[messaging] Zero-metadata object store

[Peter Parkanyi]

> 
> Is there a scenario in which nonce is reused with the same key on a different version of an object?
> 
> What about file operation in which some internal 100 bytes change? Total length of the file stays same. Will nonce be same?

If a chunk changes, their hash changes, therefore their encryption key changes. Files are always broken up into chunks, and zerostash won't rewrite an existing chunk, because it could be referenced by other files, so the nonce changes, too.