DefCamp CTF Qualification 2017 Writeup

チーム Harekaze で DefCamp CTF Qualification 2017 に参加しました。(25th/473)

[Junior] HEX Warm Up

A friend of mine is learning about encryption and now is challenging me to break it! Can you give it a go? Download 
Author: Lucian Nitescu

Downloadしたzipを解凍し、binwalk -e lock.isoで、中のindex.txtにFlag

mb% ll
total 8
-rw-r--r--@ 1 mb  staff  2113 10  4 12:26 junior3.zip
mb% unzip junior3.zip
Archive:  junior3.zip
  inflating: lock.iso
  inflating: ransomware.py
mb% ll
total 24
-rw-r--r--@ 1 mb  staff  2113 10  4 12:26 junior3.zip
-rw-rw-r--@ 1 mb  staff  1058  9 21 12:43 lock.iso
-rw-rw-r--@ 1 mb  staff  1804  9 21 12:43 ransomware.py
mb% binwalk -e lock.iso

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
0             0x0             xz compressed data
112           0x70            Zip archive data, at least v2.0 to extract, compressed size: 278, uncompressed size: 427, name: index.txt
536           0x218           End of Zip archive

mb% ll
total 24
drwxr-xr-x  6 mb  staff   192 10  4 12:29 _lock.iso.extracted
-rw-r--r--@ 1 mb  staff  2113 10  4 12:26 junior3.zip
-rw-rw-r--@ 1 mb  staff  1058  9 21 12:43 lock.iso
-rw-rw-r--@ 1 mb  staff  1804  9 21 12:43 ransomware.py
mb% cd _lock.iso.extracted
0       0.xz        70.zip      index.txt
mb% cat index.txt | grep DCTF
DCTF{474dac08d29d013515a312d1a8460050634f9b3cb6a696a4c73652d1802a1872}

よって、 DCTF{474dac08d29d013515a312d1a8460050634f9b3cb6a696a4c73652d1802a1872}

ソーシャル・エンジニアリング