If you don't know what the PRNG is for, perhaps a cursory 30 second lookover and then crap all over wasn't enough. ;-) Watch the 9 minute Tech Video, which explains, the asymmetric key generator can't use a fixed length seed; it needs to be a random stream. Also, there's a challenge/response which can only be answered by knowledge of the client's private key, so your comment about the replay attack (I think you meant relay attack) is also incorrect - whichever you actually meant, you're wrong either way.