draft-ietf-uta-tls-bcp-02.txt   draft-ietf-uta-tls-bcp-03.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: February 25, 2015 TUM Expires: March 25, 2015 TUM
P. Saint-Andre P. Saint-Andre
&yet &yet
August 24, 2014 September 21, 2014
Recommendations for Secure Use of TLS and DTLS Recommendations for Secure Use of TLS and DTLS
draft-ietf-uta-tls-bcp-02 draft-ietf-uta-tls-bcp-03
Abstract Abstract
Transport Layer Security (TLS) and Datagram Transport Security Layer Transport Layer Security (TLS) and Datagram Transport Security Layer
(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 both software implementations and deployed services the security of both software implementations and deployed services
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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
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 February 25, 2015. This Internet-Draft will expire on March 25, 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
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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. Conventions used in this document . . . . . . . . . . . . . . 3 2. Intended Audience . . . . . . . . . . . . . . . . . . . . . . 4
3. General Recommendations . . . . . . . . . . . . . . . . . . . 4 2.1. Security Services . . . . . . . . . . . . . . . . . . . . 4
3.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 4 2.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Fallback to SSL . . . . . . . . . . . . . . . . . . . . . 4 3. Conventions used in this document . . . . . . . . . . . . . . 4
3.3. Always Use TLS . . . . . . . . . . . . . . . . . . . . . 5 4. General Recommendations . . . . . . . . . . . . . . . . . . . 5
3.4. Compression . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 5
3.5. Session Resumption . . . . . . . . . . . . . . . . . . . 5 4.2. Applicability to DTLS . . . . . . . . . . . . . . . . . . 5
3.6. Renegotiation . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Fallback to SSL . . . . . . . . . . . . . . . . . . . . . 6
3.7. Server Name Indication . . . . . . . . . . . . . . . . . 6 4.4. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 6
4. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 6 4.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Cipher Suite Selection . . . . . . . . . . . . . . . . . 6 4.6. TLS Session Resumption . . . . . . . . . . . . . . . . . 7
4.2. Public Key Length . . . . . . . . . . . . . . . . . . . . 8 4.7. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 7
4.3. Cipher Suite Negotiation Details . . . . . . . . . . . . 8 4.8. Server Name Indication . . . . . . . . . . . . . . . . . 7
4.4. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 9 5. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5.1. General Guidelines . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 9
6.1. Host Name Validation . . . . . . . . . . . . . . . . . . 10 5.3. Cipher Suite Negotiation Details . . . . . . . . . . . . 9
6.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 10
6.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 10 5.5. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 10
6.4. Diffie Hellman Exponent Reuse . . . . . . . . . . . . . . 11 5.6. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 11
6.5. Certificate Revocation . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13 7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 15 7.4. Diffie Hellman Exponent Reuse . . . . . . . . . . . . . . 13
A.1. draft-ietf-tls-bcp-02 . . . . . . . . . . . . . . . . . . 15 7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 13
A.2. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 15 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
A.3. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
A.4. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 16 9.1. Normative References . . . . . . . . . . . . . . . . . . 14
A.5. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . 15
A.6. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 16 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 A.1. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 17
A.2. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 17
A.3. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 18
A.4. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 18
A.5. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 18
A.6. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 18
A.7. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
Transport Layer Security (TLS) and Datagram Transport Security Layer Transport Layer Security (TLS) and Datagram Transport Security Layer
(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. For instance, both AES-CBC and RC4, which together of operation. For instance, both AES-CBC and RC4, which together
comprise most current usage, have been attacked in the context of comprise most current usage, have been attacked in the context of
TLS. A companion document [I-D.ietf-uta-tls-attacks] provides TLS. A companion document [I-D.ietf-uta-tls-attacks] provides
detailed information about these attacks. detailed information about these 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. Note that
this document provides guidance for deployed services, as well as this document provides guidance for deployed services, as well as
software implementations. In fact, this document calls for the software implementations. In fact, this document calls for the
deployment of algorithms that are widely implemented but not yet deployment of algorithms that are widely implemented but not yet
widely deployed. widely deployed. Concerning deployment, this document targets a wide
audience, namely all deployers who wish to add authentication,
confidentiality and data integrity to their communications. This
document does not address the rare deployment scenarios where one of
these three properties is not 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.
