From The Document Foundation Wiki
- Implement OOXML agile encryption. OOXML Agile encryption can use AES-256-CBC encryption algorithm with SHA512 hash function. (Tomaž Vajngerl - Collabora)
- HMAC verification (when saving an encrypted document) is now supported as well, which verifies that the document is bit-exact as when it was saved. (Tomaž Vajngerl - Collabora)
- Change the default for OOXML to use AES-256-CBC and SHA512, which is supported by all recent Microsoft Office and LibreOffice versions. (Tomaž Vajngerl - Collabora)