Public-key crypto Cryptography demystified! Step-by-step how to encrypt and mail or save data from a Web form using PGP or Gnu Privacy Guard. We even show you how to batch-decrypt a whole pile of encrypted data.

ENV CGI programs know how to grab "the environment variables." But what are those variables, and where do they come from?

HTTP More instructive than utilitarian, these gadgets help you see inside the HTTP protocol that Web browsers and servers use to communicate.

Regex I think regular expressions are one of the most important fundamentals of programming for the Web. Here I build a (nearly) bullet-proof date validator.

More regex A set of regular expressions that will insert user data back into HTML form elements. Included are text inputs, check boxes and radio buttons, drop-down select menus and textareas.

Robots Here's a Perl tool based on Gisle Aas' LWP library that faithfully updates your IP address on dynamic name mapping services like DHS or TSX.

Snarfs Also known as a screen scraper. This handy tool (also based on LWP) grabs data straight off a Web screen.

SSL Probably the best tutorial on the Web (or anywhere) for learning how to use the OpenSSL libraries. Make SSL posts without a browser. Write code to set up SSL connections between remote servers. Finally understand how the damn stuff works!