draft-ietf-uta-tls-bcp-03.txt   draft-ietf-uta-tls-bcp-04.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: March 25, 2015 TUM Expires: April 3, 2015 TUM
P. Saint-Andre P. Saint-Andre
&yet &yet
September 21, 2014 September 30, 2014
Recommendations for Secure Use of TLS and DTLS Recommendations for Secure Use of TLS and DTLS
draft-ietf-uta-tls-bcp-03 draft-ietf-uta-tls-bcp-04
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 deployed services that use TLS and DTLS. The
that use TLS and DTLS. recommendations are applicable to the majority of use cases.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 March 25, 2015. This Internet-Draft will expire on April 3, 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
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. Intended Audience . . . . . . . . . . . . . . . . . . . . . . 4 2. Intended Audience and Applicability Statement . . . . . . . . 4
2.1. Security Services . . . . . . . . . . . . . . . . . . . . 4 2.1. Security Services . . . . . . . . . . . . . . . . . . . . 4
2.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Conventions used in this document . . . . . . . . . . . . . . 4 3. Conventions used in this document . . . . . . . . . . . . . . 5
4. General Recommendations . . . . . . . . . . . . . . . . . . . 5 4. General Recommendations . . . . . . . . . . . . . . . . . . . 5
4.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 5 4.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 5
4.2. Applicability to DTLS . . . . . . . . . . . . . . . . . . 5 4.2. Applicability to DTLS . . . . . . . . . . . . . . . . . . 6
4.3. Fallback to SSL . . . . . . . . . . . . . . . . . . . . . 6 4.3. Fallback to SSL . . . . . . . . . . . . . . . . . . . . . 6
4.4. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 6
4.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 6 4.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 7
4.6. TLS Session Resumption . . . . . . . . . . . . . . . . . 7 4.6. TLS Session Resumption . . . . . . . . . . . . . . . . . 7
4.7. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 7 4.7. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 7
4.8. Server Name Indication . . . . . . . . . . . . . . . . . 7 4.8. Server Name Indication . . . . . . . . . . . . . . . . . 8
5. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 7 5. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 8
5.1. General Guidelines . . . . . . . . . . . . . . . . . . . 8 5.1. General Guidelines . . . . . . . . . . . . . . . . . . . 8
5.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 9 5.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 9
5.3. Cipher Suite Negotiation Details . . . . . . . . . . . . 9 5.3. Cipher Suite Negotiation Details . . . . . . . . . . . . 10
5.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 10 5.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 10
5.5. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 10 5.5. Modular vs. Elliptic Curve DH Cipher Suites . . . . . . . 11
5.6. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 11 5.6. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 11 7.1. Host Name Validation . . . . . . . . . . . . . . . . . . 12
7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.2. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 12 7.3. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 12
7.4. Diffie Hellman Exponent Reuse . . . . . . . . . . . . . . 13 7.4. Diffie Hellman Exponent Reuse . . . . . . . . . . . . . . 13
7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 13 7.5. Certificate Revocation . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 17 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 18
A.1. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 17 A.1. draft-ietf-uta-tls-bcp-04 . . . . . . . . . . . . . . . . 18
A.2. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 17 A.2. draft-ietf-uta-tls-bcp-03 . . . . . . . . . . . . . . . . 18
A.3. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 18 A.3. draft-ietf-uta-tls-bcp-02 . . . . . . . . . . . . . . . . 18
A.4. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 18 A.4. draft-ietf-tls-bcp-01 . . . . . . . . . . . . . . . . . . 18
A.5. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 18 A.5. draft-ietf-tls-bcp-00 . . . . . . . . . . . . . . . . . . 19
A.6. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 18 A.6. draft-sheffer-tls-bcp-02 . . . . . . . . . . . . . . . . 19
A.7. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 19 A.7. draft-sheffer-tls-bcp-01 . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 A.8. draft-sheffer-tls-bcp-00 . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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, assuming the implementer expects his or her
deployment of algorithms that are widely implemented but not yet code to be deployed in environments defined in the following section.
widely deployed. Concerning deployment, this document targets a wide In fact, this document calls for the deployment of algorithms that
audience, namely all deployers who wish to add authentication, are widely implemented but not yet widely deployed. Concerning
confidentiality and data integrity to their communications. This deployment, this document targets a wide audience, namely all
document does not address the rare deployment scenarios where one of deployers who wish to add confidentiality and data integrity
these three properties is not desired. protection to their communications. In many (but not all) cases
authentication is also desired. This document does not address the
rare deployment scenarios where no confidentiality is desired.
The recommendations herein take into consideration the security of The recommendations herein take into consideration the security of
various mechanisms, their technical maturity and interoperability, various mechanisms, their technical maturity and interoperability,
and their prevalence in implementations at the time of writing. and their prevalence in implementations at the time of writing.
