Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. I cannot describe the question better . phase_6 Raw Blame. This function reads 6 inputs to *(ebp-0x20)~*(ebp-0xc), use n0~n5 as their alias, and it compares 5 and n1 in 8049067, n1 must be larger than 5. mov a b moves data from a to b as opposed to b to a). The binary bomb is a very good exercise to learn the assembly language.I started this exercise for fun. But when I put 4 1 6 5 2 3 or 3 6 1 2 5 4, it explodes. So my understanding is that the first input is the starting point of the array, so it should be limited to between 0 and 14, and the second input is the sum of all the values that I visited starting from array[first input]. manually. Are you sure you want to create this branch? without any ill effects. Use Git or checkout with SVN using the web URL. This works just fine, and I invite you to try it. Let me know if you have any questions in the comments. @cinos hi, I had same problem, I couldn't understand, I must have ecx 15 too, but I couldn't figure it out. If the student enters the expected string, then that phase. Bomb explosions. Can you still use Commanders Strike if the only attack available to forego is an attack against an ally? In order to solve the cypher, take a look at %esi and youll find an array of characters stored there, where each character has an index. First things first, we can see from the call to at and subsequent jump equal statement our string should be six characters long. From the first few lines, we guess that there are two arguments to enter. We can see that the last line shouldn't be contained in this switch structure, while the first four should be. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Cannot retrieve contributors at this time. On the bright side, at least now we know that our string should come out of the loop as giants. Well However, it. This second phase deals with numbers so lets try to enter the array of numbers 0 1 2 3 4 5. is "defused." My phase 5 is different from most other phase 5's I've found online, as it is the input of two integers. Now lets take a quick look at the disassebly to see what variables are being used. It is useful to check the values of these registers before/after entering a function. A binary bomb is a program that consists of a sequence of six phases. I try a input sequence "aaaaaa" and get the value after transitions doesn't change at all, which means that the output of a given input is unique. If the first character in the input string is anything but a zero then the detonation flag is set to low and passed out the function. Keep going! Ok, lets get right to it and dig into the code: So, what have we got here? Upon entry to that secret stage you likely get the string 'Curses, you've found the secret phase!' When in doubt "make stop; make start" will get everything in a stable state. Cannot retrieve contributors at this time. The Bomb Lab teaches students principles of, machine-level programs, as well as general debugger and reverse, A "binary bomb" is a Linux executable C program that consists of six, "phases." As its currently written, your answer is unclear. When in doubt "make stop; make start", However, resetting the lab deletes all old bombs, status logs, and the, scoreboard log. Then we can get the range of the first argument from the line. We can then set up a breakpoint upon entering phase_1 using b phase_1 and for the function explode_bomb to avoid losing points. Make sure you update this. There are two hard coded variables that are then initialized and they, as well as the first user inputed value, are passed to func4. Bomb Lab Write-up. I will omit this part here, you can refer to this document. If nothing happens, download GitHub Desktop and try again. And when we execute it, it expects to receive certain inputs, otherwise it 'blows' up. Any numbers entered after the first 6 can be anything. Once we understand how it works, we can reverse engineer giants into its pre-cypher form without having to waste time doing trial and error. When I get angry, Mr. Bigglesworth gets upset. Let's enter the string blah as our input to phase_1 . Jumping to the next "instruction" using gdb, Binary Bomb Phase 5 issue (my phase 5 seems to be different from everyone elses), Memory allocation and addressing in Assembly, Tikz: Numbering vertices of regular a-sided Polygon. In this exercise, we have a binary whose source we do not have. I also found strings that look like they could be related to attribution: You'll only need to have. If nothing happens, download Xcode and try again. "make stop" kills all of the running, servers. In memory there is a 16 element array of the numbers 0-15. At the . Given this info, it looks as though the loop is implementing a cypher. Identify the generic Linux machine ($SERVER_NAME) where you will, create the Bomb Lab directory (./bomblab) and, if you are offering the, online version, run the autograding service. Informal Explanations of Phases 1 through 6: I have spent approximately 26 hours on this assignment. From the code, we can see that we first read in 6 numbers. your answer turns out to be 21 115, The solution is : 5 115. