< draft-ietf-uta-tls-bcp-05.txt   draft-ietf-uta-tls-bcp-06.txt >
UTA Y. Sheffer UTA Y. Sheffer
Internet-Draft Porticor Internet-Draft Porticor
Intended status: Best Current Practice R. Holz Intended status: Best Current Practice R. Holz
Expires: April 17, 2015 TUM Expires: April 26, 2015 TUM
P. Saint-Andre P. Saint-Andre
&yet &yet
October 14, 2014 October 23, 2014
Recommendations for Secure Use of TLS and DTLS Recommendations for Secure Use of TLS and DTLS
draft-ietf-uta-tls-bcp-05 draft-ietf-uta-tls-bcp-06
Abstract Abstract
Transport Layer Security (TLS) and Datagram Transport Security Layer Transport Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) are widely used to protect data exchanged over application (DTLS) are widely used to protect data exchanged over application
protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the
last few years, several serious attacks on TLS have emerged, last few years, several serious attacks on TLS have emerged,
including attacks on its most commonly used cipher suites and modes including attacks on its most commonly used cipher suites and modes
of operation. This document provides recommendations for improving of operation. This document provides recommendations for improving
the security of deployed services that use TLS and DTLS. The the security of deployed services that use TLS and DTLS. The
recommendations are applicable to the majority of use cases. recommendations are applicable to the majority of use cases.
Status of This Memo Status of This Memo
skipping to change at page 1, line 40 skipping to change at page 1, line 40
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2015. This Internet-Draft will expire on April 26, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 17 skipping to change at page 2, line 17
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Intended Audience and Applicability Statement . . . . . . . . 4 2. Intended Audience and Applicability Statement . . . . . . . . 4
2.1. Security Services . . . . . . . . . . . . . . . . . . . . 4 2.1. Security Services . . . . . . . . . . . . . . . . . . . . 4
2.2. Unauthenticated TLS . . . . . . . . . . . . . . . . . . . 5 2.2. Unauthenticated TLS . . . . . . . . . . . . . . . . . . . 5
3. Conventions used in this document . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. General Recommendations . . . . . . . . . . . . . . . . . . . 6 4. General Recommendations . . . . . . . . . . . . . . . . . . . 6
4.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 6 4.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 6
4.1.1. SSL/TLS Protocol Versions . . . . . . . . . . . . . . 6 4.1.1. SSL/TLS Protocol Versions . . . . . . . . . . . . . . 6
4.1.2. DTLS Protocol Versions . . . . . . . . . . . . . . . 7 4.1.2. DTLS Protocol Versions . . . . . . . . . . . . . . . 7
4.1.3. Fallback to Earlier Versions . . . . . . . . . . . . 7 4.1.3. Fallback to Lower Versions . . . . . . . . . . . . . 7
4.2. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 8 4.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 8 4.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 9
4.5. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 9 4.5. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 9
4.6. Server Name Indication . . . . . . . . . . . . . . . . . 9 4.6. Server Name Indication . . . . . . . . . . . . . . . . . 10
5. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 9 5. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 10
5.1. General Guidelines . . . . . . . . . . . . . . . . . . . 10 5.1. General Guidelines . . . . . . . . . . . . . . . . . . . 10
5.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 11 5.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 11
5.3. Cipher Suite Negotiation Details . . . . . . . . . . . . 11 5.3. Cipher Suite Negotiation Details . . . . . . . . . . . . 12
5.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 12 5.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 12
5.5. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 12 5.5. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 13
5.6. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 13 5.6. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 14 7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 14
7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 14 7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 15
7.4. Diffie-Hellman Exponent Reuse . . . . . . . . . . . . . . 15 7.4. Diffie-Hellman Exponent Reuse . . . . . . . . . . . . . . 16
7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 16 7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 16
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17 9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 17 9.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 20 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 21
A.1. draft-ietf-uta-tls-bcp-05 . . . . . . . . . . . . . . . . 20 A.1. draft-ietf-uta-tls-bcp-06 . . . . . . . . . . . . . . . . 21
A.2. draft-ietf-uta-tls-bcp-04 . . . . . . . . . . . . . . . . 20 A.2. draft-ietf-uta-tls-bcp-05 . . . . . . . . . . . . . . . . 21
A.3. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 20 A.3. draft-ietf-uta-tls-bcp-04 . . . . . . . . . . . . . . . . 21
A.4. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 20 A.4. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 21
A.5. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 21 A.5. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 21
A.6. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 21 A.6. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 22
A.7. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 21 A.7. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 22
A.8. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 21 A.8. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 22
A.9. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 22 A.9. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 A.10. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
Transport Layer Security (TLS) and Datagram Transport Security Layer Transport Layer Security (TLS) [RFC5246] and Datagram Transport
(DTLS) are widely used to protect data exchanged over application Security Layer (DTLS) [RFC6347] are widely used to protect data
protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the exchanged over application protocols such as HTTP, SMTP, IMAP, POP,
last few years, several serious attacks on TLS have emerged, SIP, and XMPP. Over the last few years, several serious attacks on
including attacks on its most commonly used cipher suites and modes TLS have emerged, including attacks on its most commonly used cipher
of operation. For instance, both the AES-CBC and RC4 encryption suites and modes of operation. For instance, both the AES-CBC
algorithms, which together comprise most current usage, have been [RFC3602] and RC4 [I-D.ietf-tls-prohibiting-rc4] encryption
attacked in the context of TLS. A companion document algorithms, which together are the most widely deployed ciphers, have
been attacked in the context of TLS. A companion document
[I-D.ietf-uta-tls-attacks] provides detailed information about these [I-D.ietf-uta-tls-attacks] provides detailed information about these
attacks. attacks.
