Help Encryption

Hi, i want to use a program for encrypting a little string in sha256, but i don't find any libraries for arduino :S. I need this libraries, if we can help me i will be very happy XDDD

Try searching for AVR...
http://www.google.com/search?q=avr+sha256

This looks promising...
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1260287389

Also worth a look...
http://www.uelectronics.info/crypto-avr-library

If you're willing to create a core for the Arduino...

Why do you want to encrypt at all? Wouldn't it be sufficient to store an encrypted string? What application do you have in mind?