< draft-sheffer-tls-bcp-00.txt   draft-sheffer-tls-bcp-01.txt >
Network Working Group Y. Sheffer tls Y. Sheffer
Internet-Draft Porticor Internet-Draft Porticor
Intended status: BCP September 8, 2013 Intended status: BCP R. Holz
Expires: March 12, 2014 Expires: March 24, 2014 TUM
September 20, 2013
Recommendations for Secure Use of TLS and DTLS Recommendations for Secure Use of TLS and DTLS
draft-sheffer-tls-bcp-00 draft-sheffer-tls-bcp-01
Abstract Abstract
Over the last few years there have been several serious attacks on Over the last few years there have been several serious attacks on
TLS, including attacks on its most commonly used ciphers and modes of TLS, including attacks on its most commonly used ciphers and modes of
operation. This document offers recommendations on securely using operation. This document offers recommendations on securely using
the TLS and DTLS protocols, given existing standards and the TLS and DTLS protocols, given existing standards and
implementations. implementations.
Status of this Memo Status of this Memo
skipping to change at page 1, line 34 skipping to change at page 1, line 35
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on March 12, 2014. This Internet-Draft will expire on March 24, 2014.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . 3
2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . 3 2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . 3
2.1. BEAST . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. BEAST . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . 4 2.2. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . 4
2.3. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . 4 2.3. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . 4
2.4. Compression Attacks: CRIME and BREACH . . . . . . . . . 4 2.4. Compression Attacks: CRIME and BREACH . . . . . . . . 4
3. Selection Criteria . . . . . . . . . . . . . . . . . . 4 3. Selection Criteria . . . . . . . . . . . . . . . . . . 4
4. Recommendations . . . . . . . . . . . . . . . . . . . . 5 4. Recommendations . . . . . . . . . . . . . . . . . . . 5
4.1. Details . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Summary . . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Status . . . . . . . . . . . . . . . . . 5 4.2. Cipher Suite Negotiation Details . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . 6 4.3. Downgrade Attacks . . . . . . . . . . . . . . . . . . 6
6.1. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Alternatives . . . . . . . . . . . . . . . . . . . . . 6
6.2. Downgrade Attacks . . . . . . . . . . . . . . . . . . . 6 5. Implementation Status . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . 6 6.1. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . 6 6.2. Perfect Forward Secrecy (PFS) . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . 7 6.3. Session Resumption . . . . . . . . . . . . . . . . . . 9
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . 9
A.1. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgements . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . 10
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . . 12
A.1. -01 . . . . . . . . . . . . . . . . . . . . . . . . . 12
A.2. -00 . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
Over the last few years there have been several major attacks on TLS Over the last few years there have been several major attacks on TLS
[RFC5246], including attacks on its most commonly used ciphers and [RFC5246], including attacks on its most commonly used ciphers and
modes of operation. Details are given in Section 2, but suffice it modes of operation. Details are given in Section 2, but suffice it
to say that both AES-CBC and RC4, which together make up for most to say that both AES-CBC and RC4, which together make up for most
current usage, have been seriously attacked in the context of TLS. current usage, have been seriously attacked in the context of TLS.
Given these issues, there is need for IETF guidance on how TLS can be Given these issues, there is need for IETF guidance on how TLS can be
used securely. Unlike most IETF documents, this is guidance for used securely. Unlike most IETF documents, this is guidance for
deployers rather than for implementers. In fact the recommendations deployers, as well as for implementers. In fact the recommendations
below call for the use of widely implemented algorithms, which are below call for the use of widely implemented algorithms, which are
not seeing widespread use today. not seeing widespread use today.
Rather than standardizing new mechanisms in TLS, our goal is to
recommend a few already-specified mechanisms and cipher suites, and
to encourage the industry to use them in order to improve the overall
security of TLS-protected network traffic. When picking these
mechanisms, we consider their security, their technical maturity and
interoperability, as well as their prevalence at the time of writing.
This recommendation applies to both TLS and DTLS. TLS 1.3, when it This recommendation applies to both TLS and DTLS. TLS 1.3, when it
is standardized and deployed in the field, should resolve the current is 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 the current document.
Our knowledge about the strength of various algorithms and feasible
attacks can change quickly, and experience shows that a crypto BCP is
a point-in-time statement more than other BCPs. Readers are advised
to seek out any errata or udpates that apply to this document.
