BIP 65 and OP_CHECKLOCKTIMEVERIFY inquiry...
5 messages, 27 to 28 Nov 2014. Started by Richard Moore.
Greg Maxwell (2), Richard Moore, Peter Todd, Flavien Charlon
Heya,
I was wondering about BIP 65 regarding the OP_CHECKLOCKTIMEVERIFY, and thought it might make more sense to instead have a OP_CHECKLOCKTIME which would simply push an OP_TRUE or OP_FALSE onto the stack?
That way someone could include multiple OP_CHECKLOCKTIME conditions in a single script. It is trivial to always emulate OP_CHECKLOCKTIMEVERIFY by using a OP_CHECKLOCKTIME OP_VERIFY sequence.
As a second question, would it possibly make more sense to, rather than relying on the nLockTime in a transaction, allow an opcode that would use similar semantics, but against an item in the stack? Then you could essentially include multiple nLockTimes in a single script and make arbitrarily interesting (complicated?) scripts based on block height and/or block timestamp.
The OP_CHECKLOCKTIMEVERIFY can still be easily implemented, by using
nLockTimeThatWouldBeInTx OP_CHECKLOCKTIME OP_VERIFY
Just something that came to mind while reading about OP_CHECKLOCKTIMEVERIFY.
Thanks,
RicMoo
.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸><(((º>
Richard Moore ~ Founder Genetic Mistakes Software inc. phone: (778) 882-6125 email: ricmoo@geneticmistakes•com <mailto:ricmoo@geneticmistakes.com> www: http://GeneticMistakes.com <http://geneticmistakes.com/>
On Thu, Nov 27, 2014 at 10:56 PM, Richard Moore <me@ricmoo•com> wrote:
Quoted text (5 lines)
> Heya, > > I was wondering about BIP 65 regarding the OP_CHECKLOCKTIMEVERIFY, and > thought it might make more sense to instead have a OP_CHECKLOCKTIME which > would simply push an OP_TRUE or OP_FALSE onto the stack?
Updating the stack is not soft-fork compatible and any use would immediately fork the network.
A invertible test is also not soft-fork compatible e.g. someone writes a script that does {<new thing>) OP_NOT, in other words "the test must fail", then the network would fork because older nodes would see it as passing (which was the required criteria for non-forking the network in the non-inverted caes).
You can happily get non-nullable true/false behaviour without these risks by having the VERIFY test inside a branch and having the signer provide its falseness as an input to the branch. This is explained in the BIP.
E.g. OP_IF <limit> OP_CHECKLOCKTIMEVERIFY OP_ELSE <what you'd do if it doesn't pass> OP_END
A useful an powerful mental model is that SCRIPT is not running a program, but instead the signer is proving to the network that they know inputs that make the program return true.
(In practise we verify this by actually doing some execution, though this isn't technically necessary it's the simplest thing to implement although it is inefficient... but even in this simple model keeping in mind that we're VERIFYING not executing in the network opens our eyes to transformations like the IF bracketing of a VERIFY opcode.)
Quoted text (2 lines)
> That way someone could include multiple OP_CHECKLOCKTIME conditions in a > single script.
They can do this, with the above approach.
Quoted text (10 lines)
> As a second question, would it possibly make more sense to, rather than > relying on the nLockTime in a transaction, allow an opcode that would use > similar semantics, but against an item in the stack? Then you could > essentially include multiple nLockTimes in a single script and make > arbitrarily interesting (complicated