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#!/usr/bin/python2
# -*- coding: utf-8 -*-
import random
letters = "_abcdefghijklmnopqrstuvwxyz.0123456789,-+*/:?!'()"
tiles = zip(letters, map(lambda x: (x / 7, x % 7), range(7 * 7)))
padding_size = 10
def check_key(key):
if len(key) != len(letters):
raise ValueError('Wrong key size')
cnts = {}
for c in letters:
cnts[c] = 0
for c in key:
if not c in cnts:
raise ValueError('Letter ' + c + ' not in LS47!')
cnts[c] += 1
if cnts[c] > 1:
raise ValueError('Letter ' + c + ' duplicated in key!')
def find_ix(letter):
m = filter(lambda (l, pos): l == letter, tiles)
if len(m) != 1:
raise ValueError('Letter ' + letter + ' not in LS47!')
for (l, pos) in m:
return pos
def find_pos(key, letter):
p = key.find(letter)
if p >= 0 and p < 7 * 7:
return (p / 7, p % 7)
raise ValueError('Letter ' + letter + ' not in key?!')
def add_pos((ax, ay), (bx, by)):
return ((ax + bx) % 7, (ay + by) % 7)
def sub_pos((ax, ay), (bx, by)):
return ((ax - bx) % 7, (ay - by) % 7)
def find_at_pos(key, (row, col)):
return key[col + row * 7]
def rotate_right(key, row, n):
mid = key[7 * row:7 * (row + 1)]
n = (7 - n % 7) % 7
return key[:7 * row] + mid[n:] + mid[:n] + key[7 * (row + 1):]
def rotate_down(key, col, n):
lines = map(lambda i: key[i * 7:(i + 1) * 7], range(7))
lefts = map(lambda l: l[:col], lines)
mids = map(lambda l: l[col], lines)
rights = map(lambda l: l[col + 1:], lines)
n = (7 - n % 7) % 7
mids = mids[n:] + mids[:n]
return reduce(lambda a, b: a + b, map(lambda i: lefts[i] + mids[i] \
+ rights[i], range(7)))
def rotate_marker_right((mrow, mcol), row, n):
if mrow != row:
return (mrow, mcol)
else:
return (mrow, (mcol + n) % 7)
def rotate_marker_down((mrow, mcol), col, n):
if mcol != col:
return (mrow, mcol)
else:
return ((mrow + n) % 7, mcol)
def derive_key(password):
i = 0
k = letters
for c in password:
(row, col) = find_ix(c)
k = rotate_down(rotate_right(k, i, col), i, row)
i = (i + 1) % 7
return k
def encrypt(key, plaintext):
check_key(key)
mp = (0, 0)
ciphertext = ''
for p in plaintext:
pp = find_pos(key, p)
mix = find_ix(find_at_pos(key, mp))
cp = add_pos(pp, mix)
c = find_at_pos(key, cp)
ciphertext += c
key = rotate_right(key, pp[0], 1)
mp = rotate_marker_right(mp, pp[0], 1)
cp = find_pos(key, c)
key = rotate_down(key, cp[1], 1)
mp = rotate_marker_down(mp, cp[1], 1)
mp = add_pos(mp, find_ix(c))
return ciphertext
def decrypt(key, ciphertext):
check_key(key)
mp = (0, 0)
plaintext = ''
for c in ciphertext:
cp = find_pos(key, c)
mix = find_ix(find_at_pos(key, mp))
pp = sub_pos(cp, mix)
p = find_at_pos(key, pp)
plaintext += p
key = rotate_right(key, pp[0], 1)
mp = rotate_marker_right(mp, pp[0], 1)
cp = find_pos(key, c)
key = rotate_down(key, cp[1], 1)
mp = rotate_marker_down(mp, cp[1], 1)
mp = add_pos(mp, find_ix(c))
return plaintext
def encrypt_pad(key, plaintext, signature):
# TODO it would also be great to randomize the message length.
check_key(key)
padding = ''.join(map(lambda x: letters[random.randint(0,
len(letters) - 1)], range(padding_size)))
return encrypt(key, padding + plaintext + '---' + signature)
def decrypt_pad(key, ciphertext):
check_key(key)
return decrypt(key, ciphertext)[padding_size:]
if __name__ == '__main__':
# a bit of test!
key = derive_key('s3cret_p4ssw0rd/31337')
print 'key:', key
enc = encrypt_pad(key, 'conflagrate_the_rose_bush_at_six!',
'peace-vector-3')
print 'encrypted:', enc
dec = decrypt_pad(key, enc)
print 'decrypted:', dec
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