1.1. Conventions used in this document 1.1. Conventions used in this document
[[Are we normative? This section might go away.]] [[Are we normative? Currently we're not and this section might go
away.]]
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].
2. Attacks on TLS 2. Attacks on TLS
This section lists the attacks that motivated the current This section lists the attacks that motivated the current
recommendation. This is not intended to be an extensive survey of recommendations. This is not intended to be an extensive survey of
TLS's security. TLS's security.
While there are widely deployed mitigations for some of the attacks While there are widely deployed mitigations for some of the attacks
listed below, we believe that their root causes necessitate a more listed below, we believe that their root causes necessitate a more
systemic solution. systemic solution.
2.1. BEAST 2.1. BEAST
The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation
of CBC (that is, predictable IV) to decrypt parts of a packet, and of CBC (that is, predictable IV) to decrypt parts of a packet, and
specifically shows how this can be used to decrypt HTTP cookies when specifically shows how this can be used to decrypt HTTP cookies when
run over TLS. run over TLS.
2.2. Lucky Thirteen 2.2. Lucky Thirteen
A consequence of the MAC-then-encrypt design is the existence of A consequence of the MAC-then-encrypt design in all current versions
padding oracle attacks [Padding-Oracle]. A recent incarnation of of TLS is the existence of padding oracle attacks [Padding-Oracle].
these attacks is the Lucky Thirteen attack [CBC-Attack], a timing A recent incarnation of these attacks is the Lucky Thirteen attack
side-channel attack that allows the attacker to decrypt arbitrary [CBC-Attack], a timing side-channel attack that allows the attacker
ciphertext. to decrypt arbitrary ciphertext.
2.3. Attacks on RC4 2.3. Attacks on RC4
The RC4 algorithm [RC4] has been used with TLS (and previously, SSL) The RC4 algorithm [RC4] has been used with TLS (and previously, SSL)
for many years. Attacks have also been known for a long time, e.g. for many years. Attacks have also been known for a long time, e.g.
[RC4-Attack-FMS]. But recent attacks [RC4-Attack] have weakened this [RC4-Attack-FMS]. But recent attacks ([RC4-Attack],
algorithm even more. See [I-D.popov-tls-prohibiting-rc4] for more [RC4-Attack-AlF]) have weakened this algorithm even more. See
details. [I-D.popov-tls-prohibiting-rc4] for more details.
2.4. Compression Attacks: CRIME and BREACH 2.4. Compression Attacks: CRIME and BREACH
The CRIME attack [CRIME] allows an active attacker to decrypt The CRIME attack [CRIME] allows an active attacker to decrypt
cyphertext (specifically, cookies) when TLS is used with protocol- cyphertext (specifically, cookies) when TLS is used with protocol-
level compression. The attack is a consequence of the TLS MAC-then- level compression.
encrypt approach.
The BREACH attack [BREACH] makes similar use of HTTP-level The BREACH attack [BREACH] makes similar use of HAdded TTP-level
compression which is much more prevalent than compression at the TLS compression, which is much more prevalent than compression at the TLS
level, to decrypt secret data passed in the HTTP response. level, to decrypt secret data passed in the HTTP response.
While the former attack can be mitigated by disabling TLS The former attack can be mitigated by disabling TLS compression, as
compression, we are not aware of mitigations at the protocol level to recommended below. We are not aware of mitigations at the protocol
the latter attack, and so application-level mitigations are needed. level to the latter attack, and so application-level mitigations are
For example, implementations of HTTP that use CSRF tokens will need needed (see [BREACH]). For example, implementations of HTTP that use
to randomize them even when the recommendations of the current CSRF tokens will need to randomize them even when the recommendations
document are adopted. of the current document are adopted.
[[Is it possible to affect some length hiding using TLS 1.2 as
specified today, i.e. without draft-pironti-tls-length-hiding-01, and
using available APIs?]]
