Lock

Fun@learn

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27 Nov 2007CPOL1 min read

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LOCK is used to lock and unlock the files using symmetric key cryptography

Introduction<o:p>

This article shows a classical approach to lock a file so that it doesn't reveal its original content in any software. For locking a file, a password is required. To view the file again in its original form, it has to be unlocked with the LOCK software with the same password which was used to lock the file.

Background <o:p>

The basic approach used is the symmetric key cryptography. The file is converted into blocks of 8 bytes and repeatedly XORed with the similar block of 8 bytes obtained by the password. Because the encryption used is symmetric key cryptography, the same process is used for unlocking\decryption.

Using the code<o:p>

Following is the code for main encryption routine. For more details, look at source code for the comments.

// Replicate the byte array in the key buffer to create
         // an encryption key whose size equals or exceeds the
         // size of the I/O buffer
         int count = (1024 + keyBytes.Length-1)/keyBytes.Length;
                 for( int i=0 ; i<count ; i++)
                 Array.Copy( keyBytes , 0 , keybuf , i*keyBytes.Length , keyBytes.Length);
        // Read the file in bufsize blocks, XOR-encrypt each block,
         // and write the encrypted block back to the file
         long lBytesRemaining = stream.Length;
         while (lBytesRemaining>0)
         {
                 long lPosition = stream.Position ;
                 int nBytesRequested = (int)System.Math.Min(bufSize , lBytesRemaining); 
                 int nBytesRead = reader.Read (buffer, 0, nBytesRequested)

                 for (int i=0; i<nBytesRead; i++)
                          buffer[i] ^= keybuf[i];Stream.Seek (lPosition, SeekOrigin.Begin);
                          writer.Write (buffer, 0, nBytesRead);
                          lBytesRemaining -= nBytesRead;
            }

Screenshots<o:p>

<o:p>

Points of Interest<o:p>

This is my second article at code project. For the first article which about Handling the Big Numbers, click here. I donot have much experience of article writing. I have just tried to minimize the shortcomings I have faced drafting the First article. Suggestion regarding the clarity, confusion, code, technical writing are welcomed. Comments are also welcomed. You can also mail me at funatlearn@ontheedge.co.in with subject Lock Code Project Article regarding the same.

History<o:p>

This is the first version of the program. I have some inputs for the next version of the code. I am expecting some more inputs from the readers of the code. After finalizing all the inputs I would write next version of the code.

If you feel any shortcoming of this code/article, please leave a message about the same, so that these pitfalls may not appear in the subsequent versions.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

Fun@learn

Software Developer (Senior)

India

Software Engineer based out in Noida.

Technology skillset – .NET, WPF, WCF, LINQ, XAML.

Started blogging on http://1wpf.wordpress.com/

Stackoverflow Profile -> http://stackoverflow.com/users/649524/tilak

Comments and Discussions

Yikes.

Rich Insley27-Nov-07 9:13

Rich Insley

27-Nov-07 9:13

I don't even know where to begin on this one. Just copy and paste this into Form1.cs and I'll let you figure it out.

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.IO;
using System.Text;

namespace Lock
{
    /// <summary>
    /// Summary description for Form1.
    /// </summary>

    public class Form1 : System.Windows.Forms.Form
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.Container components = null;

        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.Label label3;
        private System.Windows.Forms.TextBox ffield;
        private System.Windows.Forms.TextBox pass;
        private System.Windows.Forms.TextBox c_pass;
        private System.Windows.Forms.Button button2;
        private System.Windows.Forms.Button button3;
        private System.Windows.Forms.Button button4;
        private System.Windows.Forms.Button button5;

        public Form1()
        {
            //
            // Required for Windows Form Designer support
            //
            InitializeComponent();

            //
            // TODO: Add any constructor code after InitializeComponent call
            //
        }

