Seccon 2015: Last Challenge

Category: Misc - Points: 50

Description:
ex1
Cipher:PXFR}QIVTMSZCNDKUWAGJB{LHYEO
Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ{}

ex2
Cipher:EV}ZZD{DWZRA}FFDNFGQO
Plain: {HELLOWORLDSECCONCTF}

quiz
Cipher:A}FFDNEA}}HDJN}LGH}PWO
Plain: ??????????????????????

The last challenge in Seccon 2015 was exactly the same as the first one. It is still a substitution cipher and we have to decode the last message. The substitution pattern is different from the other challenge but we can use the same approach.

We wrote the following python script, using maketrans and translate.

#!/usr/bin/env python

from string import translate, maketrans

table = maketrans('PXFR}QIVTMSZCNDKUWAGJB{LHYEO', 'ABCDEFGHIJKLMNOPQRSTUVWXYZ{}')
cipher = 'A}FFDNEA}}HDJN}LGH}PWO'
print translate(cipher, table)

We then execute the script:

$ ./last.py
SECCON{SEEYOUNEXTYEAR}

So the flag is: SECCON{SEEYOUNEXTYEAR}