3. Selection Criteria 3. Selection Criteria
Given the above attacks, we are proposing that deployers opt for a Given the above attacks, we are proposing that deployers opt for a
specific ciphersuite when negotiating TLS. We have used the specific cipher suite when negotiating TLS. We have used the
following criteria when framing our recommendations: following criteria when framing our recommendations:
o The ciphersuite must be secure in default use, and should not o The cipher suite must be secure in default use, and should not
require any additional security measures beyond those defined in require any additional security measures beyond those defined in
the standard. the standard.
o The cipher suite must be widely implemented, i.e. available in a
o The ciphersuite must be widely implemented, i.e. available in a
large percentage of popular cryptographic libraries. large percentage of popular cryptographic libraries.
o The ciphersuite must have undergone a significant amount of o The cipher suite must have undergone a significant amount of
analysis, and the algorithm and mode of operation must both be analysis, and the algorithm and mode of operation must both be
standardized by relevant organizations. standardized by relevant organizations.
o We prefer ciphersuites that provide client-side privacy and o We prefer cipher suites that provide client-side privacy and
perfect forward secrecy, i.e. those that use ephemeral Diffie- perfect forward secrecy, i.e. those that use ephemeral Diffie-
Hellman. Hellman. See Section 6.2 for more details.
o As currently specified and implemented, elliptic curve groups are
preferable over modular DH groups: they are easier and safer to
use within TLS.
o When there are multiple key sizes available, we have chosen the o When there are multiple key sizes available, we have chosen the
current industry standard, 128 bits of strength. Of course current industry standard, 128 bits of strength. Of course
deployers are free to opt for a stronger ciphersuite. deployers are free to opt for a stronger cipher suite.
4. Recommendations 4. Recommendations
Based on the criteria above, we recommend using as a preferred Following are recommendations for people implementing and deploying
ciphersuite the following: client and server-side TLS.
o TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 [RFC5288] 4.1. Summary
It is noted that the above ciphersuite is an authenticated encryption Based on the criteria above, we recommend using as a preferred cipher
(AEAD) algorithm [RFC5116], and therefore requires the use of TLS suite the following:
1.2.
4.1. Details o TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 [RFC5829]
We recommend that clients include this cipher suite as the first It is noted that the above cipher suite is an authenticated
encryption (AEAD) algorithm [RFC5116], and therefore requires the use
of TLS 1.2.
We recommend using 2048-bit server certificates, with a SHA-256
fingerprint. See [CAB-Baseline] for more details.
[RFC4492] allows clients and servers to negotiate ECDH parameters
(curves). We recommend that clients and servers prefer verifiably
random curves (specifically Brainpool P-256, brainpoolp256r1
[I-D.merkle-tls-brainpool]), and fall back to the commonly used NIST
P-256 (secp256r1) [RFC4492]. In addition, clients should send an
ec_point_formats extension with a single element, "uncompressed".
We recommend to always disable TLS-level compression ([RFC5246], Sec.
6.2.2).
Finally, we recommend that clients disable fallback to SSLv3 (see
Section 4.3).
4.2. Cipher Suite Negotiation Details
We recommend that clients include the above cipher suite as the first
proposal to any server, unless they have prior knowledge that the proposal to any server, unless they have prior knowledge that the
server cannot respond to a TLS 1.2 client_hello message. server cannot respond to a TLS 1.2 client_hello message.
We recommend that servers prefer this ciphersuite (or a similar but We recommend that servers prefer this cipher suite (or a similar but
stronger one) whenever it is proposed, even if it is not the first stronger one) whenever it is proposed, even if it is not the first
proposal. proposal.
Note that other profiles of TLS 1.2 exist that use different Both clients and servers should include the "Supported Elliptic
ciphersuites. For example, [RFC6460] defines a profile that uses the Curves" extension [RFC4492].
Clients are of course free to offer stronger cipher suites, e.g.
using AES-256; when they do, the server should prefer the stronger
cipher suite unless there are reasons (e.g. performance) to choose
otherwise.
Note that other profiles of TLS 1.2 exist that use different cipher
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 ciphersuites. TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 cipher suites.
This document is not an application profile standard, in the sense of
Sec. 9 of [RFC5246]. As a result, clients and servers are still
required to support the TLS mandatory cipher suite,
TLS_RSA_WITH_AES_128_CBC_SHA.
4.3. Downgrade Attacks
Some client implementations revert to SSLv3 if the server rejected
higher versions of SSL/TLS. This fallback can be forced by a MITM
attacker. Moreover, IP scans [[reference?]] show that SSLv3-only
servers amount to about 3% of the current server population. As a
result, we recommend that by default, clients should avoid falling
back to SSLv3.
4.4. Alternatives
Elliptic Curves Cryptography is not universally deployed for several
reasons, including its complexity compared to modular arithmetic and
longstanding IPR concerns. On the other hand, there are two related
issues hindering effective use of modular Diffie-Hellman cipher
suites in TLS:
o There are no protocol mechanisms to negotiate the DH groups or
parameter lengths supported by client and server.
o There are widely deployed client implementations that reject
received DH parameters, if they are longer than 1024 bits.
