With IDA Pro you can reverse-engineer just about any type in that it shows the assembly code of a binary (an executable or a dynamic link library [DLL]). Reverse Engineering with. Ida Pro. Chris Eagle [email protected] Blackhat Training large text files. – Difficult to navigate/change. • Disassembly fails to reveal obfuscated code Described in file docs/terney.info on the CD. Reverse Engineering Code with IDA terney.info Pages·· MB· Downloads. services involving a variety of platforms and languages.
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written document I am aware of (including the actual IDA Pro Manual).” — SEBASTIAN PORST, SENIOR SOFTWARE SECURITY ENGINEER, MICROSOFT . Cover for Reverse Engineering Code with IDA Pro some exceptions to this on some platforms where the assembler exports pseudo-instructions and translates . Download file Free Book PDF Reverse Engineering Code With IDA Pro English Edition at Complete PDF Library. This Book havesome digital formats such us.
So the understanding of APIs is necessary. Eg: if you are using printf function in your code and the linker links the function call to the printf function in msvcrt.
For eg: lets say we are using strlen to calculate the length of the string, strlen will return the value into EAX register..
Load file into IDA Pro.
One of the most important thing is to look on the Import and Export function tabs to get a compact view that how many and what api is our target application using.
Now run the application independently, I mean like a normal application not under debugger and feed some garbage value and note the messages that we get. As you can see in the picture that our crackme is popping up a message box on invalid input.
The String "Sorry, please try again" is important or you can say that this string will save a lot of work, situation may vary with target to target but for this crackme this string can be the starting point. But as we can see that IDA is showing the starting function and we don't have any string that can match with the error message i. Now we have two approaches one is trace the call from start function to the function that is containing our magic string. For eg.
Generally we use the combination of both to manage the analysis time. As we can see in the picture that we have now clear targets, now we can backtrace and can find out the starting point of string matching.
If you don't know the api functionality then in this case you can search on msdn win api reference guide. The guide will provide you the parameter meanings, structure and expected return values etc. Now we can say that the aHardcoded contain our hardcoded password because application is matching this string with the user entered string. Now we have to find out the solution of second challenge.
It typically shows the control flow when we enter the wrong password value. For this purpose, we can move the dashed rectangle in the graph overview by dragging it to reach a specific segment as follows: Figure 1.
Here, we can easily assume that this program prompts the user to enter the password by the scanf method mentioned in the RED BOX.
Then this value is compared to a predefined string value which is password using the strcmp method. The test eax register is holding the value 0 or 1 which would come based on the string comparison.
Finally, the jnz instructs the compiler to directly jump to the false segment branching, which is location If it has a value of 1, then the control flow diverts toward the false condition block as follows: Figure 1.
This time we move to a false condition block as follows: Figure 1.
We have come to a conclusion that the eax register value is the key hack. If its value is 0, then we entered into the true condition code block; otherwise we entered into the false condition block.
Cracking Reversing the Target So, the eax register value would be the key interest for the reverser to subvert the password mechanism. If we change that value manually during debugging, then we can reach the true condition block even if we enter the wrong password information. To do so, run this application in debugging mode.
However, place a breackpoint at eax instruction by using F2. The instruction would be submerged in red box as follows: Figure 1. Again, a couple of windows appeared, then disappeared as usual. So, just enter any value as a password and press enter. Then we have to move ahead manually by pressing the step into F7 and we step forward to the jump instruction.
Here, we notice that the green arrow in the RED BOX started blinking, which points out that the execution is about to transfer to the B method block. The transmission to the false condition block happens due to the ZF value as 0.
If this value would have 1, then the true condition block would execute. In order to change this value, right click over value and select Modify value as: Figure 1. The target binary is showing the congratulation message even if entering the wrong password value. In addition to that, this program shows the original password value as ajay. But to get rid of a common misconception, we have to reverse engineer this target file, which is actually not patched.
The password restriction is still in place, because we have not modified the corresponding bytes so far.
Alternate way of Tracing Identification of the program entry point is always complex in IDA Pro because it shows raw assembly code. We have applied such a process by moving the arrow as in Figure 1. But this is a very cumbersome task. There is another way which eases the task of identifying such entry points.