Question

Before spending any time reading this, see the self-answer below. The problem was invalid input.

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When I try to decrypt some strings it throws this exception:

    "   at System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, Int32 outputOffset, PaddingMode paddingMode, Boolean fLast)
       at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount)
       at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
       at System.Security.Cryptography.CryptoStream.Dispose(Boolean disposing)
       at System.IO.Stream.Close()
       at System.IO.Stream.Dispose()
       at EBookReader.cryptography.DecryptString(String message, String KeyString, String IVString) in C:\\Users\\XWare\\Documents\\Visual Studio 2008\\Projects\\EBookReader\\EBookReader\\cryptography.cs:line 94"

Under debugging it throws the exception on this line :

    byte[] messageBytes = Convert.FromBase64String(message);

I think this problem just appears when string to decrypt is too big because when I try to encrypt and decrypt short strings like “Hi there I am X-Ware” it works fine

    public static string DecryptString(string message, string KeyString, string IVString)
    {
        byte[] Key = ASCIIEncoding.UTF8.GetBytes(KeyString);
        byte[] IV = ASCIIEncoding.UTF8.GetBytes(IVString);

        string decrypted = null;
        RijndaelManaged rj = new RijndaelManaged();
        rj.BlockSize = 256;
        rj.Key = Key;
        rj.IV = IV;
        rj.Mode = CipherMode.CBC;
        rj.Padding = PaddingMode.PKCS7;
        try
        {
            MemoryStream ms = new MemoryStream();
            Encoding enc = new ASCIIEncoding();
            using (CryptoStream cs = new CryptoStream(ms, rj.CreateDecryptor(Key, IV), CryptoStreamMode.Write))
            {
                byte[] messageBytes = Convert.FromBase64String(message);
                cs.Write(messageBytes, 0, messageBytes.Length);
                cs.FlushFinalBlock();  
            }// This is line 94
            byte[] encoded = ms.ToArray();
            decrypted = enc.GetString(encoded);

            ms.Close();
        }
        catch (Exception e)
        {
            Console.WriteLine("An error occurred: {0}", e.Message);
        }
        finally
        {
            rj.Clear();
        }

        return decrypted;
    }

any suggestions ?!

P.S. I wrote a comment to show you line 94 // This is line 94

Answer 1

The problem is that the string I pass as Base64 string is invalid the problem is just in the input file which makes decryption impossible

Thanx all