dotnet security: Cryptography implementation using memeorystream -- dotnet security

Re: Cryptography implementation using memeorystream

rajbharati
7/19/2005 12:17:02 AM

Because memeorystream cannot support read/write at the same time, i copied
the encrypted buffer to byte array and re-instantiate another memorystream
passing that byte array which in tern is used to intantiate cryptostream. I
think i could not use seek method to reposition this cryptostream object. But
i call seek method from memorystream object before passing to cryptostream.
But no difference!

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Re: Cryptography implementation using memeorystream

William Stacey [MVP]
7/19/2005 8:18:58 AM

Here is how I do it:

RijndaelManaged rm = new RijndaelManaged();
byte[] data = Encoding.UTF8.GetBytes("Hello");
ICryptoTransform encryptor = rm.CreateEncryptor();
ICryptoTransform decryptor = rm.CreateDecryptor();
byte[] encData = RijndaelEncrypt(encryptor, data);
byte[] clearData = RijndaelDecrypt(decryptor, encData);
Console.WriteLine("Data:" + Encoding.UTF8.GetString(clearData));

private static byte[] RijndaelDecrypt(ICryptoTransform decryptor,
byte[] encrypted)
{
if ( decryptor == null )
throw new ArgumentNullException("decryptor");
if ( encrypted == null )
throw new ArgumentNullException("encrypted");

using ( MemoryStream msDecrypt = new MemoryStream(encrypted) )
using ( CryptoStream csDecrypt = new CryptoStream(msDecrypt,
decryptor, CryptoStreamMode.Read) )
{
byte[] fromEncrypt = new byte[encrypted.Length];

int read = csDecrypt.Read(fromEncrypt, 0,
fromEncrypt.Length);
if ( read < fromEncrypt.Length )
{
byte[] clearBytes = new byte[read];
Buffer.BlockCopy(fromEncrypt, 0, clearBytes, 0, read);
return clearBytes;
}
return fromEncrypt;
}
}

private static byte[] RijndaelEncrypt(ICryptoTransform encryptor,
byte[] data)
{
if ( encryptor == null )
throw new ArgumentNullException("encryptor");
if ( data == null )
throw new ArgumentNullException("data");

//Encrypt the data.
using ( MemoryStream msEncrypt = new MemoryStream() )
using ( CryptoStream csEncrypt = new CryptoStream(msEncrypt,
encryptor, CryptoStreamMode.Write) )
{
//Write all data to the crypto stream and flush it.
csEncrypt.Write(data, 0, data.Length);
csEncrypt.FlushFinalBlock();

//Get encrypted array of bytes.
byte[] encrypted = msEncrypt.ToArray();
return encrypted;
}
}

--
William Stacey [MVP]

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Re: Cryptography implementation using memeorystream

rajbharati
7/20/2005 12:00:02 AM

Thanks a lot!
By the way does encoding(you used UTF8) affect?
I usually use ASCII encoding!

Raj

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Re: Cryptography implementation using memeorystream

Joe Kaplan (MVP - ADSI)
7/21/2005 12:06:47 AM

ASCII encoding for string data has the serious down side that it cannot
properly encode non-ASCII string data. Given that .NET strings are unicode,
you run a risk when converting to ASCII that you will lose data unless you
are absolutely certain that the string will never contain non-ASCII data.

UTF8 can encode all unicode characters properly and has the benefit of
producing the same encoding as ASCII for ASCII characters, so it doesn't
waste any additional space in that case.

Joe K.

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