matryoshkryption

• Author: lemeda
• Type: steganography

Statement

Part 1

Wow! I heard about that conf from 31C3 on file formats tweaks and the result is pretty impressive.

Will you find what is hidden inside that matryoshka?

Part 2

You need to solve the first part of the challenge first.

File provided to the challenger

• ./export/matryoshkryption.tar.gz

Hints

• Part 1: none
• Part 2: Don't use deprecated software!

Build the challenge

• make phase1
• In Audacity:
  • Open ./build/spectro.wav
  • File > Import > Audio > browse to ./build/morse.mp3
  • Select All, Tracks > Mix > Mix and Render
  • File > Export > Export as MP3 → ./build/audio.mp3
• make phase2

Update flags or config files

Update config/flag1 (intermediate flag), config/flag2 (final flag) or another file in config/ and rebuild the chall (see above for rebuilding).

List of files in config:

• flag1: intermediate flag (flag of 1st part)
• flag2: final flag (flag of 2nd part)
• pdf_template: template text used for generating the music score (pdf document)
• vc_passphrase: decryption passphrase for the VeraCrypt volume

Some more files can be provided in config/ and are created if not already present:

• png_key: key to use to decrypt png file into pdf file
• pdf_key: key to use to decrypt pdf file into mp3 file
• mp3_key: key to use to decrypt mp3 file into mp4/VC hybrid file

Organization of the repo

• directory assets/ contains the resources which are necessary to build the challenge
• directory config/ contains the config files necessary to build the challenge as well as both flag files
• directory solution/ contains a write-up of the challenge..
• directory src/ contains the core of the challenge, that is to say its code and more generally any file required to make it work properly