Re: [TLS] Using Brainpool curves in TLS

mrex@sap.com (Martin Rex) Wed, 16 October 2013 05:34 UTC

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To: Watson Ladd <watsonbladd@gmail.com>
Date: Wed, 16 Oct 2013 07:34:08 +0200 (CEST)
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From: mrex@sap.com (Martin Rex)
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Cc: Patrick Pelletier <code@funwithsoftware.org>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Using Brainpool curves in TLS
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Watson Ladd wrote:
>
> I mean exactly what I said: no more and no less. Implementations must
> be carefully
> audited to establish freedom from side-channels, no matter what
> primitive they implement.

That is the theory.

Now practice is an entirely different matter.

If you look through the algorithms in the appendices of FIPS 186-3,
you'll find a lot of algorithms that contain conditionals.

If the algorithm will have to be used inband for an asymmetric
crypto operation, those algorithms leak timing information
when processing secret values.

If a crypto operation needs an ephemeral random and secret prime,
this would apply to the necessary primality tests.

If the algorithm described by the underlying specification is not
100% constant time, why would you expect implementations
to have this property?


-Martin