RE: FW: New Version Notification for draft-rafiee-6man-cga-attack-00.txt

["Hosnieh Rafiee" <[e-mail]>]

> El 29/11/13 08:28, Hosnieh Rafiee escribió:
> >
> >
> > In CGA, we have a hash function or like the above example, we have a
> > hash password. What is important for us is only find another message
> > that leads to the same hash. This is where birthday paradox applies.
> > So, in CGA, the attacker really does not care what is the content of
> > your message, it cares about the hash value. He only wants to have
> > another message (or in birthday paradox to have another person with
> > the same birthday that matches yours) to match yours.
> >
> 
> sigh, no.
> 
> the birthday paradox applies when you want to find two values that match
> each other and NOT when you have a target and you want to find a hash
> output that matches the target of your attack.
> 
> In other words, the birthday paradox is not about finding another person
that
> has the same birthday than you but about finding two persons that happen
to
> have the same birthday.
> 
> This is a critical distinction when you want to use this for an attack, as
you
> cannot rely on this to attack a specific target, you can only use it for
finding
> two random values that clash.


Birthday attack is still possible with the following approach. Check this
nice article.
http://eprint.iacr.org/2003/065.pdf   

smile,
Hosnieh