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (components != null)
                {
                    components.Dispose();
                }
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code
        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.label1 = new System.Windows.Forms.Label();
            this.ffield = new System.Windows.Forms.TextBox();
            this.button1 = new System.Windows.Forms.Button();
            this.button2 = new System.Windows.Forms.Button();
            this.label2 = new System.Windows.Forms.Label();
            this.pass = new System.Windows.Forms.TextBox();
            this.button3 = new System.Windows.Forms.Button();
            this.label3 = new System.Windows.Forms.Label();
            this.c_pass = new System.Windows.Forms.TextBox();
            this.button4 = new System.Windows.Forms.Button();
            this.button5 = new System.Windows.Forms.Button();
            this.SuspendLayout();
            // 
            // label1
            // 
            this.label1.Location = new System.Drawing.Point(24, 24);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(112, 16);
            this.label1.TabIndex = 0;
            this.label1.Text = "Enter File Name";
            // 
            // ffield
            // 
            this.ffield.BackColor = System.Drawing.SystemColors.Info;
            this.ffield.Location = new System.Drawing.Point(152, 24);
            this.ffield.Name = "ffield";
            this.ffield.Size = new System.Drawing.Size(152, 20);
            this.ffield.TabIndex = 1;
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(328, 16);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(112, 24);
            this.button1.TabIndex = 2;
            this.button1.Text = "Browse";
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // button2
            // 
            this.button2.Location = new System.Drawing.Point(24, 136);
            this.button2.Name = "button2";
            this.button2.Size = new System.Drawing.Size(120, 24);
            this.button2.TabIndex = 5;
            this.button2.Text = "Encrypt/Decrypt";
            this.button2.Click += new System.EventHandler(this.button2_Click);
            // 
            // label2
            // 
            this.label2.Location = new System.Drawing.Point(24, 64);
            this.label2.Name = "label2";
            this.label2.Size = new System.Drawing.Size(112, 24);
            this.label2.TabIndex = 4;
            this.label2.Text = "Enter Password";
            // 
            // pass
            // 
            this.pass.BackColor = System.Drawing.SystemColors.Info;
            this.pass.Location = new System.Drawing.Point(152, 56);
            this.pass.Name = "pass";
            this.pass.PasswordChar = '*';
            this.pass.Size = new System.Drawing.Size(152, 20);
            this.pass.TabIndex = 3;
            // 
            // button3
            // 
            this.button3.DialogResult = System.Windows.Forms.DialogResult.Cancel;
            this.button3.Location = new System.Drawing.Point(304, 136);
            this.button3.Name = "button3";
            this.button3.Size = new System.Drawing.Size(104, 24);
            this.button3.TabIndex = 6;
            this.button3.Text = "Exit";
            this.button3.Click += new System.EventHandler(this.button3_Click);
            // 
            // label3
            // 
            this.label3.Location = new System.Drawing.Point(24, 96);
            this.label3.Name = "label3";
            this.label3.Size = new System.Drawing.Size(112, 24);
            this.label3.TabIndex = 7;
            this.label3.Text = "Confirm Password";
            // 
            // c_pass
            // 
            this.c_pass.BackColor = System.Drawing.SystemColors.Info;
            this.c_pass.Location = new System.Drawing.Point(152, 88);
            this.c_pass.Name = "c_pass";
            this.c_pass.PasswordChar = '+';
            this.c_pass.Size = new System.Drawing.Size(152, 20);
            this.c_pass.TabIndex = 4;
            // 
            // button4
            // 
            this.button4.Location = new System.Drawing.Point(328, 56);
            this.button4.Name = "button4";
            this.button4.Size = new System.Drawing.Size(112, 24);
            this.button4.TabIndex = 8;
            this.button4.Text = "Clear";
            this.button4.Click += new System.EventHandler(this.button4_Click);
            // 
            // button5
            // 
            this.button5.Location = new System.Drawing.Point(160, 136);
            this.button5.Name = "button5";
            this.button5.Size = new System.Drawing.Size(120, 24);
            this.button5.TabIndex = 9;
            this.button5.Text = "About";
            this.button5.Click += new System.EventHandler(this.button5_Click);
            // 
            // Form1
            // 
            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
            this.BackColor = System.Drawing.Color.FromArgb(((int)(((byte)(255)))), ((int)(((byte)(192)))), ((int)(((byte)(192)))));
            this.ClientSize = new System.Drawing.Size(456, 190);
            this.Controls.Add(this.button5);
            this.Controls.Add(this.button4);
            this.Controls.Add(this.c_pass);
            this.Controls.Add(this.label3);
            this.Controls.Add(this.button3);
            this.Controls.Add(this.pass);
            this.Controls.Add(this.label2);
            this.Controls.Add(this.button2);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.ffield);
            this.Controls.Add(this.label1);
            this.Name = "Form1";
            this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
            this.Text = "Lock File";
            this.ResumeLayout(false);
            this.PerformLayout();

