Inside Bitcoin

1# Copyright (c) 2020 Pieter Wuille
2# Distributed under the MIT software license, see the accompanying
3# file COPYING or http://www.opensource.org/licenses/mit-license.php.
4"""Native Python MuHash3072 implementation."""
5
6import hashlib
7import unittest
8
9from .chacha20 import chacha20_block
10
11def data_to_num3072(data):
12    """Hash a 32-byte array data to a 3072-bit number using 6 Chacha20 operations."""
13    bytes384 = b""
14    for counter in range(6):
15        bytes384 += chacha20_block(data, bytes(12), counter)
16    return int.from_bytes(bytes384, 'little')
17
18class MuHash3072:
19    """Class representing the MuHash3072 computation of a set.
20
21    See https://cseweb.ucsd.edu/~mihir/papers/inchash.pdf and https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-May/014337.html
22    """
23
24    MODULUS = 2**3072 - 1103717
25
26    def __init__(self):
27        """Initialize for an empty set."""
28        self.numerator = 1
29        self.denominator = 1
30
31    def insert(self, data):
32        """Insert a byte array data in the set."""
33        data_hash = hashlib.sha256(data).digest()
34        self.numerator = (self.numerator * data_to_num3072(data_hash)) % self.MODULUS
35
36    def remove(self, data):
37        """Remove a byte array from the set."""
38        data_hash = hashlib.sha256(data).digest()
39        self.denominator = (self.denominator * data_to_num3072(data_hash)) % self.MODULUS
40
41    def digest(self):
42        """Extract the final hash. Does not modify this object."""
43        val = (self.numerator * pow(self.denominator, -1, self.MODULUS)) % self.MODULUS
44        bytes384 = val.to_bytes(384, 'little')
45        return hashlib.sha256(bytes384).digest()
46
47class TestFrameworkMuhash(unittest.TestCase):
48    def test_muhash(self):
49        muhash = MuHash3072()
50        muhash.insert(b'\x00' * 32)
51        muhash.insert((b'\x01' + b'\x00' * 31))
52        muhash.remove((b'\x02' + b'\x00' * 31))
53        finalized = muhash.digest()
54        # This mirrors the result in the C++ MuHash3072 unit test
55        self.assertEqual(finalized[::-1].hex(), "10d312b100cbd32ada024a6646e40d3482fcff103668d2625f10002a607d5863")
56