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#
# creditcard.py
#
# Author:
# John Lawrence M. Penafiel (penafieljlm)
#
# Python source code attachment for the article at:
# https://penafieljlm.wordpress.com/2016/10/29/ekoparty-ctf-2016-write-ups/#web-150
#
import math
def cardLuhnChecksumIsValid(card_number):
""" checks to make sure that the card passes a luhn mod-10 checksum """
sum = 0
num_digits = len(card_number)
oddeven = num_digits & 1
for count in range(0, num_digits):
digit = int(card_number[count])
if not (( count & 1 ) ^ oddeven ):
digit = digit * 2
if digit > 9:
digit = digit - 9
sum = sum + digit
return ( (sum % 10) == 0 )
# list format: [missing_len, prefix, postfix]
jobs = [
[5], [8], [7]
]
# read input formatted in the following manner:
# 4716
# rest of your number
# 6108
# Mastercard
# 5238
# rest of your number
# 5763
# American Express
# 3472
# rest of your number
# 2959
index = 0
for index in range(0, 10 + 1):
line = raw_input()
if index == 0 or index == 2:
jobs[0].append(line.strip())
if index == 4 or index == 6:
jobs[1].append(line.strip())
if index == 8 or index == 10:
jobs[2].append(line.strip())
index += 1
for job in jobs:
length, prefix, postfix = job
for i in range(0, int(math.pow(10, length))):
iteration = str(i).zfill(length)
number = prefix + iteration + postfix
if cardLuhnChecksumIsValid(number):
print iteration
break
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