The beginning of pico ctf 2022

pico-2022.clj

(ns pico)

;; basic-mod1
;;

(def data [91 322 57 124 40 406 272 147 239 285 353 272 77 110 296 262 299 323 255 337 150 102])


(def alph
  "0-25 is the alphabet (uppercase), 26-35 are the decimal digits, and 36 is an underscore."
  (clojure.string/split "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_" #""))


(->> data
     (map #(mod % 37))
     (map #(alph %))
     (clojure.string/join ""))


;; basic-mod2

(def msg-basic-mod2 (slurp "https://artifacts.picoctf.net/c/500/message.txt"))


(defn modinverse [a m]
  "https://stackoverflow.com/questions/4798654/modular-multiplicative-inverse-function-in-python"
  (->> (range 1 m)
       (filter (fn [x]
                 (when (= 1 (mod (* (mod a m) (mod x m)) m))
                   x)))
       (first)))


(defn flagify [s] (format "picoCTF{%s}" s))


(defn parse-int [s] (Integer/parseInt s))


(->> (clojure.string/split msg-basic-mod2 #" ")
     (map parse-int)
     (map #(mod % 41))
     (map #(modinverse % 41))
     (map dec)
     (map #(alph %))
     (clojure.string/join "")
     flagify)


;; 3
;;
;; 99 tegn?
;; 123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789


;; 4
;;
;; 378
;; cvpbPGS{P7e1S_54I35_71Z3}
;; https://www.dcode.fr/caesar-cipher, mens jeg venta på brew install ciphey


;; 5
;;
;; https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34527
;; picoCTF{CVE-2021-34527}