CrackMe #1 [C#]

Reverse Engineering Challenges
1

Hello guys,

this is my first CrackMe so dont except much. It quite simple to crack since there is no obfuscation involved here. But maybe i could add that later :slight_smile: The Program consists of two parts. The CrackMe1.exe and the License.dll.

Your goals are:

  • to write a keygen (really really easy)
  • to patch the programm so that you can enter anything and it says “License key valid”

Rules:
Dont modify the CrackMe1.exe in any Way! You can decompile to see what it does but dont change anything inside of it.

Have fun!

Downlaod: https://mega.nz/#!2QoTgBSD!h6sdjQDhZAbV1REUychAZ7QVdS5Q67Og4-cM5ceU8BY
Virustotal for the .exe: https://www.virustotal.com/#/file/96979226822e7b88e0c9cd058ed51c5a2dfcdeeb7e8974e09f08bc0446a4a4b4/detection (idk where this detection comes from)

Virustotal for the .dll: https://www.virustotal.com/#/file-analysis/NTEyODBkOTZkMTg5N2I5NGYwNjFiZjViMTlmYTM0MDk6MTUyNTYyNTg3Nw==

6 Likes
2
Spoiler

Username: GGen
License: D5451FA856A0814F98B800C013E6C92B
All you have to do is calculate MD5 Hash (there are many generators online) from username.
I just started .Net reflector to decompile and was just clicking around to this moment:
Bez%C2%A0tytu%C5%82u1
Then everything became clear

3 Likes
3

Hey @GGen!

Congrats on solving this :smiley:

Quick tip: on 0x00sec you can actually also use the [spoiler] something spoilery [/spoiler] format to conceal information. I noticed you found your own creative way to do it - but this is how we normally do it.

:slight_smile:

3 Likes
4

Cool! I spent 30 secs on flag1 and then spent 10 mins on flag2 but eventually find out that was only a simple patch check

5

Umm, in one of the goals you said to patch the program, then later you said to not modify anything inside the executable?

6

You can patch the program without editing the executable :slight_smile:

8

Is it possible to patch dll with same md5 ?