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Comment by derdi | Hacker News Reader

> Disclaimer: this proves integrity, not completeness (as a self-held chain proves nothing was edited but does NOT prove that nothing was omitted).

Or as the page puts it in more detail:

> A self-held chain proves integrity: nothing was edited or reordered after the fact. It cannot prove completeness: the operator of a recorder can delete the bad day and re-seal the chain, or never write a record at all, and the chain stays internally consistent.

I don't get this. If I "hold" the "chain" (I hate the jargon agents invent), why can't I edit or reorder and then "re-seal" it?

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Yeah, if you edit the log you could make a new chain when you fully control the chain. And if you send the log to someone else, they can hash it themselves to see if you tamper with it later. I don't get it too. What is the chain good for?

Thinking about this more, like every blockchain, this only makes sense if there is an incentive to publish each log entry as quickly as possible. Once it's published, of course it's tamper-proof, including against "the operator of a recorder can delete the bad day". Presumably the incentive to publish and the protection against the operator choosing to "never write a record at all" is the same: You must get paid for publishing a log entry. Because a log entry is, quite literally, "proof of work".

But if you're incentivized to publish as quickly as possible, then your customer gets the log immediately, and there is no need for a "trusted" third party to act as a "witness" and seek rents for not doing anything useful.

And none of the above protects against the vendor using your sensitive data to (a) do the work as contracted, with a cryptographically verified log and everything, but also (b) copy/analyze/abuse said data without telling you.

It's 2017 again, and someone on HN is inventing "blockchain for X", poorly. (Also note that it doesn't matter what kind of work X is, except for aligning this with HN's current main interest.)

Yep, exactly right - the publishing mechanism is the anchor schedule.

Regarding incentives, this only works if the customer (or regulation) demands it - they’ll require the checkpoints as a condition of closing the deal - and is part of the bet.

A missed checkpoint is in and of itself visible, so if the vendor sits on records instead of publishing, the customer will notice the silence.

Thanks for thinking this though and writing it down. There also still no proof of no tampering unless the agent is external and publishes right away. So maybe you could have a service that generates these, but then again, the service could just sign the logs.

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