moth/puzzles/crypto/130manchester.py

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2009-10-13 10:08:03 -06:00
#!/usr/bin/python3
'''This is the same as the previous, but it uses non-return to zero to encode
the binary.'''
import random
import crypto
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lower = b'abcdefghijklmnopqrstuvwxyz'
upper = lower.upper()
alice = b'The next one is in Morris Code. Unlike the previous two, '\
b'they will actually need to determine some sort of key.'
bob = b'Morris code with a key? That sounds bizarre. probable cause'
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def encode(text):
out = bytearray()
mask = 0x80
state = 0
for t in text:
for i in range(8):
next = t & mask
if not state and not next:
out.append(random.choice(upper))
out.append(random.choice(lower))
elif not state and next:
out.append(random.choice(lower))
out.append(random.choice(upper))
elif state and not next:
out.append(random.choice(upper))
out.append(random.choice(lower))
elif state and next:
out.append(random.choice(lower))
out.append(random.choice(upper))
state = next
t = t << 1
return bytes(out)
def decode(text):
out = bytearray()
i = 0
while i < len(text):
c = 0
mask = 0x80
for j in range(8):
a = 0 if text[i] in lower else 1
b = 0 if text[i+1] in lower else 1
assert a != b, 'bad encoding'
if b:
c = c + mask
mask = mask >> 1
i = i + 2
out.append(c)
return bytes(out)
crypto.mkIndex(encode, decode, alice, bob, crypto.groups)