Core208 applies the Salsa20/8 core function to the 64-byte array in and puts the result into the 64-byte array out.

HSalsa20 applies the HSalsa20 core function to a 16-byte input in, 32-byte key k, and 16-byte constant c, and puts the result into the 32-byte array out.

XORKeyStream crypts bytes from in to out using the given key and counters.

Sigma is the Salsa20 constant for 256-bit keys.