# Tag: writeup

## 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

## 1st Crypto CTF 2019 – Least Solved Challenges

Brief solution ideas to the least solved Crypto CTF challenges.

## 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] …

## 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 lucky.chall.polictf.it 31337 chall.py Summary: breaking truncated-to-MSB LCG with top-down bit-by-bit search.

## 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 Flag.java Summary: DSA with short secrets, lattice + meet-in-the-middle attack.

## 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 …

## 0CTF 2017 Quals – OneTimePad 1 and 2

I swear that the safest cryptosystem is used to encrypt the secret! oneTimePad.zip Well, maybe the previous one is too simple. So I designed the ultimate one to protect the top secret! oneTimePad2.zip Summary: breaking a linear and an LCG-style exponential PRNGs.

## 33C3 CTF 2016 – beeblebrox (Crypto 350)

Make bad politicians resign! nc 78.46.224.72 2048 files Summary: factorization-based attack on a signature method

## Google CTF – Spotted Wobbegong (Crypto 100)

Are you able to defeat 1024-bit RSA? public.pem Summary: breaking RSA with PCKS v1.5 padding and exponent 3.

## Google CTF – Jekyll (Crypto)

Can you access the admin page? You can look at the crypto here. source.py Summary: finding a preimage for a simple 64-bit ARX-based hash.