CTF#04 Solution
Text File Saved as Zip
Number of files: 1
Flag pattern: flag#**********
Flag: flag#gandhalf13
Solvable on which OS: Windows
This solution’s OS: Windows 11
Software: WinZip / WinRar, Text editor
Estimated solution time: 3 minutes
Internet access required: For software installation only
Details
Goal
The user will try to open the file and realize it’s in the wrong format, and then try to see which format it is. Opening the file in a text editor (e.g., Notepad), with or without changing the file’s extension to .txt, will immediately reveal the flag.
Implementation
We received the file wrong format.zip:
When we try to open the file, we get an error message:
Something’s not working. This must be a mistake. But maybe it is deliberate? We also realize the file’s size is tiny: 15 bytes in total.
If the file is so small, it won’t hurt to try to see what’s inside it.
So, let’s open it in a text editor:
(Changing the file’s extension to .txt will launch a text editor by default to open the file)
And that’s our flag.
And there’s our flag.
Even if we open the file in a text editor without changing the file’s extension, the result is still the same:
