C# - Serializing/Deserializing a DES encrypted file from a stream

Question

Does anyone have any examples of how to encrypt serialized data to a file and then read it back using DES?

I've written some code already that isn't working, but I'd rather see a fresh attempt instead of pursuing my code.

EDIT: Sorry, forgot to mention I need an example using XmlSerializer.Serialize/Deserialize.

Answer 1

Here is an example of DES encryption/decription for a string.

Answer 2

Encryption

public static void EncryptAndSerialize(string filename, MyObject obj, SymmetricAlgorithm key)
{
    using(FileStream fs = File.Open(filename, FileMode.Create))
    {
        using(Cryptostream cs = new CryptoStream(fs, key.CreateEncryptor(), CryptoStreamMode.Write))
        {
            XmlSerializer xmlser = new XmlSerializer(typeof(MyObject));
            xmlser.Serialize(cs, obj); 
        }
    }
}

Decryption:

public static MyObject DecryptAndDeserialize(string filename, SymmetricAlgorithm key)    
{
    using(FileStream fs = File.Open(filename, FileMode.Open))
    {
        using(Cryptostream cs = new CryptoStream(fs, key.CreateDecryptor(), CryptoStreamMode.Read))
        {
            XmlSerializer xmlser = new XmlSerializer(typeof(MyObject));
            return (MyObject) xmlser.Deserialize(cs);
        }
    }
}

Usage:

DESCryptoServiceProvider key = new DESCryptoServiceProvider();
MyObject obj = new MyObject();
EncryptAndSerialize("testfile.xml", obj, key);
MyObject deobj = DecryptAndDeserialize("testfile.xml", key);

You need to change MyObject to whatever the type of your object is that you are serializing, but this is the general idea. The trick is to use the same SymmetricAlgorithm instance to encrypt and decrypt.

Answer 3

Just one question.

If you need to use the same SymmetricAlgorithm instance to decrypt your data, how do you decrypt your file at a later time or from another application?