These recommendations apply to both TLS and DTLS. TLS 1.3, when it Unless noted otherwise, these recommendations apply to both TLS and
is standardized and deployed in the field, should resolve the current DTLS. TLS 1.3, when it is standardized and deployed in the field,
vulnerabilities while providing significantly better functionality, should resolve the current vulnerabilities while providing
and will very likely obsolete this document. significantly better functionality, and will very likely obsolete
this document.
These are minimum recommendations for the general use of TLS. These are minimum recommendations for the use of TLS for the
Individual specifications may have stricter requirements related to specified audience. Individual specifications may have stricter
one or more aspects of the protocol, based on their particular requirements related to one or more aspects of the protocol, based on
circumstances. When that is the case, implementers MUST adhere to their particular circumstances. When that is the case, implementers
those stricter requirements. MUST 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. Conventions used in this document 2. Intended Audience
In the following, we specify which audience this document addresses
concerning deployment. Most deployers are very likely part of this
audience, but very specialized use cases of TLS that are outside of
the intended audience can exist.
2.1. Security Services
This document provides recommendations for an audience that wishes to
secure their communication with TLS to achieve the following:
o Authentication: this means that an end-point of the TLS
communication is authenticated as the intended entity to
communicate with. TLS allows to authenticate one or both end-
points in the communication.
o Confidentiality: all (payload) communication is encrypted with the
goal that no party should be able to decrypt it except the
intended receiver.
o Data integrity: any changes made to the communication are
detectable by the receiver.
Deployers MUST verify that they do not need one of these three
properties if they deviate from the recommendations given in this
document.
2.2. Examples
The intended audience covers those services that are most commonly
used on the Internet, among many others:
o Operators of WWW servers (HTTPS).
o Operators of email servers (SMTPS, IMAPS, POPS).
o Operators of instant-messaging services (XMPPS, IRCS).
3. Conventions used in this document
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].
3. 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.
3.1. Protocol Versions 4.1. Protocol Versions
It is important both to stop using old, less secure versions of SSL/ It is important both to stop using old, less secure versions of SSL/
TLS and to start using modern, more secure versions. Therefore: TLS and to start using modern, more secure versions. Therefore:
o Implementations MUST NOT negotiate SSL version 2. o Implementations MUST NOT negotiate SSL version 2.
Rationale: SSLv2 is considered today as insecure [RFC6176]. Rationale: SSLv2 is considered today as insecure [RFC6176].
o Implementations MUST NOT negotiate SSL version 3. o Implementations MUST NOT negotiate SSL version 3.
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o Implementations MUST support, and prefer to negotiate, TLS version o Implementations MUST support, and prefer to negotiate, TLS version
1.2 [RFC5246]. 1.2 [RFC5246].
Rationale: Several stronger cipher suites are available only with Rationale: Several stronger cipher suites are available only with
TLS 1.2 (published in 2008). TLS 1.2 (published in 2008).
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.
3.2. Fallback to SSL 4.2. Applicability to DTLS
DTLS [RFC4347] [RFC6347] is an adaptation of TLS for UDP datagrams.
With respect to the recommendations in the current document, DTLS 1.0
is equivalent to TLS 1.1. The only exception is RC4 which is
disallowed in DTLS. DTLS 1.2 is equivalent to TLS 1.2.
4.3. Fallback to SSL
Some client implementations revert to lower versions of TLS or even Some client implementations revert to lower versions of TLS or even
to SSLv3 if the server rejected higher versions of the protocol. to SSLv3 if the server rejected higher versions of the protocol.
This fall back can be forced by a man in the middle (MITM) attacker. This fall back can be forced by a man in the middle (MITM) attacker.
By default, such clients MUST NOT fall back to SSLv3. By default, such clients MUST NOT fall back to SSLv3.
Rationale: TLS 1.0 and SSLv3 are significantly less secure than TLS Rationale: 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.
