Crackme 0x05

Introduction

crackme0x05, this one is very similar to crackme0x04, so this should be a quick one

Ghidra

Our main function, which is identical to crackme0x05. Lets take a look at check.

Ok, this looks very similar as well, but this time we call a function called parell, if the sum of our input is 0x10 (16)

We can see that it is doing an and between local_8, our input and 1. This & represents an and gate, which would return 1 if all the bits of our input are the same as the bits of 1 So what does this mean? Let’s take a look at this

For example lets try 97 as our input:

num	bits
97:	1100001
1:	0000001

An and gate goes through all the bits and returns 1 if 1 exists in both 97 and 1. at the weight of 1, both 97 and 1 have a 1, so the output of the and gate is 1. so this password does NOT work, because to work, the bitwise and of our input and 1 has to be equal to 0. a working example would be this:

num	bits
88:	1011000
1:	0000001

when we and 88 & 1, we get 0 as there are not 1’s in any positions in both 88 or 1. This password also sums to 16, so lets try it out

Nice! Works great.