Symmetric Encrypt and Decrypt in Golang

 

In this post we will review AES-CBC symmetric encryption in Golang.

We start by key generation.

import (
 "crypto/aes"
 "crypto/cipher"
 "crypto/rand"
 "encoding/base64"
 "encoding/json"
 "fmt"
 "radware.com/euda/commons/global/encryption/padding"
)

const keySizeBytes = 32

type EncryptedData struct {
 Cipher string `json:"cipher"`
 Iv     string `json:"iv"`
}

type Key struct {
 key []byte
}

func GenerateKey() (*Key, error) {
 key := make([]byte, keySizeBytes)
 _, err := rand.Read(key)
 if err != nil {
  return nil, fmt.Errorf("read failed: %v", err)
 }
 k := Key{key: key}
 return &k, nil
}

The key can be easily exported and imported.

func LoadKey(keyBase64 string) (*Key, error) {
 bytes, err := base64.StdEncoding.DecodeString(keyBase64)
 if err != nil {
  return nil, fmt.Errorf("base64 decode failed: %v", err)
 }
 k := Key{key: bytes}
 return &k, nil
}

func (k *Key) ExportKey() string {
 return base64.StdEncoding.EncodeToString(k.key)
}

And finally we can encrypt and decrypt using the key.

func (k *Key) Encrypt(clearText string) (string, error) {
 iv := make([]byte, aes.BlockSize)
 _, err := rand.Read(iv)
 if err != nil {
  return "", fmt.Errorf("read failed: %v", err)
 }

 aesCipher, err := aes.NewCipher(k.key)
 if err != nil {
  return "", fmt.Errorf("create cipher failed: %v", err)
 }

 cbc := cipher.NewCBCEncrypter(aesCipher, iv)

 clearBytes := []byte(clearText)
 clearBytesPadded, err := padding.Pkcs7Pad(clearBytes, aes.BlockSize)
 if err != nil {
  return "", fmt.Errorf("padding failed: %v", err)
 }

 cipherBytes := make([]byte, len(clearBytesPadded))

 cbc.CryptBlocks(cipherBytes, clearBytesPadded)
 data := EncryptedData{
  Cipher: base64.StdEncoding.EncodeToString(cipherBytes),
  Iv:     base64.StdEncoding.EncodeToString(iv),
 }

 jsonBytes, err := json.Marshal(data)
 if err != nil {
  return "", fmt.Errorf("marshal failed: %v", err)
 }

 return string(jsonBytes), nil
}

func (k *Key) Decrypt(jsonData string) (string, error) {
 var data EncryptedData
 err := json.Unmarshal([]byte(jsonData), &data)
 if err != nil {
  return "", fmt.Errorf("unmarshal failed: %v", err)
 }

 iv, err := base64.StdEncoding.DecodeString(data.Iv)
 if err != nil {
  return "", fmt.Errorf("decode iv failed: %v", err)
 }

 cipherBytes, err := base64.StdEncoding.DecodeString(data.Cipher)
 if err != nil {
  return "", fmt.Errorf("decode cipher failed: %v", err)
 }

 aesCipher, err := aes.NewCipher(k.key)
 if err != nil {
  return "", fmt.Errorf("create cipher failed: %v", err)
 }
 cbc := cipher.NewCBCDecrypter(aesCipher, iv)

 paddedClearTextBytes := make([]byte, len(cipherBytes))
 cbc.CryptBlocks(paddedClearTextBytes, cipherBytes)

 clearTextBytes, err := padding.Pkcs7Unpad(paddedClearTextBytes, aes.BlockSize)
 if err != nil {
  return "", fmt.Errorf("un-padding failed: %v", err)
 }

 clearText := string(clearTextBytes)
 return clearText, nil
}

Notice that the encryption result includes Initialization Vector (IV), which is a random buffer that is used in the encryption. The IV is returned from the encrypt function unchanged. The decrypt function uses both the cipher result and the IV along with the AES key to do its work. To simplify the usage of both IV and cipher, we use a JSON format.

We can test our code using the following:

func Test(t *testing.T) {
 key, err := GenerateKey()
 if err != nil {
  t.Fatal(err)
 }

 encrypted, err := key.Encrypt("123456789012345")
 if err != nil {
  t.Fatal(err)
 }

 t.Logf("encrypted is %v", encrypted)

 exportedKey := key.ExportKey()
 t.Logf("exported key is %v", exportedKey)

 importedKey, err := LoadKey(exportedKey)
 if err != nil {
  t.Fatal(err)
 }

 decrypted, err := importedKey.Decrypt(encrypted)
 if err != nil {
  t.Fatal(err)
 }
 t.Logf("decrypted is %v", decrypted)
}

Final Note

This post is part of a series of posts about encryption. The full posts list is below.

• Using ECDSA in GO to Sign and Verify messages
• A-Symmetic Encrypt and Decrypt on Golang
• Symmetric Encrypt and Decrypt in Golang
• Using ECDSA in JavaScript to Sign and Verify messages
• A-Symmetic Encrypt and Decrypt on JavaScript
• Symmetric Encrypt and Decrypt in Javascript
• Using ECDSA in Python to Sign and Verify messages