[dlc-dev] Oracle Event Timestamps

[Nadav Kohen]

Hi Lloyd,

> Why not just stick to "earliest_time" and "latest_time" --
"event_maturation_time" means the same thing as "earliest_time" right? Or
are you suggesting changing it's meaning to expected time? But then it
would make sense to rename it to be "expected_time".

I am suggesting that "event_maturation_time" should mean "expected_time"
and I think I'm okay with renaming it so this is good feedback.

In response to your example however, I disagree with the usage of the
timestamps presented, I think that all timestamps are expectations rather
than pure bounds. The oracle may expect midnight that night to be the
latest but what if it runs into technical difficulties and can't release an
attestation until the next day? In the end it is the DLC participants who
decide how to behave on the client side with respect to when the contract
has "timed out" and they will always be giving a good amount of leeway to
the oracle when it comes to "latest" or "expected" times. As such the
oracle should provide bounds in this example using a lower bound on how
long the game could go (as the time on the clock is known so we can lower
bound using the heuristic that there are no stoppages or time-outs) and an
upper bound which can use some addition to the scheduled game start of the
longest a game has lasted, or something like this.

Essentially having an "earliest" and "latest" in place of an "expected"
time just means that this defines an "expected time interval" in place of
just one time, perhaps we should rename to accommodate this. I think that
in your example if the game is moved back then there is a scenario where no
new event is needed, depending on the wording in the announcement. In fact,
it could be really unfair to DLC participants who will not have internet
access during this very short time window where they must close their
existing DLC and open a new one so I think that this would generally be bad
practice.

I think how DLC clients will actually be implemented is that they will ping
the server on some interval starting at earliest until latest (unless an
expected is given, in which case skip ahead to here) after which some
back-off will be used until some max-backoff is hit and the client pings
the oracle at some larger time interval until the refund locktime
(determined by users) is reached.

I'm open to other ways of thinking on this but I currently don't think it
makes any sense for oracles to be dictating lock times to users, and
timestamps should really act more as meta-data which can guide when a user
application starts looking for an attestation, and little else.

Best,
Nadav

On Wed, Feb 17, 2021 at 6:24 PM Lloyd Fournier <lloyd.fourn at gmail.com>
wrote:

