Encrypt Strings with Passwords - AES 256 & SHA256

Introduction

Greetings from Germany! In this tip, I will show you a class that allows to encrypt and decrypt strings with a password.

Background

If you don't know what AES or SHA2 is, please read the wikipedia articles...

• https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
• https://en.wikipedia.org/wiki/SHA-2

First, I create a hash with SHA2 (256 bit) from the password, this hash is the key and IV in the AES Encryption. The IV can only be 128 bit, so I just cut it to the right length.

You can only decrypt it if you have the password.

Using the Code

SecurityController.cs class code:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
 
namespace Encryption
{
  class SecurityController
  {
    public string Encrypt( string key, string data )
    {
      string encData = null;
      byte[][] keys = GetHashKeys(key);
 
      try
      {
        encData = EncryptStringToBytes_Aes( data, keys[0], keys[1] );
      }
      catch ( CryptographicException ) { }
      catch ( ArgumentNullException ) { }
 
      return encData;
    }
 
    public string Decrypt( string key, string data )
    {
      string decData = null;
      byte[][] keys = GetHashKeys(key);
 
      try
      {
        decData = DecryptStringFromBytes_Aes( data, keys[0], keys[1] );
      }
      catch ( CryptographicException ) { }
      catch ( ArgumentNullException ) { }
 
      return decData;
    }
 
    private byte[][] GetHashKeys( string key )
    {
      byte[][] result = new byte[2][];
      Encoding enc = Encoding.UTF8;
 
      SHA256 sha2 = new SHA256CryptoServiceProvider();
 
      byte[] rawKey = enc.GetBytes(key);
      byte[] rawIV = enc.GetBytes(key);
 
      byte[] hashKey = sha2.ComputeHash(rawKey);
      byte[] hashIV = sha2.ComputeHash(rawIV);
 
      Array.Resize( ref hashIV, 16 );
 
      result[0] = hashKey;
      result[1] = hashIV;
 
      return result;
    }
 
    //source: https://msdn.microsoft.com/de-de/library/system.security.cryptography.aes(v=vs.110).aspx
    private static string EncryptStringToBytes_Aes( string plainText, byte[] Key, byte[] IV )
    {
      if ( plainText == null || plainText.Length <= 0 )
        throw new ArgumentNullException( "plainText" );
      if ( Key == null || Key.Length <= 0 )
        throw new ArgumentNullException( "Key" );
      if ( IV == null || IV.Length <= 0 )
        throw new ArgumentNullException( "IV" );
 
      byte[] encrypted;
 
      using ( AesManaged aesAlg = new AesManaged() )
      {
        aesAlg.Key = Key;
        aesAlg.IV = IV;
 
        ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
 
        using ( MemoryStream msEncrypt = new MemoryStream() )
        {
          using ( CryptoStream csEncrypt = 
                  new CryptoStream( msEncrypt, encryptor, CryptoStreamMode.Write ) )
          {
            using ( StreamWriter swEncrypt = new StreamWriter( csEncrypt ) )
            {
              swEncrypt.Write( plainText );
            }
            encrypted = msEncrypt.ToArray();
          }
        }
      }
      return Convert.ToBase64String( encrypted );
    }
 
    //source: https://msdn.microsoft.com/de-de/library/system.security.cryptography.aes(v=vs.110).aspx
    private static string DecryptStringFromBytes_Aes( string cipherTextString, byte[] Key, byte[] IV )
    {
      byte[] cipherText = Convert.FromBase64String(cipherTextString);
 
      if ( cipherText == null || cipherText.Length <= 0 )
        throw new ArgumentNullException( "cipherText" );
      if ( Key == null || Key.Length <= 0 )
        throw new ArgumentNullException( "Key" );
      if ( IV == null || IV.Length <= 0 )
        throw new ArgumentNullException( "IV" );
 
      string plaintext = null;
 
      using ( Aes aesAlg = Aes.Create() )
      {
        aesAlg.Key = Key;
        aesAlg.IV = IV;
 
        ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
 
        using ( MemoryStream msDecrypt = new MemoryStream( cipherText ) )
        {
          using ( CryptoStream csDecrypt = 
                  new CryptoStream( msDecrypt, decryptor, CryptoStreamMode.Read ) )
          {
            using ( StreamReader srDecrypt = new StreamReader( csDecrypt ) )
            {
              plaintext = srDecrypt.ReadToEnd();
            }
          }
        }
      }
      return plaintext;
    }
  }
}

Example How To Use It

MainForm.cs class code:

using System.Windows.Forms;
 
namespace Encryption
{
  public partial class MainForm : Form
  {
    private SecurityController _security;
 
    public MainForm()
    {
      InitializeComponent();
      _security = new SecurityController();
    }
 
    private void button_encrypt_Click( object sender, System.EventArgs e )
    {
      string password = textBox_password.Text;
      string notEncryptedText = textBox_text.Text;
      string encryptedText = _security.Encrypt( password, notEncryptedText );
 
      textBox_text.Text = encryptedText;
    }
 
    private void button_decrypt_Click( object sender, System.EventArgs e )
    {
      string password = textBox_password.Text;
      string encryptedText = textBox_text.Text;
      string notEncryptedText = _security.Decrypt( password, encryptedText );
 
      textBox_text.Text = notEncryptedText;
    }
  }
}

Before Encryption

After Encryption

After Decryption

Conclusion

I know it's very simple and not a lot of code, but if you don't know much about encryption and you need it, this class will help you a lot!