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List:       gcrypt-devel
Subject:    Re: Libgcrypt CTR Mode Counter Value
From:       Werner Koch <wk () gnupg ! org>
Date:       2011-05-16 9:39:01
Message-ID: 87fwofvvbe.fsf () vigenere ! g10code ! de
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On Fri, 13 May 2011 18:41, nehakochar1@gmail.com said:

> But the CAVP or FIPS algorithm certificate for Libgcrypt's AES mentions that
> its CTR mode uses internal counter. Can someone please explain how?

Right.  However, you need to set the start value.

> Also, if the counter is indeed sourced internally, how does Libgcrypt ensure
> that the counter values are always unique as specified in NIST SP800-38a
> standard?

Using something like

   counter++

which is what counter mode is about.

I have not read FIPS documents for some time so I don't know exactly
what the AES specs exactly mean by internal and external counter.



Salam-Shalom,

   Werner

-- 
Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.


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