Re: [TLS] Last Call: draft-ietf-tls-rfc4346-bis (The Transport

[Martin Rex <Martin.Rex at sap.com>]

Eric Rescorla wrote:
> 
> At Tue, 4 Mar 2008 09:58:29 -0800,
> Paul Hoffman wrote:
> > 
> > At 6:19 AM -0500 3/4/08, Rob Dugal wrote:
> > >section 7.4.1.4.1
> > >
> > >Why is SHA-224 not supported as a HashAlgorithm? For completeness 
> > >shouldn't TLS 1.2 support all the SHA-2 algorithms?
> > 
> > Not everyone agrees with the utility of SHA-224, particularly in a 
> > protocol where AES-128 is mandatory to implement.
> 
> Indeed. 
> 
> If you want a MAC with effective algorithmic security the same as
> SHA-256 but shorter, that's what truncated MACs are for.

SHA-224 is effectively that:

   SHA-224 is based on SHA-256, but it uses an different
   initial value and the result is truncated to 224 bits.

-Martin

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