C implementation of MIMC using GMP (~10x faster than Python)

.gitignore

@@ -1,3 +1,6 @@
 venv/*
 .vscode/*
 .mypy_cache/*
+build/*
+dist/*
+mimcvdf.egg-info/*

mimcvdf/__init__.py

@@ -25,18 +25,18 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 DEFAULT_ROUNDS = 8000
 
 
-def _sha3_256_hash(data: bytes) -> int:
+def _sha3_256_hash(data: bytes) -> bytes:
     sha3 = sha3_256()
     sha3.update(data)
-    return int.from_bytes(sha3.digest(), byteorder='big')
+    return sha3.digest()
 
 
 def vdf_create(data: bytes, rounds: int = DEFAULT_ROUNDS, dec=False) -> str:
     assert rounds > 1
     input_data: int = _sha3_256_hash(data)
-    if not dec:
-        return hex(reverse_mimc(input_data, rounds)).replace('0x', '')
-    return reverse_mimc(input_data, rounds)
+    if dec:
+        return int.from_bytes(reverse_mimc(input_data, rounds), "big")
+    return reverse_mimc(input_data, rounds).hex()
 
 
 def vdf_verify(
@@ -45,11 +45,14 @@ def vdf_verify(
         rounds: int = DEFAULT_ROUNDS) -> bool:
     """Verify data for test_hash generated by vdf_create."""
     assert rounds > 1
-    should_match = _sha3_256_hash(data)
-    try:
-        test_hash = int(test_hash, 16)
-    except TypeError:
-        pass
+    should_match = _sha3_256_hash(data).lstrip(b'\0')
+    if isinstance(test_hash, int):
+        test_hash = test_hash.to_bytes((test_hash.bit_length() + 7) // 8, "big")
+    else:
+        try:
+            test_hash = bytes.fromhex(test_hash)
+        except ValueError:
+            return False
     return forward_mimc(test_hash, rounds) == should_match
 
 

mimcvdf/mimc/__init__.py

@@ -0,0 +1,8 @@
+"""Mimc hash function."""
+
+try:
+    from .native import forward_mimc, reverse_mimc
+    is_fast = True
+except ImportError:
+    from .fallback import forward_mimc, reverse_mimc
+    is_fast = False

mimcvdf/mimc/fallback.py

@@ -1,4 +1,4 @@
-"""Mimc hash function."""
+"""Slow fallback implementation of MIMC written in pure Python."""
 """
 This module adapted from https://github.com/OlegJakushkin/deepblockchains/blob/master/vdf/mimc/python/mimc.py by Sourabh Niyogi https://github.com/sourabhniyogi
 
@@ -15,22 +15,25 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <https://www.gnu.org/licenses/>.
 """
-modulus = 2**256 - 2**32 * 351 + 1
-little_fermat_expt = (modulus*2-1)//3
-round_constants = [(i**7) ^ 42 for i in range(64)]
+
+is_fast = False
+
+_modulus = 2**256 - 2**32 * 351 + 1
+_little_fermat_expt = (_modulus*2-1)//3
+_round_constants = [(i**7) ^ 42 for i in range(64)]
 
 
-def forward_mimc(inp: int, steps: int) -> int:
+def forward_mimc(input_data: bytes, steps: int) -> bytes:
+    inp = int.from_bytes(input_data, "big")
     for i in range(1,steps):
-        inp = (inp**3 + round_constants[i % len(round_constants)]) % modulus
-    return inp
+        inp = (inp**3 + _round_constants[i % len(_round_constants)]) % _modulus
+    return inp.to_bytes((inp.bit_length() + 7) // 8, "big")
 
