Question

I’m using C# .Net 4.0. I generate the key and IV(initialization vector) using the rijindael class. I then write both of them to a file. The IV is always correct when I read the file, but the last byte of the key is always zero. I look at the key before writing to the file and it is fine, reading it back in the last byte is always zero.

I have tried setting the padding mode to the various choices and they don’t make a difference.

using (Rijndael myRijndael = Rijndael.Create())
{
    //Create keys
    try
    {
        byte[] key;
        byte[] iv;

        key = new byte[32];
        iv = new byte[16];

        theKeys.Key = myRijndael.Key;
        theKeys.IV = myRijndael.IV;

        FileStream fs = File.Create("yyy.txt");
        fs.Write(theKeys.Key, 0, theKeys.Key.Length);
        fs.Flush();
        fs.Close();

        FileStream ts = File.Open("yyy.txt", FileMode.Append);
        ts.Write(theKeys.IV, 0, theKeys.IV.Length);
        ts.Flush();
        ts.Close();


        FileStream ms = File.Open("yyy.txt", FileMode.Open);

         ms.Read(key, 0, 31);
         ms.Seek(32, 0);
         ms.Read(iv, 0, 16);
         ms.Flush();
         ms.Close();
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

Answer 1

// Save key and IV
using (var rijndael = new RijndaelManaged())
using (var writer = new BinaryWriter(File.Create("yyy.dat")))
{
    writer.Write(rijndael.Key, 0, 32);
    writer.Write(rijndael.IV, 0, 16);
}

// Restore key and IV
using (var rijndael = new RijndaelManaged())
using (var reader = new BinaryReader(File.OpenRead("yyy.dat")))
{
    rijndael.Key = reader.ReadBytes(32);
    rijndael.IV = reader.ReadBytes(16);
}