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

Martin Thomson <> Mon, 06 April 2015 16:24 UTC

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Date: Mon, 06 Apr 2015 09:24:09 -0700
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From: Martin Thomson <>
To: Brian Smith <>
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Subject: Re: [TLS] Consensus call on Implicit IV for AEAD
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On 3 April 2015 at 20:17, Brian Smith <> wrote:
> a clear record of my objection to the
> zero-padding mechanism on the mailing list,

For the record then, the objection was this:

If you are concerned that someone might spend a large amount of
computing resources (2^60+ iterations) to gain themselves a reasonable
chance of decrypting a randomly selected session from a similar sized
set of sessions, pick a stronger cipher.

There's a history of attempting to paper over perceived weaknesses in
the crypto we use.  I get the belt and braces approach here, but I'd
rather see us develop stronger constructions (ChaCha+Poly uses a
longer key, for example).

If the complaint is specific to AES-GCM, I see nothing stopping
someone from proposing AES-GCMv2 that operates on extra keying
material internally in order to make the IV unpredictable.  I'd rather
keep the nonce sane though, it keeps it easy to reason about the