There is an old trick on unix systems to allow a non-root user to "securely" share files with particular other users.
mkdir share chmod 711 share #others can traverse share, but can't list its contents mkdir share/d2ef7c19-5d7e-446f-ab97-d7d6c3dc8a8c #(randomly chosen secret subdir name) cp -R /path/to/stuff_to_share share/d2ef7c19-5d7e-446f-ab97-d7d6c3dc8a8c chmod -R 755 share/d2ef7c19-5d7e-446f-ab97-d7d6c3dc8a8c #allow others who know the secret path to access shared files
EDIT (clarification): I have to tell the people I want to share files with the secret path (in this case, ~myid/share/d2ef7c19-5d7e-446f-ab97-d7d6c3dc8a8c) in order to share the files with them.
My question is: how secure is this? If a third party (non-root) does not know the secret share name (in the example above: d2ef7c19-5d7e-446f-ab97-d7d6c3dc8a8c), is there any way they can learn about it?