On Fri, Feb 18, 2022 at 04:38:27PM -0800, Jeremy Rubin wrote:
> > As I said, it's a new kind of pinning attack, distinct from other types
> of pinning attack.
>
> I think pinning is "formally defined" as sequences of transactions which
> prevent or make it less likely for you to make any progress (in terms of
> units of computation proceeding).
Mentioning "computation" when talking about transactions is misleading:
blockchain transactions have nothing to do with computation.
It is in fact computation. Branding it as "misleading" is misleading... The relevant literature is
https://en.wikipedia.org/wiki/Non-blocking_algorithm, sponsors helps get rid of deadlocking so that any thread can be guaranteed to make progress. E.g., this is critical in Eltoo, which is effectively a coordinated multi-party computation on-chain to compute the highest sequence number known by any worker.
That transactions are blobs of "verification" (which is also itself a computation) less so than dynamic computations is irrelevant to the fact that series of transactions do represent computations.
> Something that only increases possibility to make progress cannot be
> pinning.
It is incorrect to say that all use-cases have the property that any version of
a transaction being mined is progress.
It is progress, tautologically. Progress is formally definable as a transaction of any kind getting mined. Pinning prevents progress by an adversarial worker. Sponsoring enables progress, but it may not be your preferred interleaving. That's OK, but it's inaccurate to say it is not progress.
Your understanding of how OpenTimestamps calendars work appears to be
incorrect. There is no chain of unconfirmed transactions. Rather, OTS calendars
use RBF to _update_ the timestamp tx with a new merkle tip hash for to all
outstanding per-second commitments once per new block. In high fee situations
it's normal for there to be dozens of versions of that same tx, each with a
slightly higher feerate.
I didn't claim there to be a chain of unconfirmed, I claimed that there could be single output chain that you're RBF'ing one step per block.
E.g., it could be something like
A_0 -> {A_1 w/ CSV 1 block, OP_RETURN {blah, foo}}
A_1 -> {A_2 w/ CSV 1 block, OP_RETURN {bar}}
such that A_i provably can't have an unconfirmed descendant. The notion would be that you're replacing one with another. E.g., if you're updating the calendar like:
Version 0: A_0 -> {A_1 w/ CSV 1 block, OP_RETURN {blah, foo}}
Version 1: A_0 -> {A_1 w/ CSV 1 block, OP_RETURN {blah, foo, bar}}
Version 2: A_0 -> {A_1 w/ CSV 1 block, OP_RETURN {blah, foo, bar, delta}}
and version 1 gets mined, then in A_1's spend you simply shift delta to that (next) calendar.
A_1 -> {A_2 w/ CSV 1 block, OP_RETURN {delta}}
Thus my claim that someone sponsoring a old version only can delay by 1 block the calendar commit.
OTS calendars can handle any of those versions getting mined. But older
versions getting mined wastes money, as the remaining commitments still need to
get mined in a subsequent transaction. Those remaining commitments are also
delayed by the time it takes for the next tx to get mined.
There are many use-cases beyond OTS with this issue. For example, some entities
use "in-place" replacement for update low-time-preference settlement
transactions by adding new txouts and updating existing ones. Older versions of
those settlement transactions getting mined rather than the newer version
wastes money and delays settlement for the exact same reason it does in OTS.
> Lastly, if you do get "necromanced" on an earlier RBF'd transaction by a
> third party for OTS, you should be relatively happy because it cost you
> less fees overall, since the undoing of your later RBF surely returned some
> satoshis to your wallet.
As I said above, no it doesn't.
It does save money since you had to pay to RBF, the N+1st txn will be paying higher fee than the Nth. So if someone else sponsors an earlier version, then you save whatever feerate/fee bumps you would have paid and the funds are again in your change output (or something). You can apply those change output savings to your next batch, which can include any entries that have been dropped .