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. I know that due to x86-64 calling conventions on programs compiled with GCC that %rdi and %rsi may contain pointers to the words to compare. string_length() - This function first checks to see that the passed character pointer in %rdi is not null terminated. phase_defused If not null terminated then preserve the originally passed pointer argument by copying it to %rdx. This series will focus on CMU's Binary Bomb challenge. As an experienced engineer, I believe you can figure out that there are two arguments, each of which should be integers. The bomb explodes if the number calculated by this function does not equal 49. Good work! When we hit phase_1, we can see the following code: The code is annotated with comments describing each line. Analysis of CME bomb lab program in linux using dbg, objdump, and strings. GET /%s/submitr.pl/?userid=%s&lab=%s&result=%s&submit=submit HTTP/1.0 Learn more about bidirectional Unicode characters, #######################################################, # Copyright (c) 2002-2013, R. Bryant and D. O'Hallaron, This directory contains the files that you will use to build and run, the CS:APP Bomb Lab. In the interests of putting more Radare2 content out there, here's a noob friendly intro to r2 for those who already have a basic grasp of asm, C, and reversing in x86-64. More than 2 is fine but the code is only dependent on the first two numbers. The other option for offering an offline lab is to use the, makebomb.pl script to build a unique quiet custom bomb for each, linux> ./makebomb.pl -i -s ./src -b ./bombs -l bomblab -u -v , This will create a quiet custom bomb in ./bombs/bomb for the. Enter a random string and then we stop at the phase 1 position, then we try printing out the information around 0x402400. If you notice, (the syntax will vary based off of what sort of system the bomb is run on) the machine code will have some variation of call to: 401135: be b8 25 40 00 mov $0x4025b8,%esi. There are a ton of dead ends that you can follow in this code that all land on detonation. It also might be easier to visualize the operations by using an online disambler like https://onlinedisassembler.com/ to see a full graph. Thus the memory array contains an element that holds an integer followed by an element that holds a memory location from within the same array to one of the integers, followed by another integer, and then another memory location from within the array, etc, until the end of the array. Some of the pass phrases could be integers, or a random set of characters if that is the case then the only way to figure things out is through dynamic analysis and disassembling the code. Knowing that scanf() takes in a string format as its input, lets break right before scanf() is called and check the value of $esi. Such bombs are called "notifying bombs. Next, as we scan through each operation, we see that a register is being incremented at , followed by a jump-less-than statement right afterwards that takes us back up to . Can you help me please? Thus, they quickly learn to set breakpoints before, each phase and the function that explodes the bomb. Dump of assembler code for function phase_5: 0x0000000000401002 <+0>: sub $0x18,%rsp ; rsp = rsp - 24, 0x0000000000401006 <+4>: lea 0x8(%rsp),%rcx ; rcx = *(rsp + 8) (function argument), 0x000000000040100b <+9>: lea 0xc(%rsp),%rdx ; rdx = *(rsp + 12) (function argument), 0x0000000000401010 <+14>: mov $0x401ebe,%esi ; esi = "%d %d", 0x0000000000401015 <+19>: mov $0x0,%eax ; eax = 0, 0x000000000040101a <+24>: callq 0x400ab0 <__isoc99_sscanf@plt>, 0x000000000040101f <+29>: cmp $0x1,%eax ; if (eax > 1) goto 0x401029, 0x0000000000401022 <+32>: jg 0x401029 , 0x0000000000401024 <+34>: callq 0x40163d ; if (eax <= 1) explode_bomb(), 0x0000000000401029 <+39>: mov 0xc(%rsp),%eax ; eax = *(rsp + 12) ::function parameter, 0x000000000040102d <+43>: and $0xf,%eax ; eax = eax & 0xf (last 2 bits), 0x0000000000401030 <+46>: mov %eax,0xc(%rsp) ; *(rsp + 12) = eax, 0x0000000000401034 <+50>: cmp $0xf,%eax ; if (eax == 0xf) explode_bomb(), 0x0000000000401037 <+53>: je 0x401065 , 0x0000000000401039 <+55>: mov $0x0,%ecx ; ecx = 0, 0x000000000040103e <+60>: mov $0x0,%edx ; edx = 0, 0x0000000000401043 <+65>: add $0x1,%edx ; edx = edx + 0x1, 0x0000000000401046 <+68>: cltq ; sign extend eax to quadword (rax), 0x0000000000401048 <+70>: mov 0x401ba0(,%rax,4),%eax ; eax = *(rax * 4 + 0x401ba0), 0x000000000040104f <+77>: add %eax,%ecx ; ecx = ecx + eax, 0x0000000000401051 <+79>: cmp $0xf,%eax ; if (eax != 0xf) goto 0x401043 (inc edx), 0x0000000000401054 <+82>: jne 0x401043 , 0x0000000000401056 <+84>: mov %eax,0xc(%rsp) ; *(rsp + 12) = eax, 0x000000000040105a <+88>: cmp $0xc,%edx ; if (edx != 12) explode_bomb(), 0x000000000040105d <+91>: jne 0x401065 , 0x000000000040105f <+93>: cmp 0x8(%rsp),%ecx ; if (ecx == *(rsp + 8)) goto 0x40106a, 0x0000000000401063 <+97>: je 0x40106a , 0x0000000000401065 <+99>: callq 0x40163d ; explode_bomb(), 0x000000000040106a <+104>: add $0x18,%rsp ; rsp = rsp + 24, 0x000000000040106e <+108>: retq ; return, --------------------------------------------------------------------------------. je 0x40106a <phase_5+104> 0x0000000000401065 <+99>: callq 0x40163d <explode_bomb> ; explode_bomb . DePaul University - System I - Winter 2017, **Note: I made this repo with the intent to help others solve their own Bomb Labs. The autograding service consists of four user-level programs that run, - Request Server (bomblab-requestd.pl). node1 Try this one.'