mirror of
https://github.com/espressif/esp-idf.git
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662 lines
20 KiB
C
662 lines
20 KiB
C
/*
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* Multi-precision integer library
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* ESP-IDF hardware accelerated parts based on mbedTLS implementation
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*
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* SPDX-FileCopyrightText: The Mbed TLS Contributors
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* SPDX-FileContributor: 2016-2023 Espressif Systems (Shanghai) CO LTD
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*/
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#include <stdio.h>
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#include <string.h>
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#include <malloc.h>
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#include <limits.h>
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#include <assert.h>
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#include <stdlib.h>
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#include <sys/param.h>
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#include "esp_system.h"
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#include "esp_log.h"
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#include "esp_attr.h"
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#include "esp_intr_alloc.h"
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#if CONFIG_PM_ENABLE
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#include "esp_pm.h"
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#endif
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#include "esp_private/periph_ctrl.h"
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#include "freertos/FreeRTOS.h"
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#include "freertos/semphr.h"
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#include "bignum_impl.h"
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#include "mbedtls/bignum.h"
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#include "hal/mpi_hal.h"
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/* Some implementation notes:
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*
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* - Naming convention x_words, y_words, z_words for number of words (limbs) used in a particular
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* bignum. This number may be less than the size of the bignum
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*
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* - Naming convention hw_words for the hardware length of the operation. This number maybe be rounded up
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* for targets that requres this (e.g. ESP32), and may be larger than any of the numbers
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* involved in the calculation.
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*
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* - Timing behaviour of these functions will depend on the length of the inputs. This is fundamentally
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* the same constraint as the software mbedTLS implementations, and relies on the same
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* countermeasures (exponent blinding, etc) which are used in mbedTLS.
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*/
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static const __attribute__((unused)) char *TAG = "bignum";
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#define ciL (sizeof(mbedtls_mpi_uint)) /* chars in limb */
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#define biL (ciL << 3) /* bits in limb */
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#if defined(CONFIG_MBEDTLS_MPI_USE_INTERRUPT)
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static SemaphoreHandle_t op_complete_sem;
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#if defined(CONFIG_PM_ENABLE)
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static esp_pm_lock_handle_t s_pm_cpu_lock;
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static esp_pm_lock_handle_t s_pm_sleep_lock;
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#endif
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static IRAM_ATTR void esp_mpi_complete_isr(void *arg)
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{
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BaseType_t higher_woken;
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mpi_hal_clear_interrupt();
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xSemaphoreGiveFromISR(op_complete_sem, &higher_woken);
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if (higher_woken) {
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portYIELD_FROM_ISR();
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}
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}
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static esp_err_t esp_mpi_isr_initialise(void)
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{
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mpi_hal_clear_interrupt();
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mpi_hal_interrupt_enable(true);
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if (op_complete_sem == NULL) {
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op_complete_sem = xSemaphoreCreateBinary();
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if (op_complete_sem == NULL) {
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ESP_LOGE(TAG, "Failed to create intr semaphore");
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return ESP_FAIL;
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}
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esp_intr_alloc(ETS_RSA_INTR_SOURCE, 0, esp_mpi_complete_isr, NULL, NULL);
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}
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/* MPI is clocked proportionally to CPU clock, take power management lock */
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#ifdef CONFIG_PM_ENABLE
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if (s_pm_cpu_lock == NULL) {
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if (esp_pm_lock_create(ESP_PM_NO_LIGHT_SLEEP, 0, "mpi_sleep", &s_pm_sleep_lock) != ESP_OK) {
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ESP_LOGE(TAG, "Failed to create PM sleep lock");
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return ESP_FAIL;
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}
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if (esp_pm_lock_create(ESP_PM_CPU_FREQ_MAX, 0, "mpi_cpu", &s_pm_cpu_lock) != ESP_OK) {
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ESP_LOGE(TAG, "Failed to create PM CPU lock");
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return ESP_FAIL;
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}
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}
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esp_pm_lock_acquire(s_pm_cpu_lock);
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esp_pm_lock_acquire(s_pm_sleep_lock);
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#endif
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return ESP_OK;
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}
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static int esp_mpi_wait_intr(void)
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{
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if (!xSemaphoreTake(op_complete_sem, 2000 / portTICK_PERIOD_MS)) {
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ESP_LOGE("MPI", "Timed out waiting for completion of MPI Interrupt");
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return -1;
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}
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#ifdef CONFIG_PM_ENABLE
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esp_pm_lock_release(s_pm_cpu_lock);
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esp_pm_lock_release(s_pm_sleep_lock);
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#endif // CONFIG_PM_ENABLE
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mpi_hal_interrupt_enable(false);
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return 0;
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}
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#endif // CONFIG_MBEDTLS_MPI_USE_INTERRUPT
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/* Convert bit count to word count
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*/
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static inline size_t bits_to_words(size_t bits)
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{
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return (bits + 31) / 32;
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}
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/* Return the number of words actually used to represent an mpi
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number.
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*/
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#if defined(MBEDTLS_MPI_EXP_MOD_ALT) || defined(MBEDTLS_MPI_EXP_MOD_ALT_FALLBACK)
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static size_t mpi_words(const mbedtls_mpi *mpi)
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{
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for (size_t i = mpi->MBEDTLS_PRIVATE(n); i > 0; i--) {
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if (mpi->MBEDTLS_PRIVATE(p[i - 1]) != 0) {
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return i;
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}
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}
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return 0;
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}
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#endif //(MBEDTLS_MPI_EXP_MOD_ALT || MBEDTLS_MPI_EXP_MOD_ALT_FALLBACK)
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/**
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*
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* There is a need for the value of integer N' such that B^-1(B-1)-N^-1N'=1,
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* where B^-1(B-1) mod N=1. Actually, only the least significant part of
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* N' is needed, hence the definition N0'=N' mod b. We reproduce below the
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* simple algorithm from an article by Dusse and Kaliski to efficiently
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* find N0' from N0 and b
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*/
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static mbedtls_mpi_uint modular_inverse(const mbedtls_mpi *M)
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{
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int i;
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uint64_t t = 1;
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uint64_t two_2_i_minus_1 = 2; /* 2^(i-1) */
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uint64_t two_2_i = 4; /* 2^i */
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uint64_t N = M->MBEDTLS_PRIVATE(p[0]);
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for (i = 2; i <= 32; i++) {
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if ((mbedtls_mpi_uint) N * t % two_2_i >= two_2_i_minus_1) {
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t += two_2_i_minus_1;
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}
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two_2_i_minus_1 <<= 1;
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two_2_i <<= 1;
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}
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return (mbedtls_mpi_uint)(UINT32_MAX - t + 1);
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}
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/* Calculate Rinv = RR^2 mod M, where:
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*
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* R = b^n where b = 2^32, n=num_words,
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* R = 2^N (where N=num_bits)
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* RR = R^2 = 2^(2*N) (where N=num_bits=num_words*32)
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*
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* This calculation is computationally expensive (mbedtls_mpi_mod_mpi)
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* so caller should cache the result where possible.
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*
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* DO NOT call this function while holding esp_mpi_enable_hardware_hw_op().
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*
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*/
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static int calculate_rinv(mbedtls_mpi *Rinv, const mbedtls_mpi *M, int num_words)
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{
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int ret;
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size_t num_bits = num_words * 32;
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mbedtls_mpi RR;
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mbedtls_mpi_init(&RR);
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MBEDTLS_MPI_CHK(mbedtls_mpi_set_bit(&RR, num_bits * 2, 1));
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MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(Rinv, &RR, M));
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cleanup:
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mbedtls_mpi_free(&RR);
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return ret;
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}
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/* Z = (X * Y) mod M
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Not an mbedTLS function
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*/
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int esp_mpi_mul_mpi_mod(mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, const mbedtls_mpi *M)
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{
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int ret = 0;
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size_t x_bits = mbedtls_mpi_bitlen(X);
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size_t y_bits = mbedtls_mpi_bitlen(Y);
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size_t m_bits = mbedtls_mpi_bitlen(M);
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size_t z_bits = MIN(m_bits, x_bits + y_bits);
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size_t x_words = bits_to_words(x_bits);
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size_t y_words = bits_to_words(y_bits);
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size_t m_words = bits_to_words(m_bits);
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size_t z_words = bits_to_words(z_bits);
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size_t hw_words = mpi_hal_calc_hardware_words(MAX(x_words, MAX(y_words, m_words))); /* longest operand */
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mbedtls_mpi Rinv;
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mbedtls_mpi_uint Mprime;
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/* Calculate and load the first stage montgomery multiplication */
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mbedtls_mpi_init(&Rinv);
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MBEDTLS_MPI_CHK(calculate_rinv(&Rinv, M, hw_words));
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Mprime = modular_inverse(M);
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esp_mpi_enable_hardware_hw_op();
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/* Load and start a (X * Y) mod M calculation */
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esp_mpi_mul_mpi_mod_hw_op(X, Y, M, &Rinv, Mprime, hw_words);
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MBEDTLS_MPI_CHK(mbedtls_mpi_grow(Z, z_words));
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/* Read back the result */
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mpi_hal_read_result_hw_op(Z->MBEDTLS_PRIVATE(p), Z->MBEDTLS_PRIVATE(n), z_words);
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Z->MBEDTLS_PRIVATE(s) = X->MBEDTLS_PRIVATE(s) * Y->MBEDTLS_PRIVATE(s);
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cleanup:
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mbedtls_mpi_free(&Rinv);
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esp_mpi_disable_hardware_hw_op();
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return ret;
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}
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#if defined(MBEDTLS_MPI_EXP_MOD_ALT) || defined(MBEDTLS_MPI_EXP_MOD_ALT_FALLBACK)
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#ifdef ESP_MPI_USE_MONT_EXP
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/*
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* Return the most significant one-bit.
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*/
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static size_t mbedtls_mpi_msb( const mbedtls_mpi *X )
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{
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int i, j;
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if (X != NULL && X->MBEDTLS_PRIVATE(n) != 0) {
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for (i = X->MBEDTLS_PRIVATE(n) - 1; i >= 0; i--) {
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if (X->MBEDTLS_PRIVATE(p[i]) != 0) {
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for (j = biL - 1; j >= 0; j--) {
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if ((X->MBEDTLS_PRIVATE(p[i]) & (1 << j)) != 0) {
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return (i * biL) + j;
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}
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}
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}
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}
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}
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return 0;
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}
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/*
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* Montgomery exponentiation: Z = X ^ Y mod M (HAC 14.94)
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*/
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static int mpi_montgomery_exp_calc( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, const mbedtls_mpi *M,
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mbedtls_mpi *Rinv,
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size_t hw_words,
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mbedtls_mpi_uint Mprime )
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{
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int ret = 0;
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mbedtls_mpi X_, one;
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mbedtls_mpi_init(&X_);
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mbedtls_mpi_init(&one);
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if ( ( ( ret = mbedtls_mpi_grow(&one, hw_words) ) != 0 ) ||
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( ( ret = mbedtls_mpi_set_bit(&one, 0, 1) ) != 0 ) ) {
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goto cleanup2;
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}
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// Algorithm from HAC 14.94
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{
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// 0 determine t (highest bit set in y)
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int t = mbedtls_mpi_msb(Y);
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esp_mpi_enable_hardware_hw_op();
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// 1.1 x_ = mont(x, R^2 mod m)
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// = mont(x, rb)
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MBEDTLS_MPI_CHK( esp_mont_hw_op(&X_, X, Rinv, M, Mprime, hw_words, false) );
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// 1.2 z = R mod m
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// now z = R mod m = Mont (R^2 mod m, 1) mod M (as Mont(x) = X&R^-1 mod M)
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MBEDTLS_MPI_CHK( esp_mont_hw_op(Z, Rinv, &one, M, Mprime, hw_words, true) );
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// 2 for i from t down to 0
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for (int i = t; i >= 0; i--) {
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// 2.1 z = mont(z,z)
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if (i != t) { // skip on the first iteration as is still unity
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MBEDTLS_MPI_CHK( esp_mont_hw_op(Z, Z, Z, M, Mprime, hw_words, true) );
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}
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// 2.2 if y[i] = 1 then z = mont(A, x_)
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if (mbedtls_mpi_get_bit(Y, i)) {
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MBEDTLS_MPI_CHK( esp_mont_hw_op(Z, Z, &X_, M, Mprime, hw_words, true) );
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}
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}
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// 3 z = Mont(z, 1)
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MBEDTLS_MPI_CHK( esp_mont_hw_op(Z, Z, &one, M, Mprime, hw_words, true) );
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}
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cleanup:
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esp_mpi_disable_hardware_hw_op();
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cleanup2:
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mbedtls_mpi_free(&X_);
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mbedtls_mpi_free(&one);
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return ret;
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}
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#endif //USE_MONT_EXPONENATIATION
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/*
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* Z = X ^ Y mod M
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*
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* _Rinv is optional pre-calculated version of Rinv (via calculate_rinv()).
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*
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* (See RSA Accelerator section in Technical Reference for more about Mprime, Rinv)
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*
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*/
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static int esp_mpi_exp_mod( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, const mbedtls_mpi *M, mbedtls_mpi *_Rinv )
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{
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int ret = 0;
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mbedtls_mpi Rinv_new; /* used if _Rinv == NULL */
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mbedtls_mpi *Rinv; /* points to _Rinv (if not NULL) othwerwise &RR_new */
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mbedtls_mpi_uint Mprime;
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size_t x_words = mpi_words(X);
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size_t y_words = mpi_words(Y);
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size_t m_words = mpi_words(M);
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/* "all numbers must be the same length", so choose longest number
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as cardinal length of operation...
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*/
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size_t num_words = mpi_hal_calc_hardware_words(MAX(m_words, MAX(x_words, y_words)));
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if (num_words * 32 > SOC_RSA_MAX_BIT_LEN) {
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return MBEDTLS_ERR_MPI_NOT_ACCEPTABLE;
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}
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if (mbedtls_mpi_cmp_int(M, 0) <= 0 || (M->MBEDTLS_PRIVATE(p[0]) & 1) == 0) {
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return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
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}
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if (mbedtls_mpi_cmp_int(Y, 0) < 0) {
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return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
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}
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if (mbedtls_mpi_cmp_int(Y, 0) == 0) {
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return mbedtls_mpi_lset(Z, 1);
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}
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/* Determine RR pointer, either _RR for cached value
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or local RR_new */
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if (_Rinv == NULL) {
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mbedtls_mpi_init(&Rinv_new);
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Rinv = &Rinv_new;
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} else {
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Rinv = _Rinv;
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}
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if (Rinv->MBEDTLS_PRIVATE(p) == NULL) {
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MBEDTLS_MPI_CHK(calculate_rinv(Rinv, M, num_words));
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}
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Mprime = modular_inverse(M);
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// Montgomery exponentiation: Z = X ^ Y mod M (HAC 14.94)
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#ifdef ESP_MPI_USE_MONT_EXP
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ret = mpi_montgomery_exp_calc(Z, X, Y, M, Rinv, num_words, Mprime) ;
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MBEDTLS_MPI_CHK(ret);
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#else
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esp_mpi_enable_hardware_hw_op();
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#if defined (CONFIG_MBEDTLS_MPI_USE_INTERRUPT)
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if (esp_mpi_isr_initialise() == ESP_FAIL) {
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ret = -1;
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esp_mpi_disable_hardware_hw_op();
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goto cleanup;
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}
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#endif
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esp_mpi_exp_mpi_mod_hw_op(X, Y, M, Rinv, Mprime, num_words);
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ret = mbedtls_mpi_grow(Z, m_words);
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if (ret != 0) {
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esp_mpi_disable_hardware_hw_op();
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goto cleanup;
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}
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#if defined(CONFIG_MBEDTLS_MPI_USE_INTERRUPT)
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ret = esp_mpi_wait_intr();
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if (ret != 0) {
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esp_mpi_disable_hardware_hw_op();
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goto cleanup;
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}
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#endif //CONFIG_MBEDTLS_MPI_USE_INTERRUPT
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/* Read back the result */
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mpi_hal_read_result_hw_op(Z->MBEDTLS_PRIVATE(p), Z->MBEDTLS_PRIVATE(n), m_words);
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esp_mpi_disable_hardware_hw_op();
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#endif
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// Compensate for negative X
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if (X->MBEDTLS_PRIVATE(s) == -1 && (Y->MBEDTLS_PRIVATE(p[0]) & 1) != 0) {
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Z->MBEDTLS_PRIVATE(s) = -1;
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MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(Z, M, Z));
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} else {
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Z->MBEDTLS_PRIVATE(s) = 1;
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}
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cleanup:
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if (_Rinv == NULL) {
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mbedtls_mpi_free(&Rinv_new);
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}
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return ret;
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}
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#endif /* (MBEDTLS_MPI_EXP_MOD_ALT || MBEDTLS_MPI_EXP_MOD_ALT_FALLBACK) */
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/*
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* Sliding-window exponentiation: X = A^E mod N (HAC 14.85)
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*/
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int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
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const mbedtls_mpi *E, const mbedtls_mpi *N,
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mbedtls_mpi *_RR )
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{
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int ret;
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#if defined(MBEDTLS_MPI_EXP_MOD_ALT_FALLBACK)
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/* Try hardware API first and then fallback to software */
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ret = esp_mpi_exp_mod( X, A, E, N, _RR );
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if( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE ) {
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ret = mbedtls_mpi_exp_mod_soft( X, A, E, N, _RR );
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}
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#else
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/* Hardware approach */
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ret = esp_mpi_exp_mod( X, A, E, N, _RR );
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#endif
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/* Note: For software only approach, it gets handled in mbedTLS library.
