Mixo-Fixo: Typo and casual reverse-engineering tolerant inefficient string-token encoding method. Features: - changing a single character in the input changes many characters in the output - valid token-space is very sparse

gistfile1.py

"""
Mixo-Fixo: Typo and casual reverse-eingineering tolerant, inefficient string-token encoding method.
"""

def chunks(l, n):
    """ Yield successive n-sized chunks from l."""

    for i in xrange(0, len(l), n):
        yield l[i:i+n]


def mixo(s):

    if s == '':
        return s

    s = [ord(x) for x in s]

    result = []
    offset_x = offset_y = 0

    for x, y in zip(s, reversed(s)):
        offset_x += x
        offset_y += y
        result.append((offset_x % 256, offset_y % 256))

    # offset everythng with the final offsets
    result[:-1] = [((x + offset_x) % 256, (y + offset_y) % 256) for x, y in result[:-1]]

    return ''.join(chr(x) + chr(y) for x, y in result)


def fixo(s):

    if s == '':
        return s

    if len(s) % 2 != 0:
        raise ValueError("Invalid input.")

    s = [(ord(x), ord(y)) for x, y in chunks(s, 2)]

    result = []
    offset_x, offset_y = [-p for p in s[-1]]
    s[-1] = tuple((2 * p) % 256 for p in s[-1])

    for x, y in s:
        x += offset_x
        y += offset_y
        result.append((x % 256, y % 256))
        offset_x -= x
        offset_y -= y

    a, b = [''.join(chr(p) for p in t) for t in zip(*result)]

    if a == b[::-1]:
        return a
    else:
        raise ValueError("Invalid checksum.")


import base64

s = '023.45|034.50|254'

t = base64.encodestring(mixo(s)).strip()
u = fixo(base64.decodestring(t))
s == u