Reversing.kr - Easy Crack (100pts)

This writeup had been sitting on my PC for some time.
I think it's probably a good time to release it. :D

You can register and download this file here.
http://reversing.kr/download.php?n=1
Alternatively, here is the mirror of the file.
Easy_CrackMe.zip

Required Tools:
IDA Pro

Initial Analysis:
Let's load this binary up with IDA Pro.


From the above image, we can see the "WinMain" which is calling "DialogFunc".

If we follow to "DialogFunc", we will see that it will call "sub_401080" as shown in the image below.


So let's take a quick look at "sub_401080" and if we practice enough with keygen and crackmes, you will know by now that we should check out GetDlgItemText first.


Further Analysis on the Algorithm:
If we study hard enough, you will see that after the application grabbed the user's input data, it will do a comparison with the 2nd byte as shown here.

cmp byte ptr [esp+5], 61h ; Compare 2nd byte with 0x61.

This means that our 2nd character must be a since 61h means "a" according to http://www.asciitable.com/

Let's move on the 2nd comparison.

As we can see from the image above, it's trying to compare user's 3rd and 4th bytes with "5y"

Now let's move downwards.

Ok, now it's trying to load the 5th bytes until end of user input and comparing byte by byte with "R3versing"

Finally, we saw another comparison. This time round, it's trying to compare the 1st byte with 0x45 which is "E"

Conclusion:
Now let's move back all the newly acquired clues before we are being told whether the input key is valid or not.
E + a + 5y + R3versing == Ea5yR3versing

Now let's enter this key "Ea5yR3versing" and we have successfully solved this binary.

cheers
0x4a61636f62