draft-ietf-uta-tls-bcp-07.txt   draft-ietf-uta-tls-bcp-08.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: May 15, 2015 TUM Expires: June 10, 2015 TUM
P. Saint-Andre P. Saint-Andre
&yet &yet
November 11, 2014 December 7, 2014
Recommendations for Secure Use of TLS and DTLS Recommendations for Secure Use of TLS and DTLS
draft-ietf-uta-tls-bcp-07 draft-ietf-uta-tls-bcp-08
Abstract Abstract
Transport Layer Security (TLS) and Datagram Transport Layer Security 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
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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
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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 May 15, 2015. This Internet-Draft will expire on June 10, 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
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. General Recommendations . . . . . . . . . . . . . . . . . . . 4 3. General Recommendations . . . . . . . . . . . . . . . . . . . 4
3.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 4 3.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 4
3.1.1. SSL/TLS Protocol Versions . . . . . . . . . . . . . . 4 3.1.1. SSL/TLS Protocol Versions . . . . . . . . . . . . . . 4
3.1.2. DTLS Protocol Versions . . . . . . . . . . . . . . . 5 3.1.2. DTLS Protocol Versions . . . . . . . . . . . . . . . 5
3.1.3. Fallback to Lower Versions . . . . . . . . . . . . . 5 3.1.3. Fallback to Lower Versions . . . . . . . . . . . . . 6
3.2. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 7
3.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 7 3.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 7
3.5. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 7 3.5. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 7
3.6. Server Name Indication . . . . . . . . . . . . . . . . . 8 3.6. Server Name Indication . . . . . . . . . . . . . . . . . 8
4. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 8 4. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 8
4.1. General Guidelines . . . . . . . . . . . . . . . . . . . 8 4.1. General Guidelines . . . . . . . . . . . . . . . . . . . 8
4.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 9 4.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 9
4.2.1. Implementation Details . . . . . . . . . . . . . . . 10 4.2.1. Implementation Details . . . . . . . . . . . . . . . 10
4.3. Public Key Length . . . . . . . . . . . . . . . . . . . . 10 4.3. Public Key Length . . . . . . . . . . . . . . . . . . . . 11
4.4. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 11 4.4. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 11
4.5. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 12 4.5. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 12
5. Applicability Statement . . . . . . . . . . . . . . . . . . . 12 5. Applicability Statement . . . . . . . . . . . . . . . . . . . 13
5.1. Security Services . . . . . . . . . . . . . . . . . . . . 12 5.1. Security Services . . . . . . . . . . . . . . . . . . . . 13
5.2. Unauthenticated TLS and Opportunistic Encryption . . . . 13 5.2. Unauthenticated TLS and Opportunistic Security . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 14 7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 15
7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 15 7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 15 7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 16
7.4. Diffie-Hellman Exponent Reuse . . . . . . . . . . . . . . 16 7.4. Diffie-Hellman Exponent Reuse . . . . . . . . . . . . . . 17
7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 17 7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 17
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . 18 9.1. Normative References . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . 19 9.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 21 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 23
A.1. draft-ietf-uta-tls-bcp-07 . . . . . . . . . . . . . . . . 21 A.1. draft-ietf-uta-tls-bcp-08 . . . . . . . . . . . . . . . . 23
A.2. draft-ietf-uta-tls-bcp-06 . . . . . . . . . . . . . . . . 21 A.2. draft-ietf-uta-tls-bcp-07 . . . . . . . . . . . . . . . . 23
A.3. draft-ietf-uta-tls-bcp-05 . . . . . . . . . . . . . . . . 21 A.3. draft-ietf-uta-tls-bcp-06 . . . . . . . . . . . . . . . . 23
A.4. draft-ietf-uta-tls-bcp-04 . . . . . . . . . . . . . . . . 22 A.4. draft-ietf-uta-tls-bcp-05 . . . . . . . . . . . . . . . . 23
A.5. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 22 A.5. draft-ietf-uta-tls-bcp-04 . . . . . . . . . . . . . . . . 23
A.6. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 22 A.6. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 23
A.7. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 22 A.7. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 24
A.8. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 23 A.8. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 24
A.9. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 23 A.9. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 24
A.10. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 23 A.10. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 25
A.11. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 23 A.11. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 A.12. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
Transport Layer Security (TLS) [RFC5246] and Datagram Transport Transport Layer Security (TLS) [RFC5246] and Datagram Transport
Security Layer (DTLS) [RFC6347] are widely used to protect data Security Layer (DTLS) [RFC6347] are widely used to protect data
exchanged over application protocols such as HTTP, SMTP, IMAP, POP, exchanged over application protocols such as HTTP, SMTP, IMAP, POP,
SIP, and XMPP. Over the last few years, several serious attacks on SIP, and XMPP. Over the last few years, several serious attacks on
TLS have emerged, including attacks on its most commonly used cipher TLS have emerged, including attacks on its most commonly used cipher
suites and modes of operation. For instance, both the AES-CBC suites and modes of operation. For instance, both the AES-CBC
[RFC3602] and RC4 [I-D.ietf-tls-prohibiting-rc4] encryption [RFC3602] and RC4 [I-D.ietf-tls-prohibiting-rc4] encryption
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document is likely to be updated after TLS 1.3 gets noticeable document is likely to be updated after TLS 1.3 gets noticeable
deployment. deployment.
