Re: [TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt
"Christian Kahlo" <christian.kahlo@ageto.net> Mon, 23 September 2013 16:11 UTC
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From: Christian Kahlo <christian.kahlo@ageto.net>
To: 'Nikos Mavrogiannopoulos' <nmav@gnutls.org>
References: <CABcZeBN+0hX1-cb0V4AyaO3FrwaGrtjbRO3BGOV0KBSjRkNwkw@mail.gmail.com> <523c738f.0733cc0a.41a0.3096@mx.google.com> <523F383A.20803@drh-consultancy.co.uk> <523FE7B6.10501@gnutls.org> <524038fa.c402cd0a.127a.ffffc841@mx.google.com> <524047D1.7040601@gnutls.org>
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Date: Mon, 23 Sep 2013 18:11:25 +0200
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Cc: 'Team Neuer Personalausweis' <npa@ageto.net>, tls@ietf.org
Subject: Re: [TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt
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Hi Nikos, > > maybe you want to read http://cseweb.ucsd.edu/~mihir/papers/oem.pdf > > and http://www.iacr.org/archive/crypto2001/21390309.pdf. > > Both mentioned within this thread: > > http://crypto.stackexchange.com/questions/202/should-we-mac-then- > > encrypt-or-encrypt-then-mac > Have you actually read the papers you mention? For example have you Phew, years ago probably. I just looked them up. > seen theorem 2 of the second paper? The issue is with the Yes. > unauthenticated padding used in TLS not AtE. There are only And that's why it shouldn't be used this way. :-) > philosophical advantages of EtA over AtE when the latter is implemented > properly (i.e., as not in TLS). Today we have more clues on the issues > of AtE than it was at the time TLS was designed. That's absolutely right of course. MtE is in SSL/TLS at least since 1996-03-04. > > Please tell us which protocols are still using Mac-then-Encrypt today > > without running into any security trouble (esp. chosen ciphertext > > attacks). MtE is considered as a design fail by many researchers. > > TLS with stream ciphers. It is authenticate-pad-then-Encrypt that has > issues, please check the literature more carefully. I've read it. Actually, what we're doing with EtM is Pad-then-Encrypt- then-Mac. Regarding stream ciphers: yes, but keep in mind people like to mix it up with RC4 and you've to say you mean i.e. AES in CTR mode or similar. > > As we discussed earlier AEAD might be a solution, but AEAD is not the > > only one. I would encourage everbody to also have a look into > > ISO7816-4 secure messaging. That's the way most electronic ID cards, > > electronic purse cards, credit cards, small HSMs, etc. do > communicate. > > And now think about that there's a reason for that it's an EtM- > > scheme. > > Sorry, your attitude "there isn't a need to innovate" sounds somewhat > > unfamiliar with cryptographic primitives to me. > > Please read my mail again. The innovate refers to how the current EtA Done that. > proposal by Peter ignores all best practices in implementing EtA in OK, got it. To me it read like "no need to innovate" as in "no need to change". > protocols. Existing EtA protocols like IPSec truncate the HMAC to avoid You've got RFC 6066 truncated_hmac if you want it to do this way. Peters approach to keep things as much as simple as possible seems OK to me. > revealing the whole internal state of the hash algorithm. The Preneel- > van-Oorschot paper referenced previously in the thread gives a detailed > treatment of the issues (admittedly HMAC was designed to discourage > these attacks, but being conservative is a good design practice). We've had a lot of discussions about this. Strictly speaking if a non- truncated HMac reveals (too much) information of the internal state of the hash algorithm something totally went wrong with the hash function. As a result of this BSI TR-03116-4 chapter 2.3, 1st bullet states "do not use truncated_hmac". I'm sorry again for the lack of an english translation at the moment. The Federal Office for Information Security will probably provide one later. In THEORY a truncated_hmac offers an option for attacks as only a fraction of the original HMac has to match. Best regards, Christian
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Peter Gutmann
- [TLS] Comments/Questions on draft-gutmann-tls-enc… Eric Rescorla
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Christian Kahlo
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Dr Stephen Henson
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bill Frantz
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Nikos Mavrogiannopoulos
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Nikos Mavrogiannopoulos
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Christian Kahlo
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Peter Gutmann
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Nikos Mavrogiannopoulos
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Peter Gutmann
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Christian Kahlo
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Blumenthal, Uri - 0558 - MITLL
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Eric Rescorla
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Peter Gutmann
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Alfredo Pironti
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Ralph Holz
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Peter Gutmann
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Adam Langley
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Michael D'Errico
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Yaron Sheffer
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Michael D'Errico
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Yaron Sheffer
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Martin Rex
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Mohamad Badra
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Martin Rex
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Michael D'Errico
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Martin Rex
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Martin Rex
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Peter Gutmann
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Paul Bakker
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Paul Bakker
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Alfredo Pironti
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Paul Bakker
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Bodo Moeller
- Re: [TLS] Comments/Questions on draft-gutmann-tls… Yoav Nir