345 lines
12 KiB
C
345 lines
12 KiB
C
/* main.c
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*
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* Bare-metal SRAM PUF example for Cortex-M.
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*
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* Platform-portable PUF demonstration: enrollment, reconstruction,
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* key derivation, and device identity. HAL-specific code (UART, RNG)
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* is in a separate file (e.g., stm32.c).
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*
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* Supports both test mode (synthetic SRAM data) and real hardware SRAM PUF.
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*
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* Copyright (C) 2006-2026 wolfSSL Inc.
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*
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* This file is part of wolfSSL.
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*
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* wolfSSL is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* wolfSSL is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
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*/
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#include <wolfssl/wolfcrypt/settings.h>
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#include <wolfssl/wolfcrypt/puf.h>
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#include <wolfssl/wolfcrypt/error-crypt.h>
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#include <wolfssl/wolfcrypt/wc_port.h>
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#include <wolfssl/wolfcrypt/memory.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <string.h>
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/* Platform HAL init (implemented in stm32.c or other target file) */
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extern void hal_init(void);
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/* -------------------------------------------------------------------------- */
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/* PUF SRAM region (real hardware path) */
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/* -------------------------------------------------------------------------- */
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#ifndef WOLFSSL_PUF_TEST
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/* This buffer is placed in the .puf_sram linker section (NOLOAD).
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* The startup code must NOT zero this region - the raw power-on SRAM
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* state is the PUF entropy source. */
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__attribute__((section(".puf_sram")))
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static volatile uint8_t puf_sram_region[WC_PUF_RAW_BYTES];
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#endif
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/* -------------------------------------------------------------------------- */
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/* Helper: print hex buffer */
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/* -------------------------------------------------------------------------- */
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static void print_hex(const char* label, const uint8_t* data, uint32_t len)
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{
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uint32_t i;
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printf("%s: ", label);
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for (i = 0; i < len; i++)
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printf("%02x", data[i]);
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printf("\n");
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}
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/* -------------------------------------------------------------------------- */
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/* Main PUF demonstration */
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/* -------------------------------------------------------------------------- */
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int main(void)
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{
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wc_PufCtx ctx;
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int ret;
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uint8_t identity[WC_PUF_ID_SZ];
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uint8_t key[WC_PUF_KEY_SZ];
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uint8_t identity2[WC_PUF_ID_SZ];
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uint8_t key2[WC_PUF_KEY_SZ];
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uint8_t helperData[WC_PUF_HELPER_BYTES];
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const uint8_t info[] = "puf-example-key";
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/* Initialize platform HAL (UART, clocks, etc.) */
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hal_init();
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printf("\n--- wolfCrypt SRAM PUF Example ---\n\n");
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/* Initialize wolfCrypt */
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ret = wolfCrypt_Init();
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if (ret != 0) {
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printf("ERROR: wolfCrypt_Init failed: %d\n", ret);
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return ret;
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}
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/* Step 1: Initialize PUF context */
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ret = wc_PufInit(&ctx);
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if (ret != 0) {
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printf("ERROR: wc_PufInit failed: %d\n", ret);
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goto cleanup;
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}
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printf("PUF initialized.\n");
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#ifdef WOLFSSL_PUF_TEST
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/* ================================================================== */
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/* TEST MODE: Use synthetic SRAM data */
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/* ================================================================== */
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{
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/* Synthetic SRAM pattern for testing (deterministic) */
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uint8_t testSram[WC_PUF_RAW_BYTES];
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uint8_t noisySram[WC_PUF_RAW_BYTES];
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uint32_t i;
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printf("Mode: TEST (synthetic SRAM data)\n\n");
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/* Generate deterministic test pattern */
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for (i = 0; i < WC_PUF_RAW_BYTES; i++)
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testSram[i] = (uint8_t)((i * 37 + 13) ^ (i >> 2));
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/* Step 2: Load test SRAM data */
