ARC4_KEYSZ
if (n < ARC4_KEYSZ + ARC4_IVSZ)
chacha_keysetup(&arc4->arc4_chacha, buf, ARC4_KEYSZ * 8, 0);
chacha_ivsetup(&arc4->arc4_chacha, buf + ARC4_KEYSZ);
m = MIN(datalen, ARC4_KEYSZ + ARC4_IVSZ);
arc4_init(arc4->arc4_buf, ARC4_KEYSZ + ARC4_IVSZ);
explicit_bzero(arc4->arc4_buf, ARC4_KEYSZ + ARC4_IVSZ);
arc4->arc4_have = sizeof (arc4->arc4_buf) - ARC4_KEYSZ - ARC4_IVSZ;
uint8_t rnd[ARC4_KEYSZ + ARC4_IVSZ];