[Writeup] Vòng loại WhiteHat Grand Prix 2015: For100

Nguồn: teamavidya (https://github.com/teamavidya/ctf/tr...orensics100%5D)

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Challenge

Download the file and we get a video file with balls bouncing around. Video on youtube here.

[video=youtube;h-E8FpNbVeA]https://www.youtube.com/watch?v=h-E8FpNbVeA[/video]

Solution

After analysing the video we noticed that certain frames contain a different image. So to analyse this better we extract all the frames of the video. There are many ways to do this but in this instance we used ffmpeg:

ffmpeg -i ~/path_to_file/for100.mp4 ./frames/for100-%06d.png

Sorting the extracted frames by size made it easy to identify 6 images which contain what look like ASCII art.





Using GIMP we play around with each line until we can make readable ASCII art.



The image says sha1 so create the sha and submit it.

WhiteHat{ddbae30b37b4e46bf54f91766fa02b42c4c0927d}

Solved by

destiny & blanky