sent to the recipient addresses in the Bcc header field, which depends on the implementation:

    a) One Message for each recipient in the Bcc header field separately, with a Bcc header field containing only the address of the recipient it is sent to.

    b) The same Message for each recipient in the Bcc header field with a Bcc header field containing an indication such as "Undisclosed recipients", but no addresses.

    c) The same Message for each recipient in the Bcc header field which does not include a Bcc header field (this Message is identical to 1. / cf. above).

  3. The Message stored in the 'Sent'-Folder of the sender, which usually contains the Bcc unchanged from the original Message, i.e., with all recipient addresses.

The most privacy preserving method of the alternatives (2a, 2b, and 2c) is to standardize 2a, as in the other cases (2b and 2c), information about hidden recipients is revealed via keys. In any case, the Message has to be cloned and adjusted depending on the recipient.

Appendix C. Text Moved from Above

Note: Per an explicit request by the chair of the LAMPS WG to only present one option for the specification, the following text has been stripped from the main body of the draft. It is preserved in an Appendix for the time being and may be moved back to the main body or deleted, depending on the decision of the LAMPS WG.

C.1. MIME Format

Currently there are two options in discussion:

  1. The option according to the current S/MIME specification (cf. [RFC8551])
  2. An alternative option that is based on the former "memory hole" approach (cf. [I-D.autocrypt-lamps-protected-headers])

C.1.1. S/MIME Specification

Note: This is currently described in the main part of this document.

C.1.1.1. Alternative Option Autocrypt "Protected Headers" (Ex-"Memory Hole")

An alternative option (based on the former autocrypt "Memory Hole" approach) to be considered, is described in [I-D.autocrypt-lamps-protected-headers].

Unlike the option described in Appendix C.1.1, this option does not use a "message/RFC822" wrapper to unambiguously delimit the Inner Message.

Before choosing this option, the following two issues must be assessed to ensure no interoperability issues result from it:

  1. How current MIME parser implementations treat non-MIME Header Fields, which are not part of the outermost MIME entity and not part of a Message wrapped into a MIME entity of media type "message/rfc822", and how such Messages are rendered to the user.

    [I-D.autocrypt-lamps-protected-headers] provides some examples for testing this.

  2. MIME-conformance, i.e. whether or not this option is (fully) MIME-conformant [RFC2045] ff., in particular also Section 5.1. of [RFC2046] on "Multipart Media Type). In the following an excerpt of paragraphs that may be relevant in this context:
      The only header fields that have defined meaning for body parts
      are those the names of which begin with "Content-".  All other
      header fields may be ignored in body parts.  Although they
      should generally be retained if at all possible, they may be
      discarded by gateways if necessary.  Such other fields are
      permitted to appear in body parts but must not be depended on.
      "X-" fields may be created for experimental or private
      purposes, with the recognition that the information they
      contain may be lost at some gateways.
      NOTE:  The distinction between an RFC 822 Message and a body
      part is subtle, but important.  A gateway between Internet and
      X.400 mail, for example, must be able to tell the difference
      between a body part that contains an image and a body part
      that contains an encapsulated Message, the body of which is a
      JPEG image.  In order to represent the latter, the body part
      must have "Content-Type: message/rfc822", and its body (after
      the blank line) must be the encapsulated Message, with its own
      "Content-Type: image/jpeg" header field.  The use of similar
      syntax facilitates the conversion of Messages to body parts,
      and vice versa, but the distinction between the two must be
      understood by implementors.  (For the special case in which
      parts actually are Messages, a "digest" subtype is also
      defined.)

