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CGI Programming on the World Wide Web

Post date: December 12, 2005, 17:12 Category: Programming Views: 3075 Comments
Tutorial quote: The Common Gateway Interface (CGI) emerged as the first way to present dynamically generated information on the World Wide Web. CGI allows the computer to generate Web pages instantly at the user's request rather than being written by someone in advance. And at the time of this writing, it remains the only stable and well-understood method for creating such pages. Java presents problems that have not yet been solved. Other products are currently just in the announcement stage.

CGI is fun. You can get a kick out of writing scripts that perform tricks for you, and the users enjoy the spice the scripts add to your Web pages. But CGI has a serious side too: It lets the Internet offer the kind of interactive, user-driven applications that modern computer users have come to expect. CGI opens up an entire class of modern applications to the Web.

Creating a safe directory with PAM and Encfs

Post date: June 7, 2006, 20:06 Category: Security Views: 3234 Comments
Tutorial quote: Now, in my network (and others) the credentials provided at login could (and should) be used by those programs. How can you retrieve these credentials, providing enough security?
With a the PAM modules pam_script it's possible to store the password in a file, which will be used by fusemb and mount.cifs to read the password from.

To achieve security, one could make the user logging in owner and deny read/write for anybody else. Remove this file when the user ends his/her session.
This is enough, for runtime. But I was wondering, but what if the system crashes, and the file with the credentials remains on the harddrive? Anybody who is able to mount this harddrive with for example a lifecd, can read this file!

That's why I was looking for a way to encrypt this file.

With encfs this is very possible! At run time it gives an interface to encrypted files and directories, which does only exist at runtime! When the system is not running, there are only encrypted files, useless when you do not know the key to it. And this key is exactly the (encrypted) password! That's why I've chosen for a combination of PAM and Encfs.

Creating Really Teensy ELF Executables for Linux

Post date: April 12, 2005, 18:04 Category: Miscellaneous Views: 2616 Comments
Tutorial quote: If you're a programmer who's become fed up with software bloat, then may you find herein the perfect antidote.

This document explores methods for squeezing excess bytes out of simple programs. (Of course, the more practical purpose of this document is to describe a few of the inner workings of the ELF file format and the Linux operating system. But hopefully you can also learn something about how to make really teensy ELF executables in the process.)

Please note that the information and examples given here are, for the most part, specific to ELF executables on a Linux platform running under an Intel-386 architecture. I imagine that a good bit of the information is applicable to other ELF-based Unices, but my experiences with such are too limited for me to say with certainty.

The assembly code that appears in this document is written for use with Nasm. (Besides being more appropriate for our needs, Nasm's syntax beats the hell out of AT&T syntax for anyone who learned x86 assembly language before learning to use Gas.) Nasm is freely available and extremely portable; see http://nasm.sourceforge.net/.

Please also note that if you aren't a little bit familiar with assembly code, you may find parts of this document sort of hard to follow.
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