The hash algorithm is allowed to create larger number of data using the small number of data.

Step 1: Create a simple login form as in the following screenshot:

design

By using the following HTML code:

  1. <asp:Table ID="Table1" runat="server" Width="418px" Height="209px">
  2. <asp:TableRow>
  3. <asp:TableCell>
  4. User Name
  5. </asp:TableCell>
  6. <asp:TableCell>
  7. <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
  8. </asp:TableCell>
  9. </asp:TableRow>
  10. <asp:TableRow>
  11. <asp:TableCell>
  12. Password
  13. </asp:TableCell>
  14. <asp:TableCell>
  15. <asp:TextBox ID="TextBox2" runat="server" TextMode="Password"></asp:TextBox>
  16. </asp:TableCell>
  17. </asp:TableRow>
  18. <asp:TableRow>
  19. <asp:TableCell>
  20. <asp:Button ID="Button1" runat="server" Text="Sign Up" OnClick="Message_click" />
  21. </asp:TableCell>
  22. <asp:TableCell>
  23. <asp:Button ID="Button2" runat="server" Text="login" OnClick="login_click" />
  24. </asp:TableCell>
  25. <asp:TableCell>
  26. <asp:Label ID="Label1" runat="server" />
  27. </asp:TableCell>
  28. </asp:TableRow>
  29. </asp:Table>
Step 2: Now create the Database table as in the following screenshot:

Encrypt
Step 3: After creating the table use the following coding in Sign up button to get user name and password:
  1. public void Message_click(object sender, EventArgs e)
  2. {
  3. string username = TextBox1.Text.ToString();
  4. String password = TextBox2.Text;
  5. //Get the encrypt the password by using the class
  6. string pass = encryption(password);
  7. Label1.Text = pass;
  8. //Check whether the UseName and password are Empty
  9. if (username.Length > 0 && password.Length > 0)
  10. {
  11. //creating the connection string
  12. string connection = ConfigurationManager.ConnectionStrings["DefaultConnection"].ToString();
  13. SqlConnection con = new SqlConnection(connection);
  14. String passwords = encryption(password);
  15. con.Open();
  16. // Check whether the Username Found in the Existing DB
  17. String search = "SELECT * FROM UserAccount WHERE (UserName = '" + username + "');";
  18. SqlCommand cmds = new SqlCommand(search, con);
  19. SqlDataReader sqldrs = cmds.ExecuteReader();
  20. if (sqldrs.Read())
  21. {
  22. String passed = (string)sqldrs["Password"];
  23. Label1.Text = "Username Already Taken";
  24. }
  25. else
  26. {
  27. try
  28. {
  29. // if the Username not found create the new user accound
  30. string sql = "INSERT INTO UserAccount (UserName, Password) VALUES ('" + username + "','" + passwords + "');";
  31. SqlCommand cmd = new SqlCommand(sql, con);
  32. cmd.ExecuteNonQuery();
  33. String Message = "saved Successfully";
  34. Label1.Text = Message.ToString();
  35. TextBox1.Text = "";
  36. TextBox2.Text = "";
  37. Response.Redirect("Default2.aspx");
  38. }
  39. catch (Exception ex)
  40. {
  41. Label1.Text = ex.ToString();
  42. }
  43. con.Close();
  44. }
  45. }
  47. else
  48. {
  49. String Message = "Username or Password is empty";
  50. Label1.Text = Message.ToString();
  51. }
  52. }
Step 4: Now encrypt the password by using the following method.
  1. public string encryption(String password)
  2. {
  3. MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
  4. byte[] encrypt;
  5. UTF8Encoding encode = new UTF8Encoding();
  6. //encrypt the given password string into Encrypted data
  7. encrypt = md5.ComputeHash(encode.GetBytes(password));
  8. StringBuilder encryptdata = new StringBuilder();
  9. //Create a new string by using the encrypted data
  10. for (int i = 0; i < encrypt.Length; i++)
  11. {
  12. encryptdata.Append(encrypt[i].ToString());
  13. }
  14. return encryptdata.ToString();
  15. }
After inserting the values inside the DB it will be like the following:

Values inside the DB

In the above Database table the user name is given as it is but the password is in encrypted String format

Step 5: Now login by using already created username and password.

login

Add the following code in the Login button.
  1. public void login_click(object sender, EventArgs e)
  2. {
  3. String username = TextBox1.Text.ToString();
  4. String password = TextBox2.Text;
  5. string con = ConfigurationManager.ConnectionStrings["DefaultConnection"].ToString();
  6. SqlConnection connection = new SqlConnection(con);
  7. connection.Open();
  8. ncrypt the given password
  9. string passwords = encryption(password);
  10. String query = "SELECT UserName, Password FROM UserAccount WHERE (UserName = '" + username + "') AND (Password = '"+passwords+"');";
  12. SqlCommand cmd = new SqlCommand(query, connection);
  13. SqlDataReader sqldr = cmd.ExecuteReader();
  14. if (sqldr.Read())
  15. {
  16. Response.Redirect("Default3.aspx");
  17. }
  18. else
  19. {
  20. Label1.Text = "User or password is in correct not found";
  22. }
  24. connection.Close();
  25. }
If the Password is correct it will take us to the Default3.aspx page, else it will show a message in the following label box:

show a message in the below label box

Decryption is not possible using MD5, so I have again converted the entered password and then checked the value with the database.