package aes
  
  import (
  	"crypto/aes"
  	"crypto/cipher"
  	"crypto/rand"
  	"errors"

  	"fmt"

  	"io"
  	mrand "math/rand"
  	"time"
  )
  
  const (
  	keySize      = 32
  	allowedRunes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
  )

  // RandomKey returns a randomly generated 32 bytes long key.

  func RandomKey() (key []byte) {
  	mrand.Seed(time.Now().UnixNano())
  
  	key = make([]byte, keySize)
  
  	for i := range key {
  		key[i] = allowedRunes[mrand.Intn(len(allowedRunes))]
  	}
  
  	return key
  }
  
  // Encrypt encrypts plaintext with key and returns resulting bytes.

  func Encrypt(plaintext, key []byte) ([]byte, error) {
  	if len(key) != keySize {
  		return nil, fmt.Errorf("key size invalid: %d, must be %d
  ", len(key), keySize)
  	}

  	c, err := aes.NewCipher(key)
  	if err != nil {
  		return nil, err
  	}
  
  	gcm, err := cipher.NewGCM(c)
  	if err != nil {
  		return nil, err
  	}
  
  	nonce := make([]byte, gcm.NonceSize())
  	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
  		return nil, err
  	}
  
  	return gcm.Seal(nonce, nonce, plaintext, nil), nil
  }
  
  // Decrypt decrypts ciphertext with key and returns resulting bytes.

  func Decrypt(ciphertext, key []byte) ([]byte, error) {

  	c, err := aes.NewCipher(key)
  	if err != nil {
  		return nil, err
  	}
  
  	gcm, err := cipher.NewGCM(c)
  	if err != nil {
  		return nil, err
  	}
  
  	nonceSize := gcm.NonceSize()
  	if len(ciphertext) < nonceSize {
  		return nil, errors.New("ciphertext too short")
  	}
  
  	nonce, ciphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]

  	return gcm.Open(nil, nonce, ciphertext, nil)
  }