< draft-ietf-uta-tls-bcp-00.txt   draft-ietf-uta-tls-bcp-01.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: September 28, 2014 TUM Expires: December 26, 2014 TUM
P. Saint-Andre P. Saint-Andre
&yet &yet
March 27, 2014 June 24, 2014
Recommendations for Secure Use of TLS and DTLS Recommendations for Secure Use of TLS and DTLS
draft-ietf-uta-tls-bcp-00 draft-ietf-uta-tls-bcp-01
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 September 28, 2014. This Internet-Draft will expire on December 26, 2014.
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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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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3 3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3 3.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3
3.2. Fallback to SSL . . . . . . . . . . . . . . . . . . . . . 4 3.2. Fallback to SSL . . . . . . . . . . . . . . . . . . . . . 4
3.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 4 3.3. Always Use TLS . . . . . . . . . . . . . . . . . . . . . 4
3.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 6 3.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 6 3.5. Public Key Length . . . . . . . . . . . . . . . . . . . . 6
3.6. Session Resumption . . . . . . . . . . . . . . . . . . . 6 3.6. Compression . . . . . . . . . . . . . . . . . . . . . . . 7
4. Detailed Guidelines . . . . . . . . . . . . . . . . . . . . . 6 3.7. Session Resumption . . . . . . . . . . . . . . . . . . . 7
3.8. Renegotiation . . . . . . . . . . . . . . . . . . . . . . 7
4. Detailed Guidelines . . . . . . . . . . . . . . . . . . . . . 7
4.1. Cipher Suite Negotiation Details . . . . . . . . . . . . 7 4.1. Cipher Suite Negotiation Details . . . . . . . . . . . . 7
4.2. Alternative Cipher Suites . . . . . . . . . . . . . . . . 7 4.2. Alternative Cipher Suites . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6.1. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 8 6.2. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 6.3. Certificate Revocation . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . 11
A.1. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 11 Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 13
A.2. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 11 A.1. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 13
A.3. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 11 A.2. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 13
A.4. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 12 A.3. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 A.4. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 13
A.5. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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
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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.
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 implementatios at the time of writing. These and their prevalence in implementatios at the time of writing. These
recommendations apply to both TLS and DTLS. TLS 1.3, when it is recommendations apply to both TLS and DTLS. TLS 1.3, when it is
standardized and deployed in the field, should resolve the current standardized and deployed in the field, should resolve the current
vulnerabilities while providing significantly better functionality, vulnerabilities while providing significantly better functionality,
and will very likely obsolete the current document. and will very likely obsolete this document.
These are minimum recommendations for the general use of TLS.
Individual specifications may have stricter requirements related to
one or more aspects of the protocol, and based on their particular
circumstances. When that is the case, implementers 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. 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
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o Implementations MUST NOT negotiate SSL version 2. o Implementations MUST NOT negotiate SSL version 2.
Rationale: SSLv2 has serious security vulnerabilities [RFC6176]. Rationale: SSLv2 has serious security vulnerabilities [RFC6176].
o Implementations SHOULD NOT negotiate SSL version 3. o Implementations SHOULD NOT negotiate SSL version 3.
Rationale: SSLv3 [RFC6101] was an improvement over SSLv2 and Rationale: SSLv3 [RFC6101] was an improvement over SSLv2 and
plugged some significant security holes, but did not support plugged some significant security holes, but did not support
strong cipher suites. strong cipher suites.
o Implementations MAY negotiate TLS version 1.0 [RFC2246]. o Implementations SHOULD NOT negotiate TLS version 1.0 [RFC2246].
Rationale: TLS 1.0 (published in 1999) includes a way to downgrade Rationale: TLS 1.0 (published in 1999) includes a way to downgrade
the connection to SSLv3 and does not support more modern, strong the connection to SSLv3 and does not support more modern, strong
cipher suites. cipher suites.
o Implementations MAY negotiate TLS version 1.1 [RFC4346]. o Implementations MAY negotiate TLS version 1.1 [RFC4346].
Rationale: TLS 1.1 (published in 2006) prevents downgrade attacks Rationale: TLS 1.1 (published in 2006) prevents downgrade attacks
to SSL, but does not support certain stronger cipher suites. to SSL, but does not support certain stronger cipher suites.
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latest version of TLS is recommended. latest version of TLS is recommended.
