Git-driven file management and version control.
Read about encryption on git-annex wiki for details. MAC algorithm defaults to SHA-1, which is insecure: make sure to pass mac=HMACSHA512 when initializing a new remote.
Disclaimer: Using the recommended projects on this site will not guarantee that 100% of your communications will be shielded against surveillance states. Please do your own research before trusting these projects with sensitive information.