English [MMA 2015] [Forensics / Warmup – Splitted] Write up

Description

We were given an archive containing a network capture..

Resolution

First, we opened the .pcap file with wireshark.

In seconds we realized  the capture contains a multipart downloaded file “flag.zip” : interesting!

wireshark zip exportThen we exported all these files, making us 8 parts of zip file.

Thanks to the HTTP header “Content-Range” we were able to find the order for renaming the extracted .zip files.

| File N | Range |
|----------------|
| 1      | 0     |
| 5      | 469   |
| 6      | 938   |
| 2      | 1407  |
| 7      | 1876  |
| 0      | 2345  |
| 3      | 2814  |
| 4      | 3283  |

Then we renamed the exported files as part-X.zip, following the order of the “Content-Range”.

Finally we assembled the zip archive and extracted it .

$ cat part-*.zip > assembled.zip
$ unzip ./assembled.zip

Archive:  ./assembled.zip
inflating: flag.psd

$ file flag.psd

flag.psd: Adobe Photoshop Image, 640 x 400, RGB, 3x 8-bit channels

Oh, a psd file ! Let’s see the contents of its layers.

$ convert flag.psd flag.png
$ ls *.png

flag-0.png  flag-1.png    flag-2.png

The extracted layer in the flag-1.png file contains the flag!

flagFlag is : MMA{sneak_spy_sisters}

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