CTF Archive

This category is dedicated to hosting some of the best cryptography CTF challenges from the past. Like all our challenges, after solving, there's a page to share your write ups. However, unlike other categories, solving these challenges will not effect your position on the leaderboard.

If you are interested in having your CTF challenge hosted on our archive, please visit the following GitHub repository and make a pull request.


2022

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  • Breaking random functions is a dark art, and I need your help in this.

    Challenge written by rkm0959 and originally appeared in CODEGATE CTF 2022

    Connect at nc archive.cryptohack.org 35802

    Challenge files:
      - chal.py

    You must be logged in to submit your flag.


  • It only took me four heat deaths of the universe to encrypt this flag.

    Challenge written by CryptoHack and originally appeared in ICC Athens 2022

    Challenge files:
      - output.txt
      - functional.sage

    You must be logged in to submit your flag.


  • I got bored and made a new block cipher, but someone stole my flag and now i need to break it to get it back. Will you help me?

    Challenge written by zeski and originally appeared in DCTF 2022

    Connect at nc archive.cryptohack.org 44134

    Challenge files:
      - key_recovery.py

    You must be logged in to submit your flag.


  • I've been learning about probability distributions, but it's all very confusing so I'm just going to assume that my variant of blackjack gives an advantage to the house. I'll even bet a flag on it.

    Challenge written by Neobeo and originally appeared in SEETF 2022

    Connect at nc archive.cryptohack.org 59737

    Challenge files:
      - probability.py
      - Dockerfile

    You must be logged in to submit your flag.


  • RSA Permutation
    3 Solves · 0 Solutions

    So I got all the hex digits of the private key, but it seems that the hex digits went through some sort of a permutation.... Can you help me?

    Challenge written by rkm0959 and originally appeared in WACON 2022

    Connect at nc archive.cryptohack.org 45400

    Challenge files:
      - chal.py

    You must be logged in to submit your flag.


  • RSA Secret Sharing
    2 Solves · 0 Solutions

    ON 2-out-of-3 SECRET SHARING BASED ON RSA - MemeCrypt 2022

    Challenge written by rkm0959 and originally appeared in WACON 2022

    Connect at nc archive.cryptohack.org 42957

    Challenge files:
      - chal.py

    You must be logged in to submit your flag.


  • Another boring crypto challenge about signatures.

    Challenge written by maple3142 and originally appeared in TSJ CTF 2022

    Challenge files:
      - output.txt
      - challenge.py

    You must be logged in to submit your flag.


  • I want to keep my private key small, but I've heard this is dangerous. I think I've found a way around this though!

    Challenge written by CryptoHack and originally appeared in ICC Athens 2022

    Challenge files:
      - output.txt
      - challenge.py

    You must be logged in to submit your flag.


  • ed25519 magic
    7 Solves · 0 Solutions

    Ed25519 is all the rage these days - it's fast, has small keys and signatures, and is designed to be robust against side-channel attacks. But the scheme has some magic as originally conceived.

    Challenge written by CryptoHack and originally appeared in ICC Athens 2022

    Connect at nc archive.cryptohack.org 31144

    Challenge files:
      - chal.py
      - magic.xinetd
      - Dockerfile

    You must be logged in to submit your flag.


  • I am a bot imitating Pekora. You can talk with me through Elliptic-curve Diffie–Hellman protocol!

    Challenge written by maple3142 and originally appeared in AIS3 Pre-Exam 2022

    Connect at nc archive.cryptohack.org 45328

    Challenge files:
      - server.py
      - elliptic_curve.py

    You must be logged in to submit your flag.



2021

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  • 1337crypt is back. This time, with added complexity.

    Challenge written by joseph and originally appeared in DownUnderCTF 2021

    Challenge files:
      - 1337crypt-v2.sage
      - output.txt

    You must be logged in to submit your flag.


  • SpongeBob SquarePants / Battle for Bikini Bottom - Rehydrated
    5 Solves · 1 Solutions

    * Wait, `spongebob` and `squarepants` don't hash to the same thing?

    Challenge written by CryptoHack and originally appeared in HTB Cyber Apocalypse 2021

    Connect at nc archive.cryptohack.org 37916

    Challenge files:
      - spongebob.py

    You must be logged in to submit your flag.


  • Substitution Cipher III
    2 Solves · 0 Solutions

    Wait a MInute, that's not a substitution cipher!

    Challenge written by joseph and originally appeared in DownUnderCTF 2021

    Challenge files:
      - output.txt
      - substitution-cipher-iii.sage

    You must be logged in to submit your flag.


  • We’re about to launch a new public key cryptosystem, but its security has not been carefully reviewed yet. Can you help us?

    Challenge written by NDH and originally appeared in TETCTF 2021

    Challenge files:
      - output.txt
      - source.py

    You must be logged in to submit your flag.


  • Unimplemented
    6 Solves · 0 Solutions

    A new public key encryption algorithm is being invented, but the author is not quite sure how to implement the decryption routine correctly. Can you help him?

    Challenge written by NDH and originally appeared in TETCTF 2021

    Challenge files:
      - output.txt
      - source.py

    You must be logged in to submit your flag.



2020

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  • Can you solve my factorisation problem if I give you a hint?

    Challenge written by joseph and originally appeared in DownUnderCTF 2020

    Challenge files:
      - output.txt
      - 1337crypt.sage

    You must be logged in to submit your flag.


  • Can you guess the 2020th number?

    Challenge written by ndh and originally appeared in TETCTF 2020

    Connect at nc archive.cryptohack.org 63222

    Challenge files:
      - Dockerfile
      - 2020.py

    You must be logged in to submit your flag.


  • I am so excited having a chance talking to Alice. She told me to calm down - and sent me an encrypted secret.

    Challenge written by Mystiz and originally appeared in HKCERT CTF 2020

    Connect at nc archive.cryptohack.org 53580

    Challenge files:
      - chall.py

    You must be logged in to submit your flag.


  • Sign in Please
    7 Solves · 0 Solutions

    I have implemented a secure authentication system. You can't eavesdrop the passwords, can you?

    Challenge written by Mystiz and originally appeared in HKCERT CTF 2020

    Connect at nc archive.cryptohack.org 1024

    Challenge files:
      - chall.py

    You must be logged in to submit your flag.


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