draft-ietf-uta-tls-attacks-00.txt   draft-ietf-uta-tls-attacks-01.txt 
uta Y. Sheffer uta Y. Sheffer
Internet-Draft Porticor Internet-Draft Porticor
Intended status: Informational R. Holz Intended status: Informational 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
Summarizing Current Attacks on TLS and DTLS Summarizing Current Attacks on TLS and DTLS
draft-ietf-uta-tls-attacks-00 draft-ietf-uta-tls-attacks-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 summarizes these attacks, with the goal of operation. This document summarizes these attacks, with the goal of
motivating generic and protocol-specific recommendations on the usage motivating generic and protocol-specific recommendations on the usage
of TLS and DTLS. of TLS and DTLS.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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.
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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. Attacks on TLS . . . . . . . . . . . . . . . . . . . . . . . 2 2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. BEAST . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. SSL Stripping . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . . . 3 2.2. BEAST . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . . . 3 2.3. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . . . 3
2.4. Compression Attacks: CRIME and BREACH . . . . . . . . . . . 3 2.4. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 2.5. Compression Attacks: CRIME and BREACH . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 2.6. Certificate Attacks . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 2.7. Diffe-Hellman Parameters . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.8. Denial of Service . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
A.1. draft-ietf-uta-tls-bcp-00 . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
A.2. draft-sheffer-uta-tls-bcp-00 . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . . 5
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 7
A.1. draft-ietf-uta-tls-bcp-01 . . . . . . . . . . . . . . . . . 7
A.2. draft-ietf-uta-tls-bcp-00 . . . . . . . . . . . . . . . . . 7
A.3. draft-sheffer-uta-tls-bcp-00 . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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.
This situation motivated the creation of the UTA working group, which This situation motivated the creation of the UTA working group, which
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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
recommendations. 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. SSL Stripping
Various attacks attempt to remove the use of SSL/TLS altogether, by
modifying HTTP traffic and HTML pages as they pass on the wire.
These attacks are known collectively as SSL Stripping, and were first
introduced by Moxie Marlinspike [SSL-Stripping]. In the context of
Web traffic, these attacks are only effective if the client accesses
a Web server using a mixture of HTTP and HTTPS.
2.2. 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, the predictable initialization vector) to decrypt of CBC (that is, the predictable initialization vector) to decrypt
parts of a packet, and specifically shows how this can be used to parts of a packet, and specifically to decrypt HTTP cookies when HTTP
decrypt HTTP cookies when run over TLS. is run over TLS.
2.2. Lucky Thirteen 2.3. Lucky Thirteen
A consequence of the MAC-then-encrypt design in all current versions A consequence of the MAC-then-encrypt design in all current versions
of TLS is the existence of padding oracle attacks [Padding-Oracle]. of TLS is the existence of padding oracle attacks [Padding-Oracle].
A recent incarnation of these attacks is the Lucky Thirteen attack A recent incarnation of these attacks is the Lucky Thirteen attack
[CBC-Attack], a timing side-channel attack that allows the attacker [CBC-Attack], a timing side-channel attack that allows the attacker
to decrypt arbitrary ciphertext. to decrypt arbitrary ciphertext.
2.3. Attacks on RC4 2.4. 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. RC4 has long been known to have a variety of
[RC4-Attack-FMS]. But recent attacks ([RC4-Attack], cryptographic weaknesses, e.g. [RC4-Attack-Pau], [RC4-Attack-Man],
[RC4-Attack-AlF]) have weakened this algorithm even more. See [RC4-Attack-FMS]. Recent cryptanalysis results [RC4-Attack-AlF]
[I-D.popov-tls-prohibiting-rc4] for more details. exploit biases in the RC4 keystream to recover repeatedly encrypted
plaintexts.
2.4. Compression Attacks: CRIME and BREACH These recent results are on the verge of becoming practically
exploitable; currently they require 2^26 sessions or 13x2^30
encryptions. As a result, RC4 can no longer be seen as providing a
sufficient level of security for TLS sessions.
2.5. 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- ciphertext (specifically, cookies) when TLS is used with protocol-
level compression. level compression.
The TIME attack [TIME] and the later BREACH attack [BREACH] both make The TIME attack [TIME] and the later BREACH attack [BREACH] both make
similar use of HTTP-level compression to decrypt secret data passed similar use of HTTP-level compression to decrypt secret data passed
in the HTTP response. We note that compression of the HTTP message in the HTTP response. We note that compression of the HTTP message
body is much more prevalent than compression at the TLS level. body is much more prevalent than compression at the TLS level.
The former attack can be mitigated by disabling TLS compression, as The former attack can be mitigated by disabling TLS compression, as
recommended below. We are not aware of mitigations at the protocol recommended below. We are not aware of mitigations at the protocol
level to the latter attack, and so application-level mitigations are level to the latter attack, and so application-level mitigations are
needed (see [BREACH]). For example, implementations of HTTP that use needed (see [BREACH]). For example, implementations of HTTP that use
CSRF tokens will need to randomize them even when the recommendations CSRF tokens will need to randomize them even when the recommendations
of [I-D.ietf-uta-tls-bcp] are adopted. of [I-D.ietf-uta-tls-bcp] are adopted.
2.6. Certificate Attacks
There have been several practical attacks on TLS when used with RSA
certificates (the most common use case). These include
[Bleichenbacher98] and [Klima03]. While the Bleichenbacher attack
has been mitigated in TLS 1.0, the Klima attack that relies on a
version-check oracle is only mitigated by TLS 1.1.
The use of RSA certificates often involves exploitable timing issues
[Brumley03], unless the implementation takes care to explicitly
eliminate them.
2.7. Diffe-Hellman Parameters
TLS allows to define ephemeral Diffie-Hellman and Elliptic Curve
Diffie-Hellman parameters in its respective key exchange modes. This
results in an outstanding attack, detailed in [Cross-Protocol]. In
addition, clients that do not properly verify the received parameters
are exposed to MITM attacks. Unfortunately the TLS protocol does not
require this verification, see [RFC6989] for the IPsec analogy.
2.8. Denial of Service
Server CPU power has progressed over the years so that TLS can now be
turned on by default. However the risk of malicious clients and
coordinated groups of clients ("botnets") mounting denial of service
attacks is still very real. TLS adds another vector for
computational attacks, since a client can easily (with little
computational effort) force the server to expend relatively large
computational work. It is known that such attacks have in fact been
mounted.
3. Security Considerations 3. Security Considerations
This document describes protocol attacks in an informational manner, This document describes protocol attacks in an informational manner,
and in itself does not have any security implications. Its companion and in itself does not have any security implications. Its companion
documents certainly do. documents certainly do.
4. IANA Considerations 4. IANA Considerations
This document requires no IANA actions. This document requires no IANA actions.
5. Acknowledgements 5. Acknowledgements
We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir, We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir,
Kenny Paterson, Patrick Pelletier, and Rich Salz for their review of Kenny Paterson, Patrick Pelletier, Tom Ritter and Rich Salz for their
a previous version of this document. review of this document. We thank Andrei Popov for contributing text
on RC4.
The document was prepared using the lyx2rfc tool, created by Nico The document was prepared using the lyx2rfc tool, created by Nico
Williams. Williams.
6. References 6. References
6.1. Normative References 6.1. Normative References
[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.
6.2. Informative References 6.2. Informative References
[I-D.ietf-uta-tls-bcp] [I-D.ietf-uta-tls-bcp]
Sheffer, Y., Holz, R., and P. Saint-Andre, Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of TLS and DTLS", draft- "Recommendations for Secure Use of TLS and DTLS", draft-
ietf-uta-tls-bcp-00 (work in progress), March 2014. ietf-uta-tls-bcp-00 (work in progress), March 2014.
[I-D.popov-tls-prohibiting-rc4] [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman
Popov, A., "Prohibiting RC4 Cipher Suites", draft-popov- Tests for the Internet Key Exchange Protocol Version 2
tls-prohibiting-rc4-01 (work in progress), October 2013. (IKEv2)", RFC 6989, July 2013.
[CBC-Attack] [CBC-Attack]
AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking
the TLS and DTLS Record Protocols", IEEE Symposium on the TLS and DTLS Record Protocols", IEEE Symposium on
Security and Privacy , 2013. Security and Privacy , 2013.
[BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS", [BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS",
2011, <http://packetstormsecurity.com/files/105499/ 2011, <http://packetstormsecurity.com/files/105499/
Browser-Exploit-Against-SSL-TLS.html>. Browser-Exploit-Against-SSL-TLS.html>.
[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty [CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty
Security Conference 2012, 2012. Security Conference 2012, 2012.
[BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack", [BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack",
2013, <http://breachattack.com/>. 2013, <http://breachattack.com/>.
[TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME [TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME
Will Tell", Black Hat Europe 2013, 2013, <https:// Will Tell", Black Hat Europe 2013, 2013,
media.blackhat.com/eu-13/briefings/Beery/bh-eu-13-a <https://media.blackhat.com/eu-13/briefings/Beery/bh-
-perfect-crime-beery-wp.pdf>. eu-13-a-perfect-crime-beery-wp.pdf>.
[RC4] Schneier, B., "Applied Cryptography: Protocols, [RC4] Schneier, B., "Applied Cryptography: Protocols,
Algorithms, and Source Code in C, 2nd Ed.", 1996. Algorithms, and Source Code in C, 2nd Ed.", 1996.
[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]
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] [RC4-Attack-AlF]
AlFardan, N., Bernstein, D., Paterson, K., Poettering, B., AlFardan, N., Bernstein, D., Paterson, K., Poettering, B.,
and J. Schuldt, "On the Security of RC4 in TLS", Usenix and J. Schuldt, "On the Security of RC4 in TLS", Usenix
Security Symposium 2013, 2013, <https://www.usenix.org/ Security Symposium 2013, 2013, <https://www.usenix.org/
conference/usenixsecurity13/security-rc4-tls>. conference/usenixsecurity13/security-rc4-tls>.
[Attacks-iSec] [Attacks-iSec]
Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a
comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13 comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13
and RC4 biases", 8 2013, <https://www.isecpartners.com/ and RC4 biases", 8 2013, <https://www.isecpartners.com/
media/106031/ssl_attacks_survey.pdf>. media/106031/ssl_attacks_survey.pdf>.
[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/EUROCRYPT 2002, <http://www.iacr.org/cryptodb/archive/2002/
/2850/2850.pdf>. EUROCRYPT/2850/2850.pdf>.
[Cross-Protocol]
Mavrogiannopoulos, N., Vercauteren, F., Velichkov, V., and
B. Preneel, "A cross-protocol attack on the TLS protocol",
2012, <http://doi.acm.org/10.1145/2382196.2382206>.
[RC4-Attack-Pau]
Paul, G. and S. Maitra, "Permutation after RC4 key
scheduling reveals the secret key.", 2007,
<http://dblp.uni-trier.de/db/conf/sacrypt/
sacrypt2007.html#PaulM07>.
[RC4-Attack-Man]
Mantin, I. and A. Shamir, "A practical attack on broadcast
RC4", 2001.
[SSL-Stripping]
Marlinspike, M., "SSL Stripping", February 2009,
<http://www.thoughtcrime.org/software/sslstrip/>.
[Bleichenbacher98]
Bleichenbacher, D., "Chosen ciphertext attacks against
protocols based on the RSA encryption standard pkcs1",
1998.
[Klima03] Klima, V., Pokorny, O., and T. Rosa, "Attacking RSA-based
sessions in SSL/TLS", 2003.
[Brumley03]
Brumley, D. and D. Boneh, "Remote timing attacks are
practical", 2003.
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-uta-tls-bcp-00 A.1. draft-ietf-uta-tls-bcp-01
o Added SSL Stripping, attacks related to certificates, Diffie
Hellman parameters and denial of service.
o Expanded on RC4 attacks, thanks to Andrei Popov.
A.2. draft-ietf-uta-tls-bcp-00
o Initial WG version, with only updated references. o Initial WG version, with only updated references.
A.2. draft-sheffer-uta-tls-bcp-00 A.3. draft-sheffer-uta-tls-bcp-00
o Initial version, extracted from draft-sheffer-tls-bcp-01. o Initial version, extracted from draft-sheffer-tls-bcp-01.
Authors' Addresses Authors' Addresses
Yaron Sheffer Yaron Sheffer
Porticor Porticor
29 HaHarash St. 29 HaHarash St.
Hod HaSharon 4501303 Hod HaSharon 4501303
Israel Israel
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