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Date: Sun, 23 Aug 2015 17:15:15 +0200
From: magnum <>
Subject: Re: Formats using non-SIMD SHA2 implementations

> I might not have stated my problem clearly... I'll sum it up here: suppose I have a message of length (A + B) and I've already compute the hash of the first A bytes which is H(A); given only H(A) and the remaining B bytes of data, can I compute the hash of the entire message, i.e. H(A + B) ?
> I want to use OpenSSL's SHA function to do this, but I don't see such an interface provided. This is already in use in JtR's SIMD SHA implementation (with the SSEi_RELOAD flag), so I think it's technically doable in OpenSSL. Do I need to hack SHA_CTX somehow?

That's easy but unfortunately it's not portable (we're not guaranteed 
the ctx struct internals, names differs among various libs). A better 
alternative might be to simply use our SIMD function (with RELOAD like 
you said) using just one lane.


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