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

[marcelo bagnulo braun <[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.

Regards, marcelo