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pkparse: add new function for deriving public key from private using PSA

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Instead of using the legacy mbedtls_ecp_mul() function which makes use of
ECP's math, this commit adds a new function named pk_derive_public_key()
which implements the same behavior using PSA functions.
The flow is simple:
- import the private key into PSA
- export its public part

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
This commit is contained in:
Valerio Setti 2023-04-03 15:19:18 +02:00
parent f286664069
commit 34f6755b34
2 changed files with 80 additions and 5 deletions
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78
library/pkparse.c
View file

@ -48,6 +48,14 @@
#include "mbedtls/pkcs12.h"
#endif
#if defined(MBEDTLS_PSA_CRYPTO_C)
#include "mbedtls/psa_util.h"
#endif
#if defined(MBEDTLS_USE_PSA_CRYPTO)
#include "psa/crypto.h"
#endif
#include "mbedtls/platform.h"
#if defined(MBEDTLS_FS_IO)
@ -868,6 +876,56 @@ cleanup:
}
#endif /* MBEDTLS_RSA_C */
#if defined(MBEDTLS_USE_PSA_CRYPTO)
/*
* Helper function for deriving a public key from its private counterpart by
* using PSA functions
*/
static int pk_derive_public_key(mbedtls_ecp_group *grp, mbedtls_ecp_point *Q,
const mbedtls_mpi *d)
{
psa_status_t status;
psa_key_attributes_t key_attr = PSA_KEY_ATTRIBUTES_INIT;
size_t curve_bits;
psa_ecc_family_t curve = mbedtls_ecc_group_to_psa(grp->id, &curve_bits);
unsigned char key_buf[MBEDTLS_PSA_MAX_EC_KEY_PAIR_LENGTH];
size_t key_len = PSA_BITS_TO_BYTES(curve_bits);
mbedtls_svc_key_id_t key_id = MBEDTLS_SVC_KEY_ID_INIT;
int ret;
psa_set_key_type(&key_attr, PSA_KEY_TYPE_ECC_KEY_PAIR(curve));
psa_set_key_usage_flags(&key_attr, PSA_KEY_USAGE_EXPORT);
ret = mbedtls_mpi_write_binary(d, key_buf, key_len);
if (ret != 0) {
return ret;
}
status = psa_import_key(&key_attr, key_buf, key_len, &key_id);
if (status != PSA_SUCCESS) {
ret = psa_pk_status_to_mbedtls(status);
return ret;
}
mbedtls_platform_zeroize(key_buf, sizeof(key_buf));
status = psa_export_public_key(key_id, key_buf, sizeof(key_buf), &key_len);
if (status != PSA_SUCCESS) {
ret = psa_pk_status_to_mbedtls(status);
status = psa_destroy_key(key_id);
return (status != PSA_SUCCESS) ? psa_pk_status_to_mbedtls(status) : ret;
}
ret = mbedtls_ecp_point_read_binary(grp, Q, key_buf, key_len);
status = psa_destroy_key(key_id);
if (status != PSA_SUCCESS) {
return psa_pk_status_to_mbedtls(status);
}
return ret;
}
#endif /* MBEDTLS_USE_PSA_CRYPTO */
#if defined(MBEDTLS_ECP_C)
/*
* Parse a SEC1 encoded private EC key
@ -975,11 +1033,21 @@ static int pk_parse_key_sec1_der(mbedtls_ecp_keypair *eck,
}
}
if (!pubkey_done &&
(ret = mbedtls_ecp_mul(&eck->grp, &eck->Q, &eck->d, &eck->grp.G,
f_rng, p_rng)) != 0) {
mbedtls_ecp_keypair_free(eck);
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PK_KEY_INVALID_FORMAT, ret);
if (!pubkey_done) {
#if defined(MBEDTLS_USE_PSA_CRYPTO)
(void) f_rng;
(void) p_rng;
if ((ret = pk_derive_public_key(&eck->grp, &eck->Q, &eck->d)) != 0) {
mbedtls_ecp_keypair_free(eck);
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PK_KEY_INVALID_FORMAT, ret);
}
#else /* MBEDTLS_USE_PSA_CRYPTO */
if ((ret = mbedtls_ecp_mul(&eck->grp, &eck->Q, &eck->d, &eck->grp.G,
f_rng, p_rng)) != 0) {
mbedtls_ecp_keypair_free(eck);
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PK_KEY_INVALID_FORMAT, ret);
}
#endif /* MBEDTLS_USE_PSA_CRYPTO */
}
if ((ret = mbedtls_ecp_check_privkey(&eck->grp, &eck->d)) != 0) {

7
tests/suites/test_suite_pkparse.function
View file

@ -101,6 +101,10 @@ void pk_parse_keyfile_ec(char *key_file, char *password, int result)
mbedtls_pk_context ctx;
int res;
#if defined(MBEDTLS_USE_PSA_CRYPTO)
PSA_INIT();
#endif
mbedtls_pk_init(&ctx);
res = mbedtls_pk_parse_keyfile(&ctx, key_file, password,
@ -117,6 +121,9 @@ void pk_parse_keyfile_ec(char *key_file, char *password, int result)
exit:
mbedtls_pk_free(&ctx);
#if defined(MBEDTLS_USE_PSA_CRYPTO)
PSA_DONE();
#endif
}
/* END_CASE */