That’s clearly not the way the author intends us to interpret “one bit at a time”. They intend it as some kind of explanation for why ChaCha20 is slow. (In re

That’s clearly not the way the author intends us to interpret “one bit at a time”. They intend it as some kind of explanation for why ChaCha20 is slow. (In reality, bitwise XOR is one of the fastest operations a computer can perform; it runs with as much of a parallel speedup as you have parallelism to give it, and it’s utilized extensively by practically every cipher including AES.)