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

[Mohamad Badra (badra]

Bernard Aboba wrote:

> > First, is TLS affected by this vulnerability? This idea came in mind
> > since the PRF relies on the abovementioned (semi-)broken cryptographic
> > algorithms.
> >
> > PRF(secret, label, seed) =
> > P_MD5(S1, label + seed) XOR P_SHA-1(S2, label + seed);
> >    
>
> My understanding is that this PRF was used in part so that it would only
> be compromised if *both* MD5 and SHA-1 were broken.
>  
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. So 
you need to find also the "aleatory key" used with HMAC_hash to achieve 
such attack. Note that the actual attacks are based on known IVs.

IMO, even if someone will arrive to change a bitstream into a particular 
"text file", it remains extremely hard to him to play with the structure 
of ASN.1 used in degital signatures.

Badra