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mbedtls_psa_ecp_generate_key: don't calculate the public key

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mbedtls_ecp_gen_key() generates a private key and calculates the public key.
Calculating the public key takes most of the CPU time. But the PSA key store
doesn't store the key, in order to simplify the plumbing when drivers are
involved. So the time spent calculating the public key is a waste.

Instead, call mbedtls_ecp_gen_privkey(), which does not calculate the public
key.

This also saves 8 instructions in a sample arm thumb build.

Resolves #9732.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2024-10-29 20:58:28 +01:00
parent 2576bbc9fa
commit c8b668deae
1 changed files with 17 additions and 19 deletions
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36
library/psa_crypto_ecp.c
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@ -321,38 +321,36 @@ psa_status_t mbedtls_psa_ecp_generate_key(
const psa_key_attributes_t *attributes,
uint8_t *key_buffer, size_t key_buffer_size, size_t *key_buffer_length)
{
psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
psa_ecc_family_t curve = PSA_KEY_TYPE_ECC_GET_FAMILY(
attributes->type);
mbedtls_ecp_group_id grp_id =
mbedtls_ecc_group_from_psa(curve, attributes->bits);
const mbedtls_ecp_curve_info *curve_info =
mbedtls_ecp_curve_info_from_grp_id(grp_id);
mbedtls_ecp_keypair ecp;
if (grp_id == MBEDTLS_ECP_DP_NONE || curve_info == NULL) {
if (grp_id == MBEDTLS_ECP_DP_NONE) {
return PSA_ERROR_NOT_SUPPORTED;
}
mbedtls_ecp_keypair ecp;
mbedtls_ecp_keypair_init(&ecp);
ret = mbedtls_ecp_gen_key(grp_id, &ecp,
mbedtls_psa_get_random,
MBEDTLS_PSA_RANDOM_STATE);
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
ret = mbedtls_ecp_group_load(&ecp.grp, grp_id);
if (ret != 0) {
mbedtls_ecp_keypair_free(&ecp);
return mbedtls_to_psa_error(ret);
goto exit;
}
status = mbedtls_to_psa_error(
mbedtls_ecp_write_key_ext(&ecp, key_buffer_length,
key_buffer, key_buffer_size));
ret = mbedtls_ecp_gen_privkey(&ecp.grp, &ecp.d,
mbedtls_psa_get_random,
MBEDTLS_PSA_RANDOM_STATE);
if (ret != 0) {
goto exit;
}
ret = mbedtls_ecp_write_key_ext(&ecp, key_buffer_length,
key_buffer, key_buffer_size);
exit:
mbedtls_ecp_keypair_free(&ecp);
return status;
return mbedtls_to_psa_error(ret);
}
#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_GENERATE */