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How to Program in C,continued...

Why C Exploit Programs Might not Work

Now comes the big question. You download a bunch of exploit programs and try to compile them and tget a bunch of error messages from the compiler. Aha, you have just discovered why hacker gangs are so popular. There are many groups of criminal hackers out there who help each other out by figuring out how to compile exploits. That is how Kevin Mitnick got as far as he did -- he had his buddies compile programs for him.

However, I presume you are reading this not to become a criminal, but because you are willing to do a little work, and learn enough to not only break into computers -- but learn how to defend them, too. For this you
must become good at C programming. Here's how to get good.

1) Buy the book The C Programming Language by Brian W. Kernighan and Dennis M. Ritchie (Prentice Hall, second edition, 1988). This is the Bible of C
programming. Real hackers simply call it "K&R." You can get eliteness points by responding to guys who talk reverently about "K&R" by saying, "Oh, yes, Kernighan and Ritchie. Brilliant book." The reason this book is so good is that one of the authors, Dennis Ritchie, is the creator of the C language. Valerie Henson adds, "K&R is almost magical in the way it explains C. I have strong feelings about this book. :)" You can buy it from anywhere in the world at http://www.amazon.com.

2) You will quickly discover that no one book on C will tell you all the possible commands. If you want to learn as much as possible about C, you need to study the source code of C programs you admire. With each line, use the "man 2" command while in your shell account to learn about it, for example, "man 2 write". (This presumes your sysadmin has installed the man pages for C.) Then try writing some small programs to test each command to make sure you understand what it does. For examples of elegant C program source code complete with explanations, get Internetworking with TCP/IP Volumes 1,2 and 3, by Douglas Comer and David L. Stevens (Prentice Hall, 1995). Volumes 2 and 3 are almost all C source code.

3) You will absolutely hate this. Just as there are many kinds of Unix and many different Unix shells, there is more than one version of C out there. But help is on the way. There is a version of C called ANSI C (for the ANSI standards board) which is coming to be widely accepted. All we have to do now is persuade the people who write programs to break into computers to adopt the ANSI C standard!

4) You might need to find some new friends who will help you figure out what to do to successfully compile and run some obstreperous C program. Try enrolling in a course on C at a GOOD college or university. However, talk to the other students or the professors before you spend money signing up for a course. I swear this is true, one college teaches C using C for Dummies as a textbook. While that book may be helpful for home study -- surely a college professor can show his or her students enough respect to teach from K&R! However, if you can get a good college course, don't expect to learn how to compile exploits from it! What you can do is hang out with students and teaching assistants and professors and meet people who can give you help on how to modify programs so they will compile on your computer.

If you can't find a good college nearby, another possibility is to join a Linux Users Group (LUG). To find one in your neighborhood, see (http://sunsite.unc.edu/LDP/).

Cramer suggests, "try to post question to newsgroups and mailing lists (that discuss C programming). But ... Posting a question like "My hello.c prints 'Hello, good bye' instead of 'hello hackers -- what should I do?' to a mailing list -- say -- the Linux kernel developers list, will give you -- hrmmm -- some interesting results..."

Or get a job doing tech support at a local Internet Service Provider. Usually there will be some talented C programmers working there.

Whatever you do, don't join a gang of computer criminals! They usually know much less about C programming than do computer science students, Linux User Group members, and employees of ISPs.

5) Read Meino Christian Cramer's Guide to C programming at the Wargames page on http://www.happyhacker.org. Try emailing questions to him at the address on that Web page. He gives a great overview of the most important concepts in C programming, with some example programs for you to write.

More on C -- a computer break-in program explained --->>


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