AES-GCM: encryption with nonce appended to ciphertext

_example/aes/main.go

@@ -78,4 +78,52 @@ func main() {
 		return
 	}
 	fmt.Println("plaintext:", plaintext)
+
+	// encrypt the data with AES-128 in GCM using EncryptAesGcmWithNonceAppended function
+	ciphertext128, err = crypt.EncryptAesGcmWithNonceAppended(key128, text)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println("ciphertext (AES-128):", ciphertext128)
+
+	// decrypt the data with AES-128 in GCM using DecryptAesGcmWithNonceAppended function
+	plaintext, err = crypt.DecryptAesGcmWithNonceAppended(key128, ciphertext128)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println("plaintext:", plaintext)
+
+	// encrypt the data with AES-192 in GCM using EncryptAesGcmWithNonceAppended function
+	ciphertext192, err = crypt.EncryptAesGcmWithNonceAppended(key192, text)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println("ciphertext (AES-192):", ciphertext192)
+
+	// decrypt the data with AES-192 in GCM using DecryptAesGcmWithNonceAppended function
+	plaintext, err = crypt.DecryptAesGcmWithNonceAppended(key192, ciphertext192)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println("plaintext:", plaintext)
+
+	// encrypt the data with AES-256 in GCM using EncryptAesGcmWithNonceAppended function
+	ciphertext256, err = crypt.EncryptAesGcmWithNonceAppended(key256, text)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println("ciphertext (AES-256):", ciphertext256)
+
+	// decrypt the data with AES-256 in GCM using DecryptAesGcmWithNonceAppended function
+	plaintext, err = crypt.DecryptAesGcmWithNonceAppended(key256, ciphertext256)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println("plaintext:", plaintext)
 }

aes.go

@@ -72,3 +72,29 @@ func DecryptAesGcm(key, nonce, ciphertext []byte) (text string, err error) {
 
 	return
 }
+
+// EncryptAesGcmWithNonceAppended encrypts and authenticates the given message with AES in GCM mode
+// using the given 128, 192 or 256-bit key.
+// It appends the ciphertext to the nonce.
+func EncryptAesGcmWithNonceAppended(key []byte, text string) (ciphertext []byte, err error) {
+	ciphertext, nonce, err := EncryptAesGcm(key, text)
+	if err != nil {
+		return
+	}
+	ciphertext = append(nonce, ciphertext...)
+	return
+}
+
+// DecryptAesGcmWithNonceAppended decrypts and authenticates the given message with AES in GCM mode
+// using the given 128, 192 or 256-bit key.
+// It expects the ciphertext to have the nonce appended.
+func DecryptAesGcmWithNonceAppended(key, ciphertext []byte) (text string, err error) {
+	nonceSize := 12
+	if len(ciphertext) < nonceSize {
+		err = fmt.Errorf("ciphertext is too short")
+		return
+	}
+	nonce, ciphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]
+	text, err = DecryptAesGcm(key, nonce, ciphertext)
+	return
+}