Because of these attacks, those who implement and deploy TLS and DTLS Because of these attacks, those who implement and deploy TLS and DTLS
need updated guidance on how TLS can be used securely. Note that need updated guidance on how TLS can be used securely. This document
this document provides guidance for deployed services as well as provides guidance for deployed services as well as for software
software implementations, assuming the implementer expects his or her implementations, assuming the implementer expects his or her code to
code to be deployed in environments defined in the following section. be deployed in environments defined in the following section. In
In fact, this document calls for the deployment of algorithms that fact, this document calls for the deployment of algorithms that are
are widely implemented but not yet widely deployed. Concerning widely implemented but not yet widely deployed. Concerning
deployment, this document targets a wide audience, namely all deployment, this document targets a wide audience, namely all
deployers who wish to add confidentiality and data integrity deployers who wish to add authentication (be it one-way only or
protection to their communications. In many (but not all) cases mutual), confidentiality, and data integrity protection to their
authentication is also desired. This document does not address the communications.
rare deployment scenarios where no confidentiality is desired.
The recommendations herein take into consideration the security of The recommendations herein take into consideration the security of
various mechanisms, their technical maturity and interoperability, various mechanisms, their technical maturity and interoperability,
and their prevalence in implementations at the time of writing. and their prevalence in implementations at the time of writing.
Unless noted otherwise, these recommendations apply to both TLS and Unless noted otherwise, these recommendations apply to both TLS and
DTLS. TLS 1.3, when it is standardized and deployed in the field, DTLS. TLS 1.3, when it is standardized and deployed in the field,
should resolve the current vulnerabilities while providing should resolve the current vulnerabilities while providing
significantly better functionality and will very likely obsolete this significantly better functionality. It will very likely obsolete
document. this document.
These are minimum recommendations for the use of TLS for the These are minimum recommendations for the use of TLS for the
specified audience. Individual specifications may have stricter specified audience. Individual specifications can have stricter
requirements related to one or more aspects of the protocol, based on requirements related to one or more aspects of the protocol, based on
their particular circumstances. When that is the case, implementers their particular circumstances (e.g., for use with a particular
MUST adhere to those stricter requirements. application protocol). When that is the case, implementers are
advised to adhere to those stricter requirements.
Community knowledge about the strength of various algorithms and Community knowledge about the strength of various algorithms and
feasible attacks can change quickly, and experience shows that a feasible attacks can change quickly, and experience shows that a
security BCP is a point-in-time statement. Readers are advised to security BCP is a point-in-time statement. Readers are advised to
seek out any errata or updates that apply to this document. seek out any errata or updates that apply to this document.
2. Intended Audience and Applicability Statement 2. Intended Audience and Applicability Statement
The deployment recommendations address the operators of application The deployment recommendations of this document address the operators
layer services that are most commonly used on the Internet, of application layer services that are most commonly used on the
including, but not limited to: Internet, including, but not limited to:
o Operators of WWW servers that wish to protect HTTP with TLS. o Operators of WWW servers that wish to protect HTTP with TLS.
o Operators of email servers who wish to protect the application- o Operators of email servers who wish to protect the application-
layer protocols with TLS (e.g., IMAP, POP3 or SMTP). layer protocols with TLS (e.g., IMAP, POP3 or SMTP).
o Operators of instant-messaging services who wish to protect their o Operators of instant-messaging services who wish to protect their
application-layer protocols with TLS (e.g. XMPP or IRC). application-layer protocols with TLS (e.g., XMPP or IRC).
2.1. Security Services 2.1. Security Services
This document provides recommendations for an audience that wishes to This document provides recommendations for an audience that wishes to
secure their communication with TLS to achieve the following: secure their communication with TLS to achieve the following:
o Confidentiality: all (payload) communication is encrypted with the o Confidentiality: all (payload) communication is encrypted with the
goal that no party should be able to decrypt it except the goal that no party should be able to decrypt it except the
intended receiver. intended receiver.
o Data integrity: any changes made to the communication in transit o Data integrity: any changes made to the communication in transit
are detectable by the receiver. are detectable by the receiver.
o Authentication: this means that an end-point of the TLS o Authentication: an end-point of the TLS communication is
communication is authenticated as the intended entity to authenticated as the intended entity to communicate with. TLS
communicate with. TLS allows to authenticate one or both end- enables authentication of one or both end-points in the
points in the communication. Some TLS usage scenarios do not communication. Some TLS usage scenarios do not require
require authentication, and are further discussed in Section 2.2. authentication. They are not in the scope of this document. We
discuss them under Section 2.2.
Deployers MUST verify that they do not need one of the above security If deployers deviate from the recommendations given in this document,
services if they deviate from the recommendations given in this they MUST verify that they do not need one of the foregoing security
document. services.
This document applies only to environments where confidentiality is This document applies only to environments where confidentiality is
required. It recommends algorithms and configuration options that required. It recommends algorithms and configuration options that
enforce secrecy of the data-in-transit. While this includes the enforce secrecy of the data-in-transit.
majority of the TLS use cases, there are some notable exceptions.
This document assumes that data integrity protection is always one of This document also assumes that data integrity protection is always
the goals of a deployment. In cases when integrity is not required, one of the goals of a deployment. In cases where integrity is not
it does not make sense to employ TLS in the first place. There are required, it does not make sense to employ TLS in the first place.
attacks against confidentiality-only protection that utilize the lack There are attacks against confidentiality-only protection that
of integrity to also break confidentiality (see e.g. [DegabrieleP07] utilize the lack of integrity to also break confidentiality (see for
in the context of IPsec). instance [DegabrieleP07] in the context of IPsec).
The intended audience covers those services that are most commonly The intended audience covers those services that are most commonly
used on the Internet. Typically, all communication between clients used on the Internet. Typically, all communication between TLS
and servers requires all three of the above security services. This clients and TLS servers requires all three of the above security
is particularly true where clients are user agents like Web browsers services. This is particularly true where TLS clients are user
or email software. agents like Web browsers or email software.
