/tags/crypto/Recent content in Crypto onHugo -- gohugo.ioThu, 17 Jul 2025 21:00:16 +0100/post/sr25-toxicity/Thu, 17 Jul 2025 21:00:16 +0100/post/sr25-toxicity/Click to expand challenge code from Crypto.Util.number import bytes_to_long from os import urandom from PIL import Image import numpy as np import random class DoubleLCG: def __init__(self, a1,a2, b1,b2, m, seed1, seed2): self.a1 = a1 self.a2 = a2 self.b1 = b1 self.b2 = b2 self.m = m self.state1 = bytes_to_long(urandom(6)) if seed1 is None else seed1 self.state2 = bytes_to_long(urandom(6)) if seed2 is None else seed2 self.counter = 0 def refresh(self): self./post/sr25-jigsaw/Thu, 17 Jul 2025 20:06:16 +0100/post/sr25-jigsaw/Click to expand challenge code from random import Random from Crypto.Util.number import bytes_to_long, long_to_bytes from Crypto.Cipher import AES from Crypto.Util.Padding import pad import os FLAG = os.getenv("FLAG", "FL1TZ{dummy_dum_dum}") COLOR_BLACK = "\x1b[30m" COLOR_RED = "\x1b[31m" COLOR_GREEN = "\x1b[32m" COLOR_YELLOW = "\x1b[33m" COLOR_BLUE = "\x1b[34m" COLOR_MAGENTA = "\x1b[35m" COLOR_CYAN = "\x1b[36m" COLOR_RESET = "\x1b[0m" BOLD = "\x1b[1m" RESET_BOLD = "\x1b[22m" class Jigsaw: def __init__(self): self.dealer = Random() def get_piece(self): return self./post/sr25-lights/Thu, 17 Jul 2025 19:31:16 +0100/post/sr25-lights/Click to expand challenge code from hashlib import sha256 from Crypto.Util.number import bytes_to_long, long_to_bytes from random import randint from Crypto.Cipher import AES from Crypto.Util.Padding import pad import json FLAG = b"FL1TZ{??????????????????????????}" p = 0xa9fb57dba1eea9bc3e660a909d838d726e3bf623d52620282013481d1f6e5377 a = -3 b = 27 E = EllipticCurve(GF(p), [a,b]) G = E.gens()[0] j = E.j_invariant() def gen_random_number(): while True: P = E.random_point() if P.order() > j: break return bytes_to_long(sha256(long_to_bytes(int(P.xy()[0]))).digest()[:8]) def derive_key_iv(secret): key = sha256(long_to_bytes(secret))./post/sr25-eob/Thu, 17 Jul 2025 18:48:16 +0100/post/sr25-eob/Click to expand challenge code package main import ( "bufio" "crypto/rand" "encoding/hex" "fmt" "log" "math/big" "net" "strings" ) const LEN = 31 const MASK = (1 << LEN) - 1 const FLAG = "FL1TZ{?????????????????????????????}" var taps1 = []int{/*?, ?, ?, ?*/} var taps2 = []int{/*?, ?, ?, ?*/} type LFSR struct { state uint64 taps []int count int } func (l *LFSR) rekey(newseed uint64) { l.state = newseed } func newLFSR(taps []int) *LFSR { seed := genRandSeed() return &LFSR{state: seed, taps: taps} } func (l *LFSR)lfsrStep() uint8 { feedback := uint64(0) if l./post/sr25-novacain/Thu, 17 Jul 2025 18:06:16 +0100/post/sr25-novacain/Click to expand challenge code #!/usr/bin/env python3 """ Prove you know a satisfying assignment without revealing it—1 take per round, no pain. Protocol (each round): 1) Commit to each bit of your assignment. 2) I'll challenge you >:) 3) I'll pen either the full assignment or just the clause bits. 4) Survive all 128 rounds, and I might just give yout the flag. """ import random import hashlib from Crypto./post/sr25-puppet/Thu, 17 Jul 2025 17:57:16 +0100/post/sr25-puppet/Click to expand challenge code import os import secrets import sys import time from Crypto.Cipher import AES from Crypto.Util.Padding import pad, unpad SERVER_KEY = secrets.token_bytes(16) FLAG = os.environ.get("FLAG", "FL1TZ{????????????}") def issue_token(user_id: str) -> bytes: iv = secrets.token_bytes(16) payload = f"uid={user_id}&role=puppet".encode() cipher = AES.new(SERVER_KEY, AES.MODE_CBC, iv=iv) return iv + cipher.encrypt(pad(payload,16)) def check_token(token: bytes) -> str: iv = token[:16] ct = token[16:] cipher = AES.new(SERVER_KEY, AES.MODE_CBC, iv=iv) pt = cipher.decrypt(ct) print(f"Decrypted token: {pt!/post/sr25-ok-computer/Thu, 17 Jul 2025 17:22:16 +0100/post/sr25-ok-computer/Click to expand challenge code from Crypto.Util.number import getPrime, bytes_to_long flag = "FL1TZ{*********}" p = getPrime(512) q = getPrime(512) n = p * q e = 5 m = bytes_to_long(flag.encode()) c = pow(m, e, n) data = { "n": n, "e": e, "c": c } with open("computer.json", "w") as f: import json json.dump(data, f, indent=4) Since this CTF was destined to be pretty advanced, I didn’t want beginner players to leave with 0 solves./post/l3ak-oracle/Mon, 14 Jul 2025 19:47:16 +0100/post/l3ak-oracle/This challenge was a standard Hidden Number Problem dressed up in fantasy cosplay. The objective was clear: uncover a hidden value $\alpha$ using Babai's CVP algorithm Challenge Overview The challenge spins up a remote service that hands out: p: A 256-bit prime modulus. n: The bit length of p, which is 256. k: The number of bits to be leaked, calculated as int(n**0.5) + n.bit_length() + 1, which comes out to 26./post/r3coin/Tue, 08 Jul 2025 18:02:16 +0100/post/r3coin/This challenge involves a blockchain-like system that uses a chameleon hash function for transaction integrity. The goal is to exploit the chameleon hash properties to forge a transaction “Selling|flag|x” that allows us to buy the flag. Mechanics The app lets up perform a set of actions to interact with the chain: Work: Gives us some money Buy Gift: Appends a “Buy” entry followed by a “Selling|gift|100” onto the chain Refund oldest: Turns the oldest “Buy” transaction into a “Work|x” entry by internally forging a satisfying hash.