Written by Michael Zhang, Writeup by Tim Winters
You revieved a zip file but find that it is orrupted! You're given that it's missing a couple of bytes at the beginning. Replace these bytes and find the flag
No clue what bytes to insert? Perhaps looking into file headers would be helpful. Also, you might want to download a hex editor, such as HxD.
A google seach of .zip file headers will lead you to this website. Ctrl-F ".zip" shows that the file header for a .zip file is 50 4B 03 04
If we open the file in a hex editor program, it shows the first byte as 03 04 14 00. We need it to be 50 4B 03 04, and we have 03 04, so by adding 50 4B the first byte is 50 4B 03 04 and the file will extract.
In the extracted folder, we see a number of files (3000). Opening a file in a text editor reveals a series of characters. To find the flag, use the findstr (grep for mac) and search for "flag" in all files. To search all files, use a '*'. The final command will be grep flag *. The flag is hidden in file f2590.
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