Encrypting a short string?

Lie Lie.1296 at gmail.com
Sat Feb 16 13:13:58 CET 2008

On Feb 12, 2:45 am, erikcw <erikwickst... at gmail.com> wrote:
> Hi,
> I'm trying to devise a scheme to encrypt/obfuscate a short string that
> basically contains the user's username and record number from the
> database.  I'm using this encrypted string to identify emails from a
> user. (the string will be in the subject line of the email).
> I'm trying to figure out which approach I should use to encrypt the
> data.  The string will be less than 20 characters long, and I'd like
> the encrypted version to be about the same size.
> I tried DES in the Crypto module, but the cipher text was to long to
> be usable in this case.
> Any suggestions?
> Thanks!

There is a simple encryption, called ROT13 (Rotate 13). This is very
unsecure for any cryptographical purpose, but enough to make
uninformed user to think it's just a random piece of letters.

The ROT13 is done by adding 13 to each character, so
A => N,
B => O,
C => P,
D => Q, etc

the neat trick to this encryption is the algorithm is really simple
and you don't need a separate decoding algorithm as text ==
ROT13(ROT13(text)). This algorithm also guarantees that any two
different text would have two different ciphertext

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