blake2s_init_key
blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
blake2s_init_key(&blake, COOKIE_LEN, checker->secret, NOISE_HASH_LEN);
blake2s_init_key(&ctx, BLAKE2S_HASH_SIZE, guarded_key, key_len);