lynn

from copy import deepcopy

# puzzle = '''\
#     ...12....
#     .3.......
#     22.......
#     .2.....4.
#     .....3.3.
#     .........
#     ..24...2.

lynn

jailCTF 2025 writeup: pycryptojail

I enjoyed this crypto-based Python jail challenge at jailCTF 2025. I even found a partially unintended solution! Here's my writeup.

0. The challenge

#!/usr/local/bin/python3
from Crypto.Util.number import bytes_to_long, long_to_bytes, getPrime
import os

lynn

// ==UserScript==
// @name         Ctrl+E to End
// @version      1.0.0
// @description  Make Ctrl+E move the caret to the end of the line in input and textarea fields (Emacs-style)
// @match        https://*.github.com/*
// @grant        none
// @run-at       document-start
// ==/UserScript==

(function () {

lynn

// https://wavepot.com/

const tau = 2*Math.PI;
const bpm = 132;
const bps = bpm / 60;
const spb = 1 / bps;

function pos(t) {
  const beat = Math.floor(t / spb);
  const frac = (t / spb) % 1.0;

lynn

import random

LONGEST_KEY = 2
STROKE = "KWR*RBG"


def keysmash(alphabet, size):
    smash = ["a"] * random.randint(0, 1)
    queue = list(alphabet)
    for _ in range(size):

lynn

from PIL import Image, ImageDraw

sprite_data = bytes.fromhex('''
    00 00 3c 06 1c 06 3c 00 00 7f c3 f9 e3 f9 c3 ff
    00 00 68 2c 78 2c 34 00 00 fe ff ff ff ff ff ff
    00 01 19 07 0f 1f 07 0f ff ff e7 fb fd fe ff ff
    00 80 f0 e0 c0 f0 f8 f8 ff ff ff ff ff ff 7f 7f
    0f 0e 0c 00 80 ff ff 7f ff ff ff ff 7f 00 00 00
    e8 e0 e0 60 01 ff ff fe 7f ff ff ff fe 00 00 00
''')

lynn

import data.nat.fib
import data.matrix.basic
import data.matrix.notation
import linear_algebra.matrix.determinant

theorem matrix.map_pow {m α β : Type*} [fintype m] [decidable_eq m] [semiring α]
                       {M : matrix m m α} {n : ℕ} [semiring β] {f : α →+* β} :
  (M ^ n).map ⇑f = (M.map ⇑f) ^ n :=
begin
  induction n,

lynn

# Discord bot for playing ABC notation music.
#
# ### Installation
# - Get the dependencies: abc2midi, timidity, ffmpeg, and lame.
# - `pip install discord.py`
# - `ACCORD_TOKEN=(your bot token) python3 accord.py`
#
# ### Usage
# In any channel where the bot is, say: $play (abc notation)
# The input may be multiple lines long, and may be in a ```code block```.

lynn

module PrettyParseError (
    prettyParseError,
    PrettyParseErrorOptions(PrettyParseErrorOptions),
    prettyParseErrorDefaults
) where

import Data.List (intercalate, nub)
import Text.Parsec
import Text.Parsec.Error
import Text.Parsec.Pos

lynn

/// A "fractional part" function on f32s that does bitwise magic
/// on the representation of its argument.
pub fn frac(f: f32) -> f32 {
    f32::from_bits(_frac(f.to_bits()))
}

/// A "fractional part" function that operates on a signed integer
/// representation of an IEEE single-precision floating point number.
fn _frac(i: u32) -> u32 {
    // A floating point number consists of a sign bit,