ctf writeups ✏️

2023

Corrupted: RSA key recovery from censored private key
Dual Signature Algorithm: Leak DSA key from nonce and key reuse with different modulus using CVP
EasySSTI: Golang SSTI into RFI using echo Context scope
Check_Number_63: Recover RSA key from modulus reuse across different $e$ with CVP
ngo: Speed up LSFR with fast exponentiation
Admin Dashboard: HTTP method confusion + forging LCG token
Hardware is not so hard: SD / SPI packet carving
serverless: Reverse obfuscated RSA function in webpage
Merkle Hellman: Small cipher space on knapsack cryptosystem

janken vs kurenaif: Recover seed for python PRNG
witches_symmetric_exam: Chaining OFB padding oracle into ECB encryption oracle into GCM encryption / decryption oracle
insufficient: Break
multivariate polynomial shares with CVP
this_is_not_lsb: RSA interval oracle and binary search
BBB: Polynomial RNG parameter selection to make RNG cyclic + Hastad’s broadcast attack on RSA
pqpq: Polynomial massaging to break RSA

Bro-key-n: RSA key recovery from censored private key
Sussy ML: Exploratory data analysis and clustering on intermediate image classifier output
blackboxwarrior: imagehash.average_hash() collision
mom can we have AES: MITM on toy handshake protocol + chosen plaintext attack on AES-ECB
That-crete Log: Pohlig-Hellman on partially smooth prime
Elliptic Clock Crypto: Discrete log on ellipse curve with smooth order

Poker: Recover python PRNG behind a modulo
Secure Encoding: Base64: Revert substitution cipher on Base64 data using simulated annealing
Living Without Expectations: Break learning with errors with CVP
Lorge: Break RSA key with smooth primes using Pollard p-1 attack despite mitigations
stream: Reverse binary and derive LCG key
hash: Custom hash collision using z3
otp: Biased one time pad

Trademark: Attack-defense service with polynomial cryptosystem and authorization bypass

Probability: Recover python PRNG from random.random() output + dynamic programming to win blackjack
To Infinity: Pathfinding over finite field using CVP and continued fractions
WeirdMachine: Assembly golf with awkward branching behaviour
Welcome: Carving QR code from video with opencv
Username Generator: XSS using window.name

Feed the Beast: blind SQLi via RSS feed parser
You shall not pass!: Domain spoofing + XSS via postMessage and client side template injection
IOT RSA Token: 1602 LCD protocol sniffing + forging RSA SecurID OTP