origin of SHA 224 initial hash values

[Steven M. Bellovin]

In message <80CA5A5D-2823-11D8-94A5-00039375644C at vangelderen.org>, "Jeroen C.va
n Gelderen" writes:
>
>On Dec 6, 2003, at 3:26, Jeremiah Rogers wrote:
>
>> I'm having trouble pinpointing the origin of the initial hash values 
>> for SHA 224 and, for that matter, 128. These values are defined as hex 
>> representations of cube roots of primes for sha-1 of lengths 256, 384 
>> and 512, but  I can't find where they were obtained for the shorter 
>> lengths.
>>
>> Thanks and apologies if this is something well known.
>
>I'd like to second this request for clarification.
>
>I noted that 224 yields a security level identical to 2-key Triple DES.
>
>A quick Google search reveals that SHA-224 is mentioned a few times, in
>   draft-ietf-pkix-rsa-pkalgs-01.txt
>   draft-ietf-smime-cms-rsa-kem-01.txt
>among others.

You've nailed it -- that's precisely why SHA-224 is being defined, to
match 2-key 3DES.

There's another Internet draft that's likely of interest to this group:
'Determining Strengths For Public Keys Used For Exchanging Symmetric Keys '
<draft-orman-public-key-lengths-06.txt>.  The draft is in IETF Last 
Call until 2 January; please email any comments to iesg at ietf.org.

Wearing my IETF Security Area Director hat,



		--Steve Bellovin, http://www.research.att.com/~smb


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