Reverseme: Namegenme

This guy is here: http://crackmes.de/users/moofy/moofys_namegenme/

namegenme.zip

I had a fairly hard time with this one for some reason, although the solution was right in front of my face…

Most the logic for calculating the generation is in the function 00401852. The Serial is stored in a global variable, and the name is generated by taking certain bytes from the serial and doing addition on them.

Here is all the relevant logic, although finding it was sort of a pain.


.text:004018FD                 lea     eax, [ebp+var_10]
.text:00401900                 add     dword ptr [eax], 4
.text:00401903                 lea     eax, [ebp+var_14]
.text:00401906                 sub     dword ptr [eax], 3
.text:00401909                 lea     eax, [ebp+var_18]
.text:0040190C                 sub     dword ptr [eax], 2
.text:0040190F                 lea     eax, [ebp+var_1C]
.text:00401912                 add     dword ptr [eax], 2
.text:00401915                 lea     eax, [ebp+var_20]
.text:00401918                 dec     dword ptr [eax]
.text:0040191A                 lea     eax, [ebp+var_24]
.text:0040191D                 add     dword ptr [eax], 3
.text:00401920                 lea     eax, [ebp+var_28]
.text:00401923                 sub     dword ptr [eax], 2
.text:00401926                 lea     eax, [ebp+var_2C]
.text:00401929                 sub     dword ptr [eax], 4
.text:0040192C                 lea     eax, [ebp+var_30]
.text:0040192F                 add     dword ptr [eax], 3
.text:00401932                 lea     eax, [ebp+var_34]
.text:00401935                 inc     dword ptr [eax]

Here is a keygen written in C

void main(int argc, char* argv[]) {

  char Name [10];
  char* ser = argv[1];
  if (argc != 2 || strlen(argv[1]) < 21) {
    printf("Invalid serialn");
	return (-1);
  }

  Name[0] = ser[0] + 4;
  Name[1] = ser[1] - 3;
  Name[2] = ser[2] - 2;
  Name[3] = ser[6] + 2;
  Name[4] = ser[7] - 1;
  Name[5] = ser[8] + 3;
  Name[6] = ser[13] - 2;
  Name[7] = ser[14] - 4;
  Name[8] = ser[15] + 3;
  Name[9] = ser[20] + 1;
  Name[10] = "\0";

  printf("Name: %sn", Name);
}

One Response to Reverseme: Namegenme

  1. moofy says:

    hey i made this crackme :)
    good work!

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