eap Mailing List: RE: Re: SHA-0 Broken

[Pasi.Eronen (Pasi.Eronen]

Thomas Otto wrote:

> Mohamad Badra wrote: 
> > Add to that, if SHA-1 will be broken, this does not 
> > mean that HMAC_hash is automatically broken since TLS-PRF 
> > uses HMAC_hash instead of hash. 
> 
> A short look in the abstract of RFC 2104, HMAC, shows us the relation:
> "The cryptographic strength of HMAC depends on the properties of the 
> underlying hash function." 

You might be interested in reading the original HMAC paper
(Bellare, Canetti & Krawczyk, "Keyed Hash Functions for Message 
Authentication", CRYPTO '96), available from here:

http://www.research.ibm.com/security/keyed-md5.html

It has extensive discussion about the relation, i.e. what is
required from the underlying hash function. In particular,
secure HMACs can be constructed from some hash functions 
that on their own are not secure hash functions.

Best regards,
Pasi