These are minimum recommendations for the use of TLS in the vast These are minimum recommendations for the use of TLS in the vast
majority of implementation and deployment scenarios, with the majority of implementation and deployment scenarios, with the
exception of unauthenticated TLS (see Section 5). Other exception of unauthenticated TLS (see Section 5). Other
specifications that reference this document can have stricter specifications that reference this document 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 (e.g., for use with a particular their particular circumstances (e.g., for use with a particular
application protocol); when that is the case, implementers are application protocol); when that is the case, implementers are
advised to adhere to those stricter requirements. advised to adhere to those stricter requirements. Furthermore, this
document provides a floor, not a ceiling, so stronger options are
always allowed (e.g., depending on differing evaluations of the
importance of cryptographic strength vs. computational load).
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. Terminology 2. Terminology
A number of security-related terms in this document are used in the A number of security-related terms in this document are used in the
sense defined in [RFC4949]. sense defined in [RFC4949].
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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. SSLv3 does not support TLS extensions, some strong cipher suites. SSLv3 does not support TLS extensions, some
of which (e.g., renegotiation_info) are security-critical. In of which (e.g., renegotiation_info) are security-critical. In
addition, with the emergence of the POODLE attack [POODLE], SSLv3 addition, with the emergence of the POODLE attack [POODLE], SSLv3
is now widely recognized as fundamentally insecure. 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. In addition, TLS 1.0 lacks a per-
record IV for CBC-based cipher suites and does not warn against
common padding errors.
o Implementations MAY negotiate TLS version 1.1 [RFC4346]. o Implementations SHOULD NOT 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
suites. suites.
o Implementations MUST support, and prefer to negotiate, TLS version o Implementations MUST support TLS 1.2 [RFC5246] and MUST prefer to
1.2 [RFC5246]. negotiate TLS version 1.2 over earlier versions of TLS.
Rationale: Several stronger cipher suites are available only with Rationale: Several stronger cipher suites are available only with
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 4.2 below) are only recommended by this document (Section 4.2 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.
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Version 1.0 of DTLS correlates to version 1.1 of TLS (see above). Version 1.0 of DTLS correlates to version 1.1 of TLS (see above).
o Implementations MUST support, and prefer to negotiate, DTLS o Implementations MUST support, and prefer to negotiate, DTLS
version 1.2 [RFC6347]. version 1.2 [RFC6347].
Version 1.2 of DTLS correlates to Version 1.2 of TLS 1.2 (see Version 1.2 of DTLS correlates to Version 1.2 of TLS 1.2 (see
above). (There is no Version 1.1 of DTLS.) above). (There is no Version 1.1 of DTLS.)
3.1.3. Fallback to Lower Versions 3.1.3. Fallback to Lower Versions
Clients that "fallback" to lower versions of the protocol after the Clients that "fall back" 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 fall back 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
servers are still quite common, IP scans show that SSLv3-only servers servers are still quite common, IP scans show that SSLv3-only servers
amount to only about 3% of the current Web server population. amount to only about 3% of the current Web server population. (At
the time of this writing, an explicit method for preventing downgrade
attacks is being defined in [I-D.ietf-tls-downgrade-scsv].)
