Level 12 → 13

Level Goal

The password for the next level is stored in the file data.txt, which is a hexdump of a file that has been repeatedly compressed. For this level it may be useful to create a directory under /tmp in which you can work. Use mkdir with a hard to guess directory name. Or better, use the command mktemp -d. Then copy the datafile using cp, and rename it using mv (read the manpages!)

Write-Up

1. Create a temporary directory and copy the file:

mktemp -d
cp data.txt /tmp/tmp.83OGZ2BEJL
cd /tmp/tmp.83OGZ2BEJL

1. Reverse the hexdump:

xxd -r data.txt > data

1. Determine the file type and decompress repeatedly:

file data
mv data data.gz
gzip -d data.gz
file data
mv data data.bz2
bzip2 -d data.bz2
file data
mv data data.gz
gzip -d data.gz
file data
tar -xvf data
file data5.bin
tar -xvf data5.bin
file data6.bin
mv data6.bin data6.bz2
bzip2 -d data6.bz2
file data6
tar -xvf data6
file data8.bin
mv data8.bin data8.gz
gzip -d data8.gz
file data8

1. Finally, the password was revealed:

cat data8

The retrieved password: FO5dwFsc0cbaIiH0h8J2eUks2vdTDwAn

1. Access the next level:

ssh [e-mail] -p 2220

Enter the password when prompted.

Lessons Learned

• Hexdumps can be reversed using the xxd command

• File types can be determined using the file command

• Different compression methods require different decompression tools (gzip, bzip2, tar)

• Creating temporary directories is useful for working with complex file manipulations

• Multiple layers of compression require patience and systematic approach to unravel

-- Othmane