Why can't encrypted Verilog HDL source code be synthesized?

Description

Due to a problem in the Quartus® Prime Pro Edition Software version 17.1 and earlier,  you may see error messages when you synthesize the encrypted Verilog HDL file. This problem occurs when the file is added in the GUI.

Resolution

You can work around this problem by adding encrypted files in .qsf (Quartus Settings File) manually shown as below.

set_global_assignment -name VERILOG_FILE <file name>.vp