Difference of $SYSTEM.Encryption.AESCBCEncrypt with C# implementation

Hi All,

Hopefully  someone can help me with this case. I need to encrypt a text(querystring) with an AES265 encryption. An other vendor is decrypting this information. I have a working class in C#. I've tried to build the same in Objectscript for the encrypt part but there's a missing link somewhere.  What's the difference between the C# and Objectscript implementation?

Objectscript code (until now):

Class TEST.ENCRYPT
{

// Symmetric Keys sample to encrypt

ClassMethod DoAESCBCEncrypt() As %Status
{
	set key="pZR8qfrz7t47G+dboyJCH4NnJRrF+dJbvxq37y/cLUo="
	set iv=##class(%PopulateUtils).StringMin(16,16)	
	Write "Key="_key,!
	Write "IV="_iv,!
	Set ivBase64 = $SYSTEM.Encryption.Base64Encode(iv)
	Write "IVBase64="_ivBase64,!
	
	set plaintext="This is just an encryption test with AES256, blocksize 128, padding PKCS7, mode, CBC with an IV of 16 bytes"
	Set text=$ZCONVERT(plaintext,"O","UTF8")
	Write "Text UTF-8: "_text,!
	
	Set encrypted=$SYSTEM.Encryption.AESCBCEncrypt(text,key,iv)
	Set EncryptedBase64=$SYSTEM.Encryption.Base64Encode(encrypted)
	Write "EncryptedBase64: "_EncryptedBase64,!
	
	Set encryptedComplete = ivBase64_EncryptedBase64
	Write "EncryptedBase64WithIV: "_encryptedComplete,!
	
	Set ciphertext = $$$URLENCODE(encryptedComplete)

	write "URL Encoded:"_ciphertext,!
	return $$$OK
}

}

This give this as example output:

URL Encoded: ZlR3ckxhVmxBZXJKZlpLQg%3D%3D8TvyqZNAFsv7Nb0HYkGIfrPmUOkeQ2r%2BKZ%2BThSzVd1tqoyziSpRJsjQP/pEnAzRY5HzybCdFBDtb%0D%0AD8wNTNv1OFcXsHqk/GOhce1xdPlyJFg85llLUfBIG74lhAjtvb%2BN4eMY6jg05HkGejXlIoEo8Q%3D%3D

When decrypting with the C# code, I get the following eror.

I see a few things. When running the decrypting code the IV looks fine, also the "To Decrypt without IV" decrypt looks fine (it matches the output of the Objectscript implementation). So I think there's a difference in implementation of the encryption itself but how to find the difference?

See complete enrypt/decrypt C# code below.

using System;
using System.Security.Cryptography;
using System.Text;

class Program
{
    static void Main(string[] args)
    {
		string toEncrypt = "This is just an encryption test with AES256, blocksize 128, padding PKCS7, mode, CBC with an IV of 16 bytes";
		string hashedKey = "pZR8qfrz7t47G+dboyJCH4NnJRrF+dJbvxq37y/cLUo=";
		Console.WriteLine("SECRET KEY / HASHED KEY: "+hashedKey);
		Console.WriteLine("");

		Console.WriteLine("What to encrypt/decrypt: " + toEncrypt);
		Console.WriteLine("");

		//Ecnryption Parts
		Console.WriteLine("######## ENCRYPTION START ########");
		
		Console.WriteLine("To Encrypt: " + toEncrypt);

		//create IV
		byte[] IV = new byte[16];
		(new Random()).NextBytes(IV);

		AesCryptoServiceProvider cryptoProvider = CreateCryptoProvider(Convert.FromBase64String(hashedKey),IV);

		ICryptoTransform cryptoTransform = cryptoProvider.CreateEncryptor();
		byte[] bytes = Encoding.UTF8.GetBytes(toEncrypt);
		string encryptedUnformatted = Convert.ToBase64String(cryptoTransform.TransformFinalBlock(bytes, 0, (int)bytes.Length));
		Console.WriteLine("encryptedUnformatted: " + encryptedUnformatted);

		//add Random IV
		string randomIVBase64 = Convert.ToBase64String(IV);
		Console.WriteLine("randomIVBase64: " + randomIVBase64);

		encryptedUnformatted = string.Concat(randomIVBase64, encryptedUnformatted);
		Console.WriteLine("With Random IV: " + encryptedUnformatted);

		//escape string
		string encryptedFormatted = Uri.EscapeDataString(encryptedUnformatted);
		Console.WriteLine("encryptedFormatted: " + encryptedFormatted);

		Console.WriteLine("######## ENCRYPTION END ########");
		Console.WriteLine("");
		Console.WriteLine("#####################################################");
		Console.WriteLine("");
		Console.WriteLine("######## DECRYPTION START ########");

		//Decryption Part
		string toDecrypt = encryptedFormatted;
		//toDecrypt = "ZlR3ckxhVmxBZXJKZlpLQg%3D%3D8TvyqZNAFsv7Nb0HYkGIfrPmUOkeQ2r%2BKZ%2BThSzVd1tqoyziSpRJsjQP/pEnAzRY5HzybCdFBDtb%0D%0AD8wNTNv1OFcXsHqk/GOhce1xdPlyJFg85llLUfBIG74lhAjtvb%2BN4eMY6jg05HkGejXlIoEo8Q%3D%3D";
		Console.WriteLine("To Decrypt: " + toDecrypt);
		
		//de-escape string
		string deEscape=Uri.UnescapeDataString(toDecrypt);
		Console.WriteLine("De-Escaped: " + deEscape);

		//get IV
		string ivString = deEscape.Substring(0, 24);
		Console.WriteLine("IV String: " + ivString);

		byte[] IVDecrypt= Convert.FromBase64String(ivString);
		
		string toDecryptWithoutIV = deEscape.Substring(24);
		Console.WriteLine("To Decrypt without IV: " + toDecryptWithoutIV);

		AesCryptoServiceProvider DecryptProvider = CreateCryptoProvider(Convert.FromBase64String(hashedKey), IVDecrypt);

		ICryptoTransform cryptoTransformDecrypt = DecryptProvider.CreateDecryptor();
		byte[] numArray = Convert.FromBase64String(toDecryptWithoutIV);
		string decrypted = Encoding.UTF8.GetString(cryptoTransformDecrypt.TransformFinalBlock(numArray, 0, (int)numArray.Length));

		Console.WriteLine("Decrypted: " + decrypted);
		Console.WriteLine("######## DECRYPTION END ########");
	}
	static AesCryptoServiceProvider CreateCryptoProvider(byte[] HashedKey, byte[] IV)
	{
		return new AesCryptoServiceProvider()
		{
			KeySize = 256,
			BlockSize = 128,
			Key = HashedKey,
			IV = IV,
			Padding = PaddingMode.PKCS7,
			Mode = CipherMode.CBC
		};
	}
}