3.3. Always Use TLS 4.4. Strict TLS
Combining unprotected and TLS-protected communication opens the way Combining unprotected and TLS-protected communication opens the way
to SSL Stripping and similar attacks. Therefore: to SSL Stripping and similar attacks. Therefore:
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.
o When applicable, Web servers SHOULD advertise that they are o Client and server implementations MUST support the HTTP Strict
willing to accept TLS-only clients, using the HTTP Strict Transport Security (HSTS) header [RFC6797], in order to allow Web
Transport Security (HSTS) header [RFC6797]. servers to advertise that they are willing to accept TLS-only
clients.
3.4. Compression o When applicable, Web servers SHOULD use HSTS to indicate that they
are willing to accept TLS-only clients.
4.5. Compression
Implementations and deployments SHOULD disable TLS-level compression Implementations and deployments SHOULD disable TLS-level compression
([RFC5246], Sec. 6.2.2), because it has been subject to security ([RFC5246], Sec. 6.2.2), because it has been subject to security
attacks. attacks.
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 Sec. 2.5 of [I-D.ietf-uta-tls-attacks] for current document. See Sec. 2.5 of [I-D.ietf-uta-tls-attacks] for
further details. further details.
3.5. Session Resumption 4.6. 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, the resumption information (either session safely. In particular, when using session tickets [RFC5077], the
IDs [RFC5246] or session tickets [RFC5077]) MUST be authenticated and resumption information MUST be authenticated and encrypted to prevent
encrypted to prevent modification or eavesdropping by an attacker. modification or eavesdropping by an attacker. Further
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 as o Ticket keys MUST be changed regularly, e.g. once every week, so as
not to negate the benefits of forward secrecy (see Section 6.3 for not to negate the benefits of forward secrecy (see Section 7.3 for
details on forward secrecy). details on forward secrecy).
o Session ticket validity SHOULD be limited to a reasonable duration o Session ticket validity SHOULD be limited to a reasonable duration
(e.g. 1 day), for similar reasons. (e.g. 1 day), for similar reasons.
3.6. Renegotiation 4.7. 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 recommendation
from [triple-handshake]: TLS clients SHOULD ensure that all from [triple-handshake]: TLS clients SHOULD ensure that all
certificates received over a connection are valid for the current certificates received over a connection are valid for the current
server endpoint, and abort the handshake if they are not. In some server endpoint, and abort the handshake if they are not. In some
usages, it may be simplest to refuse any change of certificates usages, it may be simplest to refuse any change of certificates
during renegotiation. during renegotiation.
3.7. Server Name Indication 4.8. 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.
4. 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 many available cipher
suites are insecure, and so misconfiguration can easily result in suites are insecure, and so misconfiguration can easily result in
reduced security. This section includes recommendations on the reduced security. This section includes recommendations on the
selection and negotiation of cipher suites. selection and negotiation of cipher suites.
4.1. Cipher Suite Selection 5.1. General Guidelines
It is important both to stop using old, insecure cipher suites and to It is important both to stop using old, insecure cipher suites and to
start using modern, more secure cipher suites. Therefore: start using modern, more secure cipher suites. Therefore:
o Implementations MUST NOT negotiate the NULL cipher suites. o Implementations MUST NOT negotiate the NULL cipher suites.
Rationale: The NULL cipher suites offer no encryption whatsoever Rationale: The NULL cipher suites offer no encryption whatsoever
and thus are completely insecure. and thus are completely insecure.
o Implementations MUST NOT negotiate RC4 cipher suites o Implementations MUST NOT negotiate RC4 cipher suites
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o Implementations MUST support, and SHOULD prefer to negotiate, o Implementations MUST support, and SHOULD prefer to negotiate,
cipher suites offering forward secrecy, such as those in the cipher suites offering forward secrecy, such as those in the
Ephemeral Diffie-Hellman and Elliptic Curve Ephemeral Diffie Ephemeral Diffie-Hellman and Elliptic Curve Ephemeral Diffie
Hellman ("DHE" and "ECDHE") families. Hellman ("DHE" and "ECDHE") families.
Rationale: Forward secrecy (sometimes called "perfect forward Rationale: Forward secrecy (sometimes called "perfect forward
secrecy") prevents the recovery of information that was encrypted secrecy") prevents the recovery of information that was encrypted
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. which attacks can be successful.
