Re: Public Key Encryption with RSACryptoServiceProvider

From: Pieter Philippaerts (Pieter.nospam_at_mentalis.org)
Date: 06/25/04 

Date: Fri, 25 Jun 2004 20:07:28 +0200

"AlBruAn" <AlBruAn@discussions.microsoft.com> wrote in message
> I'm attempting to use the RSACryptoServiceProvider class to encrypt some
licensing information I'm storing in SQL Server, but I'm encountering a "Bad
Data" CryptographicException when I try decrypting the data and wonder how I
can get around this issue. I'm not storing any information in SQL Server
until I can get the mechanics of encryption working properly. Anyway...
> I've generated a pair of public and private keys using
RSACryptoServiceProvider's ToXml function, passing false and true arguments,
respectively, to it. I then persist these keys to the root directory of my
C: drive using an XmlTextWriter.
> When it's time to encrypt a license number, I create a new instance of the
RSACryptoServiceProvider object and read in the public key using its FromXml
function. I then call the Encrypt function, passing it the license number
and specifying no OAEP padding. My final step is to persist the encrypted
values to a separate file in the root directory of my C: drive.

>From your description, there doesn't seem to be an abvious error. Could you
post the source code you're using so we can take a closer look?

> Even tho' I'm using the string "123" as my "license number" and using the
same
> public key, I'm getting different values for the encrypted "license
number".

This is normal; whenever you encrypt something, the RSACryptoServiceProvider
will add a special padding to your data to make sure the length is equal to
the modulus size of your public key. This padding consists mostly of random
bytes, hence the difference.

Regards,
Pieter Philippaerts

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