# Tag Info

My answer follows from this answer as suggested by @DannyNiu. The constant for $128$-bit ChaCha is "expand 16-byte k" in ASCII. So the four constant words are "expa", "nd 1", "6-by" and "te k" in ASCII. Converting them to HEX code we have $c_0 = 0x61707865$ $c_1 = 0x312d646e$ $c_2 = 0x79622d36$ \$c_3 = ...