3.2. Fallback to SSL 3.2. Fallback to SSL
Some client implementations revert to SSLv3 if the server rejected Some client implementations revert to SSLv3 if the server rejected
higher versions of SSL/TLS. This fallback can be forced by a MITM higher versions of SSL/TLS. This fallback can be forced by a MITM
attacker. Moreover, IP scans [[reference?]] show that SSLv3-only attacker. Moreover, IP scans [[reference?]] show that SSLv3-only
servers amount to only about 3% of the current web server population. servers amount to only about 3% of the current web server population.
Therefore, by default clients SHOULD NOT fall back from TLS to SSLv3. Therefore, by default clients SHOULD NOT fall back from TLS to SSLv3.
3.3. Cipher Suites 3.3. Always Use TLS
Combining unprotected and TLS-protected communication opens the way
to SSL Stripping and similar attacks. In cases where an application
protocol allows implementations or deployments a choice between
strict TLS configuration and dynamic upgrade from unencrypted to TLS-
protected traffic (such as STARTTLS), clients and servers SHOULD
prefer strict TLS configuration.
When applicable, Web servers SHOULD advertise that they are willing
to accept TLS-only clients, using the HTTP Strict Transport Security
(HSTS) header [RFC6797].
3.4. Cipher Suites
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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weaknesses, as documented in [I-D.popov-tls-prohibiting-rc4]. weaknesses, as documented in [I-D.popov-tls-prohibiting-rc4].
o Implementations MUST NOT negotiate cipher suites offering only so- o Implementations MUST NOT negotiate cipher suites offering only so-
called "export-level" encryption (including algorithms with 40 called "export-level" encryption (including algorithms with 40
bits or 56 bits of security). bits or 56 bits of security).
Rationale: These cipher suites are deliberately "dumbed down" and Rationale: These cipher suites are deliberately "dumbed down" and
are very easy to break. are very easy to break.
o Implementations SHOULD NOT negotiate cipher suites that use o Implementations SHOULD NOT negotiate cipher suites that use
algorithms offering less than 128 bits of security (even if they algorithms offering less than 128 bits of security. Note that
advertise more bits, such as the 168-bit 3DES cipher suites). some legacy cipher suites (e.g. 168-bit 3DES) have an effective
key length which is smaller than their nominal key length. Such
cipher suites should be evaluated accoring to their effective key
length.
Rationale: Although these cipher suites are not actively subject Rationale: Although these cipher suites are not actively subject
to breakage, their useful life is short enough that stronger to breakage, their useful life is short enough that stronger
cipher suites are desirable. cipher suites are desirable.
o Implementations SHOULD prefer cipher suites that use algorithms o Implementations SHOULD prefer cipher suites that use algorithms
with at least 128 (and, if possible, 256) bits of security. with at least 128 (and, if possible, 256) bits of security.
Rationale: Although the useful life of such cipher suites is Rationale: Although the useful life of such cipher suites is
unknown, it is probably at least several years for the 128-bit unknown, it is probably at least several years for the 128-bit
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A future version of this document might recommend cipher suites for A future version of this document might recommend cipher suites for
earlier versions of TLS. earlier versions of TLS.
[RFC4492] allows clients and servers to negotiate ECDH parameters [RFC4492] allows clients and servers to negotiate ECDH parameters
(curves). Clients and servers SHOULD prefer verifiably random curves (curves). Clients and servers SHOULD prefer verifiably random curves
(specifically Brainpool P-256, brainpoolp256r1 [RFC7027]), and fall (specifically Brainpool P-256, brainpoolp256r1 [RFC7027]), and fall
back to the commonly used NIST P-256 (secp256r1) curve [RFC4492]. In back to the commonly used NIST P-256 (secp256r1) curve [RFC4492]. In
addition, clients SHOULD send an ec_point_formats extension with a addition, clients SHOULD send an ec_point_formats extension with a
single element, "uncompressed". single element, "uncompressed".
3.4. Public Key Length 3.5. Public Key Length
Because Diffie-Hellman keys of 1024 bits are estimated to be roughly 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 equivalent to 80-bit symmetric keys, it is better to use longer keys
for the "DH" family of cipher suites. Unfortunately, some existing for the "DH" family of cipher suites. Unfortunately, some existing
software cannot handle (or cannot easily handle) key lengths greater software cannot handle (or cannot easily handle) key lengths greater
than 1024 bits. The most common workaround for these systems is to than 1024 bits. The most common workaround for these systems is to
prefer the "ECDHE" family of cipher suites instead of the "DH" prefer the "ECDHE" family of cipher suites instead of the "DH"
family, then use longer keys. Key lengths of at least 2048 bits are family, then use longer keys. Key lengths of at least 2048 bits are
RECOMMENDED, since they are estimated to be roughly equivalent to RECOMMENDED, since they are estimated to be roughly equivalent to
112-bit symmetric keys and might be sufficient for at least the next 112-bit symmetric keys and might be sufficient for at least the next
10 years. In addition to 2048-bit server certificates, the use of 10 years.
