I have developed a variant of GLP, GLP420!

Challenge contributed by y011d4

Connect at nc archive.cryptohack.org 26931

Challenge files:
  - server.sage

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Elliptic curves were originally studied for their beauty, then mathematics came.

Challenge contributed by Shadowwws

Connect at nc archive.cryptohack.org 39003

Challenge files:
  - chall.sage

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I have reimplemented a cryptosystem, but it sometimes behaves strangely. But I don't think it matters.

Challenge contributed by y011d4

Connect at nc archive.cryptohack.org 56048

Challenge files:
  - server.py

You must be logged in to submit your flag.

In CTF, there are many people who mistakenly encrypt p, q in RSA. But this time...

Challenge contributed by y011d4

Challenge files:
  - output.txt
  - chall.py

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also known as conveyor belt sushi

Challenge contributed by y011d4

Challenge files:
  - chall.sage
  - output.txt

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What if /dev/urandom is unrandom...?

Challenge contributed by y011d4

Connect at nc archive.cryptohack.org 2783

Challenge files:
  - server.py

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Hash-based authentication is great and I have invented one. Can you prove that my system is secure?

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 40156

Challenge files:
  - chall.py

You must be logged in to submit your flag.

"Find a collision for my hash algorithm! It is basically military-graded: The output is 256-bit long, and discrete log is hard! I even made it harder such that you don't even have the public parameters!"

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 9391

Challenge files:
  - chall.py

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

Challenge contributed by rkm0959

Connect at nc archive.cryptohack.org 35802

Challenge files:
  - chal.py

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"I have designed a failproof encryption system with possibly arbitrarily small public keys. I will be as famous as Et Al one day, but only if I can somehow figure out a decryption mechanism..."

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 42351

Challenge files:
  - ctf.xinetd
  - source.py
  - Dockerfile

You must be logged in to submit your flag.

"I am sure it's failproof now, I have increased the security levels too!¬"

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 36813

Challenge files:
  - ctf.xinetd
  - source.py
  - Dockerfile

You must be logged in to submit your flag.

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

Challenge contributed by CryptoHack

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 contributed by zeski

Connect at nc archive.cryptohack.org 44134

Challenge files:
  - key_recovery.py

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Mystiz's computer is lack of entropy. He needs to reuse randomness to generate the primes for RSA...

Challenge contributed by Mystiz

Challenge files:
  - output.txt
  - chall.py

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Find a collision for my hash algorithm! It is basically military-graded: The output is 256-bit long, and discrete log is hard! I even made it harder such that you don't even have the public parameters!

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 56434

Challenge files:
  - chall.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 contributed by Neobeo

Connect at nc archive.cryptohack.org 59737

Challenge files:
  - probability.py
  - Dockerfile

You must be logged in to submit your flag.

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 contributed by rkm0959

Connect at nc archive.cryptohack.org 45400

Challenge files:
  - chal.py

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

Challenge contributed by rkm0959

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 contributed by maple3142

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 contributed by CryptoHack

Challenge files:
  - output.txt
  - challenge.py

You must be logged in to submit your flag.

"Welcome to the Diffecient Security Key Database API, for securely and efficiently saving tons of long security keys! Feel *free* to query your security keys, and pay a little to add your own to our state-of-the-art database. We trust our product so much that we even save our own keys here!"

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 29201

Challenge files:
  - ctf.xinetd
  - source.py
  - Dockerfile

You must be logged in to submit your flag.

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 contributed by CryptoHack

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 contributed by maple3142

Connect at nc archive.cryptohack.org 45328

Challenge files:
  - server.py
  - elliptic_curve.py

You must be logged in to submit your flag.

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

Challenge contributed by joseph

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

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"COVID: *exists* vaccine jokes: *challenge_name*"

Challenge contributed by deuterium

Challenge files:
  - challenge.py

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In the beginning of 2020, Khaled A. Nagaty invented a cryptosystem based on key exchange. The cipher is faster than ever... It is impossible to break, right?

Challenge contributed by Mystiz

Challenge files:
  - output.txt
  - chall.py

You must be logged in to submit your flag.

"What's the fun of rolling up a hash function if it's not chaotic enough?"

