Swift to golang AES-GCM encryption decryption working example code

swift to golang aes gcm encryption

// The following code has been tested. It compiles and works.

// Swift code
func encrypt(input: [UInt8]) -> Data? {
    let key = SymmetricKey(size: .bits256)
    let key64 = key.withUnsafeBytes {
        return Data(Array($0)).base64EncodedString()
    }
    print("key64:", key64)
    var sealedBox: AES.GCM.SealedBox
    do {
        try sealedBox = AES.GCM.seal(input, using: key)
        print("Combined:\n\(sealedBox.combined!.base64EncodedString())\n") // pass this to the decrypt function
        return sealedBox.combined!
    } catch {
        print("seal failed!")
        return nil
    }
}

// Go golang code
func decrypt(s string) string { // parameter is the sealedBox.combined!.base64EncodedString() output.
	key := decode64(key64)
	bytes := decode64(s)     //convert base 64 to bytes
	nonce := bytes[0:12]     //get the nonce
	ciphertext := bytes[12:] //get the ciphertext + tag. DO NOT split out the tag!
  
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err.Error())
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}

	plaintext, err := aesgcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		panic(err.Error())
	}

	fmt.Printf("%s\n", plaintext)
	return string(plaintext)
}