Encrypt/decrypt files

[Getox]

im trying to make a program that will encrypt a file
and then you can decrypt it, how would this be done?

 

[sizer]

i) you need to decide what crypto system do you need ( RSA,DES , TripleDes ...) , some of this are asymmetric crypto systems and other are symetric.

ii) asymmetric crypto systems have to different keys ( public and private), public key will be used for crypt some txt ( document , picture ....), and private key is used for decrypt, while symetric crypto systems have one key for both directions

iii) framework includes most of these systems ( System.Security.Cryptography ), so you dont need to worry about very large prime numbers which is base of every crypo system , implementation of oprerations for these numbers ( i hated that part ) , and other stuff like that!

iv) RSA example

using System;
using System.Security.Cryptography;
using System.Text;

class RSACSPSample
{

    static void Main()
    {
        try
        {
            //Create a UnicodeEncoder to convert between byte array and string.
            UnicodeEncoding ByteConverter = new UnicodeEncoding();

            //Create byte arrays to hold original, encrypted, and decrypted data.
            byte[] dataToEncrypt = ByteConverter.GetBytes("Data to Encrypt");
            byte[] encryptedData;
            byte[] decryptedData;
            
            //Create a new instance of RSACryptoServiceProvider to generate
            //public and private key data.
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

            //Pass the data to ENCRYPT, the public key information 
            //(using RSACryptoServiceProvider.ExportParameters(false),
            //and a boolean flag specifying no OAEP padding.
            encryptedData = RSAEncrypt(dataToEncrypt,RSA.ExportParameters(false), false);

            //Pass the data to DECRYPT, the private key information 
            //(using RSACryptoServiceProvider.ExportParameters(true),
            //and a boolean flag specifying no OAEP padding.
            decryptedData = RSADecrypt(encryptedData,RSA.ExportParameters(true), false);

            //Display the decrypted plaintext to the console. 
            Console.WriteLine("Decrypted plaintext: {0}", ByteConverter.GetString(decryptedData));
        }
        catch(ArgumentNullException)
        {
            //Catch this exception in case the encryption did
            //not succeed.
            Console.WriteLine("Encryption failed.");

        }
    }

    static public byte[] RSAEncrypt(byte[] DataToEncrypt, RSAParameters RSAKeyInfo, bool DoOAEPPadding)
    {
        try
        {    
            //Create a new instance of RSACryptoServiceProvider.
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

            //Import the RSA Key information. This only needs
            //toinclude the public key information.
            RSA.ImportParameters(RSAKeyInfo);

            //Encrypt the passed byte array and specify OAEP padding.  
            //OAEP padding is only available on Microsoft Windows XP or
            //later.  
            return RSA.Encrypt(DataToEncrypt, DoOAEPPadding);
        }
        //Catch and display a CryptographicException  
        //to the console.
        catch(CryptographicException e)
        {
            Console.WriteLine(e.Message);

            return null;
        }

    }

    static public byte[] RSADecrypt(byte[] DataToDecrypt, RSAParameters RSAKeyInfo,bool DoOAEPPadding)
    {
        try
        {
            //Create a new instance of RSACryptoServiceProvider.
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

            //Import the RSA Key information. This needs
            //to include the private key information.
            RSA.ImportParameters(RSAKeyInfo);

            //Decrypt the passed byte array and specify OAEP padding.  
            //OAEP padding is only available on Microsoft Windows XP or
            //later.  
            return RSA.Decrypt(DataToDecrypt, DoOAEPPadding);
        }
        //Catch and display a CryptographicException  
        //to the console.
        catch(CryptographicException e)
        {
            Console.WriteLine(e.ToString());

            return null;
        }

    }
}

this example outputs result to Conslole

see link for more info
http://msdn.microsoft.com/library/d...ographyrsacryptoserviceproviderclasstopic.asp

 

[Getox]

all i want to do is just use a windows form to open a file(with the OpenFileDialog) and encrypt that file
and then use the OpenFileDialog to select a encrypted file and decrypt it and display the stuff in a text box.

 

[PlausiblyDamp]

And above shows you how to encrypt and decrypt a file...