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
the the RSA certificate; moreover, 1024 bits DH parameters are
generally considered insufficient at this time.
Because of the above, we recommend using (in priority order):
1. Elliptic Curve DHE with negotiated parameters, as described in
Section 4.1.
2. TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 [RFC5288], with 2048-bit
Diffie-Hellman parameters.
3. The same cipher suite, with 1024-bit parameters.
With modular ephemeral DH, deployers should carefully evaluate
interoperability vs. security considerations when configuring their
TLS endpoints.
5. Implementation Status 5. Implementation Status
Since this document does not propose a new protocol or a new Since this document does not propose a new protocol or a new cipher
ciphersuite, we do not provide a full implementation status, as per suite, we do not provide a full implementation status, as per
[RFC6982]. However it is useful to list some known existing [RFC6982]. However it is useful to list some known existing
implementations of the recommended ciphersuite(s). implementations of the recommended cipher suite(s).
+----------+----------------+--------------+------------------------+ +----------+--------------+---------------------+-------------------+
| Category | Software | As Of | Comment | | Category | Software | As Of Version | Comment |
| | | Version | | +----------+--------------+---------------------+-------------------+
+----------+----------------+--------------+------------------------+ | Library | OpenSSL | 1.0.1 | |
| Library | OpenSSL | 1.0.1 | | | | GnuTLS | | |
| | GnuTLS | | | | | NSS | 3.11.1 | |
| | NSS | 3.11.1 | | | Browser | Internet | IE8 on Windows 7 | |
| Browser | Internet | IE8 on | | | | Explorer | | |
| | Explorer | Windows 7 | | | | Firefox | TBD | |
| | Firefox | | TBD | | | Chrome | TLS 1.2 and AES-GCM | |
| | Chrome | | TBD | | | | expected in Chrome | |
| | Safari | | TBD | | | | 30 | |
| Web | Apache | ?? | | | | Safari | TBD | |
| server | (mod_gnutls) | | | | Web | Apache | ?? | |
| | Apache | ?? | | | server | (mod_gnutls) | | |
| | (mod_ssl) | | | | | Apache | ?? | |
| | Nginx | 1.0.9, 1.1.6 | With a recent version | | | (mod_ssl) | | |
| | | | of OpenSSL | | | Nginx | 1.0.9, 1.1.6 | With a recent |
+----------+----------------+--------------+------------------------+ | | | | version of |
| | | | OpenSSL |
+----------+--------------+---------------------+-------------------+
6. Security Considerations 6. Security Considerations
6.1. AES-GCM 6.1. AES-GCM
Please refer to [RFC5246], Sec. 11 for general security Please refer to [RFC5246], Sec. 11 for general security
considerations when using TLS 1.2, and to [RFC5288], Sec. 6 for considerations when using TLS 1.2, and to [RFC5288], Sec. 6 for
security considerations that apply specifically to AES-GCM when used security considerations that apply specifically to AES-GCM when used
with TLS. with TLS.
6.2. Downgrade Attacks 6.2. Perfect Forward Secrecy (PFS)
[[Do we need to disallow some protocol variants, e.g. SSL 3.0, so PFS is a defense against an attacker who records encrypted
that there are no downgrade attacks possible?]] conversations where the session keys are only encrypted with the
communicating parties' long-term keys. Should the attacker be able
to obtain these long-term keys at some point later in the future, 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
the private key retrieved.
o A long-term key retrieved from a device that has been sold or
otherwise decommissioned without prior wiping.
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
retrieved from it either by extortion or compromise
[Soghoian2011].
o A cryptographic break-through, or the use of asymmetric keys with
insufficient length [Kleinjung2010].
PFS ensures in such cases that the session keys cannot be determined
even by an attacker who obtains the long-term keys some time after
the conversation. It also protects against an attacker who is in
possession of the long-term keys, but remains passive during the
conversation.
PFS is generally achieved by using the Diffie-Hellman scheme to
derive session keys. The Diffie-Hellman scheme has both parties
maintain private secrets and send parameters over the network as
modular powers over certain cyclic groups. The properties of the so-
called Discrete Logarithm Problem (DLP) allow to derive the session
keys without an eavesdropper being able to do so. There is currently
no known attack against DLP if sufficiently large parameters are
chosen.
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
strict use of PFS-only ciphers. These are listed in Section
Section 4.1.
