Rework mbedtls_ecp_write_key to remove unnecessary output parameter

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>

include/mbedtls/ecp.h

@@ -1152,20 +1152,20 @@ int mbedtls_ecp_read_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key,
  *
  * \param grp_id    The ECP group identifier.
  * \param key       The private key.
- * \param olen      The amount of bytes written into the output buffer.
+ * \param buf       The output buffer for containing the binary representation
- * \param buf       The output buffer containing the binary representation of
+ *                  of the key. (Big endian integer for Weierstrass curves, byte
- *                  the key. (Big endian integer for Weierstrass curves, byte
  *                  string for Montgomery curves.)
  * \param buflen    The total length of the buffer in bytes.
  *
  * \return          \c 0 on success.
- * \return          #MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if key is larger than buffer.
+ * \return          #MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the \p key
+                    representation is larger than the available space in \p buf.
  * \return          #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the operation for
  *                  the group is not implemented.
  * \return          Another negative error code on different kinds of failure.
  */
 int mbedtls_ecp_write_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key,
-                           size_t *olen, unsigned char *buf, size_t buflen );
+                           unsigned char *buf, size_t buflen );
 
 /**
  * \brief           This function checks that the keypair objects

library/ecp.c

@@ -3000,13 +3000,12 @@ cleanup:
  * 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 )
+                           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 );
@@ -3022,7 +3021,6 @@ int mbedtls_ecp_write_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key
                 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;
@@ -3033,7 +3031,6 @@ int mbedtls_ecp_write_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key
     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

library/pkwrite.c

@@ -166,10 +166,9 @@ static int pk_write_ec_private( unsigned char **p, unsigned char *start,
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t byte_length = ( ec->grp.pbits + 7 ) / 8;
-    size_t output_length;
     unsigned char tmp[MBEDTLS_ECP_MAX_BYTES];
 
-    ret = mbedtls_ecp_write_key( ec->grp.id, ec, &output_length, tmp, byte_length );
+    ret = mbedtls_ecp_write_key( ec->grp.id, ec, tmp, byte_length );
     if( ret != 0 )
         goto exit;
     ret = mbedtls_asn1_write_octet_string( p, start, tmp, byte_length );

library/psa_crypto.c

@@ -1321,14 +1321,13 @@ static psa_status_t psa_internal_export_key( const psa_key_slot_t *slot,
     if( PSA_KEY_TYPE_IS_ECC_KEY_PAIR( slot->attr.type ) && !export_public_key )
     {
         psa_status_t status;
-        size_t actual_data_size;
 
         size_t bytes = PSA_BITS_TO_BYTES( slot->attr.bits );
         if( bytes > data_size )
             return( PSA_ERROR_BUFFER_TOO_SMALL );
         status = mbedtls_to_psa_error(
             mbedtls_ecp_write_key(slot->data.ecp->grp.id, slot->data.ecp,
-                                  &actual_data_size, data, bytes) );
+                                  data, bytes) );
         if( status != PSA_SUCCESS )
             return( status );
         memset( data + bytes, 0, data_size - bytes );

tests/suites/test_suite_ecp.function

@@ -1089,42 +1089,29 @@ void mbedtls_ecp_read_key( int grp_id, data_t* in_key, int expected, int canonic
         if( canonical )
         {
             unsigned char buf[MBEDTLS_ECP_MAX_BYTES];
-            size_t olen;
 
-            ret = mbedtls_ecp_write_key( grp_id, &key, &olen, buf, in_key->len );
+            ret = mbedtls_ecp_write_key( grp_id, &key, buf, in_key->len );
             TEST_ASSERT( ret == 0 );
 
-            TEST_ASSERT( olen == in_key->len );
-
-            mbedtls_fprintf( stdout, "written key: ");
-            for( size_t i = 0; i < in_key->len; i++ ) {
-                mbedtls_fprintf( stdout, "%02x", buf[i]);
-            }
-            mbedtls_fprintf( stdout, "\n");
             ASSERT_COMPARE( in_key->x, in_key->len,
-                            buf, olen );
+                            buf, in_key->len );
         }
         else
         {
             unsigned char export1[MBEDTLS_ECP_MAX_BYTES];
-            size_t olen1;
-
             unsigned char export2[MBEDTLS_ECP_MAX_BYTES];
-            size_t olen2;
 
-            ret = mbedtls_ecp_write_key( grp_id, &key, &olen1, export1, in_key->len );
+            ret = mbedtls_ecp_write_key( grp_id, &key, export1, in_key->len );
             TEST_ASSERT( ret == 0 );
 
             ret = mbedtls_ecp_read_key( grp_id, &key2, export1, in_key->len );
             TEST_ASSERT( ret == expected );
 
-            ret = mbedtls_ecp_write_key( grp_id, &key2, &olen2, export2, in_key->len );
+            ret = mbedtls_ecp_write_key( grp_id, &key2, export2, in_key->len );
             TEST_ASSERT( ret == 0 );
 
-            TEST_ASSERT( olen2 == olen1 );
+            ASSERT_COMPARE( export1, in_key->len,
-
+                            export2, in_key->len );
-            ASSERT_COMPARE( export1, olen1,
-                            export2, olen2 );
         }
     }