3.2. Strict TLS 3.2. Strict TLS
To prevent SSL Stripping: To prevent SSL Stripping:
o In cases where an application protocol allows implementations or o In cases where an application protocol allows implementations or
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.
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Implementations and deployments SHOULD disable TLS-level compression Implementations and deployments SHOULD disable TLS-level compression
([RFC5246], Section 6.2.2). ([RFC5246], Section 6.2.2).
Rationale: TLS compression has been subject to security attacks, such Rationale: TLS compression has been subject to security attacks, such
as the CRIME attack. as the CRIME attack.
Implementers should note that compression at higher protocol levels Implementers should note that compression at higher protocol levels
can allow an active attacker to extract cleartext information from can allow an active attacker to extract cleartext information from
the connection. The BREACH attack is one such case. These issues the connection. The BREACH attack is one such case. These issues
can only be mitigated outside of TLS and are thus out of scope of the can only be mitigated outside of TLS and are thus out of scope of the
current document. See Section 2.5 of [I-D.ietf-uta-tls-attacks] for current document. See Section 2.6 of [I-D.ietf-uta-tls-attacks] for
further details. further details.
3.4. TLS Session Resumption 3.4. TLS Session Resumption
If TLS session resumption is used, care ought to be taken to do so If TLS session resumption is used, care ought to be taken to do so
safely. In particular, when using session tickets [RFC5077], the safely. In particular, when using session tickets [RFC5077], the
resumption information MUST be authenticated and encrypted to prevent resumption information MUST be authenticated and encrypted to prevent
modification or eavesdropping by an attacker. Further modification or eavesdropping by an attacker. Further
recommendations apply to session tickets: recommendations apply to session tickets:
o A strong cipher suite MUST be used when encrypting the ticket (as o A strong cipher suite MUST be used when encrypting the ticket (as
least as strong as the main TLS cipher suite). least as strong as the main TLS cipher suite).
o Ticket keys MUST be changed regularly, e.g., once every week, so o Ticket keys MUST be changed regularly, e.g., once every week, so
as not to negate the benefits of forward secrecy (see Section 7.3 as not to negate the benefits of forward secrecy (see Section 7.3
for details on forward secrecy). for details on forward secrecy).
o Session ticket validity SHOULD be limited to a reasonable duration o For similar reasons, session ticket validity SHOULD be limited to
(e.g., 1 day), for similar reasons. a reasonable duration (e.g., half as long as ticket key validity).
Rationale: session resumption is another kind of TLS handshake, and Rationale: session resumption is another kind of TLS handshake, and
therefore must be as secure as the initial handshake. This document therefore must be as secure as the initial handshake. This document
(Section 4) recommends the use of cipher suites that provide forward (Section 4) recommends the use of cipher suites that provide forward
secrecy, i.e. that prevent an attacker who gains momentary access to secrecy, i.e. that prevent an attacker who gains momentary access to
the TLS endpoint (either client or server) and its secrets from the TLS endpoint (either client or server) and its secrets from
reading either past or future communication. The tickets must be reading either past or future communication. The tickets must be
managed so as not to negate this security property. managed so as not to negate this security property.
3.5. TLS Renegotiation 3.5. TLS Renegotiation
Where handshake renegotiation is implemented, both clients and Where handshake renegotiation is implemented, both clients and
servers MUST implement the renegotiation_info extension, as defined servers MUST implement the renegotiation_info extension, as defined
in [RFC5746]. in [RFC5746].
To counter the Triple Handshake attack, we adopt the recommendation To counter the Triple Handshake attack, we adopt the recommended
from [triple-handshake]: TLS clients SHOULD ensure that all countermeasures from [triple-handshake]: TLS clients SHOULD apply the
certificates received over a connection are valid for the current same validation policy for all certificates received over a
server endpoint, and abort the handshake if they are not. In some connection, bind the master secret to the full handshake, and bind
usages, it may be simplest to refuse any change of certificates the abbreviated session resumption handshake to the original full
during renegotiation. handshake. In some usages, it may be simplest to refuse any change
of certificates during renegotiation.
