Implement C# encryption in CryptoJS

Question

I have situation where I need to create the same encryption method which is already up and running in C#. The concept behind this is, from where ever this encrypted key is logged, we will use the same C# project to decrypt it.

Below is the logic used in C#:

using var aes = new AesCryptoServiceProvider
{
    Key = Encoding.UTF8.GetBytes(key),
    Mode = CipherMode.CBC,
    Padding = PaddingMode.PKCS7
};
aes.GenerateIV();
using var encrypter = aes.CreateEncryptor(aes.Key, aes.IV);
using var cipherStream = new MemoryStream();
using (var tCryptoStream = new CryptoStream(cipherStream, encrypter, CryptoStreamMode.Write))
using (var tBinaryWriter = new BinaryWriter(tCryptoStream))
{
    cipherStream.Write(aes.IV);
    tBinaryWriter.Write(Encoding.UTF8.GetBytes(encryptMe));
    tCryptoStream.FlushFinalBlock();
}
return Convert.ToBase64String(cipherStream.ToArray());

This is the implementation I have done for now in CryptoJS:

const key = Buffer.from('abcdefgh', 'utf-8');
const iv = CryptoJS.lib.WordArray.random(128 / 8);

const encrypted = CryptoJS.AES.encrypt(this.msg, key.toString(), {
  iv: iv,
  padding: CryptoJS.pad.Pkcs7,
  mode: CryptoJS.mode.CBC,
});

return encrypted.toString();

Key is the same key used in both C# and JavaScript. But still I am not able to generate the same encryption value as in C#.

I tried to go through other Stack Overflow posts related to this topic, but unable to figure the missing part in JavaScript. Can any one please help?

Topaco · Answer

The key used in the C# code is UTF-8 encoded, so on the CryptoJS side the key must be parsed into a WordArray using the UTF-8 encoder (CryptoJS only interprets the key material as key if it is passed as a WordArray; if it is passed as string, it is interpreted as password and a key derivation function is applied, which would not be compatible with the C# code).
Also, the C# code concatenates IV and ciphertext, which must also happen in the CryptoJS code. This is necessary because the IV is required for decryption.

Fixed code:

var plaintext = 'The quick brown fox jumps over the lazy dog';
var key = CryptoJS.enc.Utf8.parse('01234567890123456789012345678901'); // Fix 1: parse as WordArray
var iv = CryptoJS.lib.WordArray.random(128 / 8);
var encrypted = CryptoJS.AES.encrypt(plaintext, key, {iv: iv}); // CBC, PKCS#7 padding by default
var ivCiphertext = iv.clone().concat(encrypted.ciphertext).toString(CryptoJS.enc.Base64); // Fix 2: concatenate IV and ciphertext
console.log(ivCiphertext); // e.g. e9iXcQ2sZ6AA2ne1c3490pAPWOrTGf4UttSSX1lOiKUqwP0oWRPFF83VhZQZMMBu9JKNWIfgS+9D5V39bI4rqg==

For a test, the ciphertexts cannot simply be compared because, due to the random IV, each encryption produces different ciphertexts.
One option for a test is to temporarily use the same IV in the C# code and in the CryptoJS code for the test (and only for the test, since a static IV is insecure!), which would produce the same ciphertexts that could then be compared.
Another option for a test is to decrypt the ciphertext produced with the CryptoJS code with the C# code for decryption.

Implement C# encryption in CryptoJS

1 Answers