. We multiply the number by 2 each step, so we guess the sequence to be 1, 2, 4, 8, 16, 32, which is the answer. phase_3 Keep going! Link to Bomb Lab Instructions (pdf) in GitHub Repository . First you must enter two integers and the bomb will detonate if you enter more or less than that. c = 1 If not then the detonation flag that was initialized to 1 is not set to low and will eventually trigger the detonate function. Run the following commands to create text files which we will look at later: You should now have two files: strings.txt and assembly.txt. phase_5 There are 6 levels in the bomb and our task is to diffuse it. Are you sure you want to create this branch? How is white allowed to castle 0-0-0 in this position? I then did the same for the possible second pointer arguement which would be in %rsi with x/s $rsi and get 'When I get angry, Mr. Bigglesworth gets upset.'. Given you ultimately needed to have the element containing 0xf to exit after 15 iterations, I saw that f was at array element index 6. You've defused the secret stage! The key part is the latter one. p # Change print mode in Visual/Graph mode. sig_handler From this, we can deduce that the input for phase_2 should be 1 2 4 8 16 32. phase 2, variant "a" for phase 3, variant "c" for phase 4, and so on. Actually I'm not that patient and I didn't go through this part on my own. If the two string are of the same length, then it looks to see that the first inputed character is a non-zero (anything but a zero). . You have 6 phases with which to blow yourself up. There was a problem preparing your codespace, please try again. Learn more about bidirectional Unicode characters. Defusing the binary bomb. The answer is that the first input had to be 1. you like without losing any information. Ok, let's get right to it and dig into the <phase_5> code: So, what have we got here? Do this when you're ready for the lab to go "live" to, Resetting is also useful while you're preparing the lab. The idea is to understand what each, assembly statement does, and then use this knowledge to infer the, defusing string. Thanks for contributing an answer to Stack Overflow! phase_1 In order to defuse the bomb, students must use a debugger, typically, gdb or ddd, to disassemble the binary and single-step through the, machine code in each phase. gdb ./bomb -q -x ~/gdbCfg. The second input had to be a 11, because the the phase_4 code did a simple compare, nothing special. $ecx is the output of the loop, Values attached to letters based on testing: For homework: defuse phases 2 and 3. node4 We can inspect its structure directly using gdb. VASPKIT and SeeK-path recommend different paths. Here are a few useful commands that are worth highlighting: This command divides the screen into two parts: the command console and a graphical view of the assembly code as you step through it. It first checks that you have inputed 6 numbers, then that they are within the range of 1 through 6, and finally that they are all unique numbers, in that no number is repeated. Contribute to hengyingchou/CSE351 development by creating an account on GitHub. Has depleted uranium been considered for radiation shielding in crewed spacecraft beyond LEO? PHASE 3. This post walks through the first 3 phases of the lab. a user account on this machine. Each time a student defuses a, bomb phase or causes an explosion, the bomb sends a short HTTP, message, called an "autoresult string," to an HTTP "result server,", which simply appends the autoresult string to a "scoreboard log file. ', It is not clear what may be the output string for solving stage 4 or 5. Bomb Lab: Phase 5. angelshark.ics.cs.cmu.edu The second number is simply linked to the first number: 0 must be followed by 704, 1 by 848, 2 by 736, 3 by 346, 4 by 607, 5 by 147, 6 by 832, and 7 by 536. Otherwise the bomb "explodes" by printing "BOOM!!!". In this part we use objdump to get the assembly code - Main daemon (bomblab.pl). A loop is occurring. If you are offering the online version, you will also need to edit the, ./src/config.h - This file lists the domain names of the hosts that, notifying bombs are allowed to run on. Each binary bomb is a program, running a sequence of phases. In this version of the lab, you build your own quiet bombs manually, and then hand them out to the students. initialize_bomb Could this mean alternative endings? Entering this string defuses phase_1. That's number 2. We can find the latter numbers from the loop structure. LabID are ignored. The request server parses the form, builds and, tars up a notifying custom bomb with bombID=n, and delivers the tar, file to the browser. If so, put zero in %eax and return. The previous output from the strings program was outputted to stout in order that the strings are found in the binary. Former New York University and Peking University student. In the "offline" version, the. On the other hand, custom quiet, Generic Bomb: A "generic bomb" has a BombID = 0, isn't associated