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() ?