 
-def reverse_mimc(input_data: int, steps: int) -> int:
-    rtrace = input_data
+def reverse_mimc(input_data: bytes, steps: int) -> bytes:
+    rtrace = int.from_bytes(input_data, "big")
 
     for i in range(steps - 1, 0, -1):
-        rtrace = pow(rtrace-round_constants[i%len(round_constants)],
-                     little_fermat_expt, modulus)
-    return rtrace
-
+        rtrace = pow(rtrace-_round_constants[i%len(_round_constants)],
+                     _little_fermat_expt, _modulus)
+    return rtrace.to_bytes((rtrace.bit_length() + 7) // 8, "big")

mimcvdf/mimc/native.c

@@ -0,0 +1,157 @@
+#define PY_SSIZE_T_CLEAN
+#include <Python.h>
+
+#include <stdbool.h>
+#include <gmp.h>
+
+/*
+This module adapted from https://github.com/OlegJakushkin/deepblockchains/blob/master/vdf/mimc/python/mimc.py by Sourabh Niyogi https://github.com/sourabhniyogi
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+static mpz_t MODULUS;
+static mpz_t LITTLE_FERMAT_EXPT;
+#define ROUND_CONSTANTS_COUNT 64
+static mpz_t ROUND_CONSTANTS[ROUND_CONSTANTS_COUNT];
+
+static void
+mimc_init_constants()
+{
+    mpz_t fortytwo;
+
+    mpz_init(fortytwo);
+    mpz_set_ui(fortytwo, 42);
+
+    // Set MODULUS to hex(2**256 - 2**32 * 351 + 1)
+    mpz_init(MODULUS);
+    mpz_set_str(MODULUS,
+                "ffffffffffffffffffffffffffffffff"
+                "fffffffffffffffffffffea100000001",
+                16);
+
+    // Set LITTLE_FERMAT_EXPT to hex((MODULUS * 2 - 1) // 3)
+    mpz_init(LITTLE_FERMAT_EXPT);
+    mpz_set_str(LITTLE_FERMAT_EXPT, 
+                "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+                "aaaaaaaaaaaaaaaaaaaaa9c0aaaaaaab",
+                16);
+
+    // Set all the constants to (i**7 ^ 42)
+    for (unsigned long int i = 0; i < ROUND_CONSTANTS_COUNT; i++) {
+       mpz_init(ROUND_CONSTANTS[i]);
+       mpz_ui_pow_ui(ROUND_CONSTANTS[i], i, 7);
+       mpz_xor(ROUND_CONSTANTS[i], ROUND_CONSTANTS[i], fortytwo);
+    }
+
+    mpz_clear(fortytwo);
+}
+
+static bool
+unpack_args(PyObject *args, mpz_t input, unsigned int *steps)
+{
+    const char *data_bytes;
+    Py_ssize_t count;
+
+    if (!PyArg_ParseTuple(args, "y#I", &data_bytes, &count, steps)) {
+        return false;
+    }
+
+    mpz_import(input, count, 1, 1, 0, 0, data_bytes);
+    return true;
+}
+
+
+static PyObject *
+convert_mpz_to_bytes(mpz_t op)
+{
+    char string[34];
+    size_t size;
+
+    mpz_export(string, &size, 1, 1, 0, 0, op);
+    PyObject *result = PyBytes_FromStringAndSize(string, size);
+    return result;
+}
+
+static PyObject *
+forward_mimc(PyObject *_self, PyObject *args)
+{
+    mpz_t result;
+    unsigned int steps;
+
+    mpz_init(result);
+    if (!unpack_args(args, result, &steps)) {
+        mpz_clear(result);
+        return NULL;
+    }
+
+    for (unsigned int i = 1; i < steps; ++i) {
+        mpz_powm_ui(result, result, 3, MODULUS);
+        mpz_add(result, result, ROUND_CONSTANTS[i % ROUND_CONSTANTS_COUNT]);
+        if (mpz_cmp(result, MODULUS) >= 0) {
+            mpz_sub(result, result, MODULUS);
+        }
+    }
+
+    PyObject *result_obj = convert_mpz_to_bytes(result);
+    mpz_clear(result);
+    return result_obj;
+}
+
+static PyObject *
+reverse_mimc(PyObject *_self, PyObject *args)
+{
+    mpz_t result;
+    unsigned int steps;
+
+    mpz_init(result);
+    if (!unpack_args(args, result, &steps)) {
+        mpz_clear(result);
+        return NULL;
+    }
+
+    for (unsigned int i = steps - 1; i > 0; --i) {
+        mpz_sub(result, result, ROUND_CONSTANTS[i % ROUND_CONSTANTS_COUNT]);
+        mpz_powm(result, result, LITTLE_FERMAT_EXPT, MODULUS);
+    }
+
+    PyObject *result_obj = convert_mpz_to_bytes(result);
+    mpz_clear(result);
+    return result_obj;
+}
+
+static PyMethodDef Methods[] = {
+    {"forward_mimc", forward_mimc, METH_VARARGS,
+     "Run MIMC forward (the fast direction)"},
+    {"reverse_mimc", reverse_mimc, METH_VARARGS,
+     "Run MIMC in reverse (the slow direction)"},
+    {NULL, NULL, 0, NULL}
+};
+
+static struct PyModuleDef moduledef = {
+    PyModuleDef_HEAD_INIT,
+    "native",
+    "Fast native implementation of MIMC.",
+    -1,
+    Methods,
+    NULL
+};
+
+PyMODINIT_FUNC
+PyInit_native()
+{
+    mimc_init_constants();
+
+    return PyModule_Create(&moduledef);
+}

