Description

1 Introduction
The nefarious Dr. Evil has planted a slew of “binary bombs” on our class 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.
Step 1: Get Your Bomb
You can obtain your bomb from the following Onedrive:
https://bit.ly/2EnQF3o
In the drive, you will find bombk.tar for some integer k, where k is your last three numbers of your student ID (e.g. 20202616 → 616, 20202016 → 16).
Save the bombk.tar file to a (protected) directory in which you plan to do your work (i.e. programming server). Then give the command: tar -xvf bombk.tar. This will create a directory called ./bombk with the following files:
• 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.
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• writeup.{pdf,ps}: The lab writeup.
After getting your bomb, please check the README and ID file if it is correct.
Step 2: Defuse Your Bomb
Your job for this lab is to defuse your bomb.
You must do the assignment on your own programming server. You can use many tools to help you defuse your bomb. The best way is to use your favorite debugger (e.g. gdb) to step through the disassembled binary.
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 solution.txt
then it will read the input lines from solution.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. This is a crucial skill that will pay big dividends the rest of your career.
Handin
• solution.txt: The contents should ideally be such that we can defuse the entire bomb simply running ./bomb solution.txt, or such that it will pass some number of phases and then blow up. Compress the solution.txt file with your original bomb file (ID, bomb, and bomb.c) and hand in the compressed file.
• report: No report format, however, explain in detail how each phase is defused.
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