title: 2-way encryption from int into a short string
body: <p>I'm building a tiny webapplication in which our customers can update some details about their company. The customers currently don't have a login/password and we don't want to validate their registration, so we want to give them a automaticly generated password/key to login to the website.</p>
  
  <p>Our plan to encrypt their customerId and give that to the customer so that he can enter that key on the webapp to allow us to decrypt the key into his ID.</p>
  
  <p>There are about 10K customers and they don't all have an email, so some will receive a letter with the URL and the code. This means that the customer has to type the code in, so the code can't be more than 8 characters (preferably 6).</p>
  
  <p>Here's an empty template:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  
  namespace ConsoleApplication1
  {
      class Program
      {
          static void Main(string[] args)
          {
              int passwordLength = 6;
              int customerId = 12345;
              string encrypted = Crypter.Encrypt(customerId, "secretKey", passwordLength);
              if (customerId == Crypter.Decrypt(encrypted, "secretKey"))
              {
                  Console.WriteLine("It worked! Well done!");
              }
          }
  
      }
  
      public static class Crypter
      {
          public static string Encrypt(int input, string key, int passwordLength)
          {
              string encryptedString = "";
              //do encrypt stuffz here
  
              return encryptedString;
          }
          public static int Decrypt(string encryoted, string key)
          {
              int decrypted = 0;
              //do decrypt stuffz here
  
              return decrypted;
          }
      }
  }
  </code></pre>
  
  <p><strong>=> Can anyone link me to more information on how to do this?</strong></p>
  
  <p>I'm not looking for a "plz send me teh codez" but if anyone has already made something like this, feel free to share.</p>
  
  <p>Thanks in advance for any information.</p>