Crypto Puzzle

gistfile1.txt

$ python3 solution.py
AMAZON ECHO IS DESIGNED AROUND YOUR
VOICE. IT'S ALWAYS ON - JUST ASK FOR
INFORMATION, MUSIC, NEWS, WEATHER, AND
MORE. ECHO BEGINS WORKING AS SOON AS IT
DETECTS THE WAKE WORD. YOU CAN PICK
ALEXA OR AMAZON AS YOUR WAKE WORD. ECHO
IS ALSO AN EXPERTLY TUNED SPEAKER THAT
CAN FILL ANY ROOM WITH IMMERSIVE SOUND.
PLEASE VISIT WWW.AMAZON.COM/ECHO IF YOU
WANT TO FIND OUT MORE.

[email protected]

solution.py

#!/usr/bin/env python

import hashlib
import itertools
import re
import string


PWORD_RE = re.compile(r'\w*P\w*')


def get_tabula_recta(*swaps):
    d = dict(itertools.chain.from_iterable(
        ([(s[0], s[1]), (s[1], s[0])] for s in swaps)))
    l = [d.get(l, l) for l in string.ascii_uppercase]
    return {c: dict(zip(l, l[i:] + l[:i])) for i, c in enumerate(l)}


def letters_only(text):
    return ''.join(c for c in text if c.isalpha())


def find_key(text, substr, known_str, tabula_recta, key_len=5):
    s = letters_only(substr)
    k = letters_only(known_str)
    assert len(s) == len(k) > key_len
    t = {k: dict((v1, k1) for k1, v1 in v.items())
         for k, v in tabula_recta.items()}
    key = [t[s[i]][k[i]] for i in range(key_len)]
    i = key_len - letters_only(text).index(s) % key_len
    if i != key_len:
        key = key[i:] + key[:i]
    return ''.join(key)


def decode(text, key, tabula_recta):
    keychar = itertools.cycle(key)
    return ''.join(tabula_recta[c][next(keychar)] if c.isalpha() else c
                   for c in text)


if __name__ == '__main__':
    text = """\
HUTFGU WWNG VY NTTVTQTH HJYART XYAP
WSGGI. VM'X SVDGIC GU - BECO HYD LGY
AQLGYUTXCPF, CATVE, QTAN, OOSOOWB, SRT
UYQI. LERU FLTGKT DSBZCUT TC TPSQ ST VM
NTOLEUC OOW SSQL OYQH. FSE GEU NGGQ
HDOWE PJ TIESSQ ST FSEQ AHLO MGYP. OGLP
AX SVNS TK IQNOQOGX UARLP XBIHLOQ OOGU
GEU QGRV HFI QGPU SOOO ACIIYYGPI NSEKH.
MDOSTL HGCCR OSM.EJGJUR.KSC/TXOS GL MPC
SSRR MY LCUP YAO JSBT."""

    tabula_recta = get_tabula_recta('CM', 'GS', 'KT', 'PV', 'QX')
    key = find_key(text, 'OSM.EJGJUR.KSC', 'WWW.AMAZON.COM', tabula_recta)
    decoded_text = decode(text, key, tabula_recta)
    print(decoded_text)
    print()
    print('{}@amazon.com'.format(
        hashlib.md5(''.join(w for w in PWORD_RE.findall(
            decoded_text)).encode()).hexdigest()))