90 lines
3.2 KiB
Python
90 lines
3.2 KiB
Python
# Copyright (c) 2020 Pieter Wuille
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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"""Native Python MuHash3072 implementation."""
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import hashlib
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from .util import modinv
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def rot32(v, bits):
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"""Rotate the 32-bit value v left by bits bits."""
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bits %= 32 # Make sure the term below does not throw an exception
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return ((v << bits) & 0xffffffff) | (v >> (32 - bits))
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def chacha20_doubleround(s):
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"""Apply a ChaCha20 double round to 16-element state array s.
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See https://cr.yp.to/chacha/chacha-20080128.pdf and https://tools.ietf.org/html/rfc8439
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"""
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QUARTER_ROUNDS = [(0, 4, 8, 12),
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(1, 5, 9, 13),
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(2, 6, 10, 14),
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(3, 7, 11, 15),
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(0, 5, 10, 15),
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(1, 6, 11, 12),
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(2, 7, 8, 13),
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(3, 4, 9, 14)]
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for a, b, c, d in QUARTER_ROUNDS:
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s[a] = (s[a] + s[b]) & 0xffffffff
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s[d] = rot32(s[d] ^ s[a], 16)
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s[c] = (s[c] + s[d]) & 0xffffffff
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s[b] = rot32(s[b] ^ s[c], 12)
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s[a] = (s[a] + s[b]) & 0xffffffff
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s[d] = rot32(s[d] ^ s[a], 8)
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s[c] = (s[c] + s[d]) & 0xffffffff
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s[b] = rot32(s[b] ^ s[c], 7)
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def chacha20_32_to_384(key32):
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"""Specialized ChaCha20 implementation with 32-byte key, 0 IV, 384-byte output."""
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# See RFC 8439 section 2.3 for chacha20 parameters
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CONSTANTS = [0x61707865, 0x3320646e, 0x79622d32, 0x6b206574]
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key_bytes = [0]*8
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for i in range(8):
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key_bytes[i] = int.from_bytes(key32[(4 * i):(4 * (i+1))], 'little')
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INITIALIZATION_VECTOR = [0] * 4
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init = CONSTANTS + key_bytes + INITIALIZATION_VECTOR
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out = bytearray()
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for counter in range(6):
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init[12] = counter
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s = init.copy()
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for _ in range(10):
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chacha20_doubleround(s)
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for i in range(16):
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out.extend(((s[i] + init[i]) & 0xffffffff).to_bytes(4, 'little'))
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return bytes(out)
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def data_to_num3072(data):
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"""Hash a 32-byte array data to a 3072-bit number using 6 Chacha20 operations."""
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bytes384 = chacha20_32_to_384(data)
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return int.from_bytes(bytes384, 'little')
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class MuHash3072:
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"""Class representing the MuHash3072 computation of a set.
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See https://cseweb.ucsd.edu/~mihir/papers/inchash.pdf and https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-May/014337.html
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"""
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MODULUS = 2**3072 - 1103717
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def __init__(self):
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"""Initialize for an empty set."""
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self.numerator = 1
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self.denominator = 1
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def insert(self, data):
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"""Insert a byte array data in the set."""
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self.numerator = (self.numerator * data_to_num3072(data)) % self.MODULUS
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def remove(self, data):
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"""Remove a byte array from the set."""
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self.denominator = (self.denominator * data_to_num3072(data)) % self.MODULUS
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def digest(self):
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"""Extract the final hash. Does not modify this object."""
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val = (self.numerator * modinv(self.denominator, self.MODULUS)) % self.MODULUS
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bytes384 = val.to_bytes(384, 'little')
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return hashlib.sha256(bytes384).digest()
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