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extmod/secp256k1mod.c: randomize context

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- provide enhanced protection against side-channel leakage
This commit is contained in:
The MMGen Project 2025-06-29 14:04:46 +00:00
commit fbeda2f071
Signed by: mmgen
GPG key ID: 3F8B1861E32B7DA2
2 changed files with 99 additions and 6 deletions
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74
extmod/random.h Normal file
View file

@ -0,0 +1,74 @@
/*
* Source: secp256k1/examples/examples_util.h
*/
/*************************************************************************
* Copyright (c) 2020-2021 Elichai Turkel *
* Distributed under the CC0 software license, see the accompanying file *
* EXAMPLES_COPYING or https://creativecommons.org/publicdomain/zero/1.0 *
*************************************************************************/
/*
* This file is an attempt at collecting best practice methods for obtaining randomness with different operating systems.
* It may be out-of-date. Consult the documentation of the operating system before considering to use the methods below.
*
* Platform randomness sources:
* Linux -> `getrandom(2)`(`sys/random.h`), if not available `/dev/urandom` should be used. http://man7.org/linux/man-pages/man2/getrandom.2.html, https://linux.die.net/man/4/urandom
* macOS -> `getentropy(2)`(`sys/random.h`), if not available `/dev/urandom` should be used. https://www.unix.com/man-page/mojave/2/getentropy, https://opensource.apple.com/source/xnu/xnu-517.12.7/bsd/man/man4/random.4.auto.html
* FreeBSD -> `getrandom(2)`(`sys/random.h`), if not available `kern.arandom` should be used. https://www.freebsd.org/cgi/man.cgi?query=getrandom, https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
* OpenBSD -> `getentropy(2)`(`unistd.h`), if not available `/dev/urandom` should be used. https://man.openbsd.org/getentropy, https://man.openbsd.org/urandom
* Windows -> `BCryptGenRandom`(`bcrypt.h`). https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
*/
#if defined(_WIN32)
/*
* The defined WIN32_NO_STATUS macro disables return code definitions in
* windows.h, which avoids "macro redefinition" MSVC warnings in ntstatus.h.
*/
#define WIN32_NO_STATUS
#include <windows.h>
#undef WIN32_NO_STATUS
#include <ntstatus.h>
#include <bcrypt.h>
#elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
#include <sys/random.h>
#elif defined(__OpenBSD__)
#include <unistd.h>
#else
#error "Couldn't identify the OS"
#endif
#include <stddef.h>
#include <limits.h>
#include <stdio.h>
/* Returns 1 on success, and 0 on failure. */
static int fill_random(unsigned char* data, size_t size) {
#if defined(_WIN32)
NTSTATUS res = BCryptGenRandom(NULL, data, size, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
if (res != STATUS_SUCCESS || size > ULONG_MAX) {
return 0;
} else {
return 1;
}
#elif defined(__linux__) || defined(__FreeBSD__)
/* If `getrandom(2)` is not available you should fallback to /dev/urandom */
ssize_t res = getrandom(data, size, 0);
if (res < 0 || (size_t)res != size ) {
return 0;
} else {
return 1;
}
#elif defined(__APPLE__) || defined(__OpenBSD__)
/* If `getentropy(2)` is not available you should fallback to either
* `SecRandomCopyBytes` or /dev/urandom */
int res = getentropy(data, size);
if (res == 0) {
return 1;
} else {
return 0;
}
#endif
return 0;
}

31
extmod/secp256k1mod.c
View file

@ -25,6 +25,28 @@
#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <secp256k1.h>
#include "random.h"
static secp256k1_context * create_context(
const unsigned char randomize
) {
secp256k1_context *ctx = secp256k1_context_create(
SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY
/* SECP256K1_CONTEXT_NONE */ /* see NOTE above */
);
if (randomize) {
unsigned char buf[32];
if (!fill_random(buf, sizeof(buf))) {
printf("Failed to generate entropy\n");
return NULL;
}
if (!secp256k1_context_randomize(ctx, buf)) {
printf("Failed to randomize context\n");
return NULL;
}
}
return ctx;
}
static int privkey_check(
const secp256k1_context * ctx,
@ -96,8 +118,7 @@ static PyObject * pubkey_gen(PyObject *self, PyObject *args) {
size_t pubkey_bytes_len = compressed == 1 ? 33 : 65;
unsigned char pubkey_bytes[pubkey_bytes_len];
secp256k1_pubkey pubkey;
/* see NOTE */
secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
secp256k1_context *ctx = create_context(1);
if (ctx == NULL) {
PyErr_SetString(PyExc_RuntimeError, "Context initialization failed");
return NULL;
@ -132,8 +153,7 @@ static PyObject * pubkey_tweak_add(PyObject *self, PyObject *args) {
PyErr_SetString(PyExc_ValueError, "Unable to parse extension mod arguments");
return NULL;
}
/* see NOTE */
secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
secp256k1_context *ctx = create_context(1);
secp256k1_pubkey pubkey;
if (!pubkey_parse_with_check(ctx, &pubkey, pubkey_bytes, pubkey_bytes_len)) {
return NULL;
@ -168,8 +188,7 @@ static PyObject * pubkey_check(PyObject *self, PyObject *args) {
PyErr_SetString(PyExc_ValueError, "Unable to parse extension mod arguments");
return NULL;
}
/* see NOTE */
secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
secp256k1_context *ctx = create_context(1);
secp256k1_pubkey pubkey;
if (!pubkey_parse_with_check(ctx, &pubkey, pubkey_bytes, pubkey_bytes_len)) {
return NULL;