Re: [Cfrg] request for comments on "Generation of Deterministic Initialization Vectors (IVs) and Nonces"

"Dan Harkins" <dharkins@lounge.org> Wed, 20 July 2011 18:36 UTC

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Date: Wed, 20 Jul 2011 11:36:46 -0700 (PDT)
From: "Dan Harkins" <dharkins@lounge.org>
To: "Peter Gutmann" <pgut001@cs.auckland.ac.nz>
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Cc: mcgrew@cisco.com, cfrg@irtf.org, pgut001@cs.auckland.ac.nz
Subject: Re: [Cfrg] request for comments on "Generation of Deterministic Initialization Vectors (IVs) and Nonces"
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  Hi Peter,

On Wed, July 20, 2011 12:50 am, Peter Gutmann wrote:
> "Dan Harkins" <dharkins@lounge.org>; writes:
>
>>Let me remind everyone of SIV mode*. It's a CTR mode derivative but is
>>resistant to nonce misuse. Unlike CBC, the nonce doesn't need to be
>>unguessable. And it even provides a strong assurance of security if the
>> nonce
>>is reused.
>
> Doesn't SIV require the entire message to be buffered, which makes it
> unusable
> in streaming implementations?
>
> [Checks]
>
> Unless I've misinterpreted some part of Fig.3 and Fig.8 of RFC 5297, this
> can't be used in a streaming implementation because the CMAC operation to
> create the IV has to make a complete pass over the message before you can
> start encrypting (this is also similar to a key-wrap mechanism that Colin
> Plumb and I came up with for RFC 3211, although it'd need a tweak to use a
> proper MAC for full integrity-protection, it was designed for
> non-expanding
> 512-byte disk sector encryption and dates from the early 1990s, so it
> predates
> pretty much all of the work that newer modes and mechanisms are built on).
> SIV is quite nice for something like 802.11, SRTP, DTLS, and others, but
> unfortunately won't work as a general-purpose mechanism.

  You're correct. All the AAD and plaintext must be known prior to
invocation of the encrypt function.

> Are there any IP issues around SIV?

  Not that I know of. The inventors have made the following statement
on the subject of IP.

http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/siv/ip.pdf

  regards,

  Dan.