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Re: [Cfrg] draft-irtf-cfrg-eddsa -- one final proposal for domain separation (context labels) for ed25519

Watson Ladd <watsonbladd@gmail.com> Sat, 21 May 2016 09:46 UTC

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Date: Sat, 21 May 2016 11:46:05 +0200
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From: Watson Ladd <watsonbladd@gmail.com>
To: Martin Thomson <martin.thomson@gmail.com>
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Cc: Simon Josefsson <simon@josefsson.org>, "cfrg@ietf.org" <cfrg@ietf.org>, draft-irtf-cfrg-eddsa.all@ietf.org
Subject: Re: [Cfrg] draft-irtf-cfrg-eddsa -- one final proposal for domain separation (context labels) for ed25519
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On Tue, May 10, 2016 at 5:47 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:
> On 11 May 2016 at 01:42, Watson Ladd <watsonbladd@gmail.com> wrote:
>> TLS 1.3 cannot rely on the
>> context mechanism of Ed25519ctx because it must work with RSA
>> signatures as well.
>
>
> That's not strictly true. It can use contexts opportunistically: if
> present, use it, otherwise use this alternative, crappier arrangement
> for the signature input.

But all the messages need to fit that "alternative, crappier" arrangement
anyway. Contexts don't give extra protection to protocols that must work
without them.

-- 
"Man is born free, but everywhere he is in chains".
--Rousseau.

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