This document does not address the rare deployment scenarios where This document does not address the rarer deployment scenarios where
one of the above three properties is not desired, with the exception one of the above three properties is not desired, such as the use
of the use case described in Section 2.2 below. An example of an case described under Section 2.2 below. Another example of an
audience not needing confidentiality is the following: a monitored audience not needing confidentiality is the following: a monitored
network where the authorities in charge of the respective traffic network where the authorities in charge of the respective traffic
domain require full access to unencrypted (plaintext) traffic, and domain require full access to unencrypted (plaintext) traffic, and
where users collaborate and send their traffic in the clear. where users collaborate and send their traffic in the clear.
2.2. Unauthenticated TLS 2.2. Unauthenticated TLS
Several important applications use TLS to protect data between a Several important applications use TLS to protect data between a TLS
client and a server, but do so without the client verifying the client and a TLS server, but do so without the TLS client verifying
server's certificate. The reader is referred to the server's certificate. The reader is referred to
[I-D.dukhovni-smtp-opportunistic-tls] for additional details and an [I-D.ietf-dane-smtp-with-dane] for an example and an explanation of
explanation why this insecure practice is still common and likely to why this less secure practice will likely remain common in the
remain so for a while. context of SMTP (especially for MTA-to-MTA communications). The
practice is also encountered in similar contexts such as server-to-
server XMPP traffic.
In many of these scenarios the actual use of TLS is optional, i.e. In some of these scenarios the use of TLS is optional, i.e. the
the client decides dynamically ("opportunistically") whether to use client decides dynamically ("opportunistically") whether to use TLS
TLS with a particular server or to connect in the clear. with a particular server or to connect in the clear. (Opportunistic
Opportunistic encryption is described at length in Sec. 2 of encryption is described at length in Section 2 of
[I-D.farrelll-mpls-opportunistic-encrypt]. [I-D.farrelll-mpls-opportunistic-encrypt].) In other scenarios, the
use of TLS is required but certificates are not always checked (e.g.,
this is often the case on the XMPP network, where multi-tenant
hosting environments make it difficult for operators to obtain proper
certificates for all of the domains they service).
Despite the threat model differing from "standard" authenticated It can be argued that the recommendations provided in this document
usage of TLS, the recommendations in this document are applicable to ought to apply equally to unauthenticated TLS as well as
unauthenticated uses of TLS, with the obvious exception of peer authenticated TLS. That would keep TLS implementations and
authentication. deployments in sync, which is a desirable property given that servers
can be used simultaneously for unauthenticated TLS and for
authenticated TLS (indeed, often a server will not know whether a
client might attempt authenticated or unauthenticated TLS). On the
other hand, it has been argued that some of the recommendations in
this document might be too strict for unauthenticated scenarios and
that any security is better than no security at all (i.e., sending
traffic in the clear), even if it means deploying outdated protocol
versions and ciphers in unauthenticated scenarios. The sense of the
UTA Working Group was to complete work on this document about
authenticated TLS and to initiate work on a separate document about
unauthenticated TLS.
3. Conventions used in this document In summary: this document does not apply to unauthenticated TLS use
cases.
3. Terminology
A number of security-related terms in this document are used in the
sense defined in [RFC4949].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
4. General Recommendations 4. General Recommendations
This section provides general recommendations on the secure use of This section provides general recommendations on the secure use of
TLS. Recommendations related to cipher suites are discussed in the TLS. Recommendations related to cipher suites are discussed in the
following section. following section.
skipping to change at page 6, line 28 skipping to change at page 6, line 47
versions: versions:
o Implementations MUST NOT negotiate SSL version 2. o Implementations MUST NOT negotiate SSL version 2.
Rationale: Today, SSLv2 is considered insecure [RFC6176]. Rationale: Today, SSLv2 is considered insecure [RFC6176].
o Implementations MUST NOT negotiate SSL version 3. o Implementations MUST NOT negotiate SSL version 3.
Rationale: SSLv3 [RFC6101] was an improvement over SSLv2 and Rationale: SSLv3 [RFC6101] was an improvement over SSLv2 and
plugged some significant security holes, but did not support plugged some significant security holes, but did not support
strong cipher suites. In addition, SSLv3 does not support TLS strong cipher suites. SSLv3 does not support TLS extensions, some
extensions, some of which (e.g. renegotiation_info) are security- of which (e.g. renegotiation_info) are security-critical. In
critical. addition, with the emergence of the POODLE attack [POODLE], SSLv3
is now widely recognized as fundamentally insecure.
o Implementations SHOULD NOT negotiate TLS version 1.0 [RFC2246]. o Implementations SHOULD NOT negotiate TLS version 1.0 [RFC2246].
Rationale: TLS 1.0 (published in 1999) does not support many Rationale: TLS 1.0 (published in 1999) does not support many
modern, strong cipher suites. modern, strong cipher suites.
o Implementations MAY negotiate TLS version 1.1 [RFC4346]. o Implementations MAY negotiate TLS version 1.1 [RFC4346].
Rationale: TLS 1.1 (published in 2006) is a security improvement Rationale: TLS 1.1 (published in 2006) is a security improvement
over TLS 1.0, but still does not support certain stronger cipher over TLS 1.0, but still does not support certain stronger cipher
skipping to change at page 7, line 11 skipping to change at page 7, line 30
TLS 1.2 (published in 2008). In fact, the cipher suites TLS 1.2 (published in 2008). In fact, the cipher suites
recommended by this document (Section 5.2 below) are only recommended by this document (Section 5.2 below) are only
available in TLS 1.2. available in TLS 1.2.
This BCP applies to TLS 1.2. It is not safe for readers to assume This BCP applies to TLS 1.2. It is not safe for readers to assume
that the recommendations in this BCP apply to any future version of that the recommendations in this BCP apply to any future version of
TLS. TLS.
