Question about proposed drbg Blake2X about blake2

[sneves]

This sort of question is better addressed to [email protected], since it does not directly concern this codebase (yet).

To answer your question, there's no source code yet. The counter is not prepended; it is part of the existing parameter block. The XOF value is there to disambiguate existing hashes from BLAKE2X hashes, so that regular BLAKE2 hashes never coincide with BLAKE2X hashes, even in their inner values. Also to disambiguate hashes of size X from hashes of size Y, so that they don't partially overlap (except in the 2^n-1 case, where this is explicitly supported).