moth/puzzles/crypto/190rotate.py

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2009-10-13 16:08:11 -06:00
import crypto
import itertools
width = 5
alice = b'''If we did the morris code encoding prior to this transposition, I don't think anyone would ever figure out the solution.'''
bob = b'''That's basically true of the combination of many of these techniques. Combining a substitution along with a permutation (or transposition) satisfies the Shannon's diffusion principle of cryptography; you want to try to get rid of as much statistical information as possible. statistical information'''
alice = alice.lower().replace(b' ', b'_')
bob = bob.lower().replace(b' ', b'_')
key = [4,2,3,1,0]
def rotate(text):
out = bytearray()
assert len(text) % width == 0, 'At %d of %d.' % (len(text) % width, width)
slices = [bytearray(text[i:i+width]) for i in range(0, len(text), width)]
for i in range(width):
for slice in slices:
out.append(slice[key[i]])
return bytes(out)
def unrotate(text):
out = bytearray()
assert len(text) % width == 0
# Make column slices, and rearrange them according to the key.
size = len(text) // width
tSlices = [bytearray(text[i*size:i*size+size]) for i in range(width)]
slices = [None] * width
for i in range(width):
slices[key[i]] = tSlices[i]
while len(out) < len(text):
for i in range(5):
out.append(slices[i].pop(0))
return bytes(out)
crypto.mkIndex(rotate, unrotate, alice, bob, crypto.groups)