The MIME structure of an Email Message looks as follows:

  <Outer Message Header Section (unprotected)>

  <Outer Message Body (protected)>

    <Inner Message Header Section>

    <Inner Message Body>

The following example demonstrates how an Original Message might be protected, i.e., the Original Message is contained as Inner Message in the Protected Body of an Outer Message. It illustrates the first Body part (of the Outer Message) as a "multipart/signed" (application/pkcs7-signature) media type:

Lines are prepended as follows:

  • "O: " Outer Message Header Section
  • "I: " Message Header Section
  O: Date: Mon, 25 Sep 2017 17:31:42 +0100 (GMT Daylight Time)
  O: Message-ID: <e4a483cb-1dfb-481d-903b-298c92c21f5e@m.example.net>
  O: Subject: Meeting at my place
  O: From: "Alexey Melnikov" <alexey.melnikov@example.net>
  O: MIME-Version: 1.0
  O: Content-Type: multipart/signed; charset=us-ascii; micalg=sha1;
  O:  protocol="application/pkcs7-signature";
  O:  boundary=boundary-AM

     This is a multipart message in MIME format.
     --boundary-AM
  I: Date: Mon, 25 Sep 2017 17:31:42 +0100 (GMT Daylight Time)
  I: From: "Alexey Melnikov" <alexey.melnikov@example.net>
  I: Message-ID: <e4a483cb-1dfb-481d-903b-298c92c21f5e@m.example.net>
  I: MIME-Version: 1.0
  I: MMHS-Primary-Precedence: 3
  I: Subject: Meeting at my place
  I: To: somebody@example.net
  I: X-Mailer: Isode Harrier Web Server
  I: Content-Type: text/plain; charset=us-ascii

     This is an important message that I don't want to be modified.

     --boundary-AM
     Content-Transfer-Encoding: base64
     Content-Type: application/pkcs7-signature

     [[base-64 encoded signature]]

     --boundary-AM--

The Outer Message Header Section is unprotected, while the remainder (Outer Message Body) is protected. The Outer Message Body consists of the Inner Message (Header Section and Body).

The Inner Message Header Section is the same as (or a subset of) the Original Message Header Section.

The Inner Message Body is the same as the Original Message Body.

The Original Message itself may contain any MIME structure.

C.1.2. Sending Side

To ease explanation, the following describes the case where an Original (message/rfc822) Message to be protected is present. If this is not the case, Original Message means the (virtual) Message that would be constructed for sending it as unprotected email.

C.1.2.1. Inner Message Header Fields

It is RECOMMENDED that the Inner Message contains all Header Fields of the Original Message with the exception of the following Header Field, which MUST NOT be included within the Inner Message nor within any other protected part of the Message:

[[ TODO: Bcc handling needs to be further specified (see also Appendix B.1). Certain MUAs cannot properly decrypt Messages with Bcc recipients. ]]

C.1.2.2. Wrapper

The wrapper is a simple MIME Header Section followed by an empty line preceding the Inner Message (inside the Outer Message Body). The media type of the wrapper MUST be "message/RFC822" and MUST contain the Content-Type header field parameter "forwarded=no" as defined in [I-D.melnikov-iana-reg-forwarded]. The wrapper unambiguously delimits the Inner Message from the rest of the Message.

C.1.2.3. Cryptographic Layers / Envelope

[[ TODO: Basically refer to S/MIME standards ]]

C.1.2.4. Sending Side Message Processing

For a protected Message the following steps are applied before a Message is handed over to the Submission Entity:

C.1.2.4.1. Step 1: Decide on Protection Level and Information Disclosure

The implementation which applies protection to a Message must decide:

  • Which Protection Level (signature and/or encryption) shall be applied to the Message? This depends on user request and/or local policy as well as availability of cryptographic keys.
  • Which Header Fields of the Original Message shall be part of the Outer Message Header Section? This typically depends on local policy. By default, the Essential Header Fields are part of the Outer Message Header Section; cf. Appendix C.1.2.5.
  • Which of these Header Fields are to be obfuscated? This depends on local policy and/or specific Privacy requirements of the user. By default only the Subject Header Field is obfuscated; cf. Appendix C.1.2.5.
C.1.2.4.2. Step 2: Compose the Outer Message Header Section

Depending on the decision in Appendix C.1.2.4.1, the implementation shall compose the Outer Message Header Section. (Note that this also includes the necessary MIME Header Section part for the following protection layer.)

Outer Header Fields that are not obfuscated should contain the same values as in the Original Message (except for MIME Header Section part, which depends on the Protection Level selected in Appendix C.1.2.4.1).

C.1.2.4.3. Step 3: Apply Protection to the Original Message

Depending on the Protection Level selected in Appendix C.1.2.4.1, the implementation applies signature and/or encryption to the Original Message, including the wrapper (as per [RFC8551]), and sets the resulting package as the Outer Message Body.