6.3. Session Resumption
TBD, https://www.imperialviolet.org/2013/06/27/botchingpfs.html.
7. IANA Considerations 7. IANA Considerations
[Note to RFC Editor: please remove this section before publication.]
This document requires no IANA actions. This document requires no IANA actions.
8. References 8. Acknowledgements
8.1. Normative References We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir,
Kenny Paterson, Patrick Pelletier, and Rich Salz for their review.
Thanks to Brian Smith whose "browser cipher suites" page is a great
resource. Finally, Thanks to all others who commented on the TLS and
other lists and are not mentioned here by name.
The document was prepared using the lyx2rfc tool, created by Nico
Williams.
9. 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.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
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.
8.2. Informative References [RFC5829] Brown, A., Clemm, G., and J. Reschke, "Link Relation Types
for Simple Version Navigation between Web Resources",
RFC 5829, April 2010.
[I-D.merkle-tls-brainpool]
Merkle, J. and M. Lochter, "ECC Brainpool Curves for
Transport Layer Security (TLS)",
draft-merkle-tls-brainpool-04 (work in progress),
July 2013.
9.2. Informative References
[I-D.popov-tls-prohibiting-rc4] [I-D.popov-tls-prohibiting-rc4]
Popov, A., "Prohibiting RC4 Cipher Suites", Popov, A., "Prohibiting RC4 Cipher Suites",
draft-popov-tls-prohibiting-rc4-00 (work in progress), draft-popov-tls-prohibiting-rc4-00 (work in progress),
August 2013. August 2013.
[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.
[RFC6460] Salter, M. and R. Housley, "Suite B Profile for Transport [RFC6460] Salter, M. and R. Housley, "Suite B Profile for Transport
skipping to change at page 8, line 8 skipping to change at page 11, line 15
[RC4-Attack-FMS] [RC4-Attack-FMS]
Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the
Key Scheduling Algorithm of RC4", Selected Areas in Key Scheduling Algorithm of RC4", Selected Areas in
Cryptography , 2001. Cryptography , 2001.
[RC4-Attack] [RC4-Attack]
ISOBE, T., OHIGASHI, T., WATANABE, Y., and M. MORII, "Full ISOBE, T., OHIGASHI, T., WATANABE, Y., and M. MORII, "Full
Plaintext Recovery Attack on Broadcast RC4", International Plaintext Recovery Attack on Broadcast RC4", International
Workshop on Fast Software Encryption , 2013. Workshop on Fast Software Encryption , 2013.
[RC4-Attack-AlF]
AlFardan, N., Bernstein, D., Paterson, K., Poettering, B.,
and J. Schuldt, "On the Security of RC4 in TLS", Usenix
Security Symposium 2013, 2013, <https://www.usenix.org/
conference/usenixsecurity13/security-rc4-tls>.
[Padding-Oracle] [Padding-Oracle]
Vaudenay, S., ""Security Flaws Induced by CBC Padding Vaudenay, S., "Security Flaws Induced by CBC Padding
Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002, Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002,
2002, <http://www.iacr.org/cryptodb/archive/2002/ 2002, <http://www.iacr.org/cryptodb/archive/2002/
EUROCRYPT/2850/2850.pdf>. EUROCRYPT/2850/2850.pdf>.
[CAB-Baseline]
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Publicly-Trusted Certificates Version 1.1.6", 2013,
<https://www.cabforum.org/documents.html>.
[TLS-IANA]
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Suite Registry", <https://www.iana.org/assignments/
tls-parameters/tls-parameters.xhtml#tls-parameters-4>.
[Heninger2012]
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Halderman, "Mining Your Ps and Qs: Detection of Widespread
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[Kleinjung2010]
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defeating government interception attacks against SSL.",
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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. -00 A.1. -01
o Clarified our motivation in the introduction.
o Added a section justifying the need for PFS.
o Added recommendations for RSA and DH parameter lengths. Moved
from DHE to ECDHE, with a discussion on whether/when DHE is
appropriate.
o Recommendation to avoid fallback to SSLv3.
o Initial information about browser support - more still needed!
o More clarity on compression.
o Client can offer stronger cipher suites.
o Discussion of the regular TLS mandatory cipher suite.
A.2. -00
o Initial version. o Initial version.
Author's Address 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
Technische Universitaet Muenchen
Boltzmannstr. 3
Garching 85748
Germany
Email: holz@net.in.tum.de
 End of changes. 46 change blocks. 
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