Internet Draft Paul Hoffman draft-hoffman-rescap-mua-00.txt Internet Mail Consortium March 23, 1999 Expires in six months Rescap Profile for Mail User Agents Status of this memo Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 1. Introduction This document defines a profile of the rescap protocol for mail user agents (MUAs) and mail recipients. It describes the attributes that a mail sender might want or need to know about a particular mail recipient before sending a message. The attributes are divided into four general categories: - MIME handling - S/MIME - OpenPGP - General Note: this list is very preliminary. The process of defining the requirements for rescap has just begun. Because the rescap protocol has not even had a first draft, it is likely that there will be many significant changes to this draft in the future as rescap gets worked on. In this document, "recipient" is used to indicate the user who can accept mail at the URL provided in the rescap request and "sender" is the person or process who requested the rescap information. Note that some of the attributes in this document apply to the MUA a recipient is using, while others apply directly to the mail recipient (which might be a human or a mail-processing program). The attributes described in this document are those that a mail sender would want to know about a recipient or the recipient's MUA. Attributes about the mail recipient that have no relevance to a mail sender (such if the MUA uses IMAP to access its message store) are not included. 2. MIME Handling The attributes in this section describe general MIME handling. They include some specific MIME profiles as well as more general MIME characteristics. Identifier: HandlesMIME Value type: Boolean Description: Conforms to [MIME-CONFORM], the general checklist for MIME conformance. Identifier: MIMEHeaderExtensions Value type: Boolean Description: Conforms to [MIME-HEADER-EXTENSIONS], which describes many extensions for MIME headers, such as for non-ASCII characters. Identifier: MIMEParamExtensions Value type: Boolean Description: Conforms to [MIME-PARAM], which describes many extensions for MIME parameter values and encoded words. Identifier: DisplayableMedia Value type: Conneg string Description: A list of MIME types and subtypes that are natively displayed by the receiving MUA without falling back to a default media type. The string is in the format of [CONNEG], as extended by [CONNEG-MEDIA]. This string should contain only MIME types and subtypes, not additional media features. Identifier: MediaFeatures Value type: Conneg string Description: A list of media features of the MUA. The string is in the format of [CONNEG]. Identifier: CharsetsDisplayed Value type: List of strings Description: The list of charset labels that describe the charsets [CHARSET] that can be displayed. The list is in order of preferred charsets, highest preference first. Identifier: PreferredLanguages Value type: List of strings Description: The lists of languages understandable to the recipient, as described in [LANG]. The list is in order of preferred languages, highest preference first. Identifier: HandlesMHTML Value type: Boolean Description: Handles MHTML content natively, as described in [MHTML]. Identifier: HandlesContentDisposition Value type: List of strings Description: Handles Conetent-Disposition headers, as described in [CONTENT-DISP]. The strings must be "inline", "attachment", and "metadata". If the MUA doesn't handle any Content-Disposition headers, then the list should be empty. Identifier: HandlesContentMD5 Value type: Boolean Description: Handles Conetent-MD5 headers, as described in [CONTENT-MD5]. Identifier: HandlesMailingListURLs Value type: Boolean Description: Handles mailing list URL headers, as described in [LIST-URLS]. Identifier: HandlesPlainFormat Value type: Boolean Description: Handles the "format" parameter for the text/plain MIME type, as described in [PLAIN-FORMAT]. Identifier: HandlesOnePassMultipart Value type: Boolean Description: Handles the "types" parameter for the multipart/alternative MIME type, as described in [MULTIPART-ONEPASS]. Identifier: RepliesToMDNs Value type: Boolean Description: Is able to reply to message disposition notification requests, as described in [MDN]. Note that this does not mean that the client will necessarily send an MDN back to a particular request, just that it is able to reply to such requests. Identifier: CalendarClient Value type: Boolean Description: Can act as an iCalendar iMIP agent [IMIP]. Identifier: FaxSimpleClient Value type: Boolean Description: Acts as a simple mode Internet FAX receiving agent [IFAX-SIMPLE]. Identifier: FaxExtendedClient Value type: Boolean Description: Acts as a extended mode Internet FAX receiving agent [IFAX-EIFAX]. 3. S/MIME The attributes in this section indicate the S/MIME capabilities of the recipient as described in [SMIME-MSG], [SMIME-CERT], and associated documents. Note that some S/MIME public keys are used for both encrypting and signing. This means that there may be duplicated certificates in the SMIMESigningCertsBasic and SMIMEEncryptingCerts lists. Identifier: SMIMEVerifiesSigned Value type: List of strings Description: Indicates that the recipient can verify the signatures on S/MIME signed messages. The strings in the list indicate the type of signatures accepted. The values currently are limited to "id-dsa" and "rsaEncryption". The list is in decreasing order of preference. Identifier: SMIMESigningCertsBasic Value type: List of binary Description: Provides the S/MIME certificates for public signing keys of the recipient. The list is in decreasing order of preference. Identifier: SMIMESigningCertsExtended Value type: List of binary Description: Provides the S/MIME certificates