Well, people have already talked about extension attacks in general, but to be specific: I can potentially calculate the state of the hash algorithm after the salt bytes have been processed, meaning I can precompute to reduce it to hash'(pass) — I consider that broken if you intended to create the function mac(salt,pass). If you have a salt per user, then that's not so bad, but why bother guessing?
Cryptography comes down to much more than using the right primitives. You also have to use the right implementations of those primitives (timing attacks), combined in the right ways (double stream cipher failure), and you have to be sure that the properties you want give you the protection you want (CBC without mac doesn't give you authentication). If you aren't using something with a wikipedia page that describes the entire system, and has some papers describing it and suggesting attacks on it, then you are inventing your own cryptography.
Comments
Well, people have already talked about extension attacks in general, but to be specific: I can potentially calculate the state of the hash algorithm after the salt bytes have been processed, meaning I can precompute to reduce it to hash'(pass) — I consider that broken if you intended to create the function mac(salt,pass). If you have a salt per user, then that's not so bad, but why bother guessing?
Cryptography comes down to much more than using the right primitives. You also have to use the right implementations of those primitives (timing attacks), combined in the right ways (double stream cipher failure), and you have to be sure that the properties you want give you the protection you want (CBC without mac doesn't give you authentication). If you aren't using something with a wikipedia page that describes the entire system, and has some papers describing it and suggesting attacks on it, then you are inventing your own cryptography.