.NET (Core and Framework)

public static string Encrypt(string strInputString, string strKeyString, string myIV)
    {
        if ((strInputString == null) || (strInputString.Length == 0))
        {
            return strInputString;
        }           
            int num4;
            int keySize = 0x100;
            int blockSize = 0x100;
            int length = keySize / 0x10;
            if (strKeyString.Length > length)
            {
                strKeyString = strKeyString.Substring(0, length);
            }
            if (strKeyString.Length < length)
            {
                strKeyString = strKeyString.PadRight(length, '#');
            }
            Encoding.Unicode.GetBytes(strKeyString);
            if (myIV.Length > length)
            {
                myIV = myIV.Substring(0, length);
            }
            if (myIV.Length < length)
            {
                myIV = myIV.PadRight(length, '#');
            }
            Encoding.Unicode.GetBytes(myIV);
            byte[] bytes = Encoding.Unicode.GetBytes(strKeyString);
            byte[] rgbIV = Encoding.Unicode.GetBytes(myIV);
            string str = "";
            RijndaelManaged managed = new RijndaelManaged
            {
                BlockSize = blockSize,
                KeySize = keySize
            };
            MemoryStream stream = new MemoryStream(Encoding.Unicode.GetBytes(strInputString));
            MemoryStream stream2 = new MemoryStream();
            CryptoStream stream3 = new CryptoStream(stream2, managed.CreateEncryptor(bytes, rgbIV), CryptoStreamMode.Write);
            while ((num4 = stream.ReadByte()) != -1)
            {
                stream3.WriteByte((byte)num4);
            }
            stream3.Close();
            stream2.Close();
            stream.Close();
            foreach (byte num5 in stream2.ToArray())
            {
                str = str + num5.ToString("X2");
            }
            return str;

    }

Encoding.Unicode.GetBytes(...);

int length = keysize / 0x10;

// Divided by 16 because we're using Unicode encoding.
// If using ASCII or UTF8, this would be divided by 8 instead.
int length = blockSize / 16;

public static byte[] UnicodeConvertStringToVector(string source, int sizeInBits)
{
	int maxStringLength = sizeInBits / (UnicodeEncoding.CharSize * 8);

	// Make sure the length of the string in Unicode characters is no longer than
	// allowed by the sizeInBits parameter.
	if (source.Length > maxStringLength) {
		source = source.Substring(0, maxStringLength);
	} else if (source.Length < maxStringLength) {
		// and make sure that it's no shorter than allowed by sizeInBits...
		source = source.PadRight(maxStringLength, "#");
	}

	return Encoding.Unicode.GetBytes(source);
}

byte[] keyData = UnicodeConvertStringToVector(myKeyString, keySize);
byte[] ivData = UnicodeConvertStringToVector(myIV, length);
byte[] encryptedData = null;

using (MemoryStream outputStream = new MemoryStream())
{
    using (CryptoStream cryptStream = new CryptoStream(outputStream, managed.CreateEncryptor(keyData, ivData), CryptoStreamMode.Write))
    {
        using (StreamWriter encryptStream = new StreamWriter(cryptStream))
        {
            encryptStream.Write(strInputString);
        }
        encryptedData = outputStream.ToArray;
    }
}

return encryptedData;

Dave Kreskowiak wrote:

If he gave you the decryption function and the correct keys, and it still doesn't work, the problem is entirely HIS, not yours.

Dave Kreskowiak wrote:

He should be giving you a library .DLL that you can use that handles this stuff.