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ret = wc_PufSetTestData(&ctx, testSram, sizeof(testSram));
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if (ret != 0) {
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printf("ERROR: wc_PufSetTestData failed: %d\n", ret);
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goto cleanup;
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}
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/* Step 3: Enroll - generates helper data from SRAM pattern */
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ret = wc_PufEnroll(&ctx);
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if (ret != 0) {
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printf("ERROR: wc_PufEnroll failed: %d\n", ret);
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goto cleanup;
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}
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printf("Enrollment complete.\n");
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/* Save helper data (in production, store to flash/NVM) */
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memcpy(helperData, ctx.helperData, WC_PUF_HELPER_BYTES);
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/* Get device identity */
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ret = wc_PufGetIdentity(&ctx, identity, sizeof(identity));
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if (ret != 0) {
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printf("ERROR: wc_PufGetIdentity failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Identity (enrollment)", identity, WC_PUF_ID_SZ);
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/* Derive a key */
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ret = wc_PufDeriveKey(&ctx, info, sizeof(info), key, sizeof(key));
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if (ret != 0) {
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printf("ERROR: wc_PufDeriveKey failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Derived key (enrollment)", key, WC_PUF_KEY_SZ);
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/* ---- Simulate power cycle with noisy SRAM ---- */
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printf("\n--- Simulating power cycle (noisy SRAM) ---\n\n");
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/* Create noisy copy: flip a few bits per 128-bit block */
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memcpy(noisySram, testSram, WC_PUF_RAW_BYTES);
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for (i = 0; i < 16; i++) {
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/* Flip 2 bits in each 16-byte (128-bit) block */
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noisySram[i * 16 + 3] ^= 0x04;
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noisySram[i * 16 + 11] ^= 0x20;
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}
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/* Re-initialize and load noisy SRAM */
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ret = wc_PufInit(&ctx);
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if (ret != 0) {
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printf("ERROR: wc_PufInit failed: %d\n", ret);
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goto cleanup;
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}
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ret = wc_PufSetTestData(&ctx, noisySram, sizeof(noisySram));
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if (ret != 0) {
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printf("ERROR: wc_PufSetTestData failed: %d\n", ret);
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goto cleanup;
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}
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/* Step 4: Reconstruct stable bits using helper data */
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ret = wc_PufReconstruct(&ctx, helperData, WC_PUF_HELPER_BYTES);
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if (ret != 0) {
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printf("ERROR: wc_PufReconstruct failed: %d\n", ret);
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goto cleanup;
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}
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printf("Reconstruction complete (BCH corrected noisy bits).\n");
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/* Verify identity matches */
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ret = wc_PufGetIdentity(&ctx, identity2, sizeof(identity2));
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if (ret != 0) {
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printf("ERROR: wc_PufGetIdentity failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Identity (reconstructed)", identity2, WC_PUF_ID_SZ);
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if (memcmp(identity, identity2, WC_PUF_ID_SZ) == 0) {
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printf("PASS: Identity matches after reconstruction.\n");
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}
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else {
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printf("FAIL: Identity mismatch!\n");
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ret = -1;
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goto cleanup;
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}
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/* Verify derived key matches */
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ret = wc_PufDeriveKey(&ctx, info, sizeof(info), key2, sizeof(key2));
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if (ret != 0) {
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printf("ERROR: wc_PufDeriveKey failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Derived key (reconstructed)", key2, WC_PUF_KEY_SZ);
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if (memcmp(key, key2, WC_PUF_KEY_SZ) == 0) {
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printf("PASS: Derived key matches after reconstruction.\n");
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}
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else {
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printf("FAIL: Derived key mismatch!\n");
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ret = -1;
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goto cleanup;
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}
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}
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#else
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/* ================================================================== */
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/* REAL HARDWARE: Read actual SRAM PUF */
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/* ================================================================== */
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{
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printf("Mode: HARDWARE (real SRAM PUF)\n\n");
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/* ---- Phase 1: Enrollment ---- */
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/* Read raw SRAM (must happen before any other access to the
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* .puf_sram region - the power-on entropy is consumed once). */
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ret = wc_PufReadSram(&ctx, (const uint8_t*)puf_sram_region,
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sizeof(puf_sram_region));
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if (ret != 0) {
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printf("ERROR: wc_PufReadSram failed: %d\n", ret);