> Hi Nadav,
>
> Keep in mind that I am not using TLV serialization for my oracle so what I
> say below is only a suggestion.
>
> On Wed, 17 Feb 2021 at 19:40, Nadav Kohen <nadavk25 at gmail.com> wrote:
>
>> Hi Lloyd and Chris,
>>
>> After having long discussions with both Matt and Thibaut I think we
>> should replace the `u32` timestamp in the `oracle_event` with an
>> `event_time` TLV type which has two instances, `event_maturation_time`
>> which has a single `u32` timestamp and `event_time_interval` which has an
>> `earliest` and a `latest` (both u32).
>>
>
> Why not just stick to "earliest_time" and "latest_time" --
> "event_maturation_time" means the same thing as "earliest_time" right? Or
> are you suggesting changing it's meaning to expected time? But then it
> would make sense to rename it to be "expected_time".
>
> I generally agreed with Lloyd's characterization above but I don't think
>> that it makes sense to have all three but rather an event has an expected
>> time which should be used or else it has a time interval which should be
>> used. Oracles should not be speculating on refund times as this is a
>> client-side decision so I don't think it makes sense to have a "Latest" in
>> an event with an "Expected" maturity time
>>
>
> Let me give an example which shows why "latest" and "expected" are
> orthogonal. Consider a basketball game. The oracle sets the expected_time
> to be the expected end of the game while it sets latest_time to be midnight
> that night.
> Here the oracle is saying that if the game is not decided by midnight then
> I will never call the outcome (or preferably attest to a backout outcome).
> If the game is rescheduled by a day then the oracle must create a new event
> for the rescheduled event.
> Here expected is used by the app to notify the user when is a good time to
> check on the app. An hour before it might notify the user "your bet on X
> will be resolved soon!".
> Hopefully this shows why these two things are independently useful and
> orthogonal.
>
>  Furthermore we have done quite a bit of work to avoid options in our
>> messages as the notion of an option is not part of TLV serialization and
>> would lead to extra work for all implementations and special complications
>> for those using TLV libraries (this is a rather technical concern as we
>> could always have 8 types in place of 3 options but this is just further
>> motivation for my solution).
>>
>
> It is not by accident that all successful serialization formats have an
> optional field as a core notion. It is an extremely useful idea. Having
> done a lot of work so far to avoid it is just more evidence of why you
> should have it IMO!
>
>
>>
>> Under this proposal, I believe all of Chris' and my worries are taken
>> care of as this allows oracles to specify a `latest` but this `latest` can
>> also be set to `u32.max_value` to functionally have an open-ended event.
>>
>
>> My only question after which I plan to PR this proposal into the spec is
>> whether Lloyd has any objections? This is strictly less expressive than
>> what he proposed but I think it captures pretty much everything we need
>> (noting that oracles can use the string field they already have for softer
>> meta-data for soft time "commitments"/recommendations).
>>
>
>> Best,
>> Nadav
>>
>> On Tue, Feb 16, 2021 at 11:42 PM Lloyd Fournier <lloyd.fourn at gmail.com>
>> wrote:
>>
>>> Hi Nadav and Chris,
>>>
>>> There are three possible times you could want to know as a client that I
>>> can see.
>>>
>>> - Earliest -- the client should start checking for outcome after this
>>> has passed
>>> - Expected -- useful to display to the user when the event is expected
>>> to transpire (so they can check back with the app).
>>> - Latest -- Good to make refund arrangements
>>>
>>> My preference would be for allowing oracle to announce all three, none
>>> or any combination of these (e.g. add optional fields earliest_time,
>>> expected_time, latest_time).
>>> I don't agree with the motivation that Chris sees for forcing any of
>>> them to be present. Clients that are doing something like a refund
>>> transaction can just refuse to do bets on announcements that don't have the
>>> requisite data. It is premature to be opinionated about this stuff IMO.
>>>
>>> Cheers,
>>>
>>> LL
>>>
>>> On Wed, 17 Feb 2021 at 00:14, Chris Stewart <chris at suredbits.com> wrote:
>>>
>>>> >Oracle attesting to whether some event occurs at all, with no built-in
>>>> oracle expiration.
>>>>
>>>> This seems like a liability for me from the oracle perspective. If an
>>>> event is not bounded with a maturation time, the oracle has to provide
>>>> support for the event indefinitely (possibly forever!).
>>>>
>>>> There are two concerns here in my opinion
>>>>
>>>> 1. Security (are oracle private keys secure indefinitely?)
>>>> 2. Liveliness of the oracle (an oracle just disappearing, life happens!)
>>>>
>>>> In (2) let's slightly adjust your example above to have a liquidation
>>>> price of $10,000 -> $1,000. BTC/USD hasn't breached the $1,000 threshold
>>>> since ~2017 (4 years ago). For our theoretical exercise, let's assume the
>>>> oracle published an announcement committing to signing the message "BTC
>>>> beneath $1,000" and did _not_ include a maturation time.
>>>>
>>>> If you and I wanted to construct a contract today based on this 2017
>>>> oracle, how do we know that the oracle will still publish that price if the
>>>> event occurs? In my opinion the heuristic of maturation time is a useful
>>>> piece of information for contract participants to use when picking an
>>>> oracle. A start_time would be another useful one.
>>>>
>>>> With our theoretical DLC, now we can see that the oracle committed to
>>>> publishing signatures for this event -- if it occurs -- until maturation
>>>> time. We can also use this information to prove bad behavior from the
