C USES pseudorandom Numbers to encrypt user passwords

The example described in this paper USES pseudorandom Numbers for user password encryption. This code is the core part of the main code, which needs to be implemented with other programs. Interested readers can further improve it by themselves.

using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Linq; 
using System.Text; 
using System.Windows.Forms; 
namespace PRanDataEncrypt 
{ 
public partial class Form1 : Form 
{ 
public Form1() 
{ 
InitializeComponent(); 
} 
private void button1_Click(object sender, EventArgs e) 
{ 
if (textBox3.Text != "") 
{ 
if (DecryptPwd(textBox3.Text) == textBox2.Text) 
MessageBox.Show(" User logged in successfully! ", " prompt ", MessageBoxButtons.OK, MessageBoxIcon.Information); 
else 
MessageBox.Show(" User password error! ", " error ", MessageBoxButtons.OK, MessageBoxIcon.Error); 
} 
} 

private void button2_Click(object sender, EventArgs e) 
{ 
textBox1.Text = textBox2.Text = textBox3.Text = string.Empty; 
textBox2.Focus(); 
} 

private void textBox2_TextChanged(object sender, EventArgs e) 
{ 
textBox3.Text = EncryptPwd(textBox2.Text); 
} 

// Defines the pseudorandom number used to encrypt the user password  
private string randStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz"; 
#region  Use pseudorandom Numbers to encrypt the user login password  
/// <summary> 
///  Use pseudorandom Numbers to encrypt the user login password  
/// </summary> 
/// <param name="str"> User login password </param> 
/// <returns> Encrypted user login password </returns> 
private string EncryptPwd(string str) 
{ 
byte[] btData = Encoding.Default.GetBytes(str); 
int j, k, m; 
int len = randStr.Length; 
StringBuilder sb = new StringBuilder(); 
Random rand = new Random(); 
for (int i = 0; i < btData.Length; i++) 
{ 
j = (byte)rand.Next(6); 
btData[i] = (byte)((int)btData[i] ^ j); 
k = (int)btData[i] % len; 
m = (int)btData[i] / len; 
m = m * 8 + j; 
sb.Append(randStr.Substring(k, 1) + randStr.Substring(m, 1)); 
} 
return sb.ToString(); 
} 
#endregion 
#region  Decrypt the user login password  
/// <summary> 
///  Decrypt the user login password  
/// </summary> 
/// <param name="str"> Encrypted user login password </param> 
/// <returns> Decrypted user login password </returns> 
private string DecryptPwd(string str) 
{ 
try 
{ 
int j, k, m, n = 0; 
int len = randStr.Length; 
byte[] btData = new byte[str.Length / 2]; 
for (int i = 0; i < str.Length; i += 2) 
{ 
k = randStr.IndexOf(str[i]); 
m = randStr.IndexOf(str[i + 1]); 
j = m / 8; 
m = m - j * 8; 
btData[n] = (byte)(j * len + k); 
btData[n] = (byte)((int)btData[n] ^ m); 
n++; 
} 
return Encoding.Default.GetString(btData); 
} 
catch { return ""; } 
} 
#endregion 
} 
}