CHACHA20_KEYBYTES
read_random_key(key, CHACHA20_KEYBYTES, &seed_version);
read_random(key, CHACHA20_KEYBYTES);
chacha_keysetup(&chacha20->ctx, key, CHACHA20_KEYBYTES*8);
CTASSERT(CHACHA20_KEYBYTES*8 >= CHACHA_MINKEYLEN);
uint8_t key[CHACHA20_KEYBYTES];