[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-sheffer-uta-tls-attacks) 00 01 02 03 04 05 RFC 7457

uta                                                           Y. Sheffer
Internet-Draft                                                  Porticor
Intended status: Informational                                   R. Holz
Expires: December 26, 2014                                           TUM
                                                          P. Saint-Andre
                                                                    &yet
                                                           June 24, 2014


              Summarizing Current Attacks on TLS and DTLS
                     draft-ietf-uta-tls-attacks-01

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 26, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



Sheffer, et al.         Expires December 26, 2014               [Page 1]


Internet-Draft                 TLS Attacks                     June 2014


   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Attacks on TLS  . . . . . . . . . . . . . . . . . . . . . . .   3
   2.1.  SSL Stripping . . . . . . . . . . . . . . . . . . . . . . .   3
   2.2.  BEAST . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.3.  Lucky Thirteen  . . . . . . . . . . . . . . . . . . . . . .   3
   2.4.  Attacks on RC4  . . . . . . . . . . . . . . . . . . . . . .   3
   2.5.  Compression Attacks: CRIME and BREACH . . . . . . . . . . .   4
   2.6.  Certificate Attacks . . . . . . . . . . . . . . . . . . . .   4
   2.7.  Diffe-Hellman Parameters  . . . . . . . . . . . . . . . . .   4
   2.8.  Denial of Service . . . . . . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.1.  Normative References  . . . . . . . . . . . . . . . . . . .   5
   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

   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].




Sheffer, et al.         Expires December 26, 2014               [Page 2]


Internet-Draft                 TLS Attacks                     June 2014


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.  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
   of CBC (that is, the predictable initialization vector) to decrypt
   parts of a packet, and specifically to decrypt HTTP cookies when HTTP
   is run over TLS.

2.3.  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].
   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.

2.4.  Attacks on RC4

   The RC4 algorithm [RC4] has been used with TLS (and previously, SSL)
   for many years.  RC4 has long been known to have a variety of
   cryptographic weaknesses, e.g.  [RC4-Attack-Pau], [RC4-Attack-Man],
   [RC4-Attack-FMS].  Recent cryptanalysis results [RC4-Attack-AlF]
   exploit biases in the RC4 keystream to recover repeatedly encrypted
   plaintexts.

   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.




Sheffer, et al.         Expires December 26, 2014               [Page 3]


Internet-Draft                 TLS Attacks                     June 2014


2.5.  Compression Attacks: CRIME and BREACH

   The CRIME attack [CRIME] allows an active attacker to decrypt
   ciphertext (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 [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




Sheffer, et al.         Expires December 26, 2014               [Page 4]


Internet-Draft                 TLS Attacks                     June 2014


   computational work.  It is known that such attacks have in fact been
   mounted.

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

   This document requires no IANA actions.

5.  Acknowledgements

   We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir,
   Kenny Paterson, Patrick Pelletier, Tom Ritter and Rich Salz for their
   review of this document.  We thank Andrei Popov for contributing text
   on RC4.

   The document was prepared using the lyx2rfc tool, created by Nico
   Williams.

6.  References

6.1.  Normative References

   [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.ietf-uta-tls-bcp]
              Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of TLS and DTLS", draft-
              ietf-uta-tls-bcp-00 (work in progress), March 2014.

   [RFC6989]  Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman
              Tests for the Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 6989, July 2013.

   [CBC-Attack]
              AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking
              the TLS and DTLS Record Protocols", IEEE Symposium on
              Security and Privacy , 2013.






Sheffer, et al.         Expires December 26, 2014               [Page 5]


Internet-Draft                 TLS Attacks                     June 2014


   [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]
              Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the
              Key Scheduling Algorithm of RC4", Selected Areas in
              Cryptography , 2001.

   [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>.

   [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>.






Sheffer, et al.         Expires December 26, 2014               [Page 6]


Internet-Draft                 TLS Attacks                     June 2014


   [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

   Note to RFC Editor: please remove this section before publication.

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.

A.3.  draft-sheffer-uta-tls-bcp-00

   o  Initial version, extracted from draft-sheffer-tls-bcp-01.







Sheffer, et al.         Expires December 26, 2014               [Page 7]


Internet-Draft                 TLS Attacks                     June 2014


Authors' Addresses

   Yaron Sheffer
   Porticor
   29 HaHarash St.
   Hod HaSharon  4501303
   Israel

   Email: yaronf.ietf@gmail.com


   Ralph Holz
   Technische Universitaet Muenchen
   Boltzmannstr. 3
   Garching  85748
   Germany

   Email: holz@net.in.tum.de


   Peter Saint-Andre
   &yet

   Email: ietf@stpeter.im



























Sheffer, et al.         Expires December 26, 2014               [Page 8]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/