How do I work around the missing crypto classes in silverlight 2/3?

Question

I'm doing some work with a server side service I don't control. The following works fine in standard C#, but fails (due to missing crypto classes) in Silverlight 2 and 3.

    static String DecryptString()
    {
        s = "<cipherTextHere>";

        byte[] toDecryptArray = Convert.FromBase64String(s);
        string key = "<key here>";

        byte[] keyArray = new byte[key.Length / 2];
        for (int i = 0; i < keyArray.Length; i++)
        {
            keyArray[i] = Convert.ToByte(Convert.ToInt32(key.Substring(i * 2, 2), 16));
        }

        using (var algo = new System.Security.Cryptography.AesManaged())
        {

            // The two lines below are the problem
            // as SL does not give me the option to select padding or ciphermode
            algo.Padding = PaddingMode.PKCS7;
            algo.Mode = CipherMode.ECB;

            algo.Key = keyArray;

            ICryptoTransform cTransform = algo.CreateDecryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(
                                 toDecryptArray, 0, toDecryptArray.Length);

            return (UTF8Encoding.UTF8.GetString(resultArray, 0, resultArray.Length));

        }
    }

What are my options?

Answer 1

Call for the Legion of the Bouncy Castle to help you out of this bind.

Answer 2

You could write your own crypto provider, or you could search for third party components which have already addressed the issue.

I know that xceed have implemented a compression provider for Silverlight so compression and encryption are definately possible.

try

Cryptography Tutorial

Answer 3

Silverlight 2 does has some of the System.Security.Cryptography namespace implemented. See the documentation here. What's missing for you?

Answer 4

Solution from someone smart: "You cannot select padding or ciphermode for AesManaged in Silverlight, so you will have to use the default. Padding by default is PKCS7 just like in your C# code, but cipher mode is CBC."

This works, but now I'm going to have to go convinnce the service provider to switch :(