Re: [TLS] comparison of draft-josefsson-salsa20-tls-02 and draft-agl-tls-chacha20poly1305-02
Robert Ransom <rransom.8774@gmail.com> Wed, 23 October 2013 16:48 UTC
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Date: Wed, 23 Oct 2013 09:47:58 -0700
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From: Robert Ransom <rransom.8774@gmail.com>
To: Nikos Mavrogiannopoulos <nmav@gnutls.org>
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Cc: "tls@ietf.org" <tls@ietf.org>, Joachim Strömbergson <joachim@secworks.se>
Subject: Re: [TLS] comparison of draft-josefsson-salsa20-tls-02 and draft-agl-tls-chacha20poly1305-02
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On 10/23/13, Nikos Mavrogiannopoulos <nmav@gnutls.org> wrote: > On 10/23/2013 04:58 PM, Adam Langley wrote: >> On Wed, Oct 23, 2013 at 10:51 AM, Nikos Mavrogiannopoulos >> <nmav@gnutls.org> wrote: >>> As far as I understand you use chacha to generate the keystream for >>> poly1305. Thus you carry state between records (chacha is a stream >>> cipher). I don't know if I have missed anything there, but I don't see >>> resetting chacha with a new IV per MAC calculation. >> >> There is no state carried between records: "ChaCha20 is run with the >> given key and nonce and with the two counter words set to zero. The >> first 32 bytes of the 64 byte output are saved to become the one-time >> key for Poly1305." (The nonce is the sequence number of the record.) >> (http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-00#section-5) > > I had assumed that you used the Poly1305-AES construction but with > Chacha in place of AES. Clearly this isn't the case, and even the > attacks described may not apply to your construction. I have not seen > this construction before. It looks pretty elegant. Has it been used > somewhere else? It's used in the 'box' and 'secretbox' operations in NaCl. See also section 2.5 of <http://cr.yp.to/antiforgery/pema-20071022.pdf>. Robert Ransom
- [TLS] comparison of draft-josefsson-salsa20-tls-0… Nikos Mavrogiannopoulos
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Eric Rescorla
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Adam Langley
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Nikos Mavrogiannopoulos
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Nikos Mavrogiannopoulos
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Adam Langley
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Eric Rescorla
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Nikos Mavrogiannopoulos
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Nikos Mavrogiannopoulos
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Adam Langley
- Re: [TLS] comparison of draft-josefsson-salsa20-t… Robert Ransom
- [TLS] DTLS resilience [was: comparison of draft-j… Nikos Mavrogiannopoulos