4.1.2. DTLS Protocol Versions 4.1.2. DTLS Protocol Versions
DTLS is an adaptation of TLS for UDP datagrams. DTLS, an adaptation of TLS for UDP datagrams, was introduced when TLS
1.1 was published. The following are the recommendations with
The following are the recommendations with respect to DTLS: respect to DTLS:
o Implementations MAY negotiate DTLS version 1.0 [RFC4347]. o Implementations MAY negotiate DTLS version 1.0 [RFC4347].
o Implementations MUST negotiate DTLS version 1.2 [RFC6347]. Version 1.0 of DTLS correlates to version 1.1 of TLS (see above).
Rationale: DTLS is an adaptation of TLS for UDP that was introduced o Implementations MUST support, and prefer to negotiate, DTLS
when TLS 1.1 was published. Version 1.0 correlates to TLS 1.1 and version 1.2 [RFC6347].
Version 1.2 correlates to TLS 1.2. There is no Version 1.1.
Version 1.2 of DTLS correlates to Version 1.2 of TLS 1.2 (see
above). (There is no Version 1.1 of DTLS.)
Note: DTLS and TLS are nearly identical. The most notable exception Note: DTLS and TLS are nearly identical. The most notable exception
is that RC4, which is a stream-based bulk encryption algorithm, is that RC4, which is a stream-based bulk encryption algorithm,
cannot be supported by DTLS. cannot be supported by DTLS.
4.1.3. Fallback to Earlier Versions 4.1.3. Fallback to Lower Versions
Clients that "fallback" to lower versions of the protocol after the Clients that "fallback" to lower versions of the protocol after the
server rejects higher versions of the protocol MUST NOT fallback to server rejects higher versions of the protocol MUST NOT fallback to
SSLv3. SSLv3.
Rationale: Some client implementations revert to lower versions of Rationale: Some client implementations revert to lower versions of
TLS or even to SSLv3 if the server rejected higher versions of the TLS or even to SSLv3 if the server rejected higher versions of the
protocol. This fallback can be forced by a man in the middle (MITM) protocol. This fallback can be forced by a man in the middle (MITM)
attacker. TLS 1.0 and SSLv3 are significantly less secure than TLS attacker. TLS 1.0 and SSLv3 are significantly less secure than TLS
1.2, the version recommended by this document. While TLS 1.0-only 1.2, the version recommended by this document. While TLS 1.0-only
skipping to change at page 8, line 7 skipping to change at page 8, line 28
deployments a choice between strict TLS configuration and dynamic deployments a choice between strict TLS configuration and dynamic
upgrade from unencrypted to TLS-protected traffic (such as upgrade from unencrypted to TLS-protected traffic (such as
STARTTLS), clients and servers SHOULD prefer strict TLS STARTTLS), clients and servers SHOULD prefer strict TLS
configuration. configuration.
o In many application protocols, clients can be configured to use o In many application protocols, clients can be configured to use
TLS even if the server has not advertised that TLS is mandatory or TLS even if the server has not advertised that TLS is mandatory or
even supported (e.g., this is often the case in messaging even supported (e.g., this is often the case in messaging
protocols such as IMAP and XMPP). Application clients SHOULD use protocols such as IMAP and XMPP). Application clients SHOULD use
TLS by default, and disable this default only through explicit TLS by default, and disable this default only through explicit
configration by the user. configuration by the user.
o HTTP client and server implementations MUST support the HTTP o HTTP client and server implementations MUST support the HTTP
Strict Transport Security (HSTS) header [RFC6797], in order to Strict Transport Security (HSTS) header [RFC6797], in order to
allow Web servers to advertise that they are willing to accept allow Web servers to advertise that they are willing to accept
TLS-only clients. TLS-only clients.
o When applicable, Web servers SHOULD use HSTS to indicate that they o When applicable, Web servers SHOULD use HSTS to indicate that they
are willing to accept TLS-only clients. are willing to accept TLS-only clients.
Rationale: Combining unprotected and TLS-protected communication Rationale: Combining unprotected and TLS-protected communication
skipping to change at page 9, line 37 skipping to change at page 10, line 13
during renegotiation. during renegotiation.
4.6. Server Name Indication 4.6. Server Name Indication
TLS implementations MUST support the Server Name Indication (SNI) TLS implementations MUST support the Server Name Indication (SNI)
extension for those higher level protocols which would benefit from extension for those higher level protocols which would benefit from
it, including HTTPS. However, unlike implementation, the use of SNI it, including HTTPS. However, unlike implementation, the use of SNI
in particular circumstances is a matter of local policy. in particular circumstances is a matter of local policy.
Rationale: SNI supports deployment of multiple TLS-protected virtual Rationale: SNI supports deployment of multiple TLS-protected virtual
servers on a single address, and therefore enables fine grain servers on a single address, and therefore enables fine-grained
security for these virtual servers, by allowing each one to have its security for these virtual servers, by allowing each one to have its
own certificate. own certificate.
5. Recommendations: Cipher Suites 5. Recommendations: Cipher Suites
TLS and its implementations provide considerable flexibility in the TLS and its implementations provide considerable flexibility in the
selection of cipher suites. Unfortunately many available cipher selection of cipher suites. Unfortunately, some available cipher
suites are insecure, and so misconfiguration can easily result in suites are insecure, some do not provide the targeted security
reduced security. This section includes recommendations on the services, and some no longer provide enough security. Incorrectly
selection and negotiation of cipher suites. configuring a server leads to no or reduced security. This section
includes recommendations on the selection and negotiation of cipher
suites.
5.1. General Guidelines 5.1. General Guidelines
Cryptographic algorithms weaken over time as cryptanalysis improves. Cryptographic algorithms weaken over time as cryptanalysis improves.
