1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
|
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# This software is hereby released into public domain. Use it wisely.
#
# Originally written by Mirek Kratochvil (2017)
# Python3 port by Bernhard Esslinger (Feb 2018)
import argparse
import random
import sys
letters = "_ABCDEFGHIJKLMNOPQRSTUVWXYZ.,:?!'()0123456789+-*/"
tiles = list(zip(letters, map(lambda x: (x // 7, x % 7), range(7 * 7))))
padding_size_min = 5
padding_size_max = 15
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(f"Letter {c} not in LS47!")
cnts[c] += 1
if cnts[c] > 1:
raise ValueError(f"Letter {c} duplicated in key!")
def find_ix(letter):
m = [l for l in tiles if l[0] == letter]
if len(m) != 1:
raise ValueError(f"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(f"Letter {letter} not in key!")
def add_pos(a, b):
return ((a[0] + b[0]) % 7, (a[1] + b[1]) % 7)
def sub_pos(a, b):
return ((a[0] - b[0]) % 7, (a[1] - b[1]) % 7)
def find_at_pos(key, coord):
return key[coord[1] + coord[0] * 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 = [key[i * 7 : (i + 1) * 7] for i in range(7)]
lefts = [l[:col] for l in lines]
mids = [l[col] for l in lines]
rights = [l[col + 1 :] for l in lines]
n = (7 - n % 7) % 7
mids = mids[n:] + mids[:n]
return "".join(lefts[i] + mids[i] + rights[i] for i in range(7))
def rotate_marker_right(m, row, n):
if m[0] != row:
return (m[0], m[1])
else:
return (m[0], (m[1] + n) % 7)
def rotate_marker_down(m, col, n):
if m[1] != col:
return (m[0], m[1])
else:
return ((m[0] + n) % 7, m[1])
def derive_key(password):
k = ''.join(reversed(letters))
i = 0
for c in password + ' ':
ix = k.find(c,i)
if ix<0:
continue
k = k[:i] + k[ix] + k[i:ix] + k[ix+1:]
i += 1
return ''.join(reversed(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)
cp = find_pos(key, c)
key = rotate_down(key, 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)
cp = find_pos(key, c)
key = rotate_down(key, cp[1], 1)
mp = add_pos(mp, find_ix(c))
return plaintext
def encrypt_pad(key, plaintext, signature):
check_key(key)
padding = "".join(
map(
lambda x: letters[random.randint(1, len(letters) - 1)],
range(random.randint(padding_size_min, padding_size_max)),
)
)
return encrypt(key, padding + "_" + plaintext + "_" + signature)
def decrypt_pad(key, ciphertext, signature):
check_key(key)
padded = decrypt(key, ciphertext)
pad_end = padded.find("_")
if pad_end < padding_size_min or pad_end > padding_size_max:
raise ValueError("mangled padding")
padded = padded[pad_end + 1 :]
if len(signature) == 0:
return padded
if padded[-len(signature) - 1 :] != "_" + signature:
raise ValueError("bad signature")
return padded[: -len(signature) - 1]
if __name__ == "__main__":
ap = argparse.ArgumentParser(
prog=sys.argv[0],
description="Computer implementation of LS47.",
epilog="This is flimsy! Encrypt physically!",
)
ap.add_argument(
"-d", "--decrypt", dest="decrypt", action="store_true", help="run decryption"
)
ap.add_argument(
"-p",
"--pad-and-sign",
dest="sign",
help="On encryption, add a random padding and a signature at the end. On decryption, expect a random padding and the exact signature. Specify empty string to attach no (or accept any) signature.",
)
ap.add_argument(
"-s",
"--password",
dest="password",
help="Password string (to be expanded by the simple swapping algorithm)",
)
ap.add_argument(
"-K",
"--full-key",
dest="fullkey",
help="Shared key (the initial state of the board, line by line, always with `_' instead of space; used only if password is not specified)",
)
ap.add_argument(
"-I",
"--exact-input",
dest="inx",
help="Do not convert input spaces to `_', ignore them instead.",
action="store_true"
)
ap.add_argument(
"-O",
"--exact-output",
dest="outx",
help="Do not convert output `_'s to spaces.",
action="store_true"
)
args = ap.parse_args()
if args.password:
key = derive_key(args.password if args.inx else args.password.replace(' ', '_'))
elif args.fullkey:
key = args.fullkey
else:
raise ValueError("Specify at least one of password and full key (options -s and -K)")
input = sys.stdin.read()
if not args.inx:
input = input.replace(' ', '_')
letter_set = set(letters)
input = ''.join(filter(lambda x:x in letter_set, input.upper()))
if args.decrypt:
if args.sign is None:
output = decrypt(key, input)
else:
output = decrypt_pad(key, input, args.sign)
else: # encrypt
if args.sign is None:
output = encrypt(key, input)
else:
output = encrypt_pad(key, input, args.sign)
if not args.outx:
output = output.replace('_', ' ')
print(output)
|
