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[TLS] Entropy of SHA-2 and the P_SHA256-based PRF

"Brian Smith" <brian@briansmith.org> Wed, 14 July 2010 22:08 UTC

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From: Brian Smith <brian@briansmith.org>
To: tls@ietf.org
Date: Wed, 14 Jul 2010 17:08:37 -0500
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Subject: [TLS] Entropy of SHA-2 and the P_SHA256-based PRF
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Here is an interesting paper regarding the entropy of the output of SHA-2
with a special mention of the TLS 1.2 PRF. If I am understanding correctly,
SHA-2 reduces the entropy of a random input by half the first time it is
applied, and the entropy slowly decreases every time it is applied
thereafter. 

 

"For illustration we can say that the entropy of E(PRF[1]) = 253.463, but
the entropy of E(PRF[60]) = 250.00."

 

"Practical consequences of the aberration of narrow-pipe hash designs from
ideal random functions"

Danilo Gligoroski and Vlastimil Klima

http://eprint.iacr.org/2010/384

 

Regards,

Brian

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