>>>> oracle if they do _not_ publish the signature "BTC beneath $1,000" if the
>>>> market price is below $1,000. We also can design our contract around this
>>>> maturation time (OR pick a new oracle with a suitable maturation time, OR
>>>> ask the existing oracle to publish a new announcement with a new maturation
>>>> time (if they are lively, they might accommodate!))
>>>>
>>>> It seems including a maturation time encourages "good hygiene" for
>>>> oracles in that
>>>>
>>>> 1. Allow the ability to rotate keys (my events now have a
>>>> pre-determined maturation time, so i don't have to secure them forever!)
>>>> 2. Up front commitment to a fixed interval of time they will be
>>>> monitoring the event.
>>>>
>>>> In general, I think we need to remember we are designing this system
>>>> around oracles and therefore need to get them to be as rigorous as possible
>>>> when outlining the conditions of signing a specific attestation. If we
>>>> force oracles to be rigorous, users of that oracle have better
>>>> understanding of when/why an oracle publishes a certain attestation. Since
>>>> we live in the real world, all events are bounded by time intervals in my
>>>> opinion.
>>>>
>>>> I think it could be interesting to include a "start_time" field so we
>>>> have a well defined interval of time the oracle is monitoring for. In our
>>>> example above, two DLC users can see that the oracle originally published
>>>> the oracle announcement in 2017, which gives us a useful heuristic when
>>>> thinking about the liveliness of the oracle.
>>>>
>>>> -Chris
>>>>
>>>> On Mon, Feb 15, 2021 at 3:59 PM Nadav Kohen via dlc-dev <
>>>> dlc-dev at mailmanlists.org> wrote:
>>>>
>>>>> Hi list,
>>>>>
>>>>> On the current specification, oracle events (
>>>>> https://github.com/discreetlogcontracts/dlcspecs/blob/master/Oracle.md#oracle-events)
>>>>> have a timestamp called `event_maturity_epoch` which is described as "the
>>>>> earliest time (UTC) at which it plans on releasing a signature over the
>>>>> event outcome, in epoch seconds."
>>>>>
>>>>> There have been arguments made in the past that, at least in some
>>>>> cases, these should be used in computing CET nLockTime values so as to
>>>>> enable such things as the "I am compromised" refund execution (
>>>>> https://github.com/discreetlogcontracts/dlcspecs/issues/94).
>>>>>
>>>>> I would like to bring to everyone's attention and open for discussion
>>>>> the issue that there seem to generally be two kinds of oracles with respect
>>>>> to event timestamps:
>>>>>
>>>>>    1. Oracle attesting to what happens at some fixed time T (in the
>>>>>    future).
>>>>>    2. Oracle attesting to whether some event occurs at all, with no
>>>>>    built-in oracle expiration.
>>>>>
>>>>> Note that while the second case seems to suggest that using such an
>>>>> oracle would lead to an unbounded amount of time that funds could be
>>>>> locked, this is not the case as users of the oracle will be introducing
>>>>> their own time-locked execution path in either the form of a refund
>>>>> transaction or else by using a Disjoint Union DLC where at least one of the
>>>>> other oracle events used is of the first kind.
>>>>>
>>>>> To make this concrete with an example, imagine having a BTC/USD price
>>>>> oracle which has an event for the price at time T (in the future), and
>>>>> another oracle which attests to whether a given price threshold is broken
>>>>> at any point, say $10,000, at which point this oracle would publish a
>>>>> signature for the message "BTC beneath $10,000" with no other possible
>>>>> messages that could be signed (a unary outcome DLC oracle event). With
>>>>> these oracles, a DLC could be opened where if the second oracle broadcasts
>>>>> its signature, then one party (the party going short) would lose all funds
>>>>> in a liquidation execution, or else if the price threshold $10,000 is not
>>>>> breached before time T then the DLC executes using the first oracle's price
>>>>> signature (using digit decomposition as usual).
>>>>>
>>>>> In this example, the CET based on the second oracle should be
>>>>> constructed using an nLockTime less than or equal to the current block
>>>>> height/time, while the first oracle's CETs can use any nLockTime less than
>>>>> or equal to T, the oracle event's maturation. However, given the structure
>>>>> of the current oracle_event message, it is not clear to DLC software how to
>>>>> interpret timestamps on oracle events of the second kind (events not linked
>>>>> to a specific time).
>>>>>
>>>>> A decision, and possibly a change, needs to be made to the
>>>>> specification to clear up this matter. The following are the options I
>>>>> could think of (there may be others):
>>>>>
>>>>>    1. Leave the field as is and simply ask oracles of the second kind
>>>>>    to either use 0 or else the time at which the event was created.
>>>>>    2. Add a new (boolean?) field which flags which kind of oracle
>>>>>    event this is which will allow client software to interpret the timestamps
>>>>>    correctly.
>>>>>    3. Add a second timestamp for event creation and have oracles of
>>>>>    the second kind use 0 for event maturity to signal what kind of oracle they
>>>>>    are.
>>>>>
>>>>> Furthermore, the specification should perhaps be more opinionated
>>>>> around the use of these timestamps and provide recommendations as to how
>>>>> the values found in the oracle_event should affect the values used as
>>>>> timeouts in the dlc_offer message, as this is currently unclear in the
>>>>> specification.
>>>>>
>>>>> Looking forward to seeing people's thoughts!
>>>>>
>>>>> Best,
>>>>> Nadav
>>>>>
>>>>> dlc-dev mailing list
>>>>> dlc-dev at mailmanlists.org
>>>>> https://mailmanlists.org/mailman/listinfo/dlc-dev
>>>>>
>>>>
>>>> dlc-dev mailing list
>>>> dlc-dev at mailmanlists.org
>>>> https://mailmanlists.org/mailman/listinfo/dlc-dev
>>>>
>>>
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