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 18948

Challenge files:
  - chaos.xinetd
  - Dockerfile
  - challenge.py

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Every slightest mistake in cryptography would lead to a disastrous result. Let's see what will happen when you allow end-users to pick the mode of operation...

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 2951

Challenge files:
  - chall.py

You must be logged in to submit your flag.

Mystiz made a key vault which could encrypts his darkest secrets (i.e., the flag). Everything is protected with a bank-level encryption (i.e., a 256-bit key). You are welcome to look at the encrypted secrets and praise his cryptographic knowledge.

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 4077

Challenge files:
  - chall.py

You must be logged in to submit your flag.

Mystiz is really lazy. He expects that someone would crack the bank-level encryption, but he doesn't care about that. After all, the darkest secret is not that dark. He decided to change the numbers and release it to the public again. Now crack it!

Challenge contributed by Mystiz

Challenge files:
  - transcript.zip
  - chall.py

You must be logged in to submit your flag.

Some of the block cipher modes of operation are pretty vulnerable, which includes but not limited to padding oracle in CBC, key-recovery attacks with repeated nonces in GCM and _Zerologon_ in CFB8... What about OFB?

Challenge contributed by Mystiz

Challenge files:
  - output.txt
  - secret.py
  - chall.py

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"Do you believe in games of luck? I hope you make your guesses real or you'll be floating around,"

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 16189

Challenge files:
  - real.xinetd
  - Dockerfile
  - challenge.py

You must be logged in to submit your flag.

Okay. My secure authentication system was proved insecure (see [here](https://github.com/samueltangz/ctf-archive-created/tree/master/20201006-hkcert-ctf/sign-in-please)) as it got exploited last year by a bunch of bad guys. I improved the system and you would not be able to eavesdrop the passwords ever again.

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 60192

Challenge files:
  - chall.py

You must be logged in to submit your flag.

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

Challenge contributed by CryptoHack

Connect at nc archive.cryptohack.org 37916

Challenge files:
  - spongebob.py

You must be logged in to submit your flag.

`AddRoundKey`, `SubBytes`, `ShiftRows` and `MixColumns` are four crucial components are AES. They are used to protect the world in 2021. I wonder what will happen if some of them is out of function.

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 36161

Challenge files:
  - aes.py
  - chall.py

You must be logged in to submit your flag.

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

Challenge contributed by joseph

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

You must be logged in to submit your flag.

The deadline for writing challenges is coming! Mystiz, who claimed himself not well-known for reusing challenges, decided to free-ride and plagarize challenges from HKCERT CTF 2020. Maybe you can reuse the solve script last year for the flag. Ciphertext: `6ccb80c46c19243a37633d316a66871ca70ec8a44f48a80134f31d8d27f920c6bd5d810831833221d0f282130d2c222de38c2080ef995b2ad10dc5af8518`

Challenge contributed by Mystiz

Challenge files:
  - challenge.py

You must be logged in to submit your flag.

"Wise men once said, “Well, shake it up, baby, now Twist and shout come on and work it on out” I obliged, not the flag is as twisted as my sense of humour"

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 46347

Challenge files:
  - twist.xinetd
  - Dockerfile
  - challenge.py

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 contributed by NDH

Challenge files:
  - output.txt
  - source.py

You must be logged in to submit your flag.

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 contributed by NDH

Challenge files:
  - output.txt
  - source.py

You must be logged in to submit your flag.

"Python is so slow! Lets use nUmPy tO MAkE iT FaSTer. Only if there was a module for crypto in it :("

Challenge contributed by deuterium

Connect at nc archive.cryptohack.org 7265

Challenge files:
  - numpymt.xinetd
  - Dockerfile
  - challenge.py

You must be logged in to submit your flag.

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

Challenge contributed by joseph

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

You must be logged in to submit your flag.

Can you guess the 2020th number?

Challenge contributed by ndh

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 contributed by Mystiz

Connect at nc archive.cryptohack.org 53580

Challenge files:
  - chall.py

You must be logged in to submit your flag.

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

Challenge contributed by Mystiz

Connect at nc archive.cryptohack.org 1024

Challenge files:
  - chall.py

You must be logged in to submit your flag.