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PwnThyBytes CTF 2019 – Wrong Ring (Crypto)

Is post quantum cryptography too complex for you? wrong_ring.sage Summary: Ring-LWE with small error, hidden under a number field

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1st Crypto CTF 2019 – Least Solved Challenges

Brief solution ideas to the least solved Crypto CTF challenges.

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Midnight CTF 2018 Finals – Snurre128

In this challenge we have a stream cipher based on LFSR and nonlinear filtering function. It has 128-bit LFSR secret state and we are also given 1600 keystream bits. Our goal is simply to recover the key which is the initial state. Here is the nonlinear filtering function: f(v) = v[0] ^ v[1] ^ v[2] …

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0CTF 2018 Quals – zer0C5 (Crypto 785)

0ops Cipher 4, hope you enjoy it:) nc 1234 Summary: related-key attack on weakened variant of RC4

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0CTF 2018 Quals – zer0SPN (Crypto 550)

0ops SPN, hope you enjoy it:) Summary: linear cryptanalysis on toy block cipher

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0CTF 2018 Quals – zer0TC (Crypto 916)

0ops Toy Cipher, hope you enjoy it:) Summary: meet-in-the-middle and key-schedule constraints

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TWCTF 2017 – Solutions for BabyPinhole, Liar’s Trap, Palindrome Pairs Challenge

Scripts with short explanations: BabyPinhole (crypto 163) Liar’s Trap (crypto/ppc 281) Palindrome Pairs – Challenge Phase (ppc 63+337)

Polictf 2017 – Lucky Consecutive Guessing (Crypto)

We implemented a random number generator. We’ve heard that rand()’s 32 bit seeds can be easily cracked, so we stayed on the safe side. nc 31337 Summary: breaking truncated-to-MSB LCG with top-down bit-by-bit search.

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Google CTF 2017 Quals – BLT (Bleichenbacher’s Lattice Task – Insanity Check)

A slow descent into the dark, into madness, futility, and despair. BLT.jar (not necessary) STDOUT Summary: DSA with short secrets, lattice + meet-in-the-middle attack.

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Google CTF 2017 Quals – Crypto writeups

Scripts with short explanations for all crypto tasks (except RSA) from Google CTF Quals 2017: Crypto Backdoor Introspective CRC Shake It RSA CTF Challenge (no writeup, but I think it’s similar to this old one) Rubik Bleichenbacher’s Lattice Task (full writeup here)

0CTF 2017 Quals – Zer0llvm

Talent Yang loves to customize his own obfuscator. Unfortunately, he lost his seed when he was watching Arsenal’s UEFA game. What a sad day! His team and his seed were lost together. To save him, could you help him to get back his seed? We can not save the game, but we may be able …

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0CTF 2017 Quals – OneTimePad 1 and 2

I swear that the safest cryptosystem is used to encrypt the secret! Well, maybe the previous one is too simple. So I designed the ultimate one to protect the top secret! Summary: breaking a linear and an LCG-style exponential PRNGs.

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33C3 CTF 2016 – beeblebrox (Crypto 350)

Make bad politicians resign! nc 2048 files Summary: factorization-based attack on a signature method

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HITCON CTF QUALS 2016 – Reverse (Reverse + PPC 500)

At least our ETA is better than M$. reverse.bin Summary: optimizing an algorithm using Treap data structure and CRC32 properties.

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HITCON CTF QUALS 2016 – PAKE / PAKE++ (Crypto 250 + 150)

pake1.rb pake2.rb Summary: attacking password-based key exchange schemes based on SPEKE with MITM.

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