5.2. Recommended Cipher Suites
Given the foregoing considerations, implementation of the following Given the foregoing considerations, implementation of the following
cipher suites is RECOMMENDED (see [RFC5289] for details): 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
We suggest that TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 be preferred in We suggest that TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 be preferred in
general. general. See [RFC5289] for additional implementation details.
It is noted that those cipher suites are supported only in TLS 1.2 It is noted that those cipher suites are supported only in TLS 1.2
since they are authenticated encryption (AEAD) algorithms [RFC5116]. since they are authenticated encryption (AEAD) algorithms [RFC5116].
[RFC4492] allows clients and servers to negotiate ECDH parameters [RFC4492] allows clients and servers to negotiate ECDH parameters
(curves). For interoperability, clients and servers SHOULD support (curves). Both clients and servers SHOULD include the "Supported
the NIST P-256 (secp256r1) curve [RFC4492]. In addition, clients Elliptic Curves" extension [RFC4492]. For interoperability, clients
SHOULD send an ec_point_formats extension with a single element, and servers SHOULD support the NIST P-256 (secp256r1) curve
"uncompressed". [RFC4492]. In addition, clients SHOULD send an ec_point_formats
extension with a single element, "uncompressed".
4.2. Public Key Length
With a key exchange based on modular Diffie-Hellman ("DHE" cipher
suites), key lengths of at least 2048 bits are RECOMMENDED.
Rationale: because Diffie-Hellman keys of 1024 bits are estimated to
be roughly equivalent to 80-bit symmetric keys, it is better to use
longer keys for the "DHE" family of cipher suites. Unfortunately,
some existing software cannot handle (or cannot easily handle) key
lengths greater than 1024 bits. The most common workaround for these
systems is to prefer the "ECDHE" family of cipher suites instead of
the "DHE" family. For modular groups, key lengths of at least 2048
bits are estimated to be roughly equivalent to 112-bit symmetric keys
and might be sufficient for at least the next 10 years.
Servers SHOULD authenticate using 2048-bit certificates. In
addition, the use of SHA-256 fingerprints 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.
4.3. Cipher Suite Negotiation Details 5.3. Cipher Suite Negotiation 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.
Both clients and servers SHOULD include the "Supported Elliptic
Curves" extension [RFC4492].
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.
Note that other profiles of TLS 1.2 exist that use different cipher Note that other profiles of TLS 1.2 exist that use different cipher
suites. For example, [RFC6460] defines a profile that uses the suites. For 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.
This document is not an application profile standard, in the sense of This document is not an application profile standard, in the sense of
Sec. 9 of [RFC5246]. As a result, clients and servers are still Sec. 9 of [RFC5246]. As a result, clients and servers are still
REQUIRED to support the mandatory TLS cipher suite, REQUIRED to support the mandatory TLS cipher suite,
TLS_RSA_WITH_AES_128_CBC_SHA. TLS_RSA_WITH_AES_128_CBC_SHA.
4.4. Modular vs. Elliptic Curve DH Cipher Suites 5.4. Public Key Length
With a key exchange based on modular Diffie-Hellman ("DHE" cipher
suites), key lengths of at least 2048 bits are RECOMMENDED.
Rationale: because Diffie-Hellman keys of 1024 bits are estimated to
be roughly equivalent to 80-bit symmetric keys, it is better to use
longer keys for the "DHE" family of cipher suites. Unfortunately,
some existing software cannot handle (or cannot easily handle) key
lengths greater than 1024 bits. The most common workaround for these
systems is to prefer the "ECDHE" family of cipher suites instead of
the "DHE" family. For modular groups, key lengths of at least 2048
bits are estimated to be roughly equivalent to 112-bit symmetric keys
and might be sufficient for at least the next 10 years.
Servers SHOULD authenticate using 2048-bit certificates. In
addition, the use of SHA-256 fingerprints 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.
5.5. 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 EC Diffie-
Hellman groups, as required by Section 4.1. Some implementations are Hellman groups, as required by Section 5.2. Some implementations are
severely limited in the length of DH values. When such severely limited in the length of DH values. When such
implementations need to be accommodated, we recommend using (in implementations need to be accommodated, we recommend using (in
priority order): 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. The same cipher suite, with 1024-bit parameters. 3. The same cipher suite, with 1024-bit parameters.
skipping to change at page 10, line 5 skipping to change at page 11, line 17
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.
