CONFidence DS CTF Teaser: add Crypto100 source

confidence-ds-ctf-teaser/crypto100/README.md

@@ -9,6 +9,7 @@
 > ```bash
 > nc 23.253.207.179 10001
 > ```
+> Use the [source](lotto.py)
 
 ## Write-up
 

confidence-ds-ctf-teaser/crypto100/lotto.py

@@ -0,0 +1,107 @@
+from Crypto.Cipher import AES
+from Crypto import Random
+from datetime import datetime
+import random
+import os
+import time
+import sys
+
+flag = open('flag.txt').read()
+
+# config
+start_money = 100
+cost = 5     # coupon price
+reward = 100 # reward for winning
+maxNumber = 1000 # we're drawing from 1 to maxNumber
+screenWidth = 79
+
+intro = [
+	'',
+	'Welcome to our Lotto!',
+	'Bid for $%d, win $%d!' % (cost, reward),
+	'Our system is provably fair:',
+	'   Before each bid you\'ll receive encrypted result',
+	'   After the whole game we will reveal the key to you',
+	'   Then, you can decrypt results and verify that we haven\'t cheated on you!',
+	'    (e.g. by drawing based on your input)',
+	''
+	]
+
+# expand to AES block with random numeric salt
+def randomExtend(block):
+	limit = 10**(16-len(block))
+	# salt
+	rnd = random.randrange(0, limit)
+	# mix it even more
+	rnd = (rnd ** random.randrange(10, 100)) % limit
+	# append it to the block
+	return block + ('%0'+str(16-len(block))+'x')%rnd
+
+def play():
+	# print intro
+	print '#' * screenWidth
+	for line in intro:
+		print  ('# %-' + str(screenWidth-4) + 's #') % line
+	print '#' * screenWidth
+	print ''
+
+	# prepare everything
+	money = start_money
+
+	key = Random.new().read(16) # slow, but secure
+	aes = AES.new(key, AES.MODE_ECB)
+
+	# main loop
+	quit = False
+	while money > 0:
+		luckyNumber = random.randrange(maxNumber + 1) # fast random should be enough
+		salted = str(luckyNumber) + '#'
+		salted = randomExtend(salted)
+
+		print 'Your money: $%d' % money
+		print 'Round verification: %s' % aes.encrypt(salted).encode('hex')
+		print ''
+		print 'Your choice:'
+		print '\t1. Buy a coupon for $%d' % cost
+		print '\t2. Withdraw your money'
+		print '\t3. Quit'
+
+		# read user input
+		while True:
+			input = raw_input().strip()
+			if input == '1':
+				# play!
+				money -= cost
+				sys.stdout.write('Your guess (0-%d): ' % maxNumber)
+				guess = int(raw_input().strip())
+				if guess == luckyNumber:
+					print 'You won $%d!' % reward
+					money += reward
+				else:
+					print 'You lost!'
+				break
+			elif input == '2':
+				# withdraw
+				if money > 1337:
+					print 'You won! Here\'s your reward:', flag
+				else:
+					print 'You cannot withdraw your money until you get $1337!'
+				break
+			elif input == '3':
+				quit = True
+				break
+			else:
+				print 'Unknown command!'
+
+		print 'The lucky number was: %d' % luckyNumber
+		if quit:
+			break
+		print '[enter] to continue...'
+		raw_input()
+
+	print 'Verification key:', key.encode('hex')
+	if money <= 0:
+		print 'You\'ve lost all your money! get out!'
+
+if __name__ == '__main__':
+	play()