From The Document Foundation Wiki

    Support for OpenPGP/GnuPG signing and encryption in LibreOffice

    Starting with version 5.4.0, LibreOffice - in addition to X509-certificates - can also use locally-available GnuPG keys to sign ODF documents on Linux

    Starting with version 6.0.0, LibreOffice supports OpenPGP keys on all desktop platforms, and also enables experimental ODF document encryption.

    From the release notes:

    • on all desktop platforms, you can now use OpenPGP keys to sign ODF documents. tdf#89037 (Katarína Behrens, Samuel Mehrbrodt, Thorsten Behrens - CIB)
    • there is (experimental) support for OpenPGP-based document encryption as well
    • you need auxiliary software to make use of that feature (LibreOffice will transparently merge available keys if you have the below installed):
      • for Windows, download [1]
      • for Mac, download [2] (some howto is here )
      • for Linux, usually installing a gnupg/gpg package will be enough, perhaps with an additional keymanagement frontend like kleopatra or seahorse. Package names will depend on your Linux distribution
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    This feature was funded in 2017 by the German Federal Office for Information Security

    Further information

    There has been a recorded talk during FrOSCon 2017 about the ongoing work, including some technical details: