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Basic statistical tests for mbedtls_psa_ecp_generate_key()

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Run a few iterations and check that there is some diversity in the results.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2024-10-29 20:56:33 +01:00
parent 77587ce12d
commit 091941e849
1 changed files with 59 additions and 9 deletions
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68
tests/suites/test_suite_psa_crypto_ecp.function
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@ -22,10 +22,16 @@ static int buffer_is_all_zero(const uint8_t *buf, size_t size)
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)
const uint8_t *key, size_t key_length,
ecc_private_key_stats_t *stats)
{
int ok = 0;
@ -59,7 +65,30 @@ static int check_ecc_private_key(psa_ecc_family_t family, size_t bits,
TEST_EQUAL(key[55] & 0x80, 0x80);
}
#endif /* MBEDTLS_PSA_BUILTIN_ECC_MONTGOMERY_448 */
(void) family; // unused in Weierstrass-only builds
/* 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:
@ -88,17 +117,38 @@ void generate_key(int family_arg, int bits_arg,
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);
TEST_EQUAL(mbedtls_psa_ecp_generate_key(&attributes,
output, output_size,
&output_length),
expected_status);
/* 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) {
TEST_LE_U(output_length, output_size);
TEST_ASSERT(check_ecc_private_key(family, bits,
output, output_length));
/* 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: