[messaging] Zero-metadata object store

[Mikalai Birukou]

>> How are nonces generated?
> Chunk nonces are `objectid XOR chunk size`, where chunk size is 4 bytes in little endian. Meta object nonces are the lower 12 bytes of the object id.

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?