Thank you. Adding a quick reference to ARX designs right away. Edit: added these paragraphs: Quick summary: Chacha20 is ARX-based hash function, keyed, runni

Thank you. Adding a quick reference to ARX designs right away. Edit: added these paragraphs: Quick summary: Chacha20 is ARX-based hash function, keyed, running in counter mode. It embodies the idea that one can use a hash function to encrypt data. The expert will immediately notice this quarter-round is an ARX based design (ARX stands for, Addition, Rotation, Xor) which despite its simplicity can be made as good as a regular permutation-substitution network.