Provides a simple caching mechanism for TRUD files.

This is deliberately not a generic download manager. It provides only
a lightweight and synchronous cache for downloads.

Check provides support for validating downloaded TRUD files.

There are three mechanisms for checking the integrity of downloaded files.

1. Checksum  (hash)
2. Signature (GPG)
3. The use of https to download the files.

It appears as if checksums are generated using a Windows command line tool
called FCIV (https://docs.microsoft.com/en-us/troubleshoot/windows-server/windows-security/fciv-availability-and-description).

<?XML version="1.0" encoding="utf-8"?>
<FCIV>
    <FILE_ENTRY>
       <name>ntdll.dll</name> <MD5>bL/ZGbqnyeA8hHGuTY+LsA==</MD5>
    </FILE_ENTRY>
</FCIV>

It appears that FCIV generates only MD5 and SHA1 hashes.

Support for the UK NHS Digital's TRUD.
TRUD is the Technology Reference data Update Distribution.