I’ve got more time during winter holiday so I will also do some crackme problems.

Today’s crackme problem is like this.

You need to input a name and a serial here. Try “sam” and “123456” you will fail let this.

OK, let’s open it in IDA. In the string subview you can find a string “Good job dude=)”. Double click it and you will come those important functions.
The first check is here.

It checks whether your name is longer than 3. Your name needs to have at least 4 characters. And in 0x42FA8A you will find that you put the first character into eax and multiply it by 29H.

For “s” you will get 24D6.

And in 0x42FACD you will find it generates the key.

Feel free to go into that function and see how it turn 24D6 into 9430. But actually it just change the hex value into decimal. Yeah, to be honest, I went into that function and spent a lot of time to analyze it and finally, I see that 24D6 and 9430 are the same number… This is sad.

Ok, so you will get the key which is “CW”+ ”the key you generate”+ ”CRACKED”.

Any question, please contact me at xudong_shao@hotmail.com