AES encryption in Golang and decryption in Java

Question

I have the following AES encryption function written in Golang.

func encrypt(key []byte, text string) string {
    plaintext := []byte(text)

    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }

    ciphertext := make([]byte, aes.BlockSize+len(plaintext))
    iv := ciphertext[:aes.BlockSize]
    if _, err := io.ReadFull(rand.Reader, iv); err != nil {
        panic(err)
    }

    stream := cipher.NewCFBEncrypter(block, iv)
    stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)

    return base64.URLEncoding.EncodeToString(ciphertext)
}

I am struggling to understand the flow in order to decrypt the generated text using Java. Any help would be greatly appreciated!

Here is the Scala code, Not sure what the problem is with it.

def decode(input:String) = {
    val keyBytes = Hex.decodeHex("someKey".toCharArray)
    val inputWithoutPadding = input.substring(0,input.size - 2)
    val inputArr:Seq[Byte] = Hex.decodeHex(inputWithoutPadding.toCharArray)

    val skSpec = new SecretKeySpec(keyBytes, "AES")
    val iv = new IvParameterSpec(inputArr.slice(0,16).toArray)
    val dataToDecrypt = inputArr.slice(16,inputArr.size)

    val cipher = Cipher.getInstance("AES/CFB/NoPadding")
    cipher.init(Cipher.DECRYPT_MODE, skSpec, iv)
    cipher.doFinal(dataToDecrypt.toArray)
}

Answer 1

Java decoder (see also the online demo version , open and click "Run"):

String decode(String base64Text, byte[] key) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
    byte[] inputArr = Base64.getUrlDecoder().decode(base64Text);
    SecretKeySpec skSpec = new SecretKeySpec(key, "AES");
    Cipher cipher = Cipher.getInstance("AES/CFB/NoPadding");
    int blockSize = cipher.getBlockSize();
    IvParameterSpec iv = new IvParameterSpec(Arrays.copyOf(inputArr, blockSize));
    byte[] dataToDecrypt = Arrays.copyOfRange(inputArr, blockSize, inputArr.length);
    cipher.init(Cipher.DECRYPT_MODE, skSpec, iv);
    byte[] result = cipher.doFinal(dataToDecrypt);
    return new String(result, StandardCharsets.UTF_8);
}

Kevin in the comments suggested this demonstration of the original Go encoder, where we can see the result:

encrypt([]byte("0123456789abcdef"), "test text 123")

there is c1bpFhxn74yzHQs-vgLcW6E5yL8zJfgceEQgYl0=.

, Java- :

String text = "c1bpFhxn74yzHQs-vgLcW6E5yL8zJfgceEQgYl0=";
byte[] key = "0123456789abcdef".getBytes();
System.out.println(decode(text, key));

test text 123 ✔

---

Scala (- ):

def decode(input:String, key:String) = {
    val cipher = Cipher.getInstance("AES/CFB/NoPadding")
    val blockSize = cipher.getBlockSize()
    val keyBytes = key.getBytes()
    val inputArr = Base64.getUrlDecoder().decode(input)
    val skSpec = new SecretKeySpec(keyBytes, "AES")
    val iv = new IvParameterSpec(inputArr.slice(0, blockSize).toArray)
    val dataToDecrypt = inputArr.slice(blockSize, inputArr.size)
    cipher.init(Cipher.DECRYPT_MODE, skSpec, iv)
    new String(cipher.doFinal(dataToDecrypt.toArray))
}

def main(args: Array[String]) {
    print(decode("c1bpFhxn74yzHQs-vgLcW6E5yL8zJfgceEQgYl0=", "0123456789abcdef"));
}

, Scala Hex.decodeHex. Base64, URL-, RFC 4648, java.util.Base64 ( Java 8) getUrlDecoder().