In other words, as time progresses, algorithms that were once In other words, as time progresses, algorithms that were once
considered strong but are now weak, need to be phased out over time considered strong but are now weak, need to be phased out over time
and replaced with more secure cipher suites to ensure that desired and replaced with more secure cipher suites to ensure that desired
security properties still hold. SSL/TLS has been in existence for security properties still hold. SSL/TLS has been in existence for
almost 20 years at this point and this section provides some much almost 20 years at this point and this section provides some much
needed recommendations concerning cipher suite selection: needed recommendations concerning cipher suite selection:
skipping to change at page 10, line 37 skipping to change at page 11, line 12
note that this guideline does not apply to DTLS, which note that this guideline does not apply to DTLS, which
specifically forbids the use of RC4. specifically forbids the use of RC4.
o Implementations MUST NOT negotiate cipher suites offering only so- o Implementations MUST NOT negotiate cipher suites offering only so-
called "export-level" encryption (including algorithms with 40 called "export-level" encryption (including algorithms with 40
bits or 56 bits of security). bits or 56 bits of security).
Rationale: These cipher suites are deliberately "dumbed down" and Rationale: These cipher suites are deliberately "dumbed down" and
are very easy to break. are very easy to break.
o Applications MUST NOT negotiate cipher suites of less than 112 o Implementations MUST NOT negotiate cipher suites offering less
bits of security. than 112 bits of security, including the so-called "export-level"
encryption (which provide 40 or 56 bits of security).
Rationale: Based on [RFC3766], at least 112 bits of security is
needed. 40-bit and 56-bit security are considered insecure today.
TLS 1.1 and 1.2 never negotiate 40-bit or 56-bit export ciphers.
o Implementations SHOULD NOT negotiate cipher suites that use o Implementations SHOULD NOT negotiate cipher suites that use
algorithms offering less than 128 bits of security. algorithms offering less than 128 bits of security.
Rationale: Cipher suites that offer between 112-bits and 128-bits Rationale: Cipher suites that offer between 112-bits and 128-bits
of security are not considered weak at this time, however it is of security are not considered weak at this time, however it is
expected that their useful lifespan is short enough to justify expected that their useful lifespan is short enough to justify
supporting stronger cipher suites at this time. 128-bit ciphers supporting stronger cipher suites at this time. 128-bit ciphers
are expected to remain secure for at least several years, and are expected to remain secure for at least several years, and
256-bit ciphers "until the next fundamental technology 256-bit ciphers "until the next fundamental technology
skipping to change at page 11, line 25 skipping to change at page 12, line 4
which attacks can be successful. which attacks can be successful.
5.2. Recommended Cipher Suites 5.2. Recommended Cipher Suites
Given the foregoing considerations, implementation and deployment of Given the foregoing considerations, implementation and deployment of
the following cipher suites is RECOMMENDED: the following cipher suites is RECOMMENDED:
o TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 o TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
o TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 o TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
o TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 o TLS_DHE_RSA_WITH_AES_256_GCM_SHA384
o TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 o TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
It is noted that those cipher suites are supported only in TLS 1.2 These cipher suites are supported only in TLS 1.2 since they are
since they are authenticated encryption (AEAD) algorithms [RFC5116]. authenticated encryption (AEAD) algorithms [RFC5116].
Typically, in order to prefer these suites, the order of suites needs
to be explicitly configured in server software.
[RFC4492] allows clients and servers to negotiate ECDH parameters [RFC4492] allows clients and servers to negotiate ECDH parameters
(curves). Both clients and servers SHOULD include the "Supported (curves). Both clients and servers SHOULD include the "Supported
Elliptic Curves" extension [RFC4492]. For interoperability, clients Elliptic Curves" extension [RFC4492]. For interoperability, clients
and servers SHOULD support the NIST P-256 (secp256r1) curve and servers SHOULD support the NIST P-256 (secp256r1) curve
[RFC4492]. In addition, clients SHOULD send an ec_point_formats [RFC4492]. In addition, clients SHOULD send an ec_point_formats
extension with a single element, "uncompressed". extension with a single element, "uncompressed".
5.3. Cipher Suite Negotiation Details 5.3. Cipher Suite Negotiation Details
skipping to change at page 14, line 27 skipping to change at page 14, line 52
Readers are referred to [RFC6125] for further details regarding Readers are referred to [RFC6125] for further details regarding
generic host name validation in the TLS context. In addition, the generic host name validation in the TLS context. In addition, the
RFC contains a long list of example protocols, some of which RFC contains a long list of example protocols, some of which
implement a policy very different from HTTPS. implement a policy very different from HTTPS.
If the host name is discovered indirectly and in an insecure manner If the host name is discovered indirectly and in an insecure manner
(e.g., by an insecure DNS query for an MX or SRV record), it SHOULD (e.g., by an insecure DNS query for an MX or SRV record), it SHOULD
NOT be used as a reference identifier [RFC6125] even when it matches NOT be used as a reference identifier [RFC6125] even when it matches
the presented certificate. This proviso does not apply if the host the presented certificate. This proviso does not apply if the host
name is discovered securely (for further discussion, see for example name is discovered securely (for further discussion, see for example
[I-D.ietf-dane-srv] and [I-D.ietf-dane-smtp]). [I-D.ietf-dane-srv] and [I-D.ietf-dane-smtp-with-dane]).
7.2. AES-GCM 7.2. AES-GCM
Section 5.2 above recommends the use of the AES-GCM authenticated Section 5.2 above recommends the use of the AES-GCM authenticated
encryption algorithm. Please refer to [RFC5246], Sec. 11 for general encryption algorithm. Please refer to [RFC5246], Sec. 11 for general
security considerations when using TLS 1.2, and to [RFC5288], Sec. 6 security considerations when using TLS 1.2, and to [RFC5288], Sec. 6
for security considerations that apply specifically to AES-GCM when for security considerations that apply specifically to AES-GCM when
used with TLS. used with TLS.