Unless noted otherwise, these recommendations apply to both TLS and Unless noted otherwise, these recommendations apply to both TLS and
DTLS. TLS 1.3, when it is standardized and deployed in the field, DTLS. TLS 1.3, when it is standardized and deployed in the field,
should resolve the current vulnerabilities while providing should resolve the current vulnerabilities while providing
significantly better functionality, and will very likely obsolete significantly better functionality, and will very likely obsolete
this document. this document.
skipping to change at page 4, line 5 skipping to change at page 4, line 5
specified audience. Individual specifications may have stricter specified audience. Individual specifications may have stricter
requirements related to one or more aspects of the protocol, based on requirements related to one or more aspects of the protocol, based on
their particular circumstances. When that is the case, implementers their particular circumstances. When that is the case, implementers
MUST adhere to 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. Intended Audience 2. Intended Audience and Applicability Statement
In the following, we specify which audience this document addresses In the following, we specify which audience this document addresses
concerning deployment. Most deployers are very likely part of this concerning deployment. This document applies only to environments
audience, but very specialized use cases of TLS that are outside of where confidentiality is required. It recommends algorithms and
the intended audience can exist. configuration options that make secrecy of the data-in-transit
mandatory. While this includes the majority of the TLS use cases,
there are some notable exceptions.
This document assumes that data integrity protection is always one of
the goals of a deployment. In cases when integrity is not required,
it does not make sense to employ TLS in the first place. There are
attacks against confidentiality-only protection that utilize the lack
of integrity to also break confidentiality (see e.g. [DegabrieleP07]
in the context of IPsec). Thus, even when using opportunistic
encryption, it is essential to provide cryptographic data integrity
protection
2.1. Security Services 2.1. Security Services
This document provides recommendations for an audience that wishes to This document provides recommendations for an audience that wishes to
secure their communication with TLS to achieve the following: secure their communication with TLS to achieve the following:
o 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 o Confidentiality: all (payload) communication is encrypted with the
goal that no party should be able to decrypt it except the goal that no party should be able to decrypt it except the
intended receiver. intended receiver.
o Data integrity: any changes made to the communication are o Data integrity: any changes made to the communication are
detectable by the receiver. detectable by the receiver.
Deployers MUST verify that they do not need one of these three o Optionally, authentication: this means that an end-point of the
properties if they deviate from the recommendations given in this TLS communication is authenticated as the intended entity to
communicate with. TLS allows to authenticate one or both end-
points in the communication.
Deployers MUST verify that they do not need one of the above security
services if they deviate from the recommendations given in this
document. document.
2.2. Examples 2.2. Examples
The intended audience covers those services that are most commonly The intended audience covers those services that are most commonly
used on the Internet, among many others: used on the Internet. Typically, all communication between clients
and servers requires all three of the above security services.
o Operators of WWW servers (HTTPS). o Operators of WWW servers (HTTPS).
o Operators of email servers (SMTPS, IMAPS, POPS). o Operators of email servers who wish to protect the application-
layer protocols with TLS (e.g., IMAP, POP3, or SMTP between client
and server).
o Operators of instant-messaging services (XMPPS, IRCS). o Operators of instant-messaging services who wish to protect their
application-layer protocols with TLS (e.g. XMPP or IRC between
client and server).
An example of an audience not needing confidentiality is the
following: a monitored network where the authorities in charge of
that traffic domain require full access to unencrypted (plaintext)
traffic, and where users collaborate and send their traffic in the
clear.
3. Conventions used in this document 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].
4. General Recommendations 4. General Recommendations
This section provides general recommendations on the secure use of This section provides general recommendations on the secure use of
skipping to change at page 6, line 32 skipping to change at page 6, line 50
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 Client and server implementations MUST support the HTTP Strict o HTTP client and server implementations MUST support the HTTP
Transport Security (HSTS) header [RFC6797], in order to allow Web Strict Transport Security (HSTS) header [RFC6797], in order to
servers to advertise that they are willing to accept TLS-only allow Web servers to advertise that they are willing to accept
clients. TLS-only clients.
o When applicable, Web servers SHOULD use HSTS to indicate that they o When applicable, Web servers SHOULD use HSTS to indicate that they
are willing to accept TLS-only clients. are willing to accept TLS-only clients.
4.5. Compression 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.
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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.
With some protocols, the host name is obtained indirectly and in an If the host name is discovered indirectly and in an insecure manner
insecure manner, e.g. by an insecure DNS query for an MX record. In (e.g., by an insecure DNS query for an MX or SRV record), it SHOULD
these cases, the host name SHOULD NOT be used as a trusted identity NOT be used as a reference identifier [RFC6125] even when it matches
even when it matches the presented certificate. the presented certificate. This proviso does not apply if the host
name is discovered securely (for further discussion, see for example
[I-D.ietf-dane-srv] and [I-D.ietf-dane-smtp]).
7.2. AES-GCM 7.2. AES-GCM
Sec. Section 5.2 above recommends the use of the AES-GCM Sec. Section 5.2 above recommends the use of the AES-GCM
authenticated encryption algorithm. Please refer to [RFC5246], Sec. authenticated encryption algorithm. Please refer to [RFC5246], Sec.