3.6. Server Name Indication 3.6. 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-grained servers on a single address, and therefore enables fine-grained
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with older session keys, thus limiting the amount of time during with older session keys, thus limiting the amount of time during
which attacks can be successful. See Section 7.3 for a detailed which attacks can be successful. See Section 7.3 for a detailed
discussion. discussion.
4.2. Recommended Cipher Suites 4.2. 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
These cipher suites are supported only in TLS 1.2 since they are
These cipher suites are supported only in TLS 1.2 because they are
authenticated encryption (AEAD) algorithms [RFC5116]. authenticated encryption (AEAD) algorithms [RFC5116].
Typically, in order to prefer these suites, the order of suites needs Typically, in order to prefer these suites, the order of suites needs
to be explicitly configured in server software. to be explicitly configured in server software.
Some devices have hardware support for AES-CCM but not AES-GCM.
There are even devices that do not support public key cryptography at
all. This BCP does not cover such devices.
4.2.1. Implementation Details 4.2.1. Implementation Details
Clients SHOULD include TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 as the Clients SHOULD include TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 as the
first proposal to any server, unless they have prior knowledge that first proposal to any server, unless they have prior knowledge that
the server cannot respond to a TLS 1.2 client_hello message. the server cannot respond to a TLS 1.2 client_hello message.
Servers SHOULD prefer this cipher suite whenever it is proposed, even Servers SHOULD prefer this cipher suite whenever it is proposed, even
if it is not the first proposal. if it is not the first proposal.
Clients are of course free to offer stronger cipher suites, e.g., Clients are of course free to offer stronger cipher suites, e.g.,
using AES-256; when they do, the server SHOULD prefer the stronger using AES-256; when they do, the server SHOULD prefer the stronger
cipher suite unless there are compelling reasons (e.g., seriously cipher suite unless there are compelling reasons (e.g., seriously
degraded performance) to choose otherwise. degraded performance) to choose otherwise.
This document is not an application profile standard, in the sense of This document does not change the mandatory-to-implement TLS cipher
Section 9 of [RFC5246]. As a result, clients and servers are still suite(s) prescribed by TLS or application protocols using TLS. To
REQUIRED to support the mandatory TLS cipher suite, maximize interoperability, RFC 5246 mandates implementation of the
TLS_RSA_WITH_AES_128_CBC_SHA. TLS_RSA_WITH_AES_128_CBC_SHA cipher suite, which is significantly
weaker than the cipher suites recommended here. Implementers should
consider the interoperability gain against the loss in security when
deploying that cipher suite. Other application protocols specify
other cipher suites as mandatory to implement (MTI).
Note that some profiles of TLS 1.2 use different cipher suites. For Note that some profiles of TLS 1.2 use different cipher suites. For
example, [RFC6460] defines a profile that uses the example, [RFC6460] defines a profile that uses the
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 and TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 and
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 cipher suites. TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 cipher suites.
[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
skipping to change at page 11, line 21 skipping to change at page 11, line 34
equivalent to a 100-bit symmetric key [RFC3766] and a DH key of 2048 equivalent to a 100-bit symmetric key [RFC3766] and a DH key of 2048
bits might be sufficient for at least the next 10 years. See bits might be sufficient for at least the next 10 years. See
Section 4.4 for additional information on the use of modular Diffie- Section 4.4 for additional information on the use of modular Diffie-
Hellman in TLS. Hellman in TLS.
As noted in [RFC3766], correcting for the emergence of a TWIRL As noted in [RFC3766], correcting for the emergence of a TWIRL
machine would imply that 1024-bit DH keys yield about 65 bits of machine would imply that 1024-bit DH keys yield about 65 bits of
equivalent strength and that a 2048-bit DH key would yield about 92 equivalent strength and that a 2048-bit DH key would yield about 92
bits of equivalent strength. bits of equivalent strength.
Servers SHOULD authenticate using at least 2048-bit certificates. In With regard to ECDH keys, the IANA named curve registry contains
addition, the use of SHA-256 fingerprints is RECOMMENDED (see 160-bit elliptic curves which are considered to be roughly equivalent
[CAB-Baseline] for more details). Clients SHOULD indicate to servers to only an 80-bit symmetric key [ECRYPT-II]. The use of curves of
that they request SHA-256, by using the "Signature Algorithms" less than 192-bits is NOT RECOMMENDED.
extension defined in TLS 1.2.