7.3. Forward Secrecy 7.3. Forward Secrecy
skipping to change at page 15, line 34 skipping to change at page 16, line 8
derive session keys. The Diffie-Hellman scheme has both parties derive session keys. The Diffie-Hellman scheme has both parties
maintain private secrets and send parameters over the network as maintain private secrets and send parameters over the network as
modular powers over certain cyclic groups. The properties of the so- modular powers over certain cyclic groups. The properties of the so-
called Discrete Logarithm Problem (DLP) allow to derive the session called Discrete Logarithm Problem (DLP) allow to derive the session
keys without an eavesdropper being able to do so. There is currently keys without an eavesdropper being able to do so. There is currently
no known attack against DLP if sufficiently large parameters are no known attack against DLP if sufficiently large parameters are
chosen. A variant of the Diffie-Hellman scheme uses Elliptic Curves chosen. A variant of the Diffie-Hellman scheme uses Elliptic Curves
instead of the originally proposed modular arithmetics. instead of the originally proposed modular arithmetics.
Unfortunately, many TLS/DTLS cipher suites were defined that do not Unfortunately, many TLS/DTLS cipher suites were defined that do not
feature PFS, e.g. TLS_RSA_WITH_AES_256_CBC_SHA256. We thus advocate feature PFS, e.g. TLS_RSA_WITH_AES_256_CBC_SHA256. We thus advocate
strict use of PFS-only ciphers. strict use of PFS-only ciphers.
7.4. Diffie-Hellman Exponent Reuse 7.4. Diffie-Hellman Exponent Reuse
For performance reasons, many TLS implementations reuse Diffie- For performance reasons, many TLS implementations reuse Diffie-
Hellman and Elliptic Curve Diffie-Hellman exponents across multiple Hellman and Elliptic Curve Diffie-Hellman exponents across multiple
connections. Such reuse can result in major security issues: connections. Such reuse can result in major security issues:
o If exponents are reused for a long time (e.g., more than a few o If exponents are reused for a long time (e.g., more than a few
hours), an attacker who gains access to the host can decrypt hours), an attacker who gains access to the host can decrypt
skipping to change at page 16, line 7 skipping to change at page 16, line 30
effects of forward secrecy. effects of forward secrecy.
o TLS implementations that reuse exponents should test the DH public o TLS implementations that reuse exponents should test the DH public
key they receive, in order to avoid some known attacks. These key they receive, in order to avoid some known attacks. These
tests are not standardized in TLS at the time of writing. See tests are not standardized in TLS at the time of writing. See
[RFC6989] for recipient tests required of IKEv2 implementations [RFC6989] for recipient tests required of IKEv2 implementations
that reuse DH exponents. that reuse DH exponents.
7.5. Certificate Revocation 7.5. Certificate Revocation
Unfortunately there is currently no effective, Internet-scale Unfortunately, no mechanism exists at this time that we can recommend
mechanism to effect certificate revocation: as a complete and efficient solution for the problem of checking the
revocation status of common public key certificates (a.k.a. PKIX
certificates, [RFC5280]). The current state of the art is as
follows:
o Certificate Revocation Lists (CRLs) are non-scalable and therefore o Certificate Revocation Lists (CRLs) are not scalable and therefore
rarely used. rarely used.
o The On-Line Certification Status Protocol (OCSP) presents both o The On-Line Certification Status Protocol (OCSP) presents both
scaling and privacy issues when used for heavy traffic Web scaling and privacy issues when used for heavy traffic Web
servers. In addition, clients typically "soft-fail", meaning they servers. In addition, clients typically "soft-fail", meaning they
do not abort the TLS connection if the OCSP server does not do not abort the TLS connection if the OCSP server does not
respond. respond.
o OCSP stapling (Sec. 8 of [RFC6066]) resolves the operational o OCSP stapling (Section 8 of [RFC6066]) resolves the operational
issues with OCSP, but is still ineffective in the presence of a issues with OCSP, but is still ineffective in the presence of a
MITM attacker because the attacker can simply ignore the client's MITM attacker because the attacker can simply ignore the client's
request for a stapled OCSP response. request for a stapled OCSP response.
o OCSP stapling as defined in [RFC6066] does not extend to o OCSP stapling as defined in [RFC6066] does not extend to
intermediate certificates used in a certificate chain. [RFC6961] intermediate certificates used in a certificate chain. [RFC6961]
addresses this shortcoming, but is a recent addition without much addresses this shortcoming, but is a recent addition without much
deployment. deployment.
o Proprietary mechanisms that embed revocation lists in the Web o Proprietary mechanisms that embed revocation lists in the Web
browser's configuration database cannot scale beyond a small browser's configuration database cannot scale beyond a small
number of the most heavily used Web servers. number of the most heavily used Web servers.
The current consensus appears to be that OCSP stapling, combined with With regard to PKIX certificates, servers SHOULD support OCSP and
a "must staple" mechanism similar to HSTS, would finally resolve this OCSP stapling, including the OCSP stapling extension defined in
problem; in particular when used together with the extension defined [RFC6961], as a best practice given the current state of the art and
in [RFC6961]. But such a mechanism has not been standardized yet. as a foundation for a possible future solution.
The foregoing considerations do not apply to DANE certificates
[RFC6698], since they do not require a revocation mechanism.
8. Acknowledgments 8. Acknowledgments
We would like to thank Uri Blumenthal, Viktor Dukhovni, Stephen We would like to thank Uri Blumenthal, Viktor Dukhovni, Stephen
Farrell, Simon Josefsson, Watson Ladd, Orit Levin, Johannes Merkle, Farrell, Simon Josefsson, Watson Ladd, Orit Levin, Johannes Merkle,
Bodo Moeller, Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom Bodo Moeller, Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom
Ritter, Rich Salz, Sean Turner, Aaron Zauner for their review and Ritter, Rich Salz, Sean Turner, and Aaron Zauner for their feedback
improvements. Thanks to Brian Smith whose "browser cipher suites" and suggested improvements. Thanks to Brian Smith whose "browser
page is a great resource. Finally, thanks to all others who cipher suites" page is a great resource. Finally, thanks to all
commented on the TLS, UTA and other lists and are not mentioned here others who commented on the TLS, UTA and other lists and are not
by name. mentioned here by name.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, April 2004.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B. [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006. for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008. August 2008.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA- [RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with
256/384 and AES Galois Counter Mode (GCM)", RFC 5289, SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008. August 2008.
