Implement and test mbedtls_ecp_write_key
mbedtls_ecp_write_key is a mirror function to mbedtls_ecp_read_key, which
writes a private key back into a byte buffer in the correct format.
This is a helpful convenience function, since the byte order is defined
differently between Montgomery and Weierstrass curves. Since this difference
is accounted for in mbedtls_ecp_read_key, it made sense to add
mbedtls_ecp_write_key for the purpose of abstracting this away such that
psa_export_key doesn't need to take byte order into account.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
diff --git a/library/ecp.c b/library/ecp.c
index 104e1f1..0aa61f1 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -2997,6 +2997,53 @@
}
/*
+ * Write a private key.
+ */
+int mbedtls_ecp_write_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key,
+ size_t *olen, unsigned char *buf, size_t buflen )
+{
+ int ret = 0;
+
+ ECP_VALIDATE_RET( key != NULL );
+ ECP_VALIDATE_RET( buf != NULL );
+ ECP_VALIDATE_RET( olen != NULL );
+
+ if( ( ret = mbedtls_ecp_group_load( &key->grp, grp_id ) ) != 0 )
+ return( ret );
+
+ ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
+
+#if defined(ECP_MONTGOMERY)
+ if( mbedtls_ecp_get_type( &key->grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
+ {
+ if( grp_id == MBEDTLS_ECP_DP_CURVE25519 )
+ {
+ if( buflen < ECP_CURVE25519_KEY_SIZE )
+ return MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
+
+ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary_le( &key->d, buf, buflen ) );
+ *olen = ECP_CURVE25519_KEY_SIZE;
+ }
+ else
+ ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
+ }
+
+#endif
+#if defined(ECP_SHORTWEIERSTRASS)
+ if( mbedtls_ecp_get_type( &key->grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )
+ {
+ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &key->d, buf, buflen ) );
+ *olen = mbedtls_mpi_size( &key->d );
+ }
+
+#endif
+cleanup:
+
+ return( ret );
+}
+
+
+/*
* Check a public-private key pair
*/
int mbedtls_ecp_check_pub_priv( const mbedtls_ecp_keypair *pub, const mbedtls_ecp_keypair *prv )