When using RSA servers SHOULD authenticate using certificates with at
least a 2048-bit modulus for the public key. In addition, the use of
the SHA-256 hash algorithm is RECOMMENDED (see [CAB-Baseline] for
more details). Clients SHOULD indicate to servers that they request
SHA-256, by using the "Signature Algorithms" extension defined in
TLS 1.2.
4.4. Modular vs. Elliptic Curve DH Cipher Suites 4.4. Modular vs. Elliptic Curve DH Cipher Suites
Not all TLS implementations support both modular and EC Diffie- Not all TLS implementations support both modular and elliptic curve
Hellman groups, as required by Section 4.2. Some implementations are Diffie-Hellman groups, as required by Section 4.2. Some
severely limited in the length of DH values. When such implementations are severely limited in the length of DH values.
implementations need to be accommodated, we recommend using (in When such implementations need to be accommodated, we recommend using
priority order): (in priority order):
1. Elliptic Curve DHE with negotiated parameters [RFC5289] 1. Elliptic Curve DHE with negotiated parameters [RFC5289]
2. TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 [RFC5288], with 2048-bit 2. TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 [RFC5288], with 2048-bit
Diffie-Hellman parameters Diffie-Hellman parameters
3. TLS_DHE_RSA_WITH_AES_128_GCM_SHA256, with 1024-bit parameters. 3. TLS_DHE_RSA_WITH_AES_128_GCM_SHA256, with 1024-bit parameters.
Rationale: Elliptic Curve Cryptography is not universally deployed Rationale: Although Elliptic Curve Cryptography is widely deployed
for several reasons, including its complexity compared to modular there are some communities where its uptake has been limited for
several reasons, including its complexity compared to modular
arithmetic and longstanding perceptions of IPR concerns (which, for arithmetic and longstanding perceptions of IPR concerns (which, for
the most part, have now been resolved [RFC6090]). On the other hand, the most part, have now been resolved [RFC6090]). Note that ECDHE
there are two related issues hindering effective use of modular cipher suites exist for both RSA and ECDSA certificates so moving to
Diffie-Hellman cipher suites in TLS: ECDHE cipher suites does not require moving away from RSA based
certificates. On the other hand, there are two related issues
hindering effective use of modular Diffie-Hellman cipher suites in
TLS:
o There are no protocol mechanisms to negotiate the DH groups or o There are no standardized, widely implemented protocol mechanisms
parameter lengths supported by client and server. to negotiate the DH groups or parameter lengths supported by
client and server.
o Many servers choose DH parameters of 1024 bits or fewer.
o There are widely deployed client implementations that reject o There are widely deployed client implementations that reject
received DH parameters if they are longer than 1024 bits. received DH parameters if they are longer than 1024 bits. In
addition, several implementations do not perform appropriate
validation of group parameters and are vulnerable to attacks
referenced in Section 2.9 of [I-D.ietf-uta-tls-attacks]
We note that with DHE and ECDHE cipher suites, the TLS master key We note that with DHE and ECDHE cipher suites, the TLS master key
only depends on the Diffie-Hellman parameters and not on the strength only depends on the Diffie-Hellman parameters and not on the strength
of the RSA certificate; moreover, 1024 bit modular DH parameters are of the RSA certificate; moreover, 1024 bit modular DH parameters are
generally considered insufficient at this time. generally considered insufficient at this time.
With modular ephemeral DH, deployers SHOULD carefully evaluate With modular ephemeral DH, deployers SHOULD carefully evaluate
interoperability vs. security considerations when configuring their interoperability vs. security considerations when configuring their
TLS endpoints. TLS endpoints.
skipping to change at page 13, line 43 skipping to change at page 14, line 21
agents like Web browsers or email software. agents like Web browsers or email software.
This document does not address the rarer deployment scenarios where This document does not address the rarer deployment scenarios where
one of the above three properties is not desired, such as the use one of the above three properties is not desired, such as the use
case described under Section 5.2 below. Another example of an case described under Section 5.2 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.
5.2. Unauthenticated TLS and Opportunistic Encryption 5.2. Unauthenticated TLS and Opportunistic Security
Several important applications use TLS to protect data between a TLS Several important applications use TLS to protect data between a TLS
client and a TLS server, but do so without the TLS client necessarily client and a TLS server, but do so without the TLS client necessarily
verifying the server's certificate. This practice is often called verifying the server's certificate. This practice is often called
"unauthenticated TLS". The reader is referred to "unauthenticated TLS". The reader is referred to
[I-D.ietf-dane-smtp-with-dane] for an example and an explanation of [I-D.ietf-dane-smtp-with-dane] for an example and an explanation of
why this less secure practice will likely remain common in the why this less secure practice will likely remain common in the
context of SMTP (especially for MTA-to-MTA communications). The context of SMTP (especially for MTA-to-MTA communications). The
practice is also encountered in similar contexts such as server-to- practice is also encountered in similar contexts such as server-to-
server traffic on the XMPP network (where multi-tenant hosting server traffic on the XMPP network (where multi-tenant hosting
environments make it difficult for operators to obtain proper environments make it difficult for operators to obtain proper
certificates for all of the domains they service). certificates for all of the domains they service).
Furthermore, in some scenarios the use of TLS itself is optional, Furthermore, in some scenarios the use of TLS itself is optional,
i.e. the client decides dynamically ("opportunistically") whether to i.e. the client decides dynamically ("opportunistically") whether to
use TLS with a particular server or to connect in the clear. This use TLS with a particular server or to connect in the clear. This
practice, often called "opportunistic encryption", and is described practice, often called "opportunistic security", and is described at
at length in Section 2 of [I-D.farrelll-mpls-opportunistic-encrypt]. length in Section 2 of [I-D.farrelll-mpls-opportunistic-encrypt].
It can be argued that the recommendations provided in this document It can be argued that the recommendations provided in this document
ought to apply equally to unauthenticated TLS as well as ought to apply equally to unauthenticated TLS as well as
authenticated TLS. That would keep TLS implementations and authenticated TLS. That would keep TLS implementations and
deployments in sync, which is a desirable property given that servers deployments in sync, which is a desirable property given that servers
can be used simultaneously for unauthenticated TLS and for can be used simultaneously for unauthenticated TLS and for
authenticated TLS (indeed, a server cannot know whether a client authenticated TLS (indeed, a server cannot know whether a client
might attempt authenticated or unauthenticated TLS). On the other might attempt authenticated or unauthenticated TLS). On the other
hand, it has been argued that some of the recommendations in this hand, it has been argued that some of the recommendations in this
document might be too strict for unauthenticated scenarios and that document might be too strict for unauthenticated scenarios and that
skipping to change at page 16, line 14 skipping to change at page 16, line 40
o A long-term key used on a device as a default key [Heninger2012]. o A long-term key used on a device as a default key [Heninger2012].
o A key generated by a Trusted Third Party like a CA, and later o A key generated by a Trusted Third Party like a CA, and later
retrieved from it either by extortion or compromise retrieved from it either by extortion or compromise
[Soghoian2011]. [Soghoian2011].
o A cryptographic break-through, or the use of asymmetric keys with o A cryptographic break-through, or the use of asymmetric keys with
insufficient length [Kleinjung2010]. insufficient length [Kleinjung2010].
o Social engineering attacks against system administrators.
o Collection of private keys from inadequately protected backups.
Forward secrecy ensures in such cases that the session keys cannot be Forward secrecy ensures in such cases that the session keys cannot be
determined even by an attacker who obtains the long-term keys some determined even by an attacker who obtains the long-term keys some
time after the conversation. It also protects against an attacker time after the conversation. It also protects against an attacker
who is in possession of the long-term keys, but remains passive who is in possession of the long-term keys, but remains passive
during the conversation. during the conversation.
Forward secrecy is generally achieved by using the Diffie-Hellman Forward secrecy is generally achieved by using the Diffie-Hellman
scheme to derive session keys. The Diffie-Hellman scheme has both scheme to derive session keys. The Diffie-Hellman scheme has both
parties maintain private secrets and send parameters over the network parties maintain private secrets and send parameters over the network
as modular powers over certain cyclic groups. The properties of the as modular powers over certain cyclic groups. The properties of the
skipping to change at page 17, line 13 skipping to change at page 17, line 41
IKEv2 implementations that reuse DH exponents. IKEv2 implementations that reuse DH exponents.
7.5. Certificate Revocation 7.5. Certificate Revocation
Unfortunately, no mechanism exists at this time that we can recommend Unfortunately, no mechanism exists at this time that we can recommend
as a complete and efficient solution for the problem of checking the as a complete and efficient solution for the problem of checking the
revocation status of common public key certificates (a.k.a. PKIX revocation status of common public key certificates (a.k.a. PKIX
certificates, [RFC5280]). The current state of the art is as certificates, [RFC5280]). The current state of the art is as
follows: follows:
o Certificate Revocation Lists (CRLs) are not scalable and therefore o Although Certificate Revocation Lists (CRLs) are the most widely
rarely used. supported mechanism for distributing revocation information, they
have known scaling challenges that limit their usefulness (despite
workarounds such as partitioned CRLS and delta CRLs).
o The On-Line Certification Status Protocol (OCSP) presents both o Proprietary mechanisms that embed revocation lists in the Web
scaling and privacy issues when used for heavy traffic Web browser's configuration database cannot scale beyond a small
servers. In addition, clients typically "soft-fail", meaning they number of the most heavily used Web servers.
do not abort the TLS connection if the OCSP server does not
respond. o The On-Line Certification Status Protocol (OCSP) [RFC6960]
presents both scaling and privacy issues. In addition, clients
typically "soft-fail", meaning that they do not abort the TLS
connection if the OCSP server does not respond (however, this
might be a workaround to avoid denial of service attacks if an
OSCP responder is taken offline).
o OCSP stapling (Section 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. Although
addresses this shortcoming, but is a recent addition without much [RFC6961] addresses this shortcoming, it is a recent addition
deployment. without much deployment.
o Proprietary mechanisms that embed revocation lists in the Web o Both CRLs and OSCP depend on relatively reliable connectivity to
browser's configuration database cannot scale beyond a small the Internet, which might not be available to certain kinds of
number of the most heavily used Web servers. nodes (such as newly provisioned devices that need to establish a
secure connection in order to boot up for the first time).
With regard to PKIX certificates, servers SHOULD support OCSP and With regard to PKIX certificates, servers SHOULD support both OCSP
OCSP stapling, including the OCSP stapling extension defined in [RFC6960] and OCSP stapling. To enable interoperability with the
[RFC6961], as a best practice given the current state of the art and widest range of clients, servers SHOULD support both the
as a foundation for a possible future solution. status_request extension defined in [RFC6066] and the
status_request_v2 extension defined in [RFC6961]. Servers also
SHOULD support the OCSP stapling extension defined in [RFC6961] as a
best practice given the current state of the art and as a foundation
for a possible future solution.
The foregoing considerations do not apply to scenarios where the The foregoing considerations do not apply to scenarios where the
DANE-TLSA resource record [RFC6698] is used to signal to a client DANE-TLSA resource record [RFC6698] is used to signal to a client
which certificate a server considers valid and good to use for TLS which certificate a server considers valid and good to use for TLS
connections. connections.
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, Paul Hoffman, Simon Josefsson, Watson Ladd, Orit Levin, Farrell, Daniel Kahn Gillmor, Paul Hoffman, Simon Josefsson, Watson
Ilari Liusvaara, Johannes Merkle, Bodo Moeller, Yoav Nir, Kenny Ladd, Orit Levin, Ilari Liusvaara, Johannes Merkle, Bodo Moeller,
Paterson, Patrick Pelletier, Tom Ritter, Rich Salz, Sean Turner, and Yoav Nir, Massimiliano Pala, Kenny Paterson, Patrick Pelletier, Tom
Aaron Zauner for their feedback and suggested improvements. Thanks Ritter, Joe St. Sauver, Joe Salowey, Rich Salz, Brian Smith, Sean
to Brian Smith, whose "browser cipher suites" page is a great Turner, and Aaron Zauner for their feedback and suggested
resource. Finally, thanks to all others who commented on the TLS, improvements. Thanks to Brian Smith, who has provided a great
UTA, and other discussion lists but who are not mentioned here by resource in his "Proposal to Change the Default TLS Ciphersuites
name. Offered by Browsers" [Smith2013]. Finally, thanks to all others who
commented on the TLS, UTA, and other discussion lists but who are not
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.
