mbedtls/tf-psa-crypto/tests/suites/test_suite_psa_crypto_ecp.function

/* BEGIN_HEADER */
/* Unit tests for internal functions for built-in ECC mechanisms. */
#include <psa/crypto.h>

#include "psa_crypto_ecp.h"

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_GENERATE)
/*
 * Check if a buffer is all-0 bytes:
 * return   1 if it is,
 *          0 if it isn't.
 *
 * TODO: we use this in multiple test suites. Move it to tests/src.
 */
static int buffer_is_all_zero(const uint8_t *buf, size_t size)
{
    for (size_t i = 0; i < size; i++) {
        if (buf[i] != 0) {
            return 0;
        }
    }
    return 1;
}

typedef struct {
    unsigned bit_bot;           /* lowest non-forced bit */
    unsigned bit_top;           /* highest non-forced bit */
} ecc_private_key_stats_t;

/* Do some sanity checks on an ECC private key. This is not intended to be
 * a full validity check, just to catch some potential mistakes. */
static int check_ecc_private_key(psa_ecc_family_t family, size_t bits,
                                 const uint8_t *key, size_t key_length,
                                 ecc_private_key_stats_t *stats)
{
    int ok = 0;

    /* Check the expected length (same calculation for all curves). */
    TEST_EQUAL(PSA_BITS_TO_BYTES(bits), key_length);

    /* All-bits zero is invalid and means no key material was copied to the
     * output buffer, or a grave RNG pluming failure. */
    TEST_ASSERT(!buffer_is_all_zero(key, key_length));

    /* Check the top byte of the value for non-byte-aligned curve sizes.
     * This is a partial endianness check. */
    if (bits % 8 != 0) {
        /* All supported non-byte-aligned curve sizes are for Weierstrass
         * curves with a big-endian representation. */
        uint8_t top_byte = key[0];
        uint8_t mask = 0xff << (bits & 8);
        TEST_EQUAL(top_byte & mask, 0);
    }

    /* Check masked bits on Curve25519 and Curve448 scalars.
     * See RFC 7748 \S4.1 (we expect the "decoded" form here). */
#if defined(MBEDTLS_PSA_BUILTIN_ECC_MONTGOMERY_255)
    if (family == PSA_ECC_FAMILY_MONTGOMERY && bits == 255) {
        TEST_EQUAL(key[0] & 0xf8, key[0]);
        TEST_EQUAL(key[31] & 0xc0, 0x40);
    }
#endif /* MBEDTLS_PSA_BUILTIN_ECC_MONTGOMERY_255 */
#if defined(MBEDTLS_PSA_BUILTIN_ECC_MONTGOMERY_448)
    if (family == PSA_ECC_FAMILY_MONTGOMERY && bits == 448) {
        TEST_EQUAL(key[0] & 0xfc, key[0]);
        TEST_EQUAL(key[55] & 0x80, 0x80);
    }
#endif /* MBEDTLS_PSA_BUILTIN_ECC_MONTGOMERY_448 */

    /* Don't bother to check that the value is in the exact permitted range
     * (1 to p-1 for Weierstrass curves, 2^{n-1} to p-1 for Montgomery curves).
     * We would need to bring in bignum machinery, and on most curves
     * the probability of a number being out of range is negligible.
     */

    /* Collect statistics on random-valued bits */
    /* Defaults for big-endian numbers */
    uint8_t bit_bot_mask = 0x01;
    size_t bit_bot_index = key_length - 1;
    uint8_t bit_top_mask = (bits % 8 == 0 ? 0x80 : 1 << (bits % 8 - 1));
    size_t bit_top_index = 0;
    if (family == PSA_ECC_FAMILY_MONTGOMERY) {
        bit_bot_index = 0;
        bit_top_index = key_length - 1;
        if (bits == 255) {
            bit_bot_mask = 0x08;
            bit_top_mask = 0x20;
        } else {
            bit_bot_mask = 0x04;
            bit_top_mask = 0x40;
        }
    }
    if (key[bit_bot_index] & bit_bot_mask) {
        ++stats->bit_bot;
    }
    if (key[bit_top_index] & bit_top_mask) {
        ++stats->bit_top;
    }

    ok = 1;
exit:
    return ok;
}
#endif

/* END_HEADER */

/* BEGIN_DEPENDENCIES
 * depends_on:MBEDTLS_PSA_CRYPTO_C:MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_PUBLIC_KEY
 * END_DEPENDENCIES
 */

/* BEGIN_CASE depends_on:MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_GENERATE */
void generate_key(int family_arg, int bits_arg,
                  int output_size_arg,
                  psa_status_t expected_status)
{
    psa_ecc_family_t family = family_arg;
    size_t bits = bits_arg;
    size_t output_size = output_size_arg;

    uint8_t *output = NULL;
    size_t output_length = SIZE_MAX;
    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
    psa_set_key_type(&attributes, PSA_KEY_TYPE_ECC_KEY_PAIR(family));
    psa_set_key_bits(&attributes, bits);
    ecc_private_key_stats_t stats = { 0, 0 };

    PSA_INIT();
    TEST_CALLOC(output, output_size);

    /* In success cases, run multiple iterations so that we can make
     * statistical observations. */
    unsigned iteration_count = expected_status == PSA_SUCCESS ? 256 : 1;
    for (unsigned i = 0; i < iteration_count; i++) {
        mbedtls_test_set_step(i);
        TEST_EQUAL(mbedtls_psa_ecp_generate_key(&attributes,
                                                output, output_size,
                                                &output_length),
                   expected_status);
        if (expected_status == PSA_SUCCESS) {
            TEST_LE_U(output_length, output_size);
            TEST_ASSERT(check_ecc_private_key(family, bits,
                                              output, output_length,
                                              &stats));
        }
    }

    if (expected_status == PSA_SUCCESS) {
        /* For selected bits, check that we saw the values 0 and 1 each
         * at least some minimum number of times. The iteration count and
         * the minimum are chosen so that a random failure is unlikely
         * to more than cryptographic levels. */
        unsigned const min_times = 10;
        TEST_LE_U(min_times, stats.bit_bot);
        TEST_LE_U(stats.bit_bot, iteration_count - min_times);
        TEST_LE_U(min_times, stats.bit_top);
        TEST_LE_U(stats.bit_top, iteration_count - min_times);
    }

exit:
    PSA_DONE();
    mbedtls_free(output);
}
/* END_CASE */