        }
        #endregion

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.Run(new Form1());
        }

        private void button2_Click(object sender, System.EventArgs e)
        {
            if (ffield.Text == "")
            {
                MessageBox.Show("File Name is empty");
                return;
            }

            if (pass.Text == "")
            {
                MessageBox.Show("Password is empty");
                return;
            }

            if ((pass.Text != c_pass.Text))
            {
                MessageBox.Show("Passwords do not match");
                return;
            }

            if (!File.Exists(ffield.Text))
            {
                MessageBox.Show("File " + ffield.Text + " does not exist");
                return;
            }

            try
            {
                byte[] keyBytes = ASCIIEncoding.ASCII.GetBytes(pass.Text);
                byte[] fileBuffer = File.ReadAllBytes(ffield.Text);
                for (int i = 0; i < fileBuffer.Length - 1; i++)
                {
                    fileBuffer[i] ^= keyBytes[i % keyBytes.Length];
                }
                File.WriteAllBytes(ffield.Text, fileBuffer);
            }
            catch (IOException ex)
            {
                MessageBox.Show(ex.Message, "IO Error");
            }
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            OpenFileDialog ofd = new OpenFileDialog();
            if (ofd.ShowDialog() == DialogResult.OK)
            {
                Text = "Lock File - " + Path.GetFileName(ofd.FileName);
                ffield.Text = ofd.FileName;
            }
            ofd.Dispose();
        }

        private void button3_Click(object sender, System.EventArgs e)
        {
            Application.Exit();
        }

        private void button4_Click(object sender, System.EventArgs e)
        {
            ffield.Text = "";
            pass.Text = "";
            c_pass.Text = "";
        }

        private void button5_Click(object sender, EventArgs e)
        {
            About abt = new About(this);
            abt.ShowDialog();
            abt.Dispose();
        }
    }
}

Re: Yikes.

Fun@learn27-Nov-07 17:25

Fun@learn

27-Nov-07 17:25

you have missed some part of the code while copying and pasting, which contains the real logic

I am posting the part you have missed. Please check the code below in your file

private void button2_Click(object sender, System.EventArgs e)
{
if(ffield.Text=="" )
{
MessageBox.Show("File Name is empty");
return;
}
if(pass.Text=="" )
{
MessageBox.Show("Password Can't be Null");
return;
}

if((pass.Text!=c_pass.Text)||pass.Text=="")
{
MessageBox.Show("password doesnot Match");
return;
}

const int bufSize =1048576 ;
String fileName = file;
String key = password;
FileStream stream = null;
try
{
try
{
// open file for reading & writing
stream = File.Open(fileName , FileMode.Open ,FileAccess.ReadWrite ) ;
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
throw;
}
// wrap a reader & writer around the file
BinaryReader reader = new BinaryReader(stream);
BinaryWriter writer = new BinaryWriter(stream);

// convert the key to byte array
ASCIIEncoding enc = new ASCIIEncoding ();
byte[] keyBytes = enc.GetBytes (key);

// Allocate an I/O buffer & key buffer
byte[] buffer = new byte[bufSize];
byte[] keybuf = new byte[bufSize + keyBytes.Length - 1];

// Replicate the byte array in the key buffer to create
// an encryption key whose size equals or exceeds the
// size of the I/O buffer
int count = (1024 + keyBytes.Length-1)/keyBytes.Length;
for( int i=0 ; i<count ;="" i++)
="" array.copy(="" keybytes="" ,="" 0="" keybuf="" i*keybytes.length="" keybytes.length);
=""
="" read="" the="" file="" in="" bufsize="" blocks,="" xor-encrypt="" each="" block,
="" and="" write="" encrypted="" block="" back="" to="" file
="" long="" lbytesremaining="stream.Length;
" while="" (lbytesremaining="">0)
{
long lPosition = stream.Position ;
int nBytesRequested = (int)System.Math.Min(bufSize , lBytesRemaining) ;
int nBytesRead = reader.Read (buffer, 0, nBytesRequested);

for (int i=0; i<nbytesread; i++)
="" buffer[i]="" ^="keybuf[i];"

="" stream.seek="" (lposition,="" seekorigin.begin);
="" writer.write="" (buffer,="" 0,="" nbytesread);
="" lbytesremaining="" -="nBytesRead;
" }<="" i=""> MessageBox.Show(fileName + " is crypted");
}
catch (Exception x)
{
Console.WriteLine(x.Message) ;
}
finally
{
if (stream != null)
stream.Close ();
}
}

Fun@learn
--------------------------------
destiny is the mirror of the past

Re: Yikes.