11 for general security considerations when using TLS 1.2, and to 11 for general security considerations when using TLS 1.2, and to
[RFC5288], Sec. 6 for security considerations that apply specifically [RFC5288], Sec. 6 for security considerations that apply specifically
to AES-GCM when used with TLS. to AES-GCM when used with TLS.
7.3. Forward Secrecy 7.3. Forward Secrecy
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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.
8. Acknowledgments 8. Acknowledgments
We would like to thank Viktor Dukhovni, Stephen Farrell, Simon We would like to thank Uri Blumenthal, Viktor Dukhovni, Stephen
Josefsson, Watson Ladd, Orit Levin, Johannes Merkle, Bodo Moeller, Farrell, Simon Josefsson, Watson Ladd, Orit Levin, Johannes Merkle,
Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom Ritter, Rich Salz, Bodo Moeller, Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom
Aaron Zauner for their review and improvements. Thanks to Brian Ritter, Rich Salz, Aaron Zauner for their review and improvements.
Smith whose "browser cipher suites" page is a great resource. Thanks to Brian Smith whose "browser cipher suites" page is a great
Finally, thanks to all others who commented on the TLS, UTA and other resource. Finally, thanks to all others who commented on the TLS,
lists and are not mentioned here by name. UTA and other lists and 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 14, line 49 skipping to change at page 15, line 25
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006. for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008. August 2008.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with [RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289, 256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008. August 2008.
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, [RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication "Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, February 2010. Extension", RFC 5746, February 2010.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
skipping to change at page 15, line 29 skipping to change at page 16, line 5
Security Version 1.2", RFC 6347, January 2012. Security Version 1.2", RFC 6347, January 2012.
9.2. Informative References 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>.
[DegabrieleP07]
Degabriele, J. and K. Paterson, "Attacking the IPsec
standards in encryption-only configurations", 2007,
<http://dx.doi.org/10.1109/SP.2007.8>.
[Heninger2012] [Heninger2012]
Heninger, N., Durumeric, Z., Wustrow, E., and J. Heninger, N., Durumeric, Z., Wustrow, E., and J.
Halderman, "Mining Your Ps and Qs: Detection of Widespread Halderman, "Mining Your Ps and Qs: Detection of Widespread
Weak Keys in Network Devices", Usenix Security Symposium Weak Keys in Network Devices", Usenix Security Symposium
2012, 2012. 2012, 2012.
[I-D.ietf-dane-smtp]
Finch, T., "Secure SMTP using DNS-Based Authentication of
Named Entities (DANE) TLSA records.", draft-ietf-dane-
smtp-01 (work in progress), February 2013.
[I-D.ietf-dane-srv]
Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", draft-ietf-dane-srv-07 (work in
progress), July 2014.
[I-D.ietf-tls-prohibiting-rc4] [I-D.ietf-tls-prohibiting-rc4]
Popov, A., "Prohibiting RC4 Cipher Suites", draft-ietf- Popov, A., "Prohibiting RC4 Cipher Suites", draft-ietf-
tls-prohibiting-rc4-00 (work in progress), July 2014. tls-prohibiting-rc4-00 (work in progress), July 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-01 (work in progress), June 2014. attacks-04 (work in progress), September 2014.
[Kleinjung2010] [Kleinjung2010]
Kleinjung, T., "Factorization of a 768-Bit RSA Modulus", Kleinjung, T., "Factorization of a 768-Bit RSA Modulus",
CRYPTO 10, 2010, <https://eprint.iacr.org/2010/006.pdf>. CRYPTO 10, 2010, <https://eprint.iacr.org/2010/006.pdf>.
[PatersonRS11] [PatersonRS11]
Paterson, K., Ristenpart, T., and T. Shrimpton, "Tag size Paterson, K., Ristenpart, T., and T. Shrimpton, "Tag size
does matter: attacks and proofs for the TLS record does matter: attacks and proofs for the TLS record
protocol", 2011, protocol", 2011,
<http://dx.doi.org/10.1007/978-3-642-25385-0_20>. <http://dx.doi.org/10.1007/978-3-642-25385-0_20>.
skipping to change at page 17, line 15 skipping to change at page 18, line 9
[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-03 A.1. draft-ietf-uta-tls-bcp-04
o Some cleanup, and input from TLS WG discussion on applicability.
A.2. 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.2. draft-ietf-uta-tls-bcp-02 A.3. 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.3. draft-ietf-tls-bcp-01 A.4. 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.4. draft-ietf-tls-bcp-00 A.5. draft-ietf-tls-bcp-00
o Initial WG version, with only updated references. o Initial WG version, with only updated references.
A.5. draft-sheffer-tls-bcp-02 A.6. 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.6. draft-sheffer-tls-bcp-01 A.7. 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.7. draft-sheffer-tls-bcp-00 A.8. 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. 38 change blocks. 
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