///<summary>
/// <para>
/// This method decrypts the given input file in either of the 2 algorithms 'DES' or 'RC2'.
/// Then it writes out the decrypted file
/// </para>
/// <para>
/// This method first reads the input file to check to see if its encrypted by which
/// algorithm. then it automatically decrypts the file.
/// </para>
/// <para>
/// It reads the first 8 bytes of the encrypted file to find the custom tag that we place
/// while encrypting.
/// If it finds "[saudes]" it uses the 'DES' algorithm to decrypt
/// If it finds "[saurc2]" it uses the 'RC2' algorithm to decrypt
/// </para>
///</summary>
private void DecryptData()
{
//try-catch block
try{
statusBar1.Text = "Decrypting....";
//open file streams to the input and outfiles
FileStream fin = new FileStream(opent.Text, FileMode.Open, FileAccess.Read);
FileStream fout = new FileStream(savet.Text, FileMode.OpenOrCreate, FileAccess.Write);
fout.SetLength(0);
//a variable to check the validity of the input file
bool filecheck = false;
//make a byte array of the size 64 bits
//this is called the 'Buffer Size' of the algorithm
//i.e. while encrypting blocks of the size 64bits are processed at a single time
//later other blocks are of the same size.
//we use 64bits because both 'DES' and 'RC2' both algorithms have 64 bit 'Buffer Size'
byte[] bin = new byte[4096];
long totlen = fin.Length;
long rdlen = 8;
int len;
// declare a object of type 'SymmetricAlgorithm'
SymmetricAlgorithm des;
//set a tempory variable to length '8' (we use '8' since the size of the tag put in the file is 8 chars long)
byte[] tag = new byte[8];
//read the first 8 bytes from the input file to check which algrothim is used to encrypt the file
fin.Read(tag, 0, tag.Length);
if ((tag[0] == (byte)'[') && (tag[1] == (byte)'S') && (tag[2] == (byte)'a') && (tag[3] == (byte)'u') && (tag[4] == (byte)'d') && (tag[5] == (byte)'e') && (tag[6] == (byte)'s') && (tag[7] == (byte)']'))
{
//If this is true then the 'DES' algorithm has been used to encrypt the file
//so set the variable 'des' to new 'DES_CSP'
des = new DES_CSP();
//set the variable to true since the file is encrypted
filecheck = true;
//generate the Key and Vector from the given password
//we send 'true' here since the algorithm used is 'DES'
GenerateKee(true);
}
else if ((tag[0] == (byte)'[') && (tag[1] == (byte)'S') && (tag[2] == (byte)'a') && (tag[3] == (byte)'u') && (tag[4] == (byte)'r') && (tag[5] == (byte)'c') && (tag[6] == (byte)'2') && (tag[7] == (byte)']'))
{
//if this is true then the 'RC2' algorithm has been used to encrypt the file
//so we set the variable 'des' to new 'RC2_CSP'
des = new RC2_CSP();
//set the keysize of the algorithm
des.KeySize = 40;
//set thevariable to true since it is encrypted
filecheck = true;
//generate the Key and Vector from the password given by the user
//we pass false here since we are using 'RC2' algorithm
GenerateKee(false);
}
else
{
MessageBox.Show("File Error !! File does not seem to be encrypted by SymEncryptor !!");
//set the des to null so no encryption occurs
des = null;
statusBar1.Text = "Error ";
}
//if the file is encrypted then decrypt it
if (filecheck)
{
//create a object of the inner class 'StoreCryptoStream'
//we pass it the FileStream
StoreCryptoStream scs = new StoreCryptoStream(fout);
//make a object of this stream passing the Key and Vector
//we use this strem since it helps us decrypt data from a
//encrypted file
SymmetricStreamDecryptor ssd = des.CreateDecryptor(symKey, symIV);
//set up the streams
ssd.SetSink(scs);
scs.SetSource(ssd);
//read the full encrypted file and decrypt
while (rdlen < totlen)
{
//set the length of the number of bytes read
len = fin.Read(bin, 0, 4096);
//write the decrypted data
ssd.Write(bin, 0, len);
//increase the total read bytes variable
rdlen = rdlen + len;
}
//free up the resources
ssd.CloseStream();
}
fin.Close();
fout.Close();
statusBar1.Text = "Decryption Compelete";
}
catch (Exception e)
{
MessageBox.Show("An exception occured while decrypting :" + e.ToString());
statusBar1.Text = "Error";
}
}
///<summary>
/// <para>
/// This method encrypts the given input file in either of the 2 algorithms 'DES' or 'RC2'.
