[TLS] Encrypt-then-MAC again (was Re: padding bug)
Michael D'Errico <mike-list@pobox.com> Sun, 10 November 2013 20:29 UTC
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Date: Sun, 10 Nov 2013 12:28:51 -0800
From: Michael D'Errico <mike-list@pobox.com>
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To: Nikos Mavrogiannopoulos <nmav@gnutls.org>
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Subject: [TLS] Encrypt-then-MAC again (was Re: padding bug)
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In trying to figure out what's stalling the encrypt-then-mac draft I came across this old message (below). The complaint against the draft appears to be that since the MAC is no longer encrypted, there may be a way to recover the secret HMAC key. HMAC-MD5 is mentioned as the problem, so I checked to see which cipher suites use it. The 13 cipher suites using MD5 are: A 0001 TLS_RSA_WITH_NULL_MD5 B 0003 TLS_RSA_EXPORT_WITH_RC4_40_MD5 C 0004 TLS_RSA_WITH_RC4_128_MD5 D 0006 TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 E 0017 TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 F 0018 TLS_DH_anon_WITH_RC4_128_MD5 G 0022 TLS_KRB5_WITH_DES_CBC_MD5 H 0023 TLS_KRB5_WITH_3DES_EDE_CBC_MD5 I 0024 TLS_KRB5_WITH_RC4_128_MD5 J 0025 TLS_KRB5_WITH_IDEA_CBC_MD5 K 0029 TLS_KRB5_EXPORT_WITH_DES_CBC_40_MD5 L 002A TLS_KRB5_EXPORT_WITH_RC2_CBC_40_MD5 M 002B TLS_KRB5_EXPORT_WITH_RC4_40_MD5 Eight of these (A, B, D, E, G, K, L, and M) are considered trivially breakable; F allows for a MitM; J uses the deprecated IDEA cipher; and C and I use RC4 which we now know is completely broken. That leaves only one cipher suite to possibly be concerned about: H 0023 TLS_KRB5_WITH_3DES_EDE_CBC_MD5 Do we really want to hold up the encrypt-then-mac draft any longer because of this one Kerberos/triple-DES/MD5 cipher suite? Mike Nikos Mavrogiannopoulos wrote: > On 09/08/2013 04:59 AM, Peter Saint-Andre wrote: > >>> As I recall there were three proposals for resolving the padding >>> bug in TLS >>> 1. An extension for Pad First (i.e. padding before an >>> otherwise standard TLS mode of operation) >>> 2. An extension for Encrypt-then-MAC (i.e. this draft) >>> 3. The replacement of each existing cipher suite with an >>> equivalent AEAD one >>> Was any consensus achieved as to the best approach? >> I never saw further discussion on this topic. Are there I-Ds for each >> approach? #3 seems onerous to me (and doubling the number of cipher >> suites doesn't seem like a desirable outcome), and as far as I can >> tell there's no specification for #1. Although I am not a TLS expert, >> the Encrypt-then-MAC I-D referenced above seems reasonable, it neatly >> solves a real-world problem, and we have running code; thus IMHO >> formalization of this approach deserves to be considered in the WG. > > It is important when trying to solve an issue not to introduce new > issues. The current proposal for #2 unfortunately does not take into > account known counter-measures for key recovery attacks in MACs (see [0]). > > regards, > Nikos > > [0]. http://www.ietf.org/mail-archive/web/tls/current/msg09520.html
- [TLS] Requesting feedback on TACK draft Trevor Perrin
- Re: [TLS] Requesting feedback on TACK draft Peter Gutmann
- Re: [TLS] Requesting feedback on TACK draft Lewis, Nick
- [TLS] padding bug (was: Re: Requesting feedback o… Peter Saint-Andre
- Re: [TLS] padding bug Dr Stephen Henson
- Re: [TLS] padding bug Dr Stephen Henson
- Re: [TLS] padding bug Nikos Mavrogiannopoulos
- Re: [TLS] padding bug Ben Laurie
- Re: [TLS] padding bug Eric Rescorla
- Re: [TLS] padding bug (was: Re: Requesting feedba… Alfredo Pironti
- Re: [TLS] padding bug Ben Laurie
- Re: [TLS] padding bug Yaron Sheffer
- Re: [TLS] padding bug (was: Re: Requesting feedba… Paterson, Kenny
- Re: [TLS] padding bug Ben Laurie
- Re: [TLS] padding bug Adam Langley
- Re: [TLS] padding bug Ben Laurie
- Re: [TLS] padding bug Dr Stephen Henson
- Re: [TLS] padding bug Nico Williams
- Re: [TLS] padding bug Nikos Mavrogiannopoulos
- Re: [TLS] padding bug Blumenthal, Uri - 0558 - MITLL
- Re: [TLS] padding bug (was: Re: Requesting feedba… Bodo Moeller
- Re: [TLS] padding bug (was: Re: Requesting feedba… Paterson, Kenny
- Re: [TLS] padding bug Brian Smith
- Re: [TLS] padding bug Martin Rex
- [TLS] Encrypt-then-MAC again (was Re: padding bug) Michael D'Errico
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Watson Ladd
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Paterson, Kenny
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Michael D'Errico
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Nikos Mavrogiannopoulos
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Ralf Skyper Kaiser
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Ben Laurie
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Bryan C. Geraghty
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Nikos Mavrogiannopoulos
- [TLS] Would this fix RC4 again? (was Re: Encrypt-… Michael D'Errico
- Re: [TLS] Would this fix RC4 again? (was Re: Encr… Watson Ladd
- Re: [TLS] Would this fix RC4 again? (was Re: Encr… Paterson, Kenny
- Re: [TLS] Would this fix RC4 again? (was Re: Encr… Nikos Mavrogiannopoulos
- Re: [TLS] Would this fix RC4 again? (was Re: Encr… Jacob Appelbaum
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Ralf Skyper Kaiser
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Nikos Mavrogiannopoulos
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Ralf Skyper Kaiser
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Ralf Skyper Kaiser
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Alex Elsayed
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Paterson, Kenny
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- Re: [TLS] Encrypt-then-MAC again (was Re: padding… Martin Rex
- [TLS] draft-mavrogiannopoulos-new-tls-padding-00 Martin Rex
- Re: [TLS] draft-mavrogiannopoulos-new-tls-padding… Nikos Mavrogiannopoulos