Merge #19105: Add Muhash3072 implementation in Python

36ec9801a4 test: Add chacha20 test vectors in muhash (Fabian Jahr)
0e2b400fea test: Add basic Python/C++ Muhash implementation parity unit test (Fabian Jahr)
b85543cb73 test: Add Python MuHash3072 implementation to test framework (Pieter Wuille)
ab30cece0e test: Move modinv to util and add unit test (Fabian Jahr)

Pull request description:

  This is the second in a [series of pull requests](https://github.com/bitcoin/bitcoin/pull/18000) to implement an Index for UTXO set statistics.

  This pull request adds a Python implementation of Muhash3072, a homomorphic hashing algorithm to be used for hashing the UTXO set. The Python implementation can then be used to compare behavior with the C++ version.

ACKs for top commit:
  jnewbery:
    utACK 36ec9801a
  laanwj:
    Code review ACK 36ec9801a4

Tree-SHA512: a3519c6e11031174f1ae71ecd8bcc7f3be42d7fc9c84c77f2fbea7cfc5ad54fcbe10b55116ad8d9a52ac5d675640eefed3bf260c58a02f2bf3bc0d8ec208baa6

test/functional/test_framework/key.py

@@ -8,22 +8,7 @@ keys, and is trivially vulnerable to side channel attacks. Do not use for
 anything but tests."""
 import random
 
-def modinv(a, n):
-    """Compute the modular inverse of a modulo n
-
-    See https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm#Modular_integers.
-    """
-    t1, t2 = 0, 1
-    r1, r2 = n, a
-    while r2 != 0:
-        q = r1 // r2
-        t1, t2 = t2, t1 - q * t2
-        r1, r2 = r2, r1 - q * r2
-    if r1 > 1:
-        return None
-    if t1 < 0:
-        t1 += n
-    return t1
+from .util import modinv
 
