HTB university ctf

potion.hs

import Data.Char (ord)
import Data.Bits (xor)

-- Complete the incantation...
flag = "HTB{4_m0n4d_15_ju57_4_m0n01d_1n_7h3_c47360ry_0f_3nd0func70r5!!}"

extractFlag :: String -> String
extractFlag (s:rest)
  | s == 'H' ||  s == 'T' ||  s == 'B'
  = extractFlag rest
  | s == '{' && last rest == '}'
  = init rest
  | otherwise = error ("Invalid format")

chunks :: Int -> [a] -> [[a]]
chunks n l
  | n == 0 = []
  | n == 1 = [[x] | x <- l]
  | length l <= n = [l]
  | otherwise = [take n l] ++ (chunks n (drop n l))

takeLast :: Int -> [a] -> [a]
takeLast n = reverse . take n . reverse

a = [-43, 61, 58, 5, -4, -11, 64, -40, -43, 61, 62, -51, 46, 15, -49, -44, 47, 4, 6, -7, 47, 7, -59, 52, -15, 11, 7, 61, 0]
b = [6, 106, 10, 0, 119, 52, 51, 101, 0, 0, 15, 48, 116, 22, 10, 58, 125, 100, 102, 33]
c = [304, 357, 303, 320, 304, 307, 349, 305, 257, 337, 340, 309, 428, 270, 66]
checkFlag :: String -> Bool
checkFlag flag =
  length content == 58 &&
  all (==True) (map (\ (l,r) -> l == r) (zip one a)) &&
  all (==True) (map (\ (l,r) -> l == r) (zip two b)) &&
  all (==True) (map (\ (l,r) -> l == r) (zip three c))
  where content = map ord (extractFlag flag)
        one     = map (\ [l, r] -> (l - r)) (chunks 2 content)
        two     = map (foldr xor 0) (chunks 3 content)
        three     = map (foldr (+) 0) (chunks 4 content)

main = putStrLn (if (checkFlag flag)
    then "The spell went off without a hitch!"
    else "You disappear in a puff of smoke!"
  )

potion.rb

$a = [-43, 61, 58, 5, -4, -11, 64, -40, -43, 61, 62, -51, 46, 15, -49, -44, 47, 4, 6, -7, 47, 7, -59, 52, -15, 11, 7, 61, 0]
$b = [6, 106, 10, 0, 119, 52, 51, 101, 0, 0, 15, 48, 116, 22, 10, 58, 125, 100, 102, 33]
$c = [304, 357, 303, 320, 304, 307, 349, 305, 257, 337, 340, 309, 428, 270, 66]

def chunks n, arr
	res = arr.each_slice(n).to_a
	return res[..-2] if res.last.length != n
	res
end

def checker flag
	one = (chunks 2, flag).map {|a,b| a - b}
	two = (chunks 3, flag).map {|a,b,c| a^b^c}
	three = (chunks 4, flag).map &:sum

	#puts "#{flag} pass a" if one == $a.first(one.length)
	#puts "#{flag} pass b" if two == $b.first(two.length)
	#puts "#{flag} pass c" if three == $c.first(three.length)

	one == $a.first(one.length) &&
	two == $b.first(two.length) &&
	three == $c.first(three.length)
end

chars = "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_!".chars.map &:ord

# returns [52, 95, 109, 48]
# for pos in chars.permutation 4
# 	# p pos if checker pos
# end

first = [52, 95, 109, 48]

possibilities = [first]

54.times do
 	newposs = []
	for c in chars
		for pos in possibilities
			flag = pos + [c]
			if checker flag
				print flag.map(&:chr).join + "         \r" 
				newposs << flag
			end
		end
	end
	possibilities = newposs
end

puts