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Encrypt and Decrypt Query String in asp.net

Introduction: In this article I have explain how we can Encrypt and Decrypt Query String in asp.net.

Description:

Add a weform to project. Drag and drop the controls from Toolbox and desgin the .aspx page as given below:
<table align="center"><tr><td>Employee Name:</td><td><asp:TextBox ID="txtname" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="rfvname" runat="server"
            ControlToValidate="txtname" ErrorMessage="Enter Employee Name"
            ForeColor="#FF3300"></asp:RequiredFieldValidator>
        </td></tr>
    <tr><td>&nbsp;</td><td> <asp:Button ID="btnSubmit" runat="server" Text="Submit"
            onclick="btnSubmit_Click" /></td></tr>
    </table>    

On Button click write the below given code (.aspx.cs)
using System.Security.Cryptography;
using System.IO;
using System.Text;

protected void btnSubmit_Click(object sender, EventArgs e)
    {
        string query = EncryptQueryString(txtname.Text);
        Response.Redirect("Decrypt_QueryString.aspx?empname=" + query);
    }

    public string EncryptQueryString(string inputString)
    {
        MemoryStream memStream = null;
        try
        {
            byte[] key = { };
            byte[] IV = { 18, 52, 86, 120, 144, 171, 205, 239 };
            string encryptKey = "aXb2uy4z";
            key = Encoding.UTF8.GetBytes(encryptKey);
            byte[] byteInput = Encoding.UTF8.GetBytes(inputString);
            DESCryptoServiceProvider provider = new DESCryptoServiceProvider();
            memStream = new MemoryStream();
            ICryptoTransform transform = provider.CreateEncryptor(key, IV);
            CryptoStream cryptoStream = new CryptoStream(memStream, transform, CryptoStreamMode.Write);
            cryptoStream.Write(byteInput, 0, byteInput.Length);
            cryptoStream.FlushFinalBlock();

        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
        return Convert.ToBase64String(memStream.ToArray());
    }

In VB (.aspx.vb)

Imports System.IO
Imports System.Text
Imports System.Security.Cryptography

Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
        Dim query As String = EncryptQueryString(txtname.Text)
        Response.Redirect("Decrypt_QueryString.aspx?empname=" & query)
    End Sub
    Public Function EncryptQueryString(ByVal inputString As String) As String
        Dim memStream As MemoryStream = Nothing
        Try
            Dim key As Byte() = {}
            Dim IV As Byte() = {18, 52, 86, 120, 144, 171, 205, 239}
            Dim encryptKey As String = "aXb2uy4z"
            key = Encoding.UTF8.GetBytes(encryptKey)
            Dim byteInput As Byte() = Encoding.UTF8.GetBytes(inputString)
            Dim provider As New DESCryptoServiceProvider()
            memStream = New MemoryStream()
            Dim transform As ICryptoTransform = provider.CreateEncryptor(key, IV)
            Dim cryptoStream As New CryptoStream(memStream, transform, CryptoStreamMode.Write)
            cryptoStream.Write(byteInput, 0, byteInput.Length)

            cryptoStream.FlushFinalBlock()
        Catch ex As Exception
            Response.Write(ex.Message)
        End Try
        Return Convert.ToBase64String(memStream.ToArray())
    End Function

Add a new webform to project. Here I keep its name Decrypt_QueryString.aspx, drag and drop the control from Toolbox and desgin the .aspx page as shown:
<table align="center"><tr><td>
       <asp:Label ID="lbl" runat="server" Text="Encrypted Employee Name:"
           Font-Bold="True"></asp:Label></td><td>
       <asp:Label ID="lblencry" runat="server" ForeColor="#FF3300" Font-Bold="True"
               Font-Italic="True"></asp:Label></td></tr>
   <tr><td>&nbsp;</td><td><asp:Button ID="btnSubmit" runat="server" Text="Decrypt Querystring"
            onclick="btnSubmit_Click" /></td></tr>
            <tr><td><b>
                <asp:Label ID="Label1" runat="server" Text="Decrypted Employee Name:"></asp:Label></b></td><td>
                <asp:Label ID="lbldecry" runat="server" ForeColor="#009933" Font-Bold="True"
                    Font-Italic="True"></asp:Label></td></tr>
   </table>