SHA-256 fingerprints is RECOMMENDED (see [CAB-Baseline] for more
details). In addition to 2048-bit server certificates, 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.
Note: The foregoing recommendations are preliminary and will likely Note: The foregoing recommendations are preliminary and will likely
be corrected and enhanced in a future version of this document. be corrected and enhanced in a future version of this document.
3.5. Compression 3.6. Compression
Implementations and deployments SHOULD disable TLS-level compression Implementations and deployments SHOULD disable TLS-level compression
([RFC5246], Sec. 6.2.2). ([RFC5246], Sec. 6.2.2), because it has been subject to security
attacks.
3.6. Session Resumption 3.7. 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, the resumption information (either session
IDs [RFC5246] or session tickets [RFC5077]) needs to be authenticated IDs [RFC5246] or session tickets [RFC5077]) needs to be authenticated
and encrypted to prevent modification or eavesdropping by an and encrypted to prevent modification or eavesdropping by an
attacker. For session tickets, a strong cipher suite SHOULD be used attacker. For session tickets, a strong cipher suite MUST be used
when encrypting the ticket (as least as strong as the main TLS cipher when encrypting the ticket (as least as strong as the main TLS cipher
suite); ticket keys MUST be changed regularly, e.g. once every week, suite); ticket keys MUST be changed regularly, e.g. once every week,
so as not to negate the effect of forward secrecy. Session ticket so as not to negate the effect of forward secrecy. Session ticket
validity SHOULD be limited to a reasonable duration (e.g. 1 day), so validity SHOULD be limited to a reasonable duration (e.g. 1 day), so
as not to negate the benefits of forward secrecy. as not to negate the benefits of forward secrecy.
3.8. Renegotiation
Where handshake renegotiation is implemented, both clients and
servers MUST implement the renegotiation_info extension, as defined
in [RFC5746].
4. Detailed Guidelines 4. Detailed Guidelines
The following sections provide more detailed information about the The following sections provide more detailed information about the
recommendations listed above. recommendations listed above.
4.1. Cipher Suite Negotiation Details 4.1. 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.
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PFS is generally achieved by using the Diffie-Hellman scheme to PFS is generally achieved by using the Diffie-Hellman scheme to
derive session keys. The Diffie-Hellman scheme has both parties derive session keys. The Diffie-Hellman scheme has both parties
maintain private secrets and send parameters over the network as maintain private secrets and send parameters over the network as
modular powers over certain cyclic groups. The properties of the so- modular powers over certain cyclic groups. The properties of the so-
called Discrete Logarithm Problem (DLP) allow to derive the session called Discrete Logarithm Problem (DLP) allow to derive the session
keys without an eavesdropper being able to do so. There is currently keys without an eavesdropper being able to do so. There is currently
no known attack against DLP if sufficiently large parameters are no known attack against DLP if sufficiently large parameters are
chosen. chosen.
Unfortunately, many TLS/DTLS cipher suites were defined that do not Unfortunately, many TLS/DTLS cipher suites were defined that do not
enable PFS, e.g. TLS_RSA_WITH_AES_256_CBC_SHA256. We thus advocate enable 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.
6.3. Certificate Revocation
Unfortunately there is currently no effective, Internet-scale
mechanism to affect certificate revocation:
o Certificate Revocation Lists (CRLs) are non-scalable and therefore
often unused.
o The On-Line Certification Status Prorocol (OCSP) presents both
scaling and privacy issues when used for heavy traffic Web
servers. In addition, clients typically "soft-fail", meaning they
do not abort the TLS connection if the OCSP server does not
respond.
o OCSP stapling (Sec. 8 of [RFC6066]) resolves the operational
issues with OCSP, but is still ineffective in the presence of a
MITM atacker, because they can simply ignore the client's request.
o Proprietary mechanisms that embed revocation lists in the Web
browser's configuration database cannot scale beyond a small
number of the most heavily used Web servers.
The current consensus appears to be that OCSP stapling, combined with
a "must staple" mechanism similar to HSTS, would finally resolve this
problem. But such a mechanism has not been standardized yet.
