The problem may be these two lines in the Decipher function:
byte[] PlainTextBytes = new byte[CipherText.Length];
int ByteCount = cryptoStream.Read(PlainTextBytes, 0, PlainTextBytes.Length);
The Read() will fill PlainTextBytes up through the number of bytes read, the rest will be 0's. I find that very often the encrypted data is longer than the decrypted data. So it's very possible that PlainTextBytes will be created as a byte[] larger than the actual decrypted data. I've also come across code like this on the internet and won't use it myself; it just doesn't look right to me. For what arbitrary reason would you determine that the length of the decrypted data is exactly the same as the length of the encrypted data? Which is essentially what the code is assuming. I prefer to play it safe and not make that assumption. I find it easier to use the CryptoStream in Write mode for both encrypting and decrypting, I find it helps avoid the aforementioned assumption. If you supply the CryptoStream an empty MemoryStream and the proper ICryptoTransform (encrypt or decrypt), then all you have to do is write the byte[] to the CryptoStream and when you Read from the MemoryStream you will get the transformed data. Doing that in the Decipher function would look like this:
MemoryStream memStream = new MemoryStream();
CryptoStream cryptoStream = new CryptoStream(memStream, Decryptor, CryptoStreamMode.Write);
cryptoStream.Write(CipherText, 0, CipherText.Length);
PlainTextBytes = memStream.ToArray();
This is pretty much how you did the encryption in the Cipher function. The cool thing about this is that the actions for encrypting and decrypted are exactly the same, the only thing different is the data and the ICryptoTransform used. So, you can put this functionality in a single function in which you only need to pass the proper ICryptoTransform and the proper byte[]. When you are encrypting pass in the unencrypted data as a byte[] and the Encryptor ICryptoTransform and when decrypting pass in the encrypted data as a byte[] and the Decryptor ICryptoTransform, and you'd have this (which is almost the same as code I've used):
private byte[] PerformTransform(byte[] data, ICryptoTransform tran)
{
