Re: Decryptionfailed to bring original text back....

The thing to know when you are encrypting string data (as opposed to
arbitrary binary data) is that if you have a .NET string object, that it
Unicode. There isn't really much reason to encrypt a .NET string with
anything other than a Unicode encoding like UTF8 or Unicode. That will
cover all possible characters. You always decode with the same encoding you
encoded with if you want to get back the same string.

If you have arbitrary data, then just pass in the binary data directly.

Regarding block ciphers (which is what you are talking about), they work by
processing a fixed number of bytes of data at a time. They keep moving
through the data X bytes at a time, encypting each block as they go. If
they reach the end of the data and it isn't long enough to fill a whole
block, then padding is added to make the length match the block size. The
padding is generally stripped off when the data is decrypted.

Joe K.

--
Joe Kaplan-MS MVP Directory Services Programming
Co-author of "The .NET Developer's Guide to Directory Services Programming"
http://www.directoryprogramming.net
--
"den 2005" <den2005@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:DE9A3290-447A-4309-A9E6-97F36AA301F1@xxxxxxxxxxxxxxxx
Thanks for the reply, Joe.
Thanks for idea...I would try different approach in converting bytes[] to
string using ASCII, UTF32, Unicode, UTF7, UTF8 to know which of them
applies
to all possible keys of text (?$%~`&^*(|\]'"). After I did this, I try
using
Hashing in encrypt/decrypt text. I just started learning cryptography.
What
is exactly Padding does to encryption/decryption process? The encrypted
text
has 40 bits so it will add to fill it up to 64 bits, how about if
encrypted
data goes over 64 bits, what happen when you decrypt the encrypted data?

Dennis


--
MCP Year 2005, Philippines


"Joe Kaplan (MVP - ADSI)" wrote:

Why do you encode with Unicode and convert back to string with ASCII?
That
makes no sense. You have to use the same encoding to go
string->binary->string. Why not also just use UTF8 for both?

Joe K.

--
Joe Kaplan-MS MVP Directory Services Programming
Co-author of "The .NET Developer's Guide to Directory Services
Programming"
http://www.directoryprogramming.net
--
"den 2005" <den2005@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:28E79C33-C926-4C12-B79D-014381297C75@xxxxxxxxxxxxxxxx
Hi everybody,

I am not sure where to put this in this forum. So, I posted this at
several topics. I created a class library that has two public methods
Encrypt() and Decrypt(). I reference this dll to a window application.
I
used
DESCryptoServiceProvider Algorithm to encrypt and decrypt then with
same
Key
and IV. But unable to decrypt it back to original text. This project I
plan
to use all algorithm and Hash. This is Phase One. There is no problem
ingenerating the Key and IV and at both encrypt and decrypt they are
the
same. Can anyone spot the mistake and know how to correct this? Thanks.

[code]

//Generate a Key
private static void GenerateDESKey(DESCryptoServiceProvider
desProv,int keySize,bool maxKeySize)
{
if (Key == null)
{
if (keySize != 0)
desProv.KeySize = keySize;
else
{
KeySizes[] keySizeSets = desProv.LegalKeySizes;
int len = keySizeSets.Length;

for (int x = 0; x < len; x++)
{
if (maxKeySize)
keySize = keySizeSets[0].MaxSize;
else
keySize = keySizeSets[0].MinSize;
}
}
desProv.KeySize = keySize;
desProv.GenerateKey();
Key = desProv.Key;
}
}

//Generate a IV
private static void GenerateDESIV(DESCryptoServiceProvider
desProv)
{
if (IV == null)
{
desProv.GenerateIV();
IV = desProv.IV;
}
}

//Encrypting String Data passed as parameter and returns it
public string Encrypt(string strData,int keySize, bool bMaxSize)
{
string strEncrypt = string.Empty;
try
{
//Variable Telling if Crypto or Managed object is
selected
MemoryStream memStream = new MemoryStream();

CryptoStream cryptStream;
UnicodeEncoding byteConvert = new UnicodeEncoding();
byte[] byteData = byteConvert.GetBytes(strData);

byte[] encryptedData = { };


if (this.CRYPTOCLASS == Algorithm.DES.ToString())
{
this.CreateDESCrypto();
if (des != null)
{
//Generate Cryptographic Key and saved it
GenerateDESKey(des, keySize, bMaxSize);
//Generate Cryptographic IV and saved it
GenerateDESIV(des);

transform =
des.CreateEncryptor((byte[])Key.Clone(),
(byte[])IV.Clone());
}
}
. . . .
//Use the created algorithm object to encrypt data
cryptStream = new CryptoStream(memStream, transform,
CryptoStreamMode.Write);

cryptStream.Write(byteData, 0, byteData.Length);
cryptStream.FlushFinalBlock();

encryptedData = memStream.ToArray();

memStream.Close();
cryptStream.Close();
transform.Dispose();

//Call to dispose data
this.DisposeActiveObjects();
//Convert encrypted bytes[] back to string
strEncrypt = Convert.ToBase64String(encryptedData);

}
catch (Exception ex)
{
this.WriteAppendLogFile(", Encrypt() " + ex.ToString());
}
return strEncrypt;
}

//Decrypting String Data passed as parameter and returns it
public string Decrypt(string strEncrypt)
{
string strData = string.Empty;
try
{
//Variable Telling if Crypto or Managed object is
selected

//Check if Key and IV is still has data
if (Key == null || IV == null)
{
return "Cryptographic Key and IV cannot be null.";
}
MemoryStream memStream;
CryptoStream cryptStream;
byte[] encryptedData =
Convert.FromBase64String(strEncrypt);
byte[] decryptedData = new Byte[encryptedData.Length];

if (this.CRYPTOCLASS == Algorithm.DES.ToString())
{
this.CreateDESCrypto();
transform = des.CreateDecryptor((byte[])
Key.Clone(),(byte[])IV.Clone());

}
........

//Use the created algorithm object to encrypt data
memStream = new MemoryStream(encryptedData);
cryptStream = new CryptoStream(memStream, transform,
CryptoStreamMode.Read);

cryptStream.Read(decryptedData, 0,
decryptedData.Length);

memStream.Close();
cryptStream.Close();
transform.Dispose();

//Call to dispose data
this.DisposeActiveObjects();
//Convert encrypted bytes[] back to string
//strEncrypt = Convert.ToBase64String(decryptedData);
strData = Encoding.ASCII.GetString(decryptedData);
}
catch (Exception ex)
{
this.WriteAppendLogFile(", Decrypt() " + ex.ToString());
}
return strData;
}
[/code]

den2005




--
MCP Year 2005, Philippines





.

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