func (c *ciphertext) UnmarshalJSON(text []byte) error {
	const (
		IVSize    = 16
		NonceSize = 12

		AES256GCM        = "AES-256-GCM-HMAC-SHA-256"
		CHACHA20POLY1305 = "ChaCha20Poly1305"
	)

	type JSON struct {
		Algorithm string `json:"aead"`
		ID        string `json:"id"`
		IV        []byte `json:"iv"`
		Nonce     []byte `json:"nonce"`
		Bytes     []byte `json:"bytes"`

		Plaintext:  "zmS7NrG765UZ0ZN85oPjybelxqVvpz01vxsSpOISy2M=",
		Ciphertext: `{"aead":"ChaCha20Poly1305","iv":"JbI+vwvYww1lCb5VpkAFuQ==","nonce":"ARjIjJxBSD541Gz8","bytes":"KCbEc2sA0TLvA7aWTWa23AdccVfJMpOxwgG8hm+4PaNrxYfy1xFWZg2gEenVrOgv"}`,
	},
	{
		KeyID:      "my-key",
		Plaintext:  "UnPWsZgVI+T4L9WGNzFlP1PsP1Z6hn2Fx8ISeZfDGnA=",

// ciphertext.
func Encrypt(k *kms.KMS, plaintext io.Reader, ctx kms.Context) (io.Reader, error) {
	algorithm := sio.AES_256_GCM
	if !fips.Enabled && !sioutil.NativeAES() {
		algorithm = sio.ChaCha20Poly1305
	}

	key, err := k.GenerateKey(context.Background(), &kms.GenerateKeyRequest{AssociatedData: ctx})
	if err != nil {
		return nil, err
	}
	stream, err := algorithm.Stream(key.Plaintext)
	if err != nil {