Monthly Archives: April 2010

code

AES encryption strategies with .Net

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I did a presentation last week on AES encryption techniques in .Net.

I’ll post some details here later, but for now, I’ve uploaded a zip file with the project code.

Here’s the key bit:

 
            string key = "1234567891123456";
            string secret = @"This is a secret.";
 
            Console.WriteLine("basic:");
            EncryptString(key, secret);
            Console.ReadKey();
 
            Console.WriteLine("salt the secret:");
            // good when there are multiple machines but a dynamic global shared secret (for example, Profile Create Date or User ID)
            string secret2 = secret + " ###" + DateTime.Now.Millisecond;
            EncryptString(key, secret2);
 
            secret2 = secret + " ###" + DateTime.Now.Millisecond;
            EncryptString(key, secret2);
 
            Console.ReadKey();
 
            Console.WriteLine("salt the key:"); 
            // good when the same machine encrypts/decrepts
            string uniqueMachineIdentifier = MachineId.GetProcessorID();
            Console.WriteLine("MachineId: " + uniqueMachineIdentifier);
            EncryptString(key + uniqueMachineIdentifier, secret);
            Console.ReadKey();
 
            Console.WriteLine("SHA1 hash the passphrase with a salt:"); 
            // note: talk about why hashing is good
            SHA1 sha = new SHA1CryptoServiceProvider();
            // This is one implementation of the abstract class SHA1.
            string password = "this is my user password and/or userid";
            byte[] saltedKey = Encoding.Default.GetBytes(key + password);
 
            byte[] result = sha.ComputeHash(saltedKey);
            EncryptString(Convert.ToBase64String(result), secret);
            Console.ReadKey();
code

Using the MySql ADO.Net adapter

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public DataSet ExecuteQuery(string commandText)
        {
            DataSet ds = new DataSet();
            using (var connection = new MySqlConnection(connString))
            {
                connection.Open();
                var command = connection.CreateCommand();
                command.CommandText = commandText;
                using (var data = new MySqlDataAdapter { SelectCommand = command })
                {
                    data.Fill(ds);
                    connection.Close();
                }
            }
            return ds;
        }
code

.Net Graphics: drawing text on a bitmap

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I use this code here.

Graphics backgroundGraphics;
backgroundImage = (Bitmap)Image.FromFile(AppDomain.CurrentDomain.BaseDirectory + "\images\Header.jpg");
backgroundGraphics = Graphics.FromImage(backgroundImage);
var font = new Font("Perpetua Titling MT", 24F, FontStyle.Regular);
backgroundGraphics.DrawString(authorname.ToUpper(), font, new SolidBrush(Color.FromArgb(100, 0, 0, 0)), 10, 5);

Now save – or output to the browser:

backgroundImage.Save(context.Response.OutputStream, ImageFormat.Jpeg);