commit e6886102ef23ad38dd8e3ac8df1e26f34c22c75e
author Gilles Peskine <Gilles.Peskine@arm.com> Wed Jun 21 18:22:06 2023 +0200
committer Gilles Peskine <Gilles.Peskine@arm.com> Fri Dec 22 21:30:03 2023 +0100
tree 283631f18f4bc6fe1b4e2963a1eeef7db504fca0
parent 69b290589b2a337bdd81c9bd0f3fc059b35cb367

New function mbedtls_ecp_keypair_get_group_id

Add a simple function to get the group id from a key object.

This information is available via mbedtls_ecp_export, but that function
consumes a lot of memory, which is a waste if all you need is to identify
the curve.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

include/mbedtls/ecp.h

diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 7f5e880..a29a6f7 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -1323,6 +1323,18 @@
     const mbedtls_ecp_keypair *pub, const mbedtls_ecp_keypair *prv,
     int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);
 
+/** \brief          Query the group that a key pair belongs to.
+ *
+ * \param key       The key pair to query.
+ *
+ * \return          The group ID for the group registered in the key pair
+ *                  object.
+ *                  This is \c MBEDTLS_ECP_DP_NONE if no group has been set
+ *                  in the key pair object.
+ */
+mbedtls_ecp_group_id mbedtls_ecp_keypair_get_group_id(
+    const mbedtls_ecp_keypair *key);
+
 /**
  * \brief           This function exports generic key-pair parameters.
  *

library/ecp.c

diff --git a/library/ecp.c b/library/ecp.c
index ee86cbc..351e9e8 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -3357,6 +3357,12 @@
 }
 #endif /* MBEDTLS_ECP_C */
 
+mbedtls_ecp_group_id mbedtls_ecp_keypair_get_group_id(
+    const mbedtls_ecp_keypair *key)
+{
+    return key->grp.id;
+}
+
 /*
  * Export generic key-pair parameters.
  */

tests/suites/test_suite_ecp.function

diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index 5751624..58d54ed 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1030,6 +1030,7 @@
                                     &mbedtls_test_rnd_pseudo_rand,
                                     &rnd_info) == 0);
 
+    TEST_EQUAL(mbedtls_ecp_keypair_get_group_id(&key), id);
     TEST_ASSERT(mbedtls_ecp_check_pubkey(&key.grp, &key.Q) == 0);
     TEST_ASSERT(mbedtls_ecp_check_privkey(&key.grp, &key.d) == 0);
 
@@ -1052,6 +1053,7 @@
     TEST_ASSERT(ret == expected);
 
     if (expected == 0) {
+        TEST_EQUAL(mbedtls_ecp_keypair_get_group_id(&key), grp_id);
         ret = mbedtls_ecp_check_privkey(&key.grp, &key.d);
         TEST_ASSERT(ret == 0);
 
@@ -1233,6 +1235,10 @@
         TEST_EQUAL(mbedtls_ecp_point_cmp(&key.Q, &export_Q), 0);
         TEST_EQUAL(mbedtls_mpi_cmp_mpi(&key.d, &export_d), 0);
         TEST_EQUAL(mbedtls_ecp_group_cmp(&key.grp, &export_grp), 0);
+
+        /* Check consistency with the group id */
+        TEST_EQUAL(export_grp.id,
+                   mbedtls_ecp_keypair_get_group_id(&key));
     }
 
 exit: