Description

data.txt is a hexdump of a file that has been compressed multiple times. The goal is to reverse each layer of compression until the final plaintext file containing the password is reached.

Overview

• xxd -r reverses a hexdump back to binary.
• The file command identifies the compression type of the binary at each stage.
• Each step decompresses with the appropriate tool: gzip, bzip2, or tar.
• The process repeats until a plain ASCII file remains.

Background: Compression Formats

• gzip files begin with magic bytes \x1f\x8b; extension .gz.
• bzip2 files begin with BZh; extension .bz2.
• POSIX tar archives begin with ustar; extension .tar.
• Each format has a corresponding -d or -x flag to decompress/extract.

Solution

Step 1: Reverse the Hexdump

mkdir /tmp/work && cd /tmp/work
cp ~/data.txt .
xxd -r data.txt > data.bin

Step 2: Iteratively Decompress

• Check type with file data.bin, rename accordingly, then decompress.
• Repeat until file reports ASCII text.

file data.bin
# e.g. "gzip compressed data" -> mv data.bin data.gz && gzip -d data.gz
# e.g. "bzip2 compressed data" -> mv data.bin data.bz2 && bzip2 -d data.bz2
# e.g. "POSIX tar archive" -> tar -xf data.tar

• After 9 rounds of decompression, a plain text file remains.

Step 3: Read the Password

cat data10.txt

Password

wbWdlBxEir4CaE8LaPhauuOo6pwRmrDw