Rich Insley27-Nov-07 17:53

Rich Insley

27-Nov-07 17:53

Fun@learn wrote:
you have missed some part of the code while copying and pasting, which contains the real logic

You are a bit obtuse. I didn't miss that part of the code, I rewrote it for you. Probably the reason you missed it is that it's much smaller than what you wrote (even though it does the exact same thing):

byte[] keyBytes = ASCIIEncoding.ASCII.GetBytes(pass.Text);
byte[] fileBuffer = File.ReadAllBytes(ffield.Text);
for (int i = 0; i < fileBuffer.Length - 1; i++)
{
    fileBuffer[i] ^= keyBytes[i % keyBytes.Length];
}
File.WriteAllBytes(ffield.Text, fileBuffer);

But while I'm here let's go over some more things that are .... well, that are just plain wrong about the article. The encryption algorithm (and I'm really stretching the definition of algorithm) is terrible. The only thing weaker than XORing a stream with a repeating password is ROT13. The other thing is, run your program and encrypt a 3 gig file. Your method creates a buffer the size of the file just to hold a repeating patern of the password, my method just loads the whole file into memory. Either way, it's not a very good way to go about it. Think smaller chunks. Oh yeah, learn how to use the modulo operation if you're going to be working in cryptology. Cryptologists and CypherPunks are notoriously unforgiving and rude to novices.

Re: Yikes.

Ri Qen-Sin27-Nov-07 18:29

Ri Qen-Sin

27-Nov-07 18:29

You know, you could've modified the algorithm to work with 32-bit or 64-bit integers and then work with the remaining bytes.

ROFLOLMFAO

Re: Yikes.

Fun@learn27-Nov-07 18:49

Fun@learn

27-Nov-07 18:49

@Yikes
either way it is the same.This is not something which has not appeared in my research before writing the code,In fact I started with this code, did some investigation and finally arrived to the current code which is again open to investigation.
If you would see, my code and the code snippet you have presented appears to be same wheteher you take is performance wise or method wise . Rather than improvement, it is just a restructring of the code.
Regarding the buffer size, if a file buffer of 3 gig can be made, than another buffer for the key can be made.
though for encrypting such a long file, some approach regarding the small chunks is appeared.
Anyway, the improvements shown would appear in the updates of the code

@Qen-Sin
Integers are never a part of the algorithm apart from the arraysize or counters.
So I could not get your point.
As far as remaining bytes are concerned, i am looking for such a approach which considers the smaller chunk one at a time rather than all the file at a time.
Here the main issue is file handling rather than the encryption algorithm.
Though algorithm would also reflect the improvements.

Fun@learn
--------------------------------
destiny is the mirror of the past

Re: Yikes.

Rich Insley28-Nov-07 6:08

Rich Insley

28-Nov-07 6:08

Fun@learn wrote:
Rather than improvement, it is just a restructring of the code.

If you don't think that's an improvement, you should do more research. Much more research.

Fun@learn wrote:
Regarding the buffer size, if a file buffer of 3 gig can be made, than another buffer for the key can be made.

How much frigging system memory do you have that creating a 3 gig buffer in system memory is such a trivial thing?

Fun@learn wrote:
Anyway, the improvements shown would appear in the updates of the code

I'm pretty sure this article is on a rocket train to Purgatory. You might want to hurry or just cut your losses and do some more research.

Re: Yikes.

Ri Qen-Sin28-Nov-07 8:22

Ri Qen-Sin

28-Nov-07 8:22

Fun@learn wrote:
@Qen-Sin
Integers are never a part of the algorithm apart from the arraysize or counters.
So I could not get your point.
As far as remaining bytes are concerned, i am looking for such a approach which considers the smaller chunk one at a time rather than all the file at a time.
Here the main issue is file handling rather than the encryption algorithm.
Though algorithm would also reflect the improvements.

You can XOR them faster if you XOR them 32 or 64 bits at a time. The idea is to do as much as you can in one operation.

That just scratches the surface of it.

Let's see what other "gems" I can find in your code.

When testing for empty strings, test for both string == null and string == String.Empty and not string == "". In fact, you should use the Path class instead if you're checking for valid paths, and extra checks to make sure you can read and/or write to them.
You should probably read about best practices for exception handling.
I believe Console.Write*(…) should be replaced with MessageBox.Show(…)?
You might want to write to a different stream. If the program crashes, then the user won't end up with a corrupt original.

ROFLOLMFAO

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