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, [RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication "Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, February 2010. Extension", RFC 5746, February 2010.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
skipping to change at page 18, line 16 skipping to change at page 18, line 48
Degabriele, J. and K. Paterson, "Attacking the IPsec Degabriele, J. and K. Paterson, "Attacking the IPsec
standards in encryption-only configurations", 2007, standards in encryption-only configurations", 2007,
<http://dx.doi.org/10.1109/SP.2007.8>. <http://dx.doi.org/10.1109/SP.2007.8>.
[Heninger2012] [Heninger2012]
Heninger, N., Durumeric, Z., Wustrow, E., and J. Heninger, N., Durumeric, Z., Wustrow, E., and J.
Halderman, "Mining Your Ps and Qs: Detection of Widespread Halderman, "Mining Your Ps and Qs: Detection of Widespread
Weak Keys in Network Devices", Usenix Security Symposium Weak Keys in Network Devices", Usenix Security Symposium
2012, 2012. 2012, 2012.
[I-D.dukhovni-smtp-opportunistic-tls]
Dukhovni, V. and W. Hardaker, "SMTP security via
opportunistic DANE TLS", draft-dukhovni-smtp-
opportunistic-tls-01 (work in progress), July 2013.
[I-D.farrelll-mpls-opportunistic-encrypt] [I-D.farrelll-mpls-opportunistic-encrypt]
Farrel, A. and S. Farrell, "Opportunistic Encryption in Farrel, A. and S. Farrell, "Opportunistic Encryption in
MPLS Networks", draft-farrelll-mpls-opportunistic- MPLS Networks", draft-farrelll-mpls-opportunistic-
encrypt-02 (work in progress), February 2014. encrypt-02 (work in progress), February 2014.
[I-D.ietf-dane-smtp] [I-D.ietf-dane-smtp-with-dane]
Finch, T., "Secure SMTP using DNS-Based Authentication of Dukhovni, V. and W. Hardaker, "SMTP security via
Named Entities (DANE) TLSA records.", draft-ietf-dane- opportunistic DANE TLS", draft-ietf-dane-smtp-with-dane-10
smtp-01 (work in progress), February 2013. (work in progress), May 2014.
[I-D.ietf-dane-srv] [I-D.ietf-dane-srv]
Finch, T., Miller, M., and P. Saint-Andre, "Using DNS- Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", draft-ietf-dane-srv-07 (work in with SRV Records", draft-ietf-dane-srv-06 (work in
progress), July 2014. progress), June 2014.
[I-D.ietf-tls-prohibiting-rc4] [I-D.ietf-tls-prohibiting-rc4]
Popov, A., "Prohibiting RC4 Cipher Suites", draft-ietf- Popov, A., "Prohibiting RC4 Cipher Suites", draft-ietf-
tls-prohibiting-rc4-00 (work in progress), July 2014. tls-prohibiting-rc4-01 (work in progress), October 2014.
[I-D.ietf-uta-tls-attacks] [I-D.ietf-uta-tls-attacks]
Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Current Attacks on TLS and DTLS", draft-ietf-uta-tls- Current Attacks on TLS and DTLS", draft-ietf-uta-tls-
attacks-04 (work in progress), September 2014. attacks-04 (work in progress), September 2014.
[Kleinjung2010] [Kleinjung2010]
Kleinjung, T., "Factorization of a 768-Bit RSA Modulus", Kleinjung, T., "Factorization of a 768-Bit RSA Modulus",
CRYPTO 10, 2010, <https://eprint.iacr.org/2010/006.pdf>. CRYPTO 10, 2010, <https://eprint.iacr.org/2010/006.pdf>.
[POODLE] Moeller, B., Duong, T., and K. Kotowicz, "This POODLE
Bites: Exploiting the SSL 3.0 Fallback", 2014, <https://
www.openssl.org/~bodo/ssl-poodle.pdf>.
[PatersonRS11] [PatersonRS11]
Paterson, K., Ristenpart, T., and T. Shrimpton, "Tag size Paterson, K., Ristenpart, T., and T. Shrimpton, "Tag size
does matter: attacks and proofs for the TLS record does matter: attacks and proofs for the TLS record
protocol", 2011, protocol", 2011,
<http://dx.doi.org/10.1007/978-3-642-25385-0_20>. <http://dx.doi.org/10.1007/978-3-642-25385-0_20>.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999. RFC 2246, January 1999.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602, September
2003.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006. (TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006. Security", RFC 4347, April 2006.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007. 4949, August 2007.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without "Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, January 2008. Server-Side State", RFC 5077, January 2008.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008. Encryption", RFC 5116, January 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011. Extension Definitions", RFC 6066, January 2011.
[RFC6101] Freier, A., Karlton, P., and P. Kocher, "The Secure [RFC6101] Freier, A., Karlton, P., and P. Kocher, "The Secure
Sockets Layer (SSL) Protocol Version 3.0", RFC 6101, Sockets Layer (SSL) Protocol Version 3.0", RFC 6101,
August 2011. August 2011.
[RFC6460] Salter, M. and R. Housley, "Suite B Profile for Transport [RFC6460] Salter, M. and R. Housley, "Suite B Profile for Transport
Layer Security (TLS)", RFC 6460, January 2012. Layer Security (TLS)", RFC 6460, January 2012.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012.
[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict [RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797, November 2012. Transport Security (HSTS)", RFC 6797, November 2012.
[RFC6961] Pettersen, Y., "The Transport Layer Security (TLS) [RFC6961] Pettersen, Y., "The Transport Layer Security (TLS)
Multiple Certificate Status Request Extension", RFC 6961, Multiple Certificate Status Request Extension", RFC 6961,
June 2013. June 2013.
[RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman
Tests for the Internet Key Exchange Protocol Version 2 Tests for the Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 6989, July 2013. (IKEv2)", RFC 6989, July 2013.
skipping to change at page 20, line 21 skipping to change at page 21, line 15
[triple-handshake] [triple-handshake]
Delignat-Lavaud, A., Bhargavan, K., and A. Pironti, Delignat-Lavaud, A., Bhargavan, K., and A. Pironti,
"Triple Handshakes Considered Harmful: Breaking and Fixing "Triple Handshakes Considered Harmful: Breaking and Fixing
Authentication over TLS", 2014, <https://secure- Authentication over TLS", 2014, <https://secure-
resumption.com/>. resumption.com/>.
Appendix A. Change Log Appendix A. Change Log
Note to RFC Editor: please remove this section before publication. Note to RFC Editor: please remove this section before publication.
A.1. draft-ietf-uta-tls-bcp-05 A.1. draft-ietf-uta-tls-bcp-06
o Undo unauthenticated TLS, following another long thread on the
list.
A.2. draft-ietf-uta-tls-bcp-05
o Lots of comments by Sean Turner. o Lots of comments by Sean Turner.
o Unauthenticated TLS, following a long thread on the list. o Unauthenticated TLS, following a long thread on the list.
A.2. draft-ietf-uta-tls-bcp-04 A.3. draft-ietf-uta-tls-bcp-04
o Some cleanup, and input from TLS WG discussion on applicability. o Some cleanup, and input from TLS WG discussion on applicability.
A.3. draft-ietf-uta-tls-bcp-03 A.4. draft-ietf-uta-tls-bcp-03
o Disallow truncated HMAC. o Disallow truncated HMAC.
o Applicability to DTLS. o Applicability to DTLS.
o Some more text restructuring. o Some more text restructuring.
o Host name validation is sometimes irrelevant. o Host name validation is sometimes irrelevant.
o HSTS: MUST implement, SHOULD deploy. o HSTS: MUST implement, SHOULD deploy.
o Session identities are not protected, only tickets are. o Session identities are not protected, only tickets are.
o Clarified the target audience. o Clarified the target audience.
A.4. draft-ietf-uta-tls-bcp-02 A.5. draft-ietf-uta-tls-bcp-02
o Rearranged some sections for clarity and re-styled the text so o Rearranged some sections for clarity and re-styled the text so
that normative text is followed by rationale where possible. that normative text is followed by rationale where possible.
o Removed the recommendation to use Brainpool curves. o Removed the recommendation to use Brainpool curves.
o Triple Handshake mitigation. o Triple Handshake mitigation.
o MUST NOT negotiate algorithms lower than 112 bits of security. o MUST NOT negotiate algorithms lower than 112 bits of security.
o MUST implement SNI, but use per local policy. o MUST implement SNI, but use per local policy.
o Changed SHOULD NOT negotiate or fall back to SSLv3 to MUST NOT. o Changed SHOULD NOT negotiate or fall back to SSLv3 to MUST NOT.
o Added hostname validation. o Added hostname validation.
o Non-normative discussion of DH exponent reuse. o Non-normative discussion of DH exponent reuse.
A.5. draft-ietf-tls-bcp-01 A.6. draft-ietf-tls-bcp-01
o Clarified that specific TLS-using protocols may have stricter o Clarified that specific TLS-using protocols may have stricter
requirements. requirements.
o Changed TLS 1.0 from MAY to SHOULD NOT. o Changed TLS 1.0 from MAY to SHOULD NOT.
o Added discussion of "optional TLS" and HSTS. o Added discussion of "optional TLS" and HSTS.
o Recommended use of the Signature Algorithm and Renegotiation Info o Recommended use of the Signature Algorithm and Renegotiation Info
extensions. extensions.
o Use of a strong cipher for a resumption ticket: changed SHOULD to o Use of a strong cipher for a resumption ticket: changed SHOULD to
MUST. MUST.
o Added an informational discussion of certificate revocation, but o Added an informational discussion of certificate revocation, but
no recommendations. no recommendations.
A.6. draft-ietf-tls-bcp-00 A.7. draft-ietf-tls-bcp-00
o Initial WG version, with only updated references. o Initial WG version, with only updated references.
A.7. draft-sheffer-tls-bcp-02 A.8. draft-sheffer-tls-bcp-02
o Reorganized the content to focus on recommendations. o Reorganized the content to focus on recommendations.
o Moved description of attacks to a separate document (draft- o Moved description of attacks to a separate document (draft-
sheffer-uta-tls-attacks). sheffer-uta-tls-attacks).
o Strengthened recommendations regarding session resumption. o Strengthened recommendations regarding session resumption.
A.8. draft-sheffer-tls-bcp-01 A.9. draft-sheffer-tls-bcp-01
o Clarified our motivation in the introduction. o Clarified our motivation in the introduction.
o Added a section justifying the need for PFS. o Added a section justifying the need for PFS.
o Added recommendations for RSA and DH parameter lengths. Moved o Added recommendations for RSA and DH parameter lengths. Moved
from DHE to ECDHE, with a discussion on whether/when DHE is from DHE to ECDHE, with a discussion on whether/when DHE is
appropriate. appropriate.
o Recommendation to avoid fallback to SSLv3. o Recommendation to avoid fallback to SSLv3.
o Initial information about browser support - more still needed! o Initial information about browser support - more still needed!
o More clarity on compression. o More clarity on compression.
o Client can offer stronger cipher suites. o Client can offer stronger cipher suites.
o Discussion of the regular TLS mandatory cipher suite. o Discussion of the regular TLS mandatory cipher suite.
A.9. draft-sheffer-tls-bcp-00 A.10. draft-sheffer-tls-bcp-00
o Initial version. o Initial version.
Authors' Addresses Authors' Addresses
Yaron Sheffer Yaron Sheffer
Porticor Porticor
29 HaHarash St. 29 HaHarash St.
Hod HaSharon 4501303 Hod HaSharon 4501303
Israel Israel
 End of changes. 69 change blocks. 
158 lines changed or deleted 222 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/