for public signing keys of the recipient, including additional signed attributes, as described in [SMIME-CERTDIST]. The list is in decreasing order of preference. Identifier: SMIMEEncryptingCerts Value type: List of binary Description: Provides the S/MIME certificates for public encrypting keys of the recipient. The list is in decreasing order of preference. Identifier: SMIMEHigherCerts Value type: List of binary Description: Provides the S/MIME certificates for certificate authorities that have signed the recipient's signing and encrypting certificates. These higher-level certificates can be used by the sender to validate the recipient's certificates. The list is in no particular order. Identifier: SMIMESignedReceipts Value type: Boolean Description: Responds to requests for S/MIME signed receipts described in [SMIME-ESS]. Identifier: SMIMESecurityLabels Value type: Boolean Description: Acts on S/MIME security labels, or is behind a gateway that does security label handling, as described in [SMIME-ESS]. Identifier: SMIMESecureMailingList Value type: Boolean Description: Is a a mailing list that uses secure mailing list handling described in [SMIME-ESS]. Identifier: SMIMEHandlesSigningCert Value type: Boolean Description: Handles the signed SigningCertificate attribute described in [SMIME-ESS]. 4. OpenPGP The attributes in this section indicate the OpenPGP capabilities of the recipient as described in [OPEN-PGP] and associated documents. Identifier: OpenPGPVerifiesSigned Value type: List of strings Description: Indicates that the recipient can verify the signatures on OpenPGP signed messages. The strings in the list indicate the type of signatures accepted. The values currently are limited to "DSA" and "RSA". The list is in decreasing order of preference. Identifier: OpenPGPSigningCertsBasic Value type: List of binary Description: Provides the OpenPGP certificates for public signing keys of the recipient. The list is in decreasing order of preference. Identifier: OpenPGPEncryptingCerts Value type: List of binary Description: Provides the OpenPGP certificates for public encrypting keys of the recipient. The list is in decreasing order of preference. Identifier: OpenPGPHigherCerts Value type: List of binary Description: Provides the OpenPGP certificates for users and certificate authorities that have signed the recipient's signing and encrypting certificates. These higher-level certificates can be used by the sender to validate the recipient's certificates. The list is in no particular order. 5. General User agent and recipient attributes that don't fit into the other categories appear in this section. Identifier: UBEPrefernces Value type: List of pairs of strings Description: Specifies the preferences of the recipient for receiving unsolicited bulk email (UBE). Each entry in the list is a pair of strings. The first entry in the pair is a tag indicating the law or policy being referred to, and the second entry is the value specified for that law or policy. The identities of the laws and policies must be registered with IANA. 6. Security Considerations The rescap protocol will control the security of the passing the values for the attributes described here. If digital signatures are not used, an attacker can alter the values that the client receives from the server, thereby causing false values or no values to be received. For example, an attacker can change the legal notices sent, which can cause damage to the named recipient. If encryption is not used, an attacker can watch the values of the attributes as they are transmitted over the Internet. 7. References [CHARSET] "IANA Charset Registration Procedures", RFC 2278 [CONNEG] "A Syntax for Describing Media Feature Sets", RFC 2553. [CONNEG-MEDIA] "MIME content types in media feature expressions", draft-ietf-conneg-feature-type. [CONTENT-DISP] "Communicating Presentation Information in Internet Messages: The Content-Disposition Header", RFC 2183; and "Metadata Content-Disposition Type", draft-newman-mime-cdisp-metadata. [CONTENT-MD5] "The Content-MD5 Header Field", RFC 1864. [IFAX-EIFAX] "Extended Facsimile Using Internet Mail", RFC 2532. [IFAX-SIMPLE] "A Simple Mode of Facsimile Using Internet Mail", RFC 2305. [IMIP] "iCalendar Message-Based Interoperability Protocol (iMIP)", RFC 2447. [LANG] "Tags for the Identification of Languages", RFC 1766. [LIST-URLS] "The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields", RFC 2369. [MDN] "An Extensible Message Format for Message Disposition Notifications", RFC 2298. [MHTML] "MIME E-mail Encapsulation of Aggregate Documents, such as HTML (MHTML)", RFC 2110. [MIME-CONFORM] "Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC 2049. [MIME-HEADER-EXTENSIONS] "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047. [MIME-PARAM] "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations", RFC 2231. [MULTIPART-ONEPASS] "One Pass Multipart/Alternative Processing", draft-lundblade-1pass-mult-alt. [OPEN-PGP] "OpenPGP Message Format", RFC 2440. [PLAIN-FORMAT] "The Text/Plain Format Parameter", draft-gellens-format. [SMIME-CERT] "S/MIME Version 3 Certificate Handling", draft-ietf-smime-cert. [SMIME-CERTDIST] "Certificate Distribution Specification", draft-ietf-smime-certdist. [SMIME-ESS] "Enhanced Security Services for S/MIME", draft-ietf-smime-ess. [SMIME-MSG] "S/MIME Version 3 Message Specification", draft-ietf-smime-msg. A. IANA Registrations A.1 Attribute Identifier Registrations [[It is likely that all the attribute identifiers in this document will need to be registered.]] A.2 Additional Registrations [[Registration of UCE law and policy identifiers]] B. Author's Address Paul Hoffman Internet Mail Consortium 127 Segre Place Santa Cruz, CA 95060 (831) 426-9827 phoffman@imc.org