Re: [TLS] Consensus call on Implicit IV for AEAD

Daniel Migault <mglt.ietf@gmail.com> Mon, 06 April 2015 13:38 UTC

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Date: Mon, 6 Apr 2015 09:38:21 -0400
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From: Daniel Migault <mglt.ietf@gmail.com>
To: Tom Ritter <tom@ritter.vg>
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Subject: Re: [TLS] Consensus call on Implicit IV for AEAD
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We had similar discussions this in IPsecme WG in Dallas [1].

AES-CBC for example would require an unpredictable IV, which makes the IV
generation more complex. Keys to generate the IV have to be negotiated and
agreed. During the WG session, we agree to limit our scope for the implicit
IV on AES-CCM/GCM/CTR and making AES-CBC out of scope.

There are at least two ways to remove the IV, either you perform a
compression that can be applied to any algorithm or you define specific
protocol suites that have an implicit IV. With compression, you may design
a mechanism that works with any suite and design the IV compression so
highest requirements are fulfilled... hoping no other conditions may be
introduced in the future. By defining specific protocols like
(AES-CCM_IMPLICIT_IV) the protocol is designed specifically to meet IV
properties. The draft presented at IPsecme adopted the second approach.

The remaining discussion point raised was how to position this implicit IV
protocol with FIPS/NIST Cryptographic Module Validation program. I have not
had enough time to check that for now.


[1] https://tools.ietf.org/html/draft-mglt-6lo-aes-implicit-iv-01
BR,
Daniel





On Mon, Apr 6, 2015 at 7:25 AM, Tom Ritter <tom@ritter.vg> wrote:

> On 6 April 2015 at 03:41, Yoav Nir <ynir.ietf@gmail.com> wrote:
> > So either IVs (actually nonces) are compressible only for such
> ciphersuites that support using the record counter as nonce/IV (add a flag
> to the registry), or else we use some method such as AGL's for generating
> unpredictable IVs from predictable nonces.
>
>
> Thanks Yoav, ekr,
>
> I obviously haven't followed all the arguments here (and from skimming
> Brian's reply) - but I prefer defining a construction that makes the
> IV given to the AEAD unpredictable and random. Doing that from a
> predictable nonce seems okay.
>
> -tom
>
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-- 
Daniel Migault
Ericsson