 def jacobi_symbol(n, k):
     """Compute the Jacobi symbol of n modulo k

test/functional/test_framework/muhash.py

@@ -0,0 +1,110 @@
+# Copyright (c) 2020 Pieter Wuille
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Native Python MuHash3072 implementation."""
+
+import hashlib
+import unittest
+
+from .util import modinv
+
+def rot32(v, bits):
+    """Rotate the 32-bit value v left by bits bits."""
+    bits %= 32  # Make sure the term below does not throw an exception
+    return ((v << bits) & 0xffffffff) | (v >> (32 - bits))
+
+def chacha20_doubleround(s):
+    """Apply a ChaCha20 double round to 16-element state array s.
+
+    See https://cr.yp.to/chacha/chacha-20080128.pdf and https://tools.ietf.org/html/rfc8439
+    """
+    QUARTER_ROUNDS = [(0, 4, 8, 12),
+                      (1, 5, 9, 13),
+                      (2, 6, 10, 14),
+                      (3, 7, 11, 15),
+                      (0, 5, 10, 15),
+                      (1, 6, 11, 12),
+                      (2, 7, 8, 13),
+                      (3, 4, 9, 14)]
+
+    for a, b, c, d in QUARTER_ROUNDS:
+        s[a] = (s[a] + s[b]) & 0xffffffff
+        s[d] = rot32(s[d] ^ s[a], 16)
+        s[c] = (s[c] + s[d]) & 0xffffffff
+        s[b] = rot32(s[b] ^ s[c], 12)
+        s[a] = (s[a] + s[b]) & 0xffffffff
+        s[d] = rot32(s[d] ^ s[a], 8)
+        s[c] = (s[c] + s[d]) & 0xffffffff
+        s[b] = rot32(s[b] ^ s[c], 7)
+
+def chacha20_32_to_384(key32):
+    """Specialized ChaCha20 implementation with 32-byte key, 0 IV, 384-byte output."""
+    # See RFC 8439 section 2.3 for chacha20 parameters
+    CONSTANTS = [0x61707865, 0x3320646e, 0x79622d32, 0x6b206574]
+
+    key_bytes = [0]*8
+    for i in range(8):
+        key_bytes[i] = int.from_bytes(key32[(4 * i):(4 * (i+1))], 'little')
+
+    INITIALIZATION_VECTOR = [0] * 4
+    init = CONSTANTS + key_bytes + INITIALIZATION_VECTOR
+    out = bytearray()
+    for counter in range(6):
+        init[12] = counter
+        s = init.copy()
+        for _ in range(10):
+            chacha20_doubleround(s)
+        for i in range(16):
+            out.extend(((s[i] + init[i]) & 0xffffffff).to_bytes(4, 'little'))
+    return bytes(out)
+
+def data_to_num3072(data):
+    """Hash a 32-byte array data to a 3072-bit number using 6 Chacha20 operations."""
+    bytes384 = chacha20_32_to_384(data)
+    return int.from_bytes(bytes384, 'little')
+
+class MuHash3072:
+    """Class representing the MuHash3072 computation of a set.
+
+    See https://cseweb.ucsd.edu/~mihir/papers/inchash.pdf and https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-May/014337.html
+    """
+
+    MODULUS = 2**3072 - 1103717
+
+    def __init__(self):
+        """Initialize for an empty set."""
+        self.numerator = 1
+        self.denominator = 1
+
+    def insert(self, data):
+        """Insert a byte array data in the set."""
+        self.numerator = (self.numerator * data_to_num3072(data)) % self.MODULUS
+
+    def remove(self, data):
+        """Remove a byte array from the set."""
+        self.denominator = (self.denominator * data_to_num3072(data)) % self.MODULUS
+
+    def digest(self):
+        """Extract the final hash. Does not modify this object."""
+        val = (self.numerator * modinv(self.denominator, self.MODULUS)) % self.MODULUS
+        bytes384 = val.to_bytes(384, 'little')
+        return hashlib.sha256(bytes384).digest()
+
+class TestFrameworkMuhash(unittest.TestCase):
+    def test_muhash(self):
+        muhash = MuHash3072()
+        muhash.insert([0]*32)
+        muhash.insert([1] + [0]*31)
+        muhash.remove([2] + [0]*31)
+        finalized = muhash.digest()
+        # This mirrors the result in the C++ MuHash3072 unit test
+        self.assertEqual(finalized[::-1].hex(), "a44e16d5e34d259b349af21c06e65d653915d2e208e4e03f389af750dc0bfdc3")
+
+    def test_chacha20(self):
+        def chacha_check(key, result):
+            self.assertEqual(chacha20_32_to_384(key)[:64].hex(), result)
+
+        # Test vectors from https://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-04#section-7
+        # Since the nonce is hardcoded to 0 in our function we only use those vectors.
+        chacha_check([0]*32, "76b8e0ada0f13d90405d6ae55386bd28bdd219b8a08ded1aa836efcc8b770dc7da41597c5157488d7724e03fb8d84a376a43b8f41518a11cc387b669b2ee6586")
+        chacha_check([0]*31 + [1], "4540f05a9f1fb296d7736e7b208e3c96eb4fe1834688d2604f450952ed432d41bbe2a0b6ea7566d2a5d1e7e20d42af2c53d792b1c43fea817e9ad275ae546963")

test/functional/test_framework/util.py

@@ -15,6 +15,7 @@ import os
 import random
 import re
 import time
+import unittest
 
 from . import coverage
 from .authproxy import AuthServiceProxy, JSONRPCException
@@ -625,3 +626,33 @@ def find_vout_for_address(node, txid, addr):
         if any([addr == a for a in tx["vout"][i]["scriptPubKey"]["addresses"]]):
             return i
     raise RuntimeError("Vout not found for address: txid=%s, addr=%s" % (txid, addr))
+
+def modinv(a, n):
+    """Compute the modular inverse of a modulo n using the extended Euclidean
+    Algorithm. See https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm#Modular_integers.
+    """
+    # TODO: Change to pow(a, -1, n) available in Python 3.8
+    t1, t2 = 0, 1
+    r1, r2 = n, a
+    while r2 != 0:
+        q = r1 // r2
+        t1, t2 = t2, t1 - q * t2
+        r1, r2 = r2, r1 - q * r2
+    if r1 > 1:
+        return None
+    if t1 < 0:
+        t1 += n
+    return t1
+
+class TestFrameworkUtil(unittest.TestCase):
+    def test_modinv(self):
+        test_vectors = [
+            [7, 11],
+            [11, 29],
+            [90, 13],
+            [1891, 3797],
+            [6003722857, 77695236973],
+        ]
+
+        for a, n in test_vectors:
+            self.assertEqual(modinv(a, n), pow(a, n-2, n))

test/functional/test_runner.py

@@ -69,7 +69,9 @@ TEST_EXIT_SKIPPED = 77
 TEST_FRAMEWORK_MODULES = [
     "address",
     "blocktools",
+    "muhash",
     "script",
+    "util",
 ]
 
 EXTENDED_SCRIPTS = [