Re: [TLS] Consensus call on Implicit IV for AEAD
Eric Rescorla <ekr@rtfm.com> Mon, 06 April 2015 02:13 UTC
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From: Eric Rescorla <ekr@rtfm.com>
Date: Sun, 05 Apr 2015 19:13:04 -0700
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To: Tom Ritter <tom@ritter.vg>
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Subject: Re: [TLS] Consensus call on Implicit IV for AEAD
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On Sun, Apr 5, 2015 at 6:10 PM, Tom Ritter <tom@ritter.vg> wrote: > On 3 April 2015 at 15:34, Joseph Salowey <joe@salowey.net> wrote: > > In the interim meeting we had consensus to use an implicit IV for AEAD. > The > > proposal was to use the record sequence number and pad with zeros as > > described in pull request 155 > > (https://github.com/tlswg/tls13-spec/pull/155/files). This was also > > discussed in the IETF-92 meeting in Dallas along with options to change > the > > offset. The consensus was to stay with the original proposal. We are > > posting to the mailing list to confirm this consensus. If you have > comments, > > please reply by April 17, 2015. > > > I apologize if I'm mistaken or this has been raised previously, but I > feel compelled to speak up and not assume it has. > > The record sequence number is predictable. It's not in the clear on > the wire, but it begins at 0 and increments with every record. > (Right?) > > This will result in a predictable IV for the AEAD mode. We have two > AEAD modes today: > - GCM - IV must be unique, being predictable doesn't matter (Right?) > - poly1305 - IV/Nonce must be unique, being predictable doesn't matter > (Right?) > > But we also don't know what AEAD modes we will add in the future. I'm > far from being 'up' on the CAESER competition, but I skimmed the first > ~10 entries, and one, CMCC is based on CBC mode. It seems like a > predictable IV = BEAST. Am I right in thinking we will be > pigeonholing ourselves into only allowing AEAD modes that do _not_ > require an unpredictable IV? I think we are restricting ourselves to AEAD modes that allow a predictable nonce (this is the 5116 terminology). However, it's worth noting two points about this: 1. All of the proposed constructions use related nonces in the sense that if you knew the nonce for a single record, you could derive the nonce for all records sent in that direction. 2. A predictable nonce does not mean that you have a predictable IV for an underlying cipher. For instance, as AGL noted in a previous e-mail [0], it is possible to construct an unpredictable IV from a predictable nonce. -Ekr [0] https://www.ietf.org/mail-archive/web/tls/current/msg15533.html > > -tom > > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls >
- [TLS] Consensus call on Implicit IV for AEAD Joseph Salowey
- Re: [TLS] Consensus call on Implicit IV for AEAD Martin Thomson
- Re: [TLS] Consensus call on Implicit IV for AEAD Daniel Migault
- Re: [TLS] Consensus call on Implicit IV for AEAD Brian Smith
- Re: [TLS] Consensus call on Implicit IV for AEAD Dave Garrett
- Re: [TLS] Consensus call on Implicit IV for AEAD Eric Rescorla
- Re: [TLS] Consensus call on Implicit IV for AEAD Ilari Liusvaara
- Re: [TLS] Consensus call on Implicit IV for AEAD Tom Ritter
- Re: [TLS] Consensus call on Implicit IV for AEAD David Leon Gil
- Re: [TLS] Consensus call on Implicit IV for AEAD Eric Rescorla
- Re: [TLS] Consensus call on Implicit IV for AEAD Yoav Nir
- Re: [TLS] Consensus call on Implicit IV for AEAD Tom Ritter
- Re: [TLS] Consensus call on Implicit IV for AEAD Yoav Nir
- Re: [TLS] Consensus call on Implicit IV for AEAD Daniel Migault
- Re: [TLS] Consensus call on Implicit IV for AEAD Martin Thomson
- Re: [TLS] Consensus call on Implicit IV for AEAD Daniel Migault
- Re: [TLS] Consensus call on Implicit IV for AEAD Ilari Liusvaara
- Re: [TLS] Consensus call on Implicit IV for AEAD Martin Thomson
- Re: [TLS] Consensus call on Implicit IV for AEAD Ilari Liusvaara
- Re: [TLS] Consensus call on Implicit IV for AEAD Michael Hamburg
- Re: [TLS] Consensus call on Implicit IV for AEAD Brian Smith
- Re: [TLS] Consensus call on Implicit IV for AEAD Yoav Nir