The resulting (Outer) Message is then typically handed over to the Submission Entity.

[[ TODO: Example ]]

C.1.2.5. Outer Message Header Fields

C.1.2.5.1. Encrypted Messages

To maximize Privacy, it is strongly RECOMMENDED to follow the principle of Data Minimization (cf. Section 2.1).

However, the Outer Message Header Section SHOULD contain the Essential Header Fields and, in addition, MUST contain the Header Fields of the MIME Header Section part to describe Cryptographic Layer of the protected MIME subtree as per [RFC8551].

The following Header Fields are defined as the Essential Header Fields:

  • From
  • To (if present in the Original Message)
  • Cc (if present in the Original Message)
  • Bcc (if present in the Original Message, see also Appendix B.1)
  • Date
  • Message-ID
  • Subject

Further processing by the Submission Entity normally depends on part of these Header Fields, e.g. From and Date HFs are required by [RFC5322]. Furthermore, not including certain Header Fields may trigger spam detection to flag the Message, and/or lead to user experience (UX) issues.

For further Data Minimization, the value of the Subject Header Field SHOULD be obfuscated as follows:

* Subject: [...]

and it is RECOMMENDED to replace the Message-ID by a new randomly generated Message-ID.

In addition, the value of other Essential Header Fields MAY be obfuscated.

Non-Essential Header Fields SHOULD be omitted from the Outer Message Header Section where possible. If Non-essential Header Fields are included in the Outer Message Header Section, those MAY be obfuscated too.

Header Fields that are not obfuscated should contain the same values as in the Original Message.

If an implementation obfuscates the From, To, and/or Cc Header Fields, it may need to provide access to the clear text content of these Header Fields to the Submission Entity for processing purposes. This is particularly relevant, if proprietary Submission Entities are used. Obfuscation of Header Fields may adversely impact spam filtering.

(A use case for obfuscation of all Outer Message Header Fields is routing email through the use of onion routing or mix networks, e.g. [pEp.mixnet].)

The MIME Header Section part is the collection of MIME Header Fields describing the following MIME structure as defined in [RFC2045]. A MIME Header Section part typically includes the following Header Fields:

  • Content-Type
  • Content-Transfer-Encoding
  • Content-Disposition

The following example shows the MIME Header Section part of an S/MIME signed Message (using application/pkcs7-mime with SignedData):

   MIME-Version: 1.0
   Content-Type: application/pkcs7-mime; smime-type=signed-data;
      name=smime.p7m
   Content-Transfer-Encoding: base64
   Content-Disposition: attachment; filename=smime.p7m

Depending on the scenario, further Header Fields MAY be exposed in the Outer Message Header Section, which is NOT RECOMMENDED unless justified. Such Header Fields may include e.g.:

  • References
  • Reply-To
  • In-Reply-To
C.1.2.5.2. Unencrypted Messages

The Outer Message Header Section of unencrypted Messages SHOULD contain at least the Essential Header Fields and, in addition, MUST contain the Header Fields of the MIME Header Section part to describe Cryptographic Layer of the protected MIME subtree as per [RFC8551]. It may contain further Header Fields, in particular those also present in the Inner Message Header Section.

Appendix D. Document Considerations

[[ RFC Editor: This section is to be removed before publication ]]

This draft is built from markdown source, and its development is tracked in a git repository.

While minor editorial suggestions and nit-picks can be made as merge requests, please direct all substantive discussion to the LAMPS mailing list at spasm@ietf.org.

Appendix E. Document Changelog

[[ RFC Editor: This section is to be removed before publication ]]

Appendix F. Open Issues

[[ RFC Editor: This section should be empty and is to be removed before publication. ]]

Authors' Addresses

Daniel Kahn Gillmor
American Civil Liberties Union
125 Broad St.
New York, NY, 10004
United States of America
Bernie Hoeneisen
pEp Foundation
Oberer Graben 4
CH- CH-8400 Winterthur
Switzerland
Alexey Melnikov
Isode Ltd
14 Castle Mews
Hampton, Middlesex
TW12 2NP
United Kingdom