[Mono-list] Which algorithm to crypt strings ?

Sebastien Pouliot sebastien.pouliot at gmail.com
Tue Dec 6 07:54:02 EST 2005

Hello Salvatore,

On Tue, 2005-12-06 at 11:08 +0100, Salvatore Scarciglia wrote:
> Hi all,
> what's the simplest algorithm (and related Class) to, given a well known
> string, crypt and encrypt another string using the first as key for
> cryptography ??

There are no class in the framework to do this directly (with strings).
If you Google you'll find *lots* of sample code to do this - but be
aware that a lot of it is *bad*. IIRC there is a good sample from Igor
on MSDN blogs.

> Something lik this:
> ...
> ...
> ClassForCrypt X = new ClassForCrypt();
> X.key = well_known_string;
> string crypted = X.Crypt("string to be crypted");
> string decrypted = X.Decrypt("string to be decrypted");
> ...
> ...

Using string can be problematic in many ways (e.g. encoding, line ends).
That's why most classes (and sample code) are using byte[] arrays and
let the user convert his data (like string) into byte arrays (e.g.
calling System.Text.Encoding.UTF8.GetBytes).

For similar reason the output cannot be directly a string (some invalid
characters could be present for certain encoding). A safe and
(relatively) compact to use strings is to convert the encrypted byte
array into base64 (Convert.ToBase64String).

You may also want to look at System.Security.Cryptography.ProtectedData
as an easier alternative (i.e. automatic key management) if you are
using 2.0 and aren't moving the data from one computer to another.

Sebastien Pouliot
email: sebastien at ximian.com
blog: http://pages.infinit.net/ctech/

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