An alternative: You talk about text files.  If you want the encrypted file to also be a text file, rather than a byte, then you could consider the Vigenère cipher.  With a long randomly generated key it can be reasonably secure.  If the key is as long as the plaintext file and is only used once, then it becomes a form of One Time Pad.

If you want byte-based encryption, but still want text in the encrypted file, then use Base64 to encode bytes as text.  Of course you will need to decode from Base64 back to bytes before decrypting.

simple algorithm to encrypt/decrypt a text file
What are sources where I can learn how to use GeoServer?

I know of these two sites:


http://geoserver.org/ - which in fact is not working (at least at the moment)
http://workshops.opengeo.org/geoserver-intro/ - not only (tutorials) for GeoServer


But I am interested in more complex information, and not to read only documentation.
