C语言代写 | CS 429 Assignment 4: Defusing a Binary Bomb


1 Introduction

The nefarious Dr. Evil has planted a slew of “binary bombs” on our class machines. A binary bomb is
program that consists of a sequence of phases. Each phase expects you to type a particular string on stdi
If you type the correct string, then the phase is defused and the bomb proceeds to the next phase. Otherwis
the bomb explodes by printing “BOOM!!!” and then terminating. The bomb is defused when every pha
has been defused.

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

Step 1: Get Your Bomb

This assignment uses an online server for distributing handout tarballs and grading. You can obtain your
bomb by pointing your web browser at:


This will display a binary bomb request form for you to fill in. Enter your UT EID 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.
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. This will create a directory called ./bombk with the following

• README: Identifies the bomb and its owners.
• bomb: The executable binary bomb.
• bomb.c: Source file with the bomb’s main routine and a friendly greeting from Dr. Evil.

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 lab machines posted on Piazza. 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 Section 3 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 1/2 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!
If you work on multiple bombs, point deductions on each of them will aggregate to your final score.

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,

linux> ./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.

1 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 as-
sembly 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. This is a crucial skill that will pay big dividends the rest of your career.


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