setup.py

@@ -1,4 +1,4 @@
-from setuptools import setup, find_packages
+from setuptools import setup, find_packages, Extension
 
 setup(name='mimcvdf',
       version='1.1.0',
@@ -8,6 +8,12 @@ setup(name='mimcvdf',
       url='https://www.chaoswebs.net/',
       packages=find_packages(exclude=['contrib', 'docs', 'tests']),
       install_requires=[],
+      ext_package="mimcvdf",
+      ext_modules=[
+        Extension('mimc.native', ['mimcvdf/mimc/native.c'],
+                  libraries=['gmp'], optional=True,
+                  extra_compile_args=['-O2'])
+      ],
       classifiers=[
         "Programming Language :: Python :: 3",
         "License :: OSI Approved :: GNU General Public License v3 (GPLv3)",

tests/test_mimc.py

@@ -14,14 +14,23 @@ class TestMimc(unittest.TestCase):
         data = b"a" * 6000000
         h = sha3_256()
         h.update(data)
-        data = int(h.hexdigest(), 16)
+        data = h.digest()
 
         forw = mimcvdf.forward_mimc(data, 2000)
 
         rev = mimcvdf.reverse_mimc(forw, 2000)
 
-        print(data)
-        print(forw, rev)
+        print(data.hex())
+        print(forw.hex(), rev.hex())
         self.assertEqual(rev, data)
 
+    def test_expected_data(self):
+        h = sha3_256()
+        h.update(b"test")
+        data = h.digest()
+        self.assertEqual(
+            "66ea2a863bd103f2c7f190503cf8456198f31660069d4903afbd5f2e40a28695",
+            mimcvdf.forward_mimc(data, 2000).hex()
+        )
+
 unittest.main()

tests/test_vdf.py

@@ -3,6 +3,7 @@ import os
 sys.path.append('..')
 import unittest
 from time import time
+from hashlib import sha3_256
 
 import mimcvdf
 
@@ -38,5 +39,11 @@ class TestVDF(unittest.TestCase):
         h = mimcvdf.vdf_create(b"test", dec=True)
         self.assertTrue(mimcvdf.vdf_verify(b"test", h))
 
+    def test_hash_starting_with_zero(self):
+        s = b"test vector 1097"
+        self.assertEqual(0, sha3_256(s).digest()[0])
+        h = mimcvdf.vdf_create(s)
+        self.assertTrue(mimcvdf.vdf_verify(s, h))
+
 
 unittest.main()