buffer.Write(metadata)

	return io.MultiReader(
		&buffer,
		stream.EncryptReader(plaintext, nonce, nil),
	), nil
}

// Decrypt decrypts the ciphertext using a key managed by the KMS.
// The same context that have been used during encryption must be
// provided.
func Decrypt(k kms.KMS, ciphertext io.Reader, context kms.Context) (io.Reader, error) {
	const (
		MaxMetadataSize = 1 << 20 // max. size of the metadata