CHACHA20POLY1305_AUTHTAG_SIZE
uint8_t mac[CHACHA20POLY1305_AUTHTAG_SIZE];
if (src_len < CHACHA20POLY1305_AUTHTAG_SIZE)
dst_len = src_len - CHACHA20POLY1305_AUTHTAG_SIZE;
ret = timingsafe_bcmp(b.mac, src + dst_len, CHACHA20POLY1305_AUTHTAG_SIZE);
#define NOISE_AUTHTAG_LEN CHACHA20POLY1305_AUTHTAG_SIZE