AES encryption in JS equivalent of C#

Question

I need to encrypt a string using AES encryption. This encryption was happening in C# earlier, but it needs to be converted into JavaScript (will be run on a browser).

The current code in C# for encryption is as following -

public static string EncryptString(string plainText, string encryptionKey)
{
    byte[] clearBytes = Encoding.Unicode.GetBytes(plainText);

    using (Aes encryptor = Aes.Create())

    {
        Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(encryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
        encryptor.Key = pdb.GetBytes(32);
        encryptor.IV = pdb.GetBytes(16);
        using (MemoryStream ms = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))

            {
                cs.Write(clearBytes, 0, clearBytes.Length);
                cs.Close();
            }
            plainText = Convert.ToBase64String(ms.ToArray());
        }
    }
    return plainText;
}

I have tried to use CryptoJS to replicate the same functionality, but it's not giving me the equivalent encrypted base64 string. Here's my CryptoJS code -

function encryptString(encryptString, secretKey) {
    var iv = CryptoJS.enc.Hex.parse('Ivan Medvedev');
    var key = CryptoJS.PBKDF2(secretKey, iv, { keySize: 256 / 32, iterations: 500 });

    var encrypted = CryptoJS.AES.encrypt(encryptString, key,{iv:iv);
    return encrypted;
}

The encrypted string has to be sent to a server which will be able to decrypt it. The server is able to decrypt the encrypted string generated from the C# code, but not the encrypted string generated from JS code. I tried to compare the encrypted strings generated by both the code and found that the C# code is generating longer encrypted strings. For example keeping 'Example String' as plainText and 'Example Key' as the key, I get the following result -

C# - eAQO+odxOdGlNRB81SHR2XzJhyWtz6XmQDko9HyDe0w=
JS - 9ex5i2g+8iUCwdwN92SF+A==

The length of JS encrypted string is always shorter than the C# one. Is there something I am doing wrong? I just have to replicated the C# code into the JS code.

Update:
My current code after Zergatul's answer is this -

function encryptString(encryptString, secretKey) {
    var keyBytes = CryptoJS.PBKDF2(secretKey, 'Ivan Medvedev', { keySize: 48 / 4, iterations: 1000 });
    console.log(keyBytes.toString());

    // take first 32 bytes as key (like in C# code)
    var key = new CryptoJS.lib.WordArray.init(keyBytes.words, 32);
    // skip first 32 bytes and take next 16 bytes as IV
    var iv = new CryptoJS.lib.WordArray.init(keyBytes.words.splice(32 / 4), 16);

    console.log(key.toString());
    console.log(iv.toString());

    var encrypted = CryptoJS.AES.encrypt(encryptString, key, { iv: iv });
    return encrypted;
}

As illustrated in his/her answer that if the C# code converts the plainText into bytes using ASCII instead of Unicode, both the C# and JS code will produce exact results. But since I am not able to modify the decryption code, I have to convert the code to be equivalent of the original C# code which was using Unicode.

So, I tried to see, what's the difference between both the bytes array between ASCII and Unicode byte conversion in C#. Here's what I found -

ASCII Byte Array: [69,120,97,109,112,108,101,32,83,116, 114, 105, 110, 103]
Unicode Byte Array: [69,0,120,0,97,0,109,0,112,0,108,0,101,0,32,0,83,0,116,0, 114,0, 105,0, 110,0, 103,0]

So some extra bytes are available for each character in C# (So Unicode allocates twice as much bytes to each character than ASCII).

Here's the difference between both Unicode and ASCII conversion respectively -

ASCII
clearBytes: [69,120,97,109,112,108,101,32,83,116,114,105,110,103,]
encryptor.Key: [123,213,18,82,141,249,182,218,247,31,246,83,80,77,195,134,230,92,0,125,232,210,135,115,145,193,140,239,228,225,183,13,]
encryptor.IV: [101,74,46,177,46,233,68,252,83,169,211,13,249,61,118,167,]
Result: eQus9GLPKULh9vhRWOJjog==

Unicode:
clearBytes: [69,0,120,0,97,0,109,0,112,0,108,0,101,0,32,0,83,0,116,0,114,0,105,0,110,0,103,0,]
encryptor.Key: [123,213,18,82,141,249,182,218,247,31,246,83,80,77,195,134,230,92,0,125,232,210,135,115,145,193,140,239,228,225,183,13,]
encryptor.IV: [101,74,46,177,46,233,68,252,83,169,211,13,249,61,118,167,]
Result: eAQO+odxOdGlNRB81SHR2XzJhyWtz6XmQDko9HyDe0w=

So since both the key and iv being generated have exact same byte array in both Unicode and ASCII approach, it should not have generated different output, but somehow it's doing that. I think it's because of clearBytes' length, as it's using its length to write to CryptoStream.

I tried to see what's the output of the generated bytes in the JS code is and found that it uses words which needed to be converted into Strings using toString() method.

keyBytes: 7bd512528df9b6daf71ff653504dc386e65c007de8d2877391c18cefe4e1b70d654a2eb12ee944fc53a9d30df93d76a7
key: 7bd512528df9b6daf71ff653504dc386e65c007de8d2877391c18cefe4e1b70d
iv: 654a2eb12ee944fc53a9d30df93d76a7

Since, I am not able to affect the generated encrypted string's length in the JS code (No access to the write stream directly), thus still stuck here.

Zergatul · Accepted Answer

Here is the example how to reproduce the same ciphertext between C# and CryptoJS:

static void Main(string[] args)
{
    byte[] plainText = Encoding.Unicode.GetBytes("Example String"); // this is UTF-16 LE
    string cipherText;
    using (Aes encryptor = Aes.Create())
    {
        var pdb = new Rfc2898DeriveBytes("Example Key", Encoding.ASCII.GetBytes("Ivan Medvedev"));
        encryptor.Key = pdb.GetBytes(32);
        encryptor.IV = pdb.GetBytes(16);
        using (MemoryStream ms = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
            {
                cs.Write(plainText, 0, plainText.Length);
                cs.Close();
            }
            cipherText = Convert.ToBase64String(ms.ToArray());
        }
    }

    Console.WriteLine(cipherText);
}

And JS:

var keyBytes = CryptoJS.PBKDF2('Example Key', 'Ivan Medvedev', { keySize: 48 / 4, iterations: 1000 });
// take first 32 bytes as key (like in C# code)
var key = new CryptoJS.lib.WordArray.init(keyBytes.words, 32);
// skip first 32 bytes and take next 16 bytes as IV
var iv = new CryptoJS.lib.WordArray.init(keyBytes.words.splice(32 / 4), 16);
// use the same encoding as in C# code, to convert string into bytes
var data = CryptoJS.enc.Utf16LE.parse("Example String");
var encrypted = CryptoJS.AES.encrypt(data, key, { iv: iv });
console.log(encrypted.toString());

Both codes return: eAQO+odxOdGlNRB81SHR2XzJhyWtz6XmQDko9HyDe0w=

AES encryption in JS equivalent of C#

Answers (2)

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