with. This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. "/> dearborn police incident reports. However, you know that the loop is doing some transitions on your input string. phase_3 This command lists all the current breakpoints as well as how many times each breakpoint has been hit on the current run. The first number must be between 0 and 7. Please Okay, we know it works. GitHub; Linkedin; Bomb Lab 7 minute read On this page. phase_5 () - This function requires you to go backwards through an array of numbers to crack the code. So we can plug in 6 d characters and get a valid comparison! I think the second number should be. solution to each bomb is available to the instructor. For more information, you can refer to this document, which gives a handy tutorial on the phase 6. The third bomb is about the switch expression. To see the format of how we enter the six numbers, lets set a breakpoint at read_six_numbers. Increment %rdx by 1 to point to the next character byte and move to %eax. The request server, responds by sending an HTML form back to the browser. Phase 1: There are two main ways of getting the answer. What is scrcpy OTG mode and how does it work? There is a small amount of extra credit for each additional phase . phase_5 As we can see, it is fairly obvious that there is a loop somewhere in this function (by following the arrows). This post walks through CMUs bomb lab, which involves defusing a bomb by finding the correct inputs to successive phases in a binary executable using GDB. I will likely take another shot at figureing out exactly how to come up with the solution by following the implemented logic but I eventually brute forced it, which took a whole 30 seconds to figure out. Option 2. First, interesting sections/function names: The "report daemon" periodically, scans the scoreboard log file. (**Please feel free to fork or star if helpful!). Alternative paths? There are no explicit handins and the lab is self-grading. "make cleanallfiles" resets the lab from scratch, deleting all data specific to a particular instance of the lab, such, as the status log, all bombs created by the request server, and the, scoreboard log. phase_defused() - So this function implements stack protection by adding, checking, and removing a canary. string_length Help/Collaboration: I recieved no outside help with this bomb, other than. CSO1 - Bomb lab. Are you sure you want to create this branch? invalid_phase correctly, else you and your students won't be able to run your bombs. CMU Bomb Lab with Radare2 Phase 1. Either way, eventually youll find that the pre-cyphered version of giants is actually opekmq. Congratulations! A Mad Programmer got really mad and created a slew of binary bombs. node6 If the line is correct, then the phase is defused and the bomb proceeds to the next phase. Connect and share knowledge within a single location that is structured and easy to search. This command lists out all the values that each of the registers hold. What' more, there's a function call to read_six_numbers(), we can inspect it, Up till now, you should be able to find out that in this part, we are required to enter six numbers. start Then you set a breakpoint at 4010b3 and find the target string to be "flyers". 3 lea's, a cmp of the output to 2 and a jump if greater than. Tools: Starting challenge; Phase_1: Phase_2: Phase_3: Phase_4: Phase_5: Phase_6: Bomb Lab Write-up. If your, Linux box crashes or reboots, simply restart the daemons with "make, * Information and error messages from the servers are appended to the, "status log" in bomblab/log-status.txt. Also note that the binary follow the AT&T standard so instruction operations are reversed (e.g. Asking for help, clarification, or responding to other answers. Going back to the code for phase_2, we see that the first number has to be 1. But finding it and solving it are quite different A note to the reader: For explanation on how to set up the lab environment see the "Introduction" section of the post. You get to know that the input sequence must be an arbitary combination of number 1,2,3,4,5,6. readOK = sscanf(cString, "%d %d", &p, &q); --------------------------------------------------------. A tag already exists with the provided branch name. instructor builds, hands out, and grades the student bombs manually, While both version give the students a rich experience, we recommend, the online version. Let's start with when it calls sym.read_six_numbers. You have 6 phases with node3 b = 6 Are you sure you want to create this branch? which to blow yourself up. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Pull up the function in Graph mode with VV, press p to cycle between views, and select the minigraph. (Add 16 each time) ecx is compared to rsp, which is 15, so we need ecx to equal to 15. Now switch to Visual mode with v, cycle the print mode with p until you see the disassembled function, toggle your cursor with c, then finally move down to the movzx edx, byte . Using gdb we can convince our guess. What I know so far: first input cannot be 15, 31, 47, etc. Halfway there! Stepping through the code with the GDB debugger I can say plenty about the various functions called in this program:
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