The US Postal Service filed a patent application for blockchain tracking tech implanted in mail-in ballots in Feb 2020. It was published in Aug 2020, titled SECURE VOTING SYSTEM, and is 47 pages long. Patent #: US 20200258338 A1.
https://pdfaiw.uspto.gov/.aiw?PageNum=0&docid=20200258338&IDKey=7A4F4EA40D1F