Write the given code on .aspx.cs page:
using System.Security.Cryptography;
using System.IO;
using System.Text;

protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.QueryString["empname"] != null)
        {
            lblencry.Text = (Request.QueryString["empname"]);
        }
        else
        {
            btnSubmit.Visible = false;
            lbldecry.Visible = false;
            Label1.Visible = false;
            lbl.Visible = false;
            lblencry.Text = "No Records";
        }
    }
    public string DecryptQueryString(string inputString)
    {
        MemoryStream memStream = null;
        try
        {
            byte[] key = { };
            byte[] IV = { 18, 52, 86, 120, 144, 171, 205, 239 };
            string encryptKey = "aXb2uy4z";
            key = Encoding.UTF8.GetBytes(encryptKey);
            byte[] byteInput = new byte[inputString.Length];
            byteInput = Convert.FromBase64String(inputString);
            DESCryptoServiceProvider provider = new DESCryptoServiceProvider();
            memStream = new MemoryStream();
            ICryptoTransform transform = provider.CreateDecryptor(key, IV);
            CryptoStream cryptoStream = new CryptoStream(memStream, transform, CryptoStreamMode.Write);
            cryptoStream.Write(byteInput, 0, byteInput.Length);
            cryptoStream.FlushFinalBlock();
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }

        Encoding encoding1 = Encoding.UTF8;
        return encoding1.GetString(memStream.ToArray());
    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        string name= DecryptQueryString(Request.QueryString["empname"]);
       lbldecry.Text=(name);
       lblencry.Visible = false;
       lbl.Visible = false;
    }

In VB (.aspx.vb)
Imports System.IO
Imports System.Text
Imports System.Security.Cryptography

  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Request.QueryString("empname") IsNot Nothing Then
            lblencry.Text = (Request.QueryString("empname"))
        Else
            btnSubmit.Visible = False
            lbldecry.Visible = False
            Label1.Visible = False
            lbl.Visible = False
            lblencry.Text = "No Records"
        End If
    End Sub
    Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
        Dim nameAs String = DecryptQueryString(Request.QueryString("empname"))
        lbldecry.Text = (name)
        lblencry.Visible = False
        lbl.Visible = False
    End Sub
  
    Public Function DecryptQueryString(ByVal inputString As String) As String
        Dim memStream As MemoryStream = Nothing
        Try
            Dim key As Byte() = {}
            Dim IV As Byte() = {18, 52, 86, 120, 144, 171, 205, 239}
            Dim encryptKey As String = "aXb2uy4z"
            key = Encoding.UTF8.GetBytes(encryptKey)
            Dim byteInput As Byte() = New Byte(inputString.Length - 1) {}
            byteInput = Convert.FromBase64String(inputString)
            Dim provider As New DESCryptoServiceProvider()
            memStream = New MemoryStream()
            Dim transform As ICryptoTransform = provider.CreateDecryptor(key, IV)
            Dim cryptoStream As New CryptoStream(memStream, transform, CryptoStreamMode.Write)
            cryptoStream.Write(byteInput, 0, byteInput.Length)
            cryptoStream.FlushFinalBlock()
        Catch ex As Exception
            Response.Write(ex.Message)
        End Try

        Dim encoding1 As Encoding = Encoding.UTF8
        Return encoding1.GetString(memStream.ToArray())
    End Function


Now run the project and check the result. If it helps you than submit your comment.

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There is an error in this code in Decrypt_QueryString.aspx page.
In method public string DecryptQueryString(string inputString){}
lines are:
Encoding encoding1 = Encoding.UTF8;
return encoding1.GetString(memStream.ToArray());
while returning value it shows up an error.
Required change is:
Encoding encoding1 = Encoding.UTF8;
string decrypt =" ";
decrypt =encoding1.GetString(memStream.ToArray());
return decrypt;

This code was tested. There is no such problem in code. Stay in touch and keep reading.

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