5. IANA Considerations 5.6. Truncated HMAC
The truncated HMAC extension, defined in Sec. 7 of [RFC6066] does not
apply to the AEAD cipher suites recommended above. However it does
apply to most other TLS cipher suites. Its use has been shown to be
insecure in [PatersonRS11], and implementations MUST NOT use it.
6. IANA Considerations
This document requests no actions of IANA. [Note to RFC Editor: This document requests no actions of IANA. [Note to RFC Editor:
please remove this whole section before publication.] please remove this whole section before publication.]
6. Security Considerations 7. Security Considerations
This entire document discusses security practices, and this section This entire document discusses the security practices directly
adds a few security considerations and includes further discussion of affecting applications using the TLS protocol. This section contains
particular recommendations. broader security considerations related to technologies used in
conjunction with or by TLS.
6.1. Host Name Validation 7.1. Host Name Validation
Application authors should take note that TLS implementations Application authors should take note that TLS implementations
frequently do not validate host names, and must therefore determine frequently do not validate host names, and must therefore determine
if the TLS implementation they are using does, and if not write their if the TLS implementation they are using does, and if not write their
own validation code or consider changing the TLS implementation. own validation code or consider changing the TLS implementation.
It is noted that the requirements regarding host name validation (and It is noted that the requirements regarding host name validation (and
in general, binding between the TLS layer and the protocol that runs in general, binding between the TLS layer and the protocol that runs
above it) vary between different protocols. For HTTPS, these above it) vary between different protocols. For HTTPS, these
requirements are defined by Sec. 3 of [RFC2818]. requirements are defined by Sec. 3 of [RFC2818].
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.
6.2. AES-GCM With some protocols, the host name is obtained indirectly and in an
insecure manner, e.g. by an insecure DNS query for an MX record. In
these cases, the host name SHOULD NOT be used as a trusted identity
even when it matches the presented certificate.
Please refer to [RFC5246], Sec. 11 for general security 7.2. AES-GCM
considerations when using TLS 1.2, and to [RFC5288], Sec. 6 for
security considerations that apply specifically to AES-GCM when used
with TLS.
6.3. Forward Secrecy Sec. Section 5.2 above recommends the use of the AES-GCM
authenticated encryption algorithm. Please refer to [RFC5246], Sec.
11 for general security considerations when using TLS 1.2, and to
[RFC5288], Sec. 6 for security considerations that apply specifically
to AES-GCM when used with TLS.
Forward secrecy (also often called Perfect Forward Secrecy or "PFS") 7.3. Forward Secrecy
is a defense against an attacker who records encrypted conversations
where the session keys are only encrypted with the communicating Forward secrecy (also often called Perfect Forward Secrecy or "PFS",
parties' long-term keys. Should the attacker be able to obtain these and defined in [RFC4949]) is a defense against an attacker who
long-term keys at some point later in time, he will be able to records encrypted conversations where the session keys are only
decrypt the session keys and thus the entire conversation. In the encrypted with the communicating parties' long-term keys. Should the
context of TLS and DTLS, such compromise of long-term keys is not attacker be able to obtain these long-term keys at some point later
entirely implausible. It can happen, for example, due to: in time, he will be able to decrypt the session keys and thus the
entire conversation. In the context of TLS and DTLS, such compromise
of long-term keys is not entirely implausible. It can happen, for
example, due to:
o A client or server being attacked by some other attack vector, and o A client or server being attacked by some other attack vector, and
the private key retrieved. the private key retrieved.
o A long-term key retrieved from a device that has been sold or o A long-term key retrieved from a device that has been sold or
otherwise decommissioned without prior wiping. otherwise decommissioned without prior wiping.
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
skipping to change at page 11, line 37 skipping to change at page 13, line 16
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.
6.4. 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
previous connections. In other words, exponent reuse negates the previous connections. In other words, exponent reuse negates the
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.
