findme_packet_format.example

>>> from findme_packet_format import *
>>>
>>> # generate a public / private key pair for demonstration
>>> # curve and backend are hard-coded for convenience
>>> private = ec.generate_private_key(curve, backend)
>>> public = private.public_key()
>>>
>>> # take a peek at what the serialized public key looks like
>>> encode_public_key(public).hex()
'bbae416a73aac8b64786006b4b358d7261cc57eb780aeb61c15537d88eb9a6e68d48a0f737aafde8c99f6821be199aef49da91f7e60f3a42d524be06aac811a5'
>>>
>>> # test that serializing + deserializing the public key works
>>> reference = public.public_numbers()
>>> example = decode_public_key(encode_public_key(public)).public_numbers()
>>> reference == example
True

findme_packet_format.py

import cryptography.hazmat.backends

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.serialization import (Encoding, PublicFormat)

# instantiate a common backend and curve
backend = default_backend()
curve = ec.SECP256K1()


def encode_public_key(public_key):
    """Encode public key to 64 bytes.

    Serialization format for network packets and hash entries.
    """
    public_numbers = public_key.public_numbers()
    (x, y) = (public_numbers.x, public_numbers.y)
    return x.to_bytes(32, 'big') + y.to_bytes(32, 'big')


def decode_public_key(encoded_public_key):
    """Decode public key from 64 bytes."""
    x = int.from_bytes(encoded_public_key[:32], 'big')
    y = int.from_bytes(encoded_public_key[32:], 'big')
    return backend.load_elliptic_curve_public_numbers(
        ec.EllipticCurvePublicNumbers(x, y, curve),
    )


# TODO: signatures