I have to answer myself! :DDD I have found the function crypt() in perl standard function library. It crypts a string with a key string so nice, and the crypted resultant string does not contain any strange characters, so I can pass it trough a QUERY CGI But I have another big problem !... There's not a function to decrypt it!!! aaarghh! How do I decrypt a string crypted with crypt() ? Or ... what's the algorithm used internally by crypt() ?