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Encrypt a file using AES encryption in C#

Posted on 2011-03-24
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Last Modified: 2012-05-11
There are several resources in the internet which give sample code for encrypting/ decrypting a PLAINTEXT using C#, which uses RijndaelManaged or AES encryption.

I am searching for some sample code which will help me encrypt/ decrypt a file and give me another file as output. The contents of the file to be encrypted can be a PLAINTEXT, BINARY DATA or ZIPPED DATA.

Can someone help please.
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Question by:tknayak123
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Accepted Solution

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Mike Tomlinson earned 500 total points
ID: 35209291
Here's an example where the key to encrypt/decrypt is entered by the user into textBox1:
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;

using System.Security.Cryptography;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        // Make a random string to base your Initialization Vector from:  *This is NOT the password or key!!!
        private const string _IV = "stick some string in here"; // thus must be the same to decrypt your encrypted file!

        private void btnEncrypt_Click(object sender, EventArgs e)
        {
            if (textBox1.Text.Trim().Length > 0)
            {
                using (OpenFileDialog ofd = new OpenFileDialog())
                {
                    ofd.Title = "Select Source File to Encrypt";
                    if (ofd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                    {
                        using (SaveFileDialog sfd = new SaveFileDialog())
                        {
                            sfd.Title = "Save Encrypted File To";
                            if (sfd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                            {
                                if (ofd.FileName != sfd.FileName)
                                {
                                    try
                                    {
                                        EncryptFile(ofd.FileName, sfd.FileName, textBox1.Text);
                                        MessageBox.Show("Done Encrypting File!");
                                    }
                                    catch (Exception ex)
                                    {
                                        MessageBox.Show(ex.ToString(), "Error Encrypting File", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                    }
                                }
                                else
                                {
                                    MessageBox.Show("Source and Target File cannot be the same!");
                                }
                            }
                        }
                    }
                }
            }
            else
            {
                MessageBox.Show("Please enter a Key!");
            }
        }

        private void btnDecrypt_Click(object sender, EventArgs e)
        {
            if (textBox1.Text.Trim().Length > 0)
            {
                using (OpenFileDialog ofd = new OpenFileDialog())
                {
                    ofd.Title = "Select Source File to Decrypt";
                    if (ofd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                    {
                        using (SaveFileDialog sfd = new SaveFileDialog())
                        {
                            sfd.Title = "Save Decrypted File To";
                            if (sfd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                            {
                                if (ofd.FileName != sfd.FileName)
                                {
                                    try
                                    {
                                        DecryptFile(ofd.FileName, sfd.FileName, textBox1.Text);
                                        MessageBox.Show("Done Decrypting File!");
                                    }
                                    catch (System.Security.Cryptography.CryptographicException cryptoEx)
                                    {
                                        MessageBox.Show(cryptoEx.ToString(), "Invalid Key");
                                    }
                                    catch (Exception ex)
                                    {
                                        MessageBox.Show(ex.ToString(), "Error Reading or Writing File", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                    }
                                }
                                else
                                {
                                    MessageBox.Show("Source and Target File cannot be the same!");
                                }
                            }
                        }
                    }
                }
            }
            else
            {
                MessageBox.Show("Please enter a Key!");
            }
        }

        private void EncryptFile(string sourceFile, string targetFile, string key)
        {
            AesManaged AES = new AesManaged();
            using (MD5CryptoServiceProvider MD5 = new MD5CryptoServiceProvider())
            {
                AES.KeySize = MD5.HashSize; // they are 128 bit compatible
                AES.BlockSize = MD5.HashSize; // they are 128 bit compatible
                AES.IV = MD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(_IV));
                AES.Key = MD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(key));
            }
            using (FileStream reader = new FileStream(sourceFile, FileMode.Open, FileAccess.Read))
            {
                using (FileStream writer = new FileStream(targetFile, FileMode.OpenOrCreate, FileAccess.Write))
                {
                    using (CryptoStream cs = new CryptoStream(writer, AES.CreateEncryptor(), CryptoStreamMode.Write))
                    {
                        int bufferSize = 4096;
                        byte[] buffer = new byte[bufferSize];
                        int bytesRead;
                        do
                        {
                            bytesRead = reader.Read(buffer, 0, bufferSize);
                            if (bytesRead != 0)
                            {
                                cs.Write(buffer, 0, bytesRead);
                            }
                        } 
                        while (bytesRead != 0);
                        cs.FlushFinalBlock(); 
                    }
                }
            }
        }

        private void DecryptFile(string sourceFile, string targetFile, string key)
        {
            AesManaged AES = new AesManaged();
            using (MD5CryptoServiceProvider MD5 = new MD5CryptoServiceProvider())
            {
                AES.KeySize = MD5.HashSize; // they are 128 bit compatible
                AES.BlockSize = MD5.HashSize; // they are 128 bit compatible
                AES.IV = MD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(_IV));
                AES.Key = MD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(key));
            }
            using (FileStream reader = new FileStream(sourceFile, FileMode.Open, FileAccess.Read))
            {
                using (FileStream writer = new FileStream(targetFile, FileMode.OpenOrCreate, FileAccess.Write))
                {
                    using (CryptoStream cs = new CryptoStream(reader, AES.CreateDecryptor(), CryptoStreamMode.Read))
                    {
                        int bufferSize = 4096;
                        byte[] buffer = new byte[bufferSize];
                        int bytesRead;
                        do
                        {
                            bytesRead = cs.Read(buffer, 0, bufferSize);
                            if (bytesRead != 0)
                            {
                                writer.Write(buffer, 0, bytesRead);
                            }
                        }
                        while (bytesRead != 0);
                    }
                }
            }
        }

    }

}

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Author Closing Comment

by:tknayak123
ID: 35210462
This is the exact code I was looking for.

Thanks
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