Cybersecurity Notes
MathematicsCryptography
  • Cybersecurity Notes
  • Binary Exploitation
    • Stack
      • Introduction
      • ret2win
      • De Bruijn Sequences
      • Shellcode
      • NOPs
      • 32- vs 64-bit
      • No eXecute
      • Return-Oriented Programming
        • Calling Conventions
        • Gadgets
        • Exploiting Calling Conventions
        • ret2libc
        • Stack Alignment
      • Format String Bug
      • Stack Canaries
      • PIE
        • Pwntools, PIE and ROP
        • PIE Bypass with Given Leak
        • PIE Bypass
      • ASLR
        • ASLR Bypass with Given Leak
        • PLT and GOT
        • ret2plt ASLR bypass
      • GOT Overwrite
        • Exploiting a GOT overwrite
      • RELRO
      • Reliable Shellcode
        • ROP and Shellcode
        • Using RSP
        • ret2reg
          • Using ret2reg
      • One Gadgets and Malloc Hook
      • Syscalls
        • Exploitation with Syscalls
        • Sigreturn-Oriented Programming (SROP)
          • Using SROP
      • ret2dlresolve
        • Exploitation
      • ret2csu
        • Exploitation
        • CSU Hardening
      • Exploiting over Sockets
        • Exploit
        • Socat
      • Forking Processes
      • Stack Pivoting
        • Exploitation
          • pop rsp
          • leave
    • Heap
      • Introduction to the Heap
      • Chunks
      • Freeing Chunks and the Bins
        • Operations of the Fastbin
        • Operations of the Other Bins
      • Malloc State
      • malloc_consolidate()
      • Heap Overflow
        • heap0
        • heap1
      • Use-After-Free
      • Double-Free
        • Double-Free Protections
        • Double-Free Exploit
      • Unlink Exploit
      • The Tcache
        • Tcache: calloc()
        • Tcache Poisoning
      • Tcache Keys
      • Safe Linking
    • Kernel
      • Introduction
      • Writing a Char Module
        • An Interactive Char Driver
        • Interactivity with IOCTL
      • A Basic Kernel Interaction Challenge
      • Compiling, Customising and booting the Kernel
      • Double-Fetch
        • Double-Fetch without Sleep
      • The Ultimate Aim of Kernel Exploitation - Process Credentials
      • Kernel ROP - ret2usr
      • Debugging a Kernel Module
      • SMEP
        • Kernel ROP - Disabling SMEP
        • Kernel ROP - Privilege Escalation in Kernel Space
      • SMAP
      • modprobe_path
      • KASLR
      • KPTI
    • Browser Exploitation
      • *CTF 2019 - oob-v8
        • The Challenge
      • picoCTF 2021 - Kit Engine
      • picoCTF 2021 - Download Horsepower
  • Reverse Engineering
    • Strings in C++
    • C++ Decompilation Tricks
    • Reverse Engineering ARM
  • Blockchain
    • An Introduction to Blockchain
  • Smart Contracts and Solidity
  • Hosting a Testnet and Deploying a Contract
  • Interacting with Python
  • Writeups
    • Hack The Box
      • Linux Machines
        • Easy
          • Traceback
        • Medium
          • Magic
          • UpDown
        • Hard
          • Intense
      • Challenges
        • Web
          • Looking Glass
          • Sanitize
          • Baby Auth
          • Baby Website Rick
        • Pwn
          • Dream Diary: Chapter 1
            • Unlink Exploit
            • Chunk Overlap
          • Ropme
    • picoGym
      • Cryptography
        • Mod 26
        • Mind Your Ps and Qs
        • Easy Peasy
        • The Numbers
        • New Caesar
        • Mini RSA
        • Dachshund Attacks
        • No Padding, No Problem
        • Easy1
        • 13
        • Caesar
        • Pixelated
        • Basic-Mod1
        • Basic-Mod2
        • Credstuff
        • morse-code
        • rail-fence
        • Substitution0
        • Substitution1
        • Substitution2
        • Transposition-Trial
        • Vigenere
        • HideToSee
    • CTFs
      • Fword CTF 2020
        • Binary Exploitation
          • Molotov
        • Reversing
          • XO
      • X-MAS CTF 2020
        • Pwn
          • Do I Know You?
          • Naughty
        • Web
          • PHP Master
      • HTB CyberSanta 2021
        • Crypto
          • Common Mistake
          • Missing Reindeer
          • Xmas Spirit
          • Meet Me Halfway
  • Miscellaneous
    • pwntools
      • Introduction
      • Processes and Communication
      • Logging and Context
      • Packing
      • ELF
      • ROP
    • scanf Bypasses
    • Challenges in Containers
    • Using Z3
    • Cross-Compiling for arm32
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  1. Writeups
  2. picoGym
  3. Cryptography

Credstuff

We found a leak of a blackmarket website's login credentials. Can you find the password of the user cultiris and successfully decrypt it? Download the leak here.

Opening up usernames.txt and passwords.txt in Pycharm, we see cultiris is on line 378 of usernames.txt so we go to line 378 of passwords.txt and find an encrypted password:

cvpbPGS{P7e1S_54I35_71Z3}

The {} are in place, implying that it's some sort of transposition cipher for the letters. We've done it numerous times, but we try a caesar cipher decode:

from string import ascii_lowercase, ascii_uppercase

enc_flag = 'cvpbPGS{P7e1S_54I35_71Z3}'

for shift in range(26):
    flag = ''

    for c in enc_flag:
        if c in ascii_lowercase:
            flag += ascii_lowercase[(ascii_lowercase.index(c) + shift) % 26]
        elif c in ascii_uppercase:
            flag += ascii_uppercase[(ascii_uppercase.index(c) + shift) % 26]
        else:
            flag += c

    print(flag)

# picoCTF{C7r1F_54V35_71M3}

In fact the shift is 13, so it's just a ROT13.

Last updated 4 months ago

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