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This file is not part of build objects for that case */
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return ret;
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}
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#if defined(MBEDTLS_MPI_MUL_MPI_ALT) /* MBEDTLS_MPI_MUL_MPI_ALT */
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static int mpi_mult_mpi_failover_mod_mult( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, size_t z_words);
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static int mpi_mult_mpi_overlong(mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, size_t y_words, size_t z_words);
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/* Z = X * Y */
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int mbedtls_mpi_mul_mpi( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y )
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{
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int ret = 0;
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size_t x_bits = mbedtls_mpi_bitlen(X);
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size_t y_bits = mbedtls_mpi_bitlen(Y);
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size_t x_words = bits_to_words(x_bits);
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size_t y_words = bits_to_words(y_bits);
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size_t z_words = bits_to_words(x_bits + y_bits);
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size_t hw_words = mpi_hal_calc_hardware_words(MAX(x_words, y_words)); // length of one operand in hardware
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/* Short-circuit eval if either argument is 0 or 1.
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This is needed as the mpi modular division
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argument will sometimes call in here when one
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argument is too large for the hardware unit, but the other
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argument is zero or one.
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*/
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if (x_bits == 0 || y_bits == 0) {
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mbedtls_mpi_lset(Z, 0);
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return 0;
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}
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if (x_bits == 1) {
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ret = mbedtls_mpi_copy(Z, Y);
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Z->MBEDTLS_PRIVATE(s) *= X->MBEDTLS_PRIVATE(s);
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return ret;
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}
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if (y_bits == 1) {
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ret = mbedtls_mpi_copy(Z, X);
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Z->MBEDTLS_PRIVATE(s) *= Y->MBEDTLS_PRIVATE(s);
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return ret;
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}
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/* Grow Z to result size early, avoid interim allocations */
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MBEDTLS_MPI_CHK( mbedtls_mpi_grow(Z, z_words) );
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/* If either factor is over 2048 bits, we can't use the standard hardware multiplier
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(it assumes result is double longest factor, and result is max 4096 bits.)
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However, we can fail over to mod_mult for up to 4096 bits of result (modulo
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multiplication doesn't have the same restriction, so result is simply the
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number of bits in X plus number of bits in in Y.)
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*/
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if (hw_words * 32 > SOC_RSA_MAX_BIT_LEN/2) {
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if (z_words * 32 <= SOC_RSA_MAX_BIT_LEN) {
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/* Note: it's possible to use mpi_mult_mpi_overlong
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for this case as well, but it's very slightly
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slower and requires a memory allocation.
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*/
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return mpi_mult_mpi_failover_mod_mult(Z, X, Y, z_words);
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} else {
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/* Still too long for the hardware unit... */
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if (y_words > x_words) {
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return mpi_mult_mpi_overlong(Z, X, Y, y_words, z_words);
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} else {
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return mpi_mult_mpi_overlong(Z, Y, X, x_words, z_words);
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}
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}
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}
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/* Otherwise, we can use the (faster) multiply hardware unit */
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esp_mpi_enable_hardware_hw_op();
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esp_mpi_mul_mpi_hw_op(X, Y, hw_words);
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/* Read back the result */
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mpi_hal_read_result_hw_op(Z->MBEDTLS_PRIVATE(p), Z->MBEDTLS_PRIVATE(n), z_words);
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esp_mpi_disable_hardware_hw_op();
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Z->MBEDTLS_PRIVATE(s) = X->MBEDTLS_PRIVATE(s) * Y->MBEDTLS_PRIVATE(s);
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cleanup:
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return ret;
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}
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int mbedtls_mpi_mul_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_uint b )
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{
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mbedtls_mpi _B;
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mbedtls_mpi_uint p[1];
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_B.MBEDTLS_PRIVATE(s) = 1;
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_B.MBEDTLS_PRIVATE(n) = 1;
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_B.MBEDTLS_PRIVATE(p) = p;
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p[0] = b;
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return( mbedtls_mpi_mul_mpi( X, A, &_B ) );
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}
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/* Deal with the case when X & Y are too long for the hardware unit, by splitting one operand
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into two halves.
