PicoCTF_2017: Missing Identity

Category: Master Points: 100 Description:

Turns out, some of the files back from Master Challenge 1 were corrupted. Restore this one file and find the flag.

Hint:

What file is this? What do you expect to find in the file structure? All characters in the file are lower case or numberical. There will not be any zeros.

Write-up

This seems to be a zip file, unzipped contents doesn't appear to contain flags, however we get an interesting error.

Archive:  picoctf_2017_writeup/master/master_2/file
file #1:  bad zipfile offset (local header sig):  0

Hmmm... Let's try to extract it with offsets

$ dd if=file of=flag.png bs=1 count=93628 skip=43

Now we get a black PNG file? Hmm... Courtesy of @zst123, apparently JD-GUI happens to fix archives too! Doing a rename on file to file.zip and running it through JD-GUI gives us the flag! Even though I'm sure that's cheating, heh!

Therefore, the flag is zippidydooda29494995.

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