func (c Cipher) Encrypt(plaintext interface{}, key []byte, additionalData string) (ciphertext string, err error) {
	if isEmpty(plaintext) {
		return "", nil
	}
	aescipher, err := cryptoaes.NewCipher(key)
	if err != nil {
		return "", fmt.Errorf("Could not initialize AES GCM encryption cipher: %s", err)
	}
	var iv []byte
	if stash, ok := c.stash[stashKey{plaintext: plaintext, additionalData: additionalData}]; !ok {
		iv = make([]byte, nonceSize)
		_, err = rand.Read(iv)
		if err != nil {
			return "", fmt.Errorf("Could not generate random bytes for IV: %s", err)
		}
	} else {
		iv = stash
	}
	gcm, err := cipher.NewGCMWithNonceSize(aescipher, nonceSize)
	if err != nil {
		return "", fmt.Errorf("Could not create GCM: %s", err)
	}
…
	out := gcm.Seal(nil, iv, plainBytes, []byte(additionalData))
	return fmt.Sprintf("ENC[AES256_GCM,data:%s,iv:%s,tag:%s,type:%s]",
		base64.StdEncoding.EncodeToString(out[:len(out)-cryptoaes.BlockSize]),
		base64.StdEncoding.EncodeToString(iv),
		base64.StdEncoding.EncodeToString(out[len(out)-cryptoaes.BlockSize:]),
		encryptedType), nil
}

Warm-up