evalphobia/hierogolyph

package aesgcm

import (
    "crypto/aes"
    "crypto/cipher"
    "crypto/rand"
    "fmt"
)

// Encrypt encrypts plainText using AES GCM mode.
func Encrypt(plainText string, key []byte) ([]byte, error) {
    // use first 32byte if the key length is longer than 32byte.
    if len(key) > 32 {
        key = key[0:32]
    }

    block, err := aes.NewCipher(key)
    if err != nil {
        return nil, err
    }

    gcm, err := cipher.NewGCM(block)
    if err != nil {
        return nil, err
    }

    nonce := make([]byte, gcm.NonceSize())
    _, err = rand.Read(nonce)
    if err != nil {
        return nil, err
    }

    cipherText := gcm.Seal(nil, nonce, []byte(plainText), nil)
    cipherText = append(nonce, cipherText...)

    return cipherText, nil
}

// Decrypt decrypts cipherText using AES GCM mode.
func Decrypt(cipherText, key []byte) (string, error) {
    // use first 32byte if the key length is longer than 32byte.
    if len(key) > 32 {
        key = key[0:32]
    }

    block, err := aes.NewCipher(key)
    if err != nil {
        return "", err
    }
    gcm, err := cipher.NewGCM(block)
    if err != nil {
        return "", err
    }

    nonceSize := gcm.NonceSize()
    if len(cipherText) < nonceSize {
        return "", fmt.Errorf("cipherText is too short: textsize=[%d], noncesize=[%d]", len(cipherText), nonceSize)
    }

    nonce := cipherText[:nonceSize]
    plainByte, err := gcm.Open(nil, nonce, cipherText[nonceSize:], nil)
    if err != nil {
        return "", err
    }

    return string(plainByte), nil
}