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Y must be the longer operand
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Slice Y into Yp, Ypp such that:
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Yp = lower 'b' bits of Y
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Ypp = upper 'b' bits of Y (right shifted)
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Such that
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Z = X * Y
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Z = X * (Yp + Ypp<<b)
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Z = (X * Yp) + (X * Ypp<<b)
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Note that this function may recurse multiple times, if both X & Y
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are too long for the hardware multiplication unit.
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*/
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static int mpi_mult_mpi_overlong(mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, size_t y_words, size_t z_words)
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{
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int ret = 0;
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mbedtls_mpi Ztemp;
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/* Rather than slicing in two on bits we slice on limbs (32 bit words) */
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const size_t words_slice = y_words / 2;
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/* Yp holds lower bits of Y (declared to reuse Y's array contents to save on copying) */
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const mbedtls_mpi Yp = {
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.MBEDTLS_PRIVATE(p) = Y->MBEDTLS_PRIVATE(p),
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.MBEDTLS_PRIVATE(n) = words_slice,
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.MBEDTLS_PRIVATE(s) = Y->MBEDTLS_PRIVATE(s)
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};
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/* Ypp holds upper bits of Y, right shifted (also reuses Y's array contents) */
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const mbedtls_mpi Ypp = {
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.MBEDTLS_PRIVATE(p) = Y->MBEDTLS_PRIVATE(p) + words_slice,
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.MBEDTLS_PRIVATE(n) = y_words - words_slice,
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.MBEDTLS_PRIVATE(s) = Y->MBEDTLS_PRIVATE(s)
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};
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mbedtls_mpi_init(&Ztemp);
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/* Get result Ztemp = Yp * X (need temporary variable Ztemp) */
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi(&Ztemp, X, &Yp) );
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/* Z = Ypp * Y */
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi(Z, X, &Ypp) );
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/* Z = Z << b */
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MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l(Z, words_slice * 32) );
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/* Z += Ztemp */
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MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi(Z, Z, &Ztemp) );
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cleanup:
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mbedtls_mpi_free(&Ztemp);
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return ret;
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}
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static int mpi_mult_mpi_failover_mod_mult( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, size_t z_words)
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{
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int ret;
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size_t hw_words = mpi_hal_calc_hardware_words(z_words);
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esp_mpi_enable_hardware_hw_op();
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esp_mpi_mult_mpi_failover_mod_mult_hw_op(X, Y, hw_words );
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MBEDTLS_MPI_CHK( mbedtls_mpi_grow(Z, hw_words) );
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/* Read back the result */
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mpi_hal_read_result_hw_op(Z->MBEDTLS_PRIVATE(p), Z->MBEDTLS_PRIVATE(n), hw_words);
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Z->MBEDTLS_PRIVATE(s) = X->MBEDTLS_PRIVATE(s) * Y->MBEDTLS_PRIVATE(s);
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/*
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* Relevant: https://github.com/espressif/esp-idf/issues/11850
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*
|
|
* If z_words < mpi_words(Z) (the actual words taken by the MPI result),
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* the assert fails due to unsigned arithmetic - most likely hardware
|
|
* peripheral has produced an incorrect result for MPI operation.
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* This can happen if data fed to the peripheral register was incorrect.
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*
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* z_words is calculated as the worst-case possible size of the result
|
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* MPI Z. The difference between z_words and the actual words taken by
|
|
* the MPI result (mpi_words(Z)) can be a maximum of 1 word.
|
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* The value z_bits (actual bits taken by the MPI result) is calculated
|
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* as x_bits + y_bits bits, however, in some cases, z_bits can be
|
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* x_bits + y_bits - 1 bits (see example below).
|
|
* 0b1111 * 0b1111 = 0b11100001 -> 8 bits
|
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* 0b1000 * 0b1000 = 0b01000000 -> 7 bits.
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* The code rounds up to the nearest word size, so the maximum difference
|
|
* could be of only 1 word. The assert handles this.
|
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*
|
|
*/
|
|
assert(z_words - mpi_words(Z) <= (size_t)1);
|
|
cleanup:
|
|
esp_mpi_disable_hardware_hw_op();
|
|
return ret;
|
|
}
|
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|
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#endif /* MBEDTLS_MPI_MUL_MPI_ALT */
|