6.5. Certificate Revocation 7.5. Certificate Revocation
Unfortunately there is currently no effective, Internet-scale Unfortunately there is currently no effective, Internet-scale
mechanism to affect certificate revocation: mechanism to affect certificate revocation:
o Certificate Revocation Lists (CRLs) are non-scalable and therefore o Certificate Revocation Lists (CRLs) are non-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
skipping to change at page 12, line 38 skipping to change at page 14, line 19
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 The current consensus appears to be that OCSP stapling, combined with
a "must staple" mechanism similar to HSTS, would finally resolve this a "must staple" mechanism similar to HSTS, would finally resolve this
problem; in particular when used together with the extension defined problem; in particular when used together with the extension defined
in [RFC6961]. But such a mechanism has not been standardized yet. in [RFC6961]. But such a mechanism has not been standardized yet.
7. Acknowledgments 8. Acknowledgments
We would like to thank Stephen Farrell, Simon Josefsson, Watson Ladd, We would like to thank Viktor Dukhovni, Stephen Farrell, Simon
Johannes Merkle, Bodo Moeller, Yoav Nir, Kenny Paterson, Patrick Josefsson, Watson Ladd, Orit Levin, Johannes Merkle, Bodo Moeller,
Pelletier, Tom Ritter, Rich Salz, Aaron Zauner for their review. Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom Ritter, Rich Salz,
Thanks to Brian Smith whose "browser cipher suites" page is a great Aaron Zauner for their review and improvements. Thanks to Brian
resource. Finally, thanks to all others who commented on the TLS, Smith whose "browser cipher suites" page is a great resource.
UTA and other lists and are not mentioned here by name. Finally, thanks to all others who commented on the TLS, UTA and other
lists and are not mentioned here by name.
8. References 9. References
8.1. 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.
[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.
skipping to change at page 13, line 39 skipping to change at page 15, line 18
[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
Security (TLS)", RFC 6125, March 2011. Security (TLS)", RFC 6125, March 2011.
[RFC6176] Turner, S. and T. Polk, "Prohibiting Secure Sockets Layer [RFC6176] Turner, S. and T. Polk, "Prohibiting Secure Sockets Layer
(SSL) Version 2.0", RFC 6176, March 2011. (SSL) Version 2.0", RFC 6176, March 2011.
8.2. Informative References [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
9.2. Informative References
[CAB-Baseline] [CAB-Baseline]
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>.
[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
skipping to change at page 14, line 18 skipping to change at page 15, line 48
[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-01 (work in progress), June 2014. attacks-01 (work in progress), June 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>.
[PatersonRS11]
Paterson, K., Ristenpart, T., and T. Shrimpton, "Tag size
does matter: attacks and proofs for the TLS record
protocol", 2011,
<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.
[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
Security", RFC 4347, April 2006.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
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.
[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.
skipping to change at page 15, line 21 skipping to change at page 17, 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-tls-bcp-02 A.1. draft-ietf-uta-tls-bcp-03
o Disallow truncated HMAC.
o Applicability to DTLS.
o Some more text restructuring.
o Host name validation is sometimes irrelevant.
o HSTS: MUST implement, SHOULD deploy.
o Session identities are not protected, only tickets are.
o Clarified the target audience.
A.2. 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.2. draft-ietf-tls-bcp-01 A.3. 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.3. draft-ietf-tls-bcp-00 A.4. draft-ietf-tls-bcp-00
o Initial WG version, with only updated references. o Initial WG version, with only updated references.
A.4. draft-sheffer-tls-bcp-02 A.5. 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.5. draft-sheffer-tls-bcp-01 A.6. 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.6. draft-sheffer-tls-bcp-00 A.7. 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
Email: yaronf.ietf@gmail.com Email: yaronf.ietf@gmail.com
Ralph Holz Ralph Holz
Technische Universitaet Muenchen Technische Universitaet Muenchen
skipping to change at page 17, line 22 skipping to change at page 19, line 31
Ralph Holz Ralph Holz
Technische Universitaet Muenchen Technische Universitaet Muenchen
Boltzmannstr. 3 Boltzmannstr. 3
Garching 85748 Garching 85748
Germany Germany
Email: holz@net.in.tum.de Email: holz@net.in.tum.de
Peter Saint-Andre Peter Saint-Andre
&yet &yet
P.O. Box 787
Parker, CO 80134
USA
Email: ietf@stpeter.im Email: peter@andyet.com
 End of changes. 57 change blocks. 
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