I know that for HMAC/SHA there are default IV values. But if I want to supply my own IV (different from a default), there doesn't seem to be a way to implement it in — for example — Java. (At least, so far I hadn't found a solution in
javax/bouncy castle. Looks like
MessageDigest class isn't providing us with such methods).
Why are default values for IV (HMAC/SHA) used? What is the reason not expose them to a user?