- * Arguments: @const char *tag@ = tag to use for passphrase
- * @key_data *k@ = source key data block
- * @key_data *kt@ = target key data block
+ * Arguments: @key_data **kt@ = where to store the destination pointer
+ * @key_data *k@ = source key data block or null to use @*kt@
+ * @const char *tag@ = tag to use for passphrase