Friday, April 27, 2012

How to Encrypt/Decrypt Text in Silverlight/.NET

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As web or application developers it is advisable to never transmit or store passwords as plain text. If unencrypted, a person could intentionally (or unintentionally) discover somebody else’s password. The technique described in this post is certainly not 100% secure but it makes password cracking difficult. To obtain a person’s original password the hacker must have the encrypted password and the key embedded in the client application.

The code included below will work in both Silverlight and .NET. An Advanced Encryption Standard (AES) symmetric algorithm is used to scramble/descramble text as shown in the screenshot above.

using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

using System.Windows;

 

namespace TestPasswordEncryption {

    public partial class MainWindow : Window {

        public MainWindow() {

            InitializeComponent();

 

            // Encrypt Text

            this.ButtonEncrypt.Click += (s, e) => {

                this.TextBoxEncrypted.Text =
                   
Scrambler.Encrypt(this.TextBoxOriginal.Text);

            };

 

            // Decrypt Text

            this.ButtonDecrypt.Click += (s, e) => {

                this.TextBoxDecrypted.Text =
                   
Scrambler.Decrypt(this.TextBoxEncrypted.Text);

            };

        }

    }

 

    internal class Scrambler {

        private const string PASS = "6D114A94-375E-4FFD-9F48-CF2C7A12620F";

        private const string SALT = "E5A8DB1B-5EAB-4C62-B322-CE24CE274303";

 

        internal static string Encrypt(string input) {

            // Test data

            byte[] utfdata = UTF8Encoding.UTF8.GetBytes(input);

            byte[] saltBytes = UTF8Encoding.UTF8.GetBytes(Scrambler.SALT);

 

            // We're using the PBKDF2 standard for password-based key generation

            Rfc2898DeriveBytes rfc = new Rfc2898DeriveBytes(

                Scrambler.PASS, saltBytes, 1000);

 

            // Our symmetric encryption algorithm

            AesManaged aes = new AesManaged();

            aes.BlockSize = aes.LegalBlockSizes[0].MaxSize;

            aes.KeySize = aes.LegalKeySizes[0].MaxSize;

            aes.Key = rfc.GetBytes(aes.KeySize / 8);

            aes.IV = rfc.GetBytes(aes.BlockSize / 8);

 

            // Encryption

            ICryptoTransform encryptTransf = aes.CreateEncryptor();

 

            // Output stream, can be also a FileStream

            MemoryStream encryptStream = new MemoryStream();

            CryptoStream encryptor = new CryptoStream(

                encryptStream, encryptTransf, CryptoStreamMode.Write);

            encryptor.Write(utfdata, 0, utfdata.Length);

            encryptor.Flush();

            encryptor.Close();

 

            // Showing our encrypted content

            byte[] encryptBytes = encryptStream.ToArray();

            string encryptedString = Convert.ToBase64String(encryptBytes);

 

            // Close stream

            encryptStream.Close();

 

            // Return encrypted text

            return encryptedString;

        }

        internal static string Decrypt(string base64Input) {

            // Get inputs as bytes

            byte[] encryptBytes = Convert.FromBase64String(base64Input);

            byte[] saltBytes = Encoding.UTF8.GetBytes(Scrambler.SALT);

 

            // We're using the PBKDF2 standard for password-based key generation

            Rfc2898DeriveBytes rfc = new Rfc2898DeriveBytes(

                Scrambler.PASS, saltBytes);

 

            // Our symmetric encryption algorithm

            AesManaged aes = new AesManaged();

            aes.BlockSize = aes.LegalBlockSizes[0].MaxSize;

            aes.KeySize = aes.LegalKeySizes[0].MaxSize;

            aes.Key = rfc.GetBytes(aes.KeySize / 8);

            aes.IV = rfc.GetBytes(aes.BlockSize / 8);

 

            // Now, decryption

            ICryptoTransform decryptTrans = aes.CreateDecryptor();

 

            // Output stream, can be also a FileStream

            MemoryStream decryptStream = new MemoryStream();

            CryptoStream decryptor = new CryptoStream(

                decryptStream, decryptTrans, CryptoStreamMode.Write);

            decryptor.Write(encryptBytes, 0, encryptBytes.Length);

            decryptor.Flush();

            decryptor.Close();

 

            // Showing our decrypted content

            byte[] decryptBytes = decryptStream.ToArray();

            string decryptedString = UTF8Encoding.UTF8.GetString(

                decryptBytes, 0, decryptBytes.Length);

 

            // Close Stream

            decryptStream.Close();

 

            // Return decrypted text

            return decryptedString;

        }

    }

}

 

 

2 comments:

  1. Hello, this is gonna be offtopic.
    Your RSS doesn't update. Its stuck on 16.12.2011.

    ReplyDelete