skipping to change at page 19, line 18 skipping to change at page 20, line 18
CA/Browser Forum, , "Baseline Requirements for the CA/Browser Forum, , "Baseline Requirements for the
Issuance and Management of Publicly-Trusted Certificates Issuance and Management of Publicly-Trusted Certificates
Version 1.1.6", 2013, <https://www.cabforum.org/ Version 1.1.6", 2013, <https://www.cabforum.org/
documents.html>. documents.html>.
[DegabrieleP07] [DegabrieleP07]
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>.
[ECRYPT-II]
Smart, N., "ECRYPT II Yearly Report on Algorithms and
Keysizes (2011-2012)", 2012,
<http://www.ecrypt.eu.org/documents/D.SPA.20.pdf>.
[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.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.
skipping to change at page 19, line 40 skipping to change at page 20, line 45
Dukhovni, V. and W. Hardaker, "SMTP security via Dukhovni, V. and W. Hardaker, "SMTP security via
opportunistic DANE TLS", draft-ietf-dane-smtp-with-dane-10 opportunistic DANE TLS", draft-ietf-dane-smtp-with-dane-10
(work in progress), May 2014. (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-06 (work in with SRV Records", draft-ietf-dane-srv-06 (work in
progress), June 2014. progress), June 2014.
[I-D.ietf-tls-downgrade-scsv]
Moeller, B. and A. Langley, "TLS Fallback Signaling Cipher
Suite Value (SCSV) for Preventing Protocol Downgrade
Attacks", draft-ietf-tls-downgrade-scsv-02 (work in
progress), November 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-rc4-01 (work in progress), October 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]
skipping to change at page 21, line 15 skipping to change at page 22, line 30
[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 [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS) of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012. 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.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, June 2013.
[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.
[Smith2013]
Smith, B., "Proposal to Change the Default TLS
Ciphersuites Offered by Browsers.", 2013, <https://
briansmith.org/browser-ciphersuites-01.html>.
[Soghoian2011] [Soghoian2011]
Soghoian, C. and S. Stamm, "Certified lies: Detecting and Soghoian, C. and S. Stamm, "Certified lies: Detecting and
defeating government interception attacks against SSL.", defeating government interception attacks against SSL.",
Proc. 15th Int. Conf. Financial Cryptography and Data Proc. 15th Int. Conf. Financial Cryptography and Data
Security , 2011. Security , 2011.
[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-07 A.1. draft-ietf-uta-tls-bcp-08
o More WGLC feedback.
o TLS 1.1 is now SHOULD NOT, just like TLS 1.0.
o SHOULD NOT use curves of less than 192 bits for ECDH.
o Clarification regarding OCSP and OSCP stapling.
A.2. draft-ietf-uta-tls-bcp-07
o WGLC feedback. o WGLC feedback.
A.2. draft-ietf-uta-tls-bcp-06 A.3. draft-ietf-uta-tls-bcp-06
o Undo unauthenticated TLS, following another long thread on the o Undo unauthenticated TLS, following another long thread on the
list. list.
A.3. draft-ietf-uta-tls-bcp-05 A.4. 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.4. draft-ietf-uta-tls-bcp-04 A.5. 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.5. draft-ietf-uta-tls-bcp-03 A.6. 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.6. draft-ietf-uta-tls-bcp-02 A.7. 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.7. draft-ietf-tls-bcp-01 A.8. 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.8. draft-ietf-tls-bcp-00 A.9. draft-ietf-tls-bcp-00
o Initial WG version, with only updated references. o Initial WG version, with only updated references.
A.9. draft-sheffer-tls-bcp-02 A.10. 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.10. draft-sheffer-tls-bcp-01 A.11. 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 forward secrecy. o Added a section justifying the need for forward secrecy.
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.11. draft-sheffer-tls-bcp-00 A.12. 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
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