General interface for pseudorandom function with varying input length.
A pseudorandom function with varying input length does not have predefined input length.
The input length may be different for each function call, and is determined upon user request.
The interface PrfVaryingInputLength, groups and provides type safety for every PRF with varying input length.
Cryptography and Computer Security Research Group Department of Computer Science Bar-Ilan University (Meital Levy)