Right, that's what I had in mind. Of course, it's a bit of a jump to assume that the result is the same when you use a cryptographic hash function instead of a

Right, that's what I had in mind. Of course, it's a bit of a jump to assume that the result is the same when you use a cryptographic hash function instead of a trivial one. But regardless of the hash function, the same problem will occur unless there are no collisions for input between 0 and 2^160 - 1 (inclusive). From what I can tell, SHA1 can't guarantee this.