Use nonce instead of timestampin "9.1 Last-Write Replace"

[oed]

The use of timestamp in the DAG-JOSE header can be problematic. If a users computer has a miscsonfigured system clock they may end up with a timestamp that is in the future and it will be impossible to replace the object for a (long) while. Also, timestamp is not a registered header property in IANA. We could however use nonce where the highest nonce would always be the one that's selected to mitigate these issues.

Note: we do something similar in the suggested DID Publish stream type in Ceramic. We also use the URL property to indicate which object is being replaced.

[csuwildcat]

@oed good point, was just looking for highest incremented change anyway, so whatever standard value format is best seems fine.

[bumblefudge]

by "nonce" do you mean a "cnonce" or just a monotonic counter?

[oed]

@bumblefudge just an incrementing number similar to the transaction nonce in ethereum for example.

[csuwildcat]

Has been amended in the current spec, closing as completed.