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goto cleanup;
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}
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printf("SRAM read complete (%d bytes).\n",
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(int)sizeof(puf_sram_region));
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ret = wc_PufEnroll(&ctx);
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if (ret != 0) {
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printf("ERROR: wc_PufEnroll failed: %d\n", ret);
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goto cleanup;
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}
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printf("Enrollment complete.\n");
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/* Save helper data. In production this is written to flash/NVM
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* for use across reboots; here it stays in RAM so the same run
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* can also exercise the reconstruction path below. */
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memcpy(helperData, ctx.helperData, WC_PUF_HELPER_BYTES);
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print_hex("Helper data (store to NVM)", helperData,
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WC_PUF_HELPER_BYTES);
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ret = wc_PufGetIdentity(&ctx, identity, sizeof(identity));
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if (ret != 0) {
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printf("ERROR: wc_PufGetIdentity failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Identity (enrollment)", identity, WC_PUF_ID_SZ);
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ret = wc_PufDeriveKey(&ctx, info, sizeof(info), key, sizeof(key));
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if (ret != 0) {
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printf("ERROR: wc_PufDeriveKey failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Derived key (enrollment)", key, WC_PUF_KEY_SZ);
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/* ---- Phase 2: Reconstruction ---- */
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/* On real hardware the same .puf_sram contents are still in
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* RAM, so re-reading them yields the same bytes and BCH runs
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* with zero errors. Under m33mu, run the example a second time
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* with a different --puf-cold-boot or with --puf-noise to feed
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* a noisy SRAM image through wc_PufReconstruct using the
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* helper data captured above. */
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printf("\n--- Reconstructing from saved helper data ---\n\n");
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ret = wc_PufInit(&ctx);
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if (ret != 0) {
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printf("ERROR: wc_PufInit (reconstruct) failed: %d\n", ret);
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goto cleanup;
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}
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ret = wc_PufReadSram(&ctx, (const uint8_t*)puf_sram_region,
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sizeof(puf_sram_region));
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if (ret != 0) {
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printf("ERROR: wc_PufReadSram (reconstruct) failed: %d\n", ret);
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goto cleanup;
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}
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ret = wc_PufReconstruct(&ctx, helperData, WC_PUF_HELPER_BYTES);
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if (ret != 0) {
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printf("ERROR: wc_PufReconstruct failed: %d\n", ret);
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goto cleanup;
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}
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printf("Reconstruction complete (BCH error correction ran).\n");
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ret = wc_PufGetIdentity(&ctx, identity2, sizeof(identity2));
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if (ret != 0) {
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printf("ERROR: wc_PufGetIdentity (reconstruct) failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Identity (reconstructed)", identity2, WC_PUF_ID_SZ);
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if (memcmp(identity, identity2, WC_PUF_ID_SZ) == 0) {
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printf("PASS: Identity matches after reconstruction.\n");
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}
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else {
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printf("FAIL: Identity mismatch after reconstruction!\n");
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ret = -1;
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goto cleanup;
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}
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ret = wc_PufDeriveKey(&ctx, info, sizeof(info), key2, sizeof(key2));
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if (ret != 0) {
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printf("ERROR: wc_PufDeriveKey (reconstruct) failed: %d\n", ret);
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goto cleanup;
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}
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print_hex("Derived key (reconstructed)", key2, WC_PUF_KEY_SZ);
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if (memcmp(key, key2, WC_PUF_KEY_SZ) == 0) {
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printf("PASS: Derived key matches after reconstruction.\n");
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}
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else {
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printf("FAIL: Derived key mismatch after reconstruction!\n");
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ret = -1;
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goto cleanup;
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}
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}
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#endif /* WOLFSSL_PUF_TEST */
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printf("\n--- PUF example complete ---\n");
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cleanup:
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/* Securely zeroize all PUF secrets */
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wc_ForceZero(key, sizeof(key));
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wc_ForceZero(identity, sizeof(identity));
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wc_ForceZero(key2, sizeof(key2));
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wc_ForceZero(identity2, sizeof(identity2));
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wc_ForceZero(helperData, sizeof(helperData));
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wc_PufZeroize(&ctx);
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wolfCrypt_Cleanup();
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return ret;
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}
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