// escape to the heap.
	out := make([]byte, 32)
	return hChaCha20(out, key, nonce)
}

func hChaCha20(out, key, nonce []byte) ([]byte, error) {
	if len(key) != KeySize {
		return nil, errors.New("chacha20: wrong HChaCha20 key size")
	}
	if len(nonce) != 16 {
		return nil, errors.New("chacha20: wrong HChaCha20 nonce size")
	}

	x0, x1, x2, x3 := j0, j1, j2, j3