ABCTF - 30 - TGIF - Programming

Information#

Version#

By	Version	Comment
noraj	1.0	Creation

CTF#

• Name : ABCTF 2016
• Website : http://abctf.xyz/
• Type : Online
• Format : Jeopardy - Student
• CTF Time : link

Description#

Friday is the best day of the week, and so I really want to know how many Fridays there are in [this][this] file. But, with a twist. I want to know how many Fridays there are one year later than each date. [this]:https://gist.github.com/LiamRahav/0cbf82b8bc3a41deafc0403f1b1dd573 "Gist"

Hint: For example, if you got November 21, 2001, I want to know if November 21, 2002 is a Friday. Also, the answer is in the format ABCTF{}

Note: TGIF stands for Thank God It's Friday

Solution#

1. Write a script that parse the date.txt file and count the number of Friday

#!/usr/bin/env python2
import locale

from datetime import datetime
import calendar

locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
calendar.setfirstweekday(calendar.MONDAY)

# strptime : https://docs.python.org/2/library/datetime.html#datetime.datetime.strptime
# format : https://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior

date_format = '%B %d, %Y'
i = 0

with open('date.txt', 'r') as date_file:
    for line in date_file:
        date_string = line.rstrip()
        date_object = datetime.strptime(date_string, date_format)
        if not (calendar.isleap(date_object.year) and date_object.day == 29):
            date_object = date_object.replace(year = date_object.year + 1)
            if date_object.isoweekday() == 5: # Friday
                i += 1

print('ABCTF{' + str(i) + '}')

2. This instruction if not (calendar.isleap(date_object.year) and date_object.day == 29) : was to avoid bug with February 29, 2004 because 2004 was a leap year and that February 29, 2005 is not existing so.
3. So when running my script I got:

python3 date.py
ABCTF{193}

4. That's not the good flag but maybe that is because of the 29 of February so I tried ABCTF{194} and it's good!