7. Acknowledgements 7. Acknowledgements
We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir, We would like to thank Stephen Farrell, Simon Josefsson, Johannes
Kenny Paterson, Patrick Pelletier, and Rich Salz for their review. Merkle, Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom Ritter and
Thanks to Brian Smith whose "browser cipher suites" page is a great Rich Salz for their review. Thanks to Brian Smith whose "browser
resource. Finally, thanks to all others who commented on the TLS and cipher suites" page is a great resource. Finally, thanks to all
other lists and are not mentioned here by name. others who commented on the TLS and other lists and are not mentioned
here by name.
8. References 8. References
8.1. Normative References 8.1. 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.
[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
skipping to change at page 10, line 9 skipping to change at page 11, line 27
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008. August 2008.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with [RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with
SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289, SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008. August 2008.
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, February 2010.
[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.
[RFC7027] Merkle, J. and M. Lochter, "Elliptic Curve Cryptography [RFC7027] Merkle, J. and M. Lochter, "Elliptic Curve Cryptography
(ECC) Brainpool Curves for Transport Layer Security (ECC) Brainpool Curves for Transport Layer Security
(TLS)", RFC 7027, October 2013. (TLS)", RFC 7027, October 2013.
8.2. Informative References 8.2. Informative References
[CAB-Baseline] [CAB-Baseline]
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<https://www.cabforum.org/documents.html>. <https://www.cabforum.org/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
Weak Keys in Network Devices", Usenix Security Symposium Weak Keys in Network Devices", Usenix Security Symposium
2012, 2012. 2012, 2012.
[I-D.popov-tls-prohibiting-rc4] [I-D.popov-tls-prohibiting-rc4]
Popov, A., "Prohibiting RC4 Cipher Suites", draft-popov- Popov, A., "Prohibiting RC4 Cipher Suites", draft-popov-
tls-prohibiting-rc4-01 (work in progress), October 2013. tls-prohibiting-rc4-02 (work in progress), April 2014.
[I-D.sheffer-uta-tls-attacks] [I-D.sheffer-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-sheffer-uta-tls- Current Attacks on TLS and DTLS", draft-sheffer-uta-tls-
attacks-00 (work in progress), February 2014. attacks-00 (work in progress), February 2014.
[Kleinjung2010] [Kleinjung2010]
Kleinjung, T., "Factorization of a 768-Bit RSA Modulus", Kleinjung, T., "Factorization of a 768-Bit RSA Modulus",
CRYPTO 10, 2010. CRYPTO 10, 2010.
skipping to change at page 11, line 8 skipping to change at page 12, line 31
[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.
[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:
Extension Definitions", RFC 6066, January 2011.
[RFC6101] Freier, A., Karlton, P., and P. Kocher, "The Secure [RFC6101] Freier, A., Karlton, P., and P. Kocher, "The Secure
Sockets Layer (SSL) Protocol Version 3.0", RFC 6101, Sockets Layer (SSL) Protocol Version 3.0", RFC 6101,
August 2011. August 2011.
[RFC6460] Salter, M. and R. Housley, "Suite B Profile for Transport [RFC6460] Salter, M. and R. Housley, "Suite B Profile for Transport
Layer Security (TLS)", RFC 6460, January 2012. Layer Security (TLS)", RFC 6460, January 2012.
[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797, November 2012.
[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.
Appendix A. Appendix: Change Log Appendix A. Appendix: 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-00 A.1. draft-ietf-tls-bcp-01
o Clarified that specific TLS-using protocols may have stricter
requirements.
o Changed TLS 1.0 from MAY to SHUOLD NOT.
o Added discussion of "optional TLS" and HSTS.
o Recommended use of the Signature Algorithm and Renegotiation Info
extensions.
o Use of a strong cipher for a resumption ticket: changed SHOULD to
MUST.
o Added an informational discussion of certificate revocation, but
no recommendations.
A.2. draft-ietf-tls-bcp-00
o Initial WG version, with only updated references. o Initial WG version, with only updated references.
A.2. draft-sheffer-tls-bcp-02 A.3. 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.3. draft-sheffer-tls-bcp-01 A.4. 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.
skipping to change at page 11, line 51 skipping to change at page 14, line 4
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.4. draft-sheffer-tls-bcp-00 A.5. draft-sheffer-tls-bcp-00
o Initial version. o Initial version.
Authors' Addresses Authors' Addresses
Yaron Sheffer Yaron Sheffer
Porticor Porticor
29 HaHarash St. 29 HaHarash St.
Hod HaSharon 4501303 Hod HaSharon 4501303
Israel Israel
 End of changes. 29 change blocks. 
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