There is a lot of code duplicated in convenience methods in each hash
implementation, and having a generic hash type makes implementing
higher-level constructs such as HMAC significantly easier down the road.
Assertions can be disabled, but at the point where cryptographic
anything is involved, a single branch has an infinitesimally small
performance impact.
The correct thing to do is to punch the caller in the face if they do
something that is blatantly incorrect, especially in a security critical
setting.
Yawning Angel
gingerBill