/// Then it writes out the encrypted file
/// </para>
/// <para>
/// This method first reads the input file to check to see if its already encrypted by this
/// same program. If its already encrypted it gives a error.
/// </para>
/// <para>
/// According to the algorithm specified it then encrypts the file.
/// Also in the first 8 bytes of the new Encrypted it writes out "[saudes]" or "[saurc2]"
/// This is done so the while decrypting the program can know which algorithm was used to
/// encrypt the file. Also it used to check if the file has already encrypted
/// </para>
///</summary>
private void EncryptData()
{
//try-catch block
try{
bool algo; //a boolean variable to check which algorithm to use in encrypting
//open the 'FileStream' on the file to be encrypted
FileStream fin = new FileStream(opent.Text, FileMode.Open, FileAccess.Read);
//Make a file to save the encrypted data to and open a 'FileStream' on it
FileStream fout = new FileStream(savet.Text, FileMode.OpenOrCreate, FileAccess.Write);
//set the position of the 'cursor' to the start of the file
fout.SetLength(0);
//make a byte array of the size 64 bits
//this is called the 'Buffer Size' of the algorithm
//i.e. while encrypting blocks of the size 64bits are processed at a single time
//later other blocks are of the same size.
//we use 64bits because both 'DES' and 'RC2' both algorithms have 64 bit 'Buffer Size'
byte[] bin = new byte[4096];
//set the total length of the file to me encrypted to a variable
long totlen = fin.Length;
long rdlen = 0;
int len;
//the code below is used to check if the file has already been encrypted by this program
//make a byte array of length '4'
byte[] tag = new byte[4];
//read the first 4 bytes from the file to be encrypted
fin.Read(tag, 0, tag.Length);
//if it contains the chars "[sau" then it has been already encrypted by this program
if ((tag[0] == (byte)'[') && (tag[1] == (byte)'S') && (tag[2] == (byte)'a') && (tag[3] == (byte)'u'))
{
//genrate a error to let the user know of the error
MessageBox.Show("This file is already Encrypted or in Invalid format!");
statusBar1.Text = "Error - Invalid File Format !!";
}
else
{
//if the file if ok the proceed with encryption
statusBar1.Text = "Encrypting...";
//set the file read cursor back to the 'Begning' of the opened file
fin.Seek(0, SeekOrigin.Begin);
}
//make a object of the class 'SymmetricAlgorithm'
SymmetricAlgorithm des;
if (radioButton1.Checked)
{
//if the algorithm to be used is 'DES' then initilize the 'SymmetricAlgorithm' to 'DES_CSP'
des = new DES_CSP();
//set the variable to true because we are using 'DES' algorithm.
algo = true;
}
else
{
//if the algorithm to be used is 'RC2' then initilize the variable 'des' to 'RC2_CSP'
des = new RC2_CSP();
//set the key size of the algorithm to 40 bits since we are using a 40 bit key
des.KeySize = 40;
//uncomment the below code to kind out the bits of keys supported by RC2 algorithm
/*KeySizes[] ks = des.LegalKeySizes ;
* Console.WriteLine("Key Sizes Supported :") ;
* Console.WriteLIne("Minimum Size:" +ks[0].MinSize) ;
* Console.WriteLine("Skip size of key: "+ks[0].SkipSize) ;
* Console.WriteLine("Maximum Size: "+ks[0].MaxSize) ;
*/
//set the bool variable to false since we are using the RC2 algorithm
algo = false;
}
//Make a object of the inner class 'StoreCryptoStream' we pass the bool variable
//containing the algotithm information and the FileStream
StoreCryptoStream scs = new StoreCryptoStream(algo, fout);
//make an object of the 'SymmetricStreamEncryptor' class and pass it the 'Key and the 'Vector'
//this starem helps to encrypt data according to the algorithm used
SymmetricStreamEncryptor sse = des.CreateEncryptor(symKey, symIV);
// a little extra feature here to show how to compose crypto
// components that support ICryptoStream
SHA1_CSP sha = new SHA1_CSP();
// wire up the encryptor - hash - StoreCryptoStream
sse.SetSink(sha);
sha.SetSource(sse);
sha.SetSink(scs);
scs.SetSource(sha);
//read from the file to encrypt
while (rdlen < totlen)
{
//set the number of bytes read
len = fin.Read(bin, 0, 4096);
//write the encrypted data
sse.Write(bin, 0, len);
//increase the size of bytes read
rdlen = rdlen + len;
}
//free up the resources
sse.CloseStream();
fin.Close();
fout.Close();
statusBar1.Text = "Encryption Compelete !";
}
catch (Exception e)
{
MessageBox.Show("An exception occured while encrypting :" + e.ToString());
statusBar1.Text = "Error";
}
}