integer-pairing 0.7.0

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integer-pairing

This library enables encodings of integer tuples as one integer. It implements two types of encodings - Cantor and Szudzik. There is a great article on those two types.

Usage

The base example is

from integer_pairing import cantor, szudzik

cantor.pair(11, 13) # 313
cantor.unpair(313) # (11, 13)

szudzik.pair(11, 13) # 180
szudzik.unpair(180) # (11, 13)

You can pair tuples of any size, but have to give the size when unpairing

cantor.pair(11, 13, 17, 19, 23) # 1115111727200556569
cantor.unpair(1251, dim=5) # (11, 13, 17, 19, 23)

It is also possible to include negative numbers, but you need to imply that when decoding

cantor.pair(11, 13, -1) # 726618
cantor.unpair(726618, dim=3, neg=True) # (11, 13, -1)

Naive implementations of the above algorithms, fail to account for very large integers, as they use numeric calculation of the square root. Python allows for integers of any size to be stored, but converts them to float (64 bits) when doing numeric operations, so this approximation ruins the unpairing. Luckily this can be (efficiently) solved and is implemented here.

cantor.pair(655482261805334959278882253227, 730728447469919519177553911051)
# 960790065254702046274404114853633027146937669672812473623832
cantor.unpair(960790065254702046274404114853633027146937669672812473623832)
# (655482261805334959278882253227, 730728447469919519177553911051)

Complexity

The pairing of n integers will result in an integer of the size of about their product.

Example usage from Cryptography

When encrypting messages deterministically, an attacker can always reproduce the encryption of any chosen messages. If those possibilities are few (like 0 / 1), those kinds of algorithms are pretty useless. This is solved by appending a random number, called salt, to the message. It can be useful to implement this appending via pairing.

from random import getrandbites
from pairing import szudzik

salt = getrandbites(200)
message = 0
encoded = cantor.pair(message, salt)