hmac

crypto.go

@@ -3,11 +3,14 @@ package main
 import (
 	"crypto/aes"
 	"crypto/cipher"
+	"crypto/hmac"
 	"crypto/rand"
+	"crypto/sha256"
+	"errors"
 	"io"
 )
 
-// AES encryption
+// AES encryption with HMAC
 func EncryptAES(key, message []byte) ([]byte, error) {
 	// Initialize block cipher
 	block, err := aes.NewCipher(key)
@@ -18,9 +21,9 @@ func EncryptAES(key, message []byte) ([]byte, error) {
 	// Create the byte slice that will hold encrypted message
 	cipherText := make([]byte, aes.BlockSize+len(message))
 
-	// Generate the Initialization Vector (# IV) nonce which is
-	// stored at the beginning of the byte slice. The IV is the same
-	// length as the AES blocksize
+	// Generate the Initialization Vector nonce which is
+	// stored at the beginning of the byte slice.
+	// The IV is the same length as the AES blocksize
 	iv := cipherText[:aes.BlockSize]
 	_, err = io.ReadFull(rand.Reader, iv)
 	if err != nil {
@@ -29,21 +32,47 @@ func EncryptAES(key, message []byte) ([]byte, error) {
 
 	// Create the AES cipher stream
 	cfb := cipher.NewCFBEncrypter(block, iv)
-	// Generate the encrypted message and store it in the remaining
-	// bytes after the IV nonce
+
+	// Generate the encrypted message and store it in
+	// the remaining bytes after the IV nonce
 	cfb.XORKeyStream(cipherText[aes.BlockSize:], message)
 
+	// Create a new HMAC
+	h := hmac.New(sha256.New, key)
+
+	// Write the ciphertext to the HMAC
+	h.Write(cipherText)
+
+	// Append the HMAC to the ciphertext
+	cipherText = h.Sum(cipherText)
+
 	return cipherText, nil
 }
 
-// AES decryption
+// AES decryption with HMAC
 func DecryptAES(key, cipherText []byte) ([]byte, error) {
 	// Initialize block cipher
 	block, err := aes.NewCipher(key)
 	if err != nil {
 		return nil, err
 	}
 
+	// Separate the HMAC from the ciphertext
+	hmacSize := sha256.Size
+	if len(cipherText) < hmacSize {
+		return nil, errors.New("ciphertext too short")
+	}
+	msgHMAC := cipherText[len(cipherText)-hmacSize:]
+	cipherText = cipherText[:len(cipherText)-hmacSize]
+
+	// Verify the HMAC
+	h := hmac.New(sha256.New, key)
+	h.Write(cipherText)
+	expectedHMAC := h.Sum(nil)
+	if !hmac.Equal(msgHMAC, expectedHMAC) {
+		return nil, errors.New("HMAC verification failed")
+	}
+
 	// Separate the IV nonce from the encrypted message bytes
 	iv := cipherText[:aes.BlockSize]
 	cipherText = cipherText[aes.BlockSize:]