Internet DRAFT - draft-sheffer-uta-tls-attacks
draft-sheffer-uta-tls-attacks
uta Y. Sheffer
Internet-Draft Porticor
Intended status: Informational R. Holz
Expires: August 11, 2014 TUM
P. Saint-Andre
&yet
February 7, 2014
Summarizing Current Attacks on TLS and DTLS
draft-sheffer-uta-tls-attacks-00
Abstract
Over the last few years there have been several serious attacks on
TLS, including attacks on its most commonly used ciphers and modes of
operation. This document summarizes these attacks, with the goal of
motivating generic and protocol-specific recommendations on the usage
of TLS and DTLS.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 11, 2014.
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Copyright (c) 2014 IETF Trust and the persons identified as the
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . 3
2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . 3
2.1. BEAST . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . 3
2.3. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . 4
2.4. Compression Attacks: CRIME and BREACH . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . 5
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . . 6
A.1. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . 6
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1. Introduction
Over the last few years there have been several major attacks on TLS
[RFC5246], including attacks on its most commonly used ciphers and
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
current usage, have been seriously attacked in the context of TLS.
This situation motivated the creation of the UTA working group, which
is tasked with the creation of generic and protocol-specific
recommendation for the use of TLS and DTLS.
"Attacks always get better; they never get worse" (ironically, this
saying is attributed to the NSA). This list of attacks describes our
knowledge as of this writing. It seems likely that new attacks will
be invented in the future.
For a more detailed discussion of the attacks listed here, the
interested reader is referred to [Attacks-iSec].
1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Attacks on TLS
This section lists the attacks that motivated the current
recommendations. This is not intended to be an extensive survey of
TLS's security.
While there are widely deployed mitigations for some of the attacks
listed below, we believe that their root causes necessitate a more
systemic solution.
2.1. BEAST
The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation
of CBC (that is, the predictable initialization vector) to decrypt
parts of a packet, and specifically shows how this can be used to
decrypt HTTP cookies when run over TLS.
2.2. Lucky Thirteen
A consequence of the MAC-then-encrypt design in all current versions
of TLS is the existence of padding oracle attacks [Padding-Oracle].
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A recent incarnation of these attacks is the Lucky Thirteen attack
[CBC-Attack], a timing side-channel attack that allows the attacker
to decrypt arbitrary ciphertext.
2.3. Attacks on RC4
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.
[RC4-Attack-FMS]. But recent attacks ([RC4-Attack],
[RC4-Attack-AlF]) have weakened this algorithm even more. See
[I-D.popov-tls-prohibiting-rc4] for more details.
2.4. Compression Attacks: CRIME and BREACH
The CRIME attack [CRIME] allows an active attacker to decrypt
cyphertext (specifically, cookies) when TLS is used with protocol-
level compression.
The TIME attack [TIME] and the later BREACH attack [BREACH] both make
similar use of HTTP-level compression to decrypt secret data passed
in the HTTP response. We note that compression of the HTTP message
body is much more prevalent than compression at the TLS level.
The former attack can be mitigated by disabling TLS compression, as
recommended below. We are not aware of mitigations at the protocol
level to the latter attack, and so application-level mitigations are
needed (see [BREACH]). For example, implementations of HTTP that use
CSRF tokens will need to randomize them even when the recommendations
of [TBD] are adopted.
3. Security Considerations
This document describes protocol attacks in an informational manner,
and in itself does not have any security implications. Its companion
documents certainly do.
4. IANA Considerations
[Note to RFC Editor: please remove this section before publication.]
This document requires no IANA actions.
5. Acknowledgements
We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir,
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Kenny Paterson, Patrick Pelletier, and Rich Salz for their review of
a previous version of this document.
The document was prepared using the lyx2rfc tool, created by Nico
Williams.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
6.2. Informative References
[I-D.popov-tls-prohibiting-rc4]
Popov, A., "Prohibiting RC4 Cipher Suites",
draft-popov-tls-prohibiting-rc4-01 (work in progress),
October 2013.
[CBC-Attack]
AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking
the TLS and DTLS Record Protocols", IEEE Symposium on
Security and Privacy , 2013.
[BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS",
2011, <http://packetstormsecurity.com/files/105499/
Browser-Exploit-Against-SSL-TLS.html>.
[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty
Security Conference 2012, 2012.
[BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack",
2013, <http://breachattack.com/>.
[TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME
Will Tell", Black Hat Europe 2013, 2013, <https://
media.blackhat.com/eu-13/briefings/Beery/
bh-eu-13-a-perfect-crime-beery-wp.pdf>.
[RC4] Schneier, B., "Applied Cryptography: Protocols,
Algorithms, and Source Code in C, 2nd Ed.", 1996.
[RC4-Attack-FMS]
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Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the
Key Scheduling Algorithm of RC4", Selected Areas in
Cryptography , 2001.
[RC4-Attack]
ISOBE, T., OHIGASHI, T., WATANABE, Y., and M. MORII, "Full
Plaintext Recovery Attack on Broadcast RC4", International
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>.
[Attacks-iSec]
Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a
comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13
and RC4 biases", 8 2013, <https://www.isecpartners.com/
media/106031/ssl_attacks_survey.pdf>.
[Padding-Oracle]
Vaudenay, S., "Security Flaws Induced by CBC Padding
Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002,
2002, <http://www.iacr.org/cryptodb/archive/2002/
EUROCRYPT/2850/2850.pdf>.
Appendix A. Appendix: Change Log
Note to RFC Editor: please remove this section before publication.
A.1. -00
o Initial version, extracted from draft-sheffer-tls-bcp-01.
Authors' Addresses
Yaron Sheffer
Porticor
29 HaHarash St.
Hod HaSharon 4501303
Israel
Email: yaronf.ietf@gmail.com
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Ralph Holz
Technische Universitaet Muenchen
Boltzmannstr. 3
Garching 85748
Germany
Email: holz@net.in.tum.de
Peter Saint-Andre
&yet
Email: ietf@stpeter.im
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