Target : Crackme 1.02 by Vizion/Mexelite (on Eternal Bliss site :

                http://www.crackmes.cjb.net )



                  ...a little tut by SiFLyiNG...



In this little tutorial (if we can call that a tutorial, i'll only explain

brievly the method i used to find a correct serial for this crackme.



Let's go :



        Name: what you want

        Serial : 12345678  

   advise : note your personal code, it could be useful for the following

        Bpx hmemcpy in sice



1. At the beginning of the check, it compares the len of the entered

   code to Eh (h means hexadecimal, so Eh = 14 in decimal base ). So it means that the serial must look like : XXXXXXXXXXXXXX (14 times)



2. then it compares the fourth char of the serial with 2Dh, so it compares

   with "-". So the serial must be XXX-XXXXXXXXXXX



3.there is a first comparation : 



	the asm code is :



        MOV ECX, EAX            ; first part XXX of the entered serial

                                (in my case 123)

        MOV EAX, [00430700]     ; personal code (in my case 1078268636

        MOV EBX, FF             ; move FFh in EBX

        CDQ

        IDIV EBX                ; EAX = EAX/EBX = EAX/FFh

                                the rest from the division is stored

                                in EDX ; in my case EDX = 74h

		

then the verification : XOR ECX, EDX

		JNZ bad cracker



So, it means that ECX should be equal to EDX so that the prog won't jump.

ECX XOR EDX = 0 means that ECX = EDX so ECX must be 74h = 116 not to jump

to the bad cracker code

		

So the first part of the serial is : 116

There I know that my serial must look like : 116-YYYYYYYYYY (10 times)



4.Then there is some loops which calculate the second part of the code from

the entered name and the personnal code. Then there is - I don't show any

adress so you have got some work to make  :



XOR ESI, EAX    ; EAX = entered second part of code and ESI = real second

                  	part of code

JNZ bad cracker ; the result must be ESI = 0 not to jump so EAX(our code)

                  must be equal to ESI(good code)



so you can get the valid second part of the code. But you should first look

at the calculation code and try to make a keygen :)



 	I press the test button and look at the status bar : 

		"Correct serial... it's time for a keymaker..."



Try with your name & personnal code with the same scheme :

                                        you must manage now :)



i haven't time to write a real tutor, so mail me if you have questions :

 siflying@ifrance.com