The ODF standard has some cases where it uses the term "implementation-defined". That means, that the implementer has to publish the values he uses. I have added the page https://wiki.documentfoundation.org/Development/ODF_Implementer_Notes/List_of_LibreOffice_ODF_implementation-defined_items to collect such information.
In this case: For the attribute manifest:algorithm-name an implementation-defined IRI is needed for the new feature PGP encryption. Reference: Forth list item in Section 4.16.1 in OpenDocument-v1.3-part2-packages.
Suggestion: Add it to the above mentioned page.
And the identifier in 4.17 manifest:PGPAlgorithm.
@Michael: DO you know this identifier for LibreOffice? Or does LibreOffice not need it?
hmm ... looking at a GPG file written as ODF 1.3 by LO, it has:
<manifest:algorithm manifest:algorithm-name="http://www.w3.org/2001/04/xmlenc#aes256-cbc" manifest:initialisation-vector="..."/>
so PGP is only used to create a key for AES to use, which makes sense as AES is much faster.
this URI is listed in section 5.2.3 AES.
for PGPAlgorithm, there is:
this URI is listed in section 5.5.2 RSA-OAEP.
... i've added this to the wiki.