How can i export a PDF with 128-bit AES encryption in LibreOffice Writer?

At this time - in default settings - LibreOffice exports with 128bit RC4. This old stream cipher is not secure anymore and very assailable. I would like to use a modern Encryption Standard like AES.
How can i configure that LibreOffice use a more secure encryption.

RC4 - Wikipedia

Advanced Encryption Standard - Wikipedia

What is your LibreOffice version? See the Help | About menu for version info. Where did you get and info that LibreOffice is using 128-bit RC4 cipher?

I use the versions and
You can see this if you open the pdf file in adobe reader and check properties > security.

At this time - in default settings - LibreOffice exports with 128bit RC4.

Apologies for initially misreading the question. I imagine LibreOffice uses the encryption in the related version of the PDF specification:

  • v1.1, MD5 or RC4 40 bit
  • v1.4, RC4 40-128 bit
  • v1.5, Public Key Cryptography Standard (PKCS) #7 i.e., SHA-1, RSA up to 4096 bit
  • v1.6, AES, PKCS#7 with SHA256, DSA up to 4096 bit
  • v1.7-extension-level-3, AES 256 bit
  • v1.7-extension-level-8, AES 256 bit with different password handling

At present, LO only supports v1.4 of the PDF specification (in terms of encryption). There is a TO DO note in the source code (/vcl/source/gdi/pdfwriter_impl2.cxx) for v1.5 and v1.6 of the PDF specification. Bug fdo#55425 is possibly related.

LibreOffice 3.5 Release notes are describing ODF encryption, is there the same encryption for PDF? I don’t know, I haven’t found out this info.

i talked about exporting PDF! not odf standard file format.

Well you can export the PDF as it is (without pw) and then use pdftk (free software / GPL) and add a password with that. (or many other PDF readers can do this, too)…

Most is already said by @oweng