Then the phase defused and the bomb proceeds the next phase

Step to perform: Defuse Your Bomb

To protect the computer, this bomb can’t run on all computer, 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.

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. We added this feature, so you don't have to keep retyping the solutions to phases you have already defused.

There are many ways of defusing your bomb. You can examine it in detail without ever running the program and figure out exactly what it does. This is a useful technique, but it is 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. This is probably the fastest way of defusing it. You may not modify your bomb in any way to defuse it; your inputs are attempted on a fresh copy of your bomb for grading purposes so you can't circumvent it this way.

We 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:

• gdb The GNU debugger is a command line debugger tool available on virtually every platform. You can trace through a program line by line, examine memory and registers, look at both the source code and assembly code (we are not giving you the source code for most of your bomb), set breakpoints, set memory watch points, and write scripts. Here are some tips for using gdb. To keep the bomb from blowing up every time you type in a wrong input, you'll want to learn how to set breakpoints.

oFor other documentation, type help at the gdb command prompt, or type man gdb, or info gdb at a Unix prompt. Some people also like to run gdb under gdb-mode in emacs.

• strings This utility will display the printable strings in your bomb.

Looking for a particular tool? How about documentation? Don't forget, the command man is your friend. You can use this to look up information on system functions that the binary executable might use. In particular, man ascii might come in useful.

• If you end up inside a function that you don't want to step through, the gdb command finish will take you to the end. A better approach is to use nexti to step over that call instead.

• The bomb functions typically have a generic name like fn7 or phase2. If a function has a descriptive name, you can assume that the function behaves as expected and that they are NOT trying to trick you. Do not waste your time trying to reverse engineer functions like read_six_numbers or strings_not_equal.

• Remember the compiler will work with different sizes. %eax, %ecx, and other registers will show up often!

GDB Layout Modes:
When using gdb, there are two layout modes that you may find helpful.

The second layout mode is to show the registers at the top of the screen.

layout regs