Signing with DSA Algorithm

[Abo Homam]

Hello everybody
I am trying to build a small program that can discover whether file/files has been accessed or modified using DSA Signing algorithm.

I will give you this small example code to describe the issue. suppose that we have a text . We have in our program 2 buttons. When we click the first button we create a digital signature on the text , we also export the parameters and save them. On the second button click we recreate the sign on the same text using the parameters that we exported earlier and compare the new signature with the previous.

the problem here is that the program (always) gives me a result that the signatures are not the same !!!!

I used the debugger to know where the problem and found that all variables values are identical between the 2 button_click events, and the difference occures in the signing process. Would you please tell me where the problem is? Here is the code

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.IO;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Security.Cryptography;



namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        string filename = @"C:\Temporary\Temp.txt";
        DSAParameters parameters;
        byte[] data_to_sign, signature;


    public Form1()
    {
        InitializeComponent();
    }

    

    private void Sign_button_Click(object sender, EventArgs e)
    {
;
        UnicodeEncoding byteEncoder = new UnicodeEncoding();
        data_to_sign = byteEncoder.GetBytes(filename);
        DSACryptoServiceProvider dsaprovider = new DSACryptoServiceProvider();
        parameters = dsaprovider.ExportParameters(true);
        signature = dsaprovider.SignData(data_to_sign);
        label1.Text = " Signature generated";
    }

    private void Verify_button_Click(object sender, EventArgs e)
    {

        UnicodeEncoding byteEncoder = new UnicodeEncoding();
        data_to_sign = byteEncoder.GetBytes(filename);
        DSACryptoServiceProvider dsaprovider2 = new DSACryptoServiceProvider();
        dsaprovider2.ImportParameters(parameters);
        byte [] signature2 = dsaprovider2.SignData(data_to_sign);
        if (signature == signature2)
            label1.Text = "The signatres are same";
        else
            label1.Text = "Opp... The signatures are different";

    }

}

[dglienna]

signatures are time-based

[Abo Homam]

Thank you "dglienna" for help
I finally knew why that happens
DSA algorithm depends on a random number which is generated first before creating keys.
This random number - of course- will be different from one DSA object to other and that's cause the difference in signatures.