Specified key is not a valid size for this algorithm.

[ichoes]

I occasionally get the following error "Specified key is not a valid size for this algorithm".
When it happens it occurs on the Transform method the key is getting 7 bytes instead of 8.

[sgbj]

Thanks for taking the time to report this issue. It's because of the GetBytes extension method:

public static byte[] GetBytes(this BigInteger number)
{
    return number.ToByteArray().Reverse().SkipWhile(b => b == 0).ToArray();
}

It skips any zeros it sees in the beginning of the array. I added some code to the Dukpt.Transform method to counteract this behavior and add them back in instead of making the extension method context-aware.

It should be fixed now. =)

[ichoes]

Tested the change and it works perfectly now.
Thank you for the fix.

[ichoes]

Hi,
I will reopen the ticket because i am getting the same error.
this time i am getting 15 bytes instead of 16.
to Fix it i did the following

if (k.Length > 8)
{
     cipher.Key = new byte[Math.Max(0, 16 - k.Length)].Concat(key.GetBytes()).ToArray();
}
else
{
     cipher.Key = new byte[Math.Max(0, 8 - k.Length)].Concat(key.GetBytes()).ToArray();
}

let me know if this is an acceptable solution.
Thanks

[ichoes]

I have a better solution,

   public static BigInteger Transform(string name, bool encrypt, BigInteger key, BigInteger message)
        {
            using (var cipher = SymmetricAlgorithm.Create(name))
            {
                var k = key.GetBytes();
//gets the next multiple of 8
                cipher.Key = new byte[Math.Max(0, GetNearestWholeMultiple(k.Length,8) - k.Length)].Concat(key.GetBytes()).ToArray();
                cipher.IV = new byte[8];
                cipher.Mode = CipherMode.CBC;
                cipher.Padding = PaddingMode.Zeros;
                using (var crypto = encrypt ? cipher.CreateEncryptor() : cipher.CreateDecryptor())
                {
                    var data = message.GetBytes();
                    return BigInt.FromBytes(crypto.TransformFinalBlock(data, 0, data.Length));
                }
            }
        }

//gets the next multiple of 8
//Works with both scenarios, getting 7 bytes instead of 8 and Works when expecting 16 bytes and getting 15.
        private static int GetNearestWholeMultiple(decimal input, int X)
        {
            var output = Math.Round(input / X);
            if (output == 0 && input > 0) output += 1;
            output *= X;

            return (int)output;
        }

[sgbj]

Thank you ichoes for fixing this issue!

[easytomanage]

In order to support either TripleDES or AES, you can use cipher.BlockSize / 8 instead of the hardcoded 8. This is for Key, IV, and data lines.