On this page:
Step 1:   Get Your Bomb
Step 2:   Defuse Your Bomb
Logistics
Handin
Hints (Please read this!)

Bomb Assignment

The bomb lab is by Bryant and O’Hallaron for Computer Systems: A Programmer’s Perspective, Third Edition

Due: Wednesday, September 20, 11:59pm

The nefarious Dr. Evil has planted a slew of “binary bombs” on our lab1-n.eng.utah.edu machines. A binary bomb is a program that consists of a sequence of phases. Each phase expects you to type a particular string on stdin. If you type the correct string, then the phase is defused and the bomb proceeds to the next phase. Otherwise, the bomb explodes by printing "BOOM!!!" and then terminating. The bomb is defused when every phase has been defused.

There are too many bombs for us to deal with, so we are giving each student a bomb to defuse. Your mission, which you have no choice but to accept, is to defuse your bomb before the due date. Good luck, and welcome to the bomb squad!

Step 1: Get Your Bomb

You can obtain your bomb by pointing your Web browser at:

http://cs4400.eng.utah.edu:4400/

That page will display a binary bomb request form for you to fill in. Enter your username and email address and hit the Submit button. The server will build your bomb and return it to your browser in a tar file called bombk.tar, where k is the unique number of your bomb.

You should request only one bomb and save it. Unlike the match lab, if you request a second bomb with the same uID, the bomb will be different—so, don’t do that. It’s ok if you need a few attempts over a few minutes to download a bomb. Beyond that, if you have an issue with a bomb and need a new one, please alert the course staff.

Save the bombk.tar file to a (protected) directory in which you plan to do your work. Then give the command: tar -xvf bombk.tar. That command will create a directory called ./bombk with the following files:

If for some reason you request multiple bombs, this is not a problem. Choose one bomb to work on and delete the rest.

Step 2: Defuse Your Bomb

Your job for this lab is to defuse your bomb.

You must do the assignment on one of the lab1-n.eng.utah.edu machines. In fact, there is a rumor that Dr. Evil really is evil, and the bomb will always blow up if run elsewhere. There are several other tamper-proofing devices built into the bomb as well, or so we hear.

You can use many tools to help you defuse your bomb. Please look at the hints section for some tips and ideas. The best way is to use your favorite debugger to step through the disassembled binary.

Each time your bomb explodes it notifies the bomblab server, and you lose ½ point (up to a max of 20 points) in the final score for the lab. So there are consequences to exploding the bomb. You must be careful!

The first four phases are worth 10 points each. Phases 5 and 6 are a little more difficult, so they are worth 15 points each. So the maximum score you can get is 70 points.

Although phases get progressively harder to defuse, the expertise you gain as you move from phase to phase should offset this difficulty. However, the last phase will challenge even the best students, so please don’t wait until the last minute to start.

The bomb ignores blank input lines. If you run your bomb with a command line argument, for example,

  $ ./bomb psol.txt

then it will read the input lines from psol.txt until it reaches EOF (end of file), and then switch over to stdin. In a moment of weakness, Dr. Evil added this feature so you don’t have to keep retyping the solutions to phases you have already defused.

To avoid accidentally detonating the bomb, you will need to learn how to single-step through the assembly code and how to set breakpoints. You will also need to learn how to inspect both the registers and the memory states. One of the nice side-effects of doing the lab is that you will get very good at using a debugger, which is a crucial skill that will pay big dividends the rest of your career.

Logistics

This is an individual project. All handins are electronic. Clarifications and corrections will be posted on the course message board.

Handin

There is no explicit handin. The bomb will notify your instructor automatically about your progress as you work on it. You can keep track of how you are doing by looking at the class scoreboard at:

http://cs4400.eng.utah.edu:4400/scoreboard

This web page is updated continuously to show the progress for each bomb.

Hints (Please read this!)

There are many ways of defusing your bomb. You can examine it in great detail without ever running the program, and figure out exactly what it does. That’s is a useful technique, but it not always easy to do. You can also run it under a debugger, watch what it does step by step, and use this information to defuse it. That’s probably the fastest way of defusing it.

We do make one request, please do not use brute force! You could write a program that will try every possible key to find the right one. But this is no good for several reasons:

There are many tools which are designed to help you figure out both how programs work, and what is wrong when they don’t work. Here is a list of some of the tools you may find useful in analyzing your bomb, and hints on how to use them.

Looking for a particular tool? How about documentation? Don’t forget, the commands apropos, man, and info are your friends. In particular, man ascii might come in useful. info gas will give you more than you ever wanted to know about the GNU Assembler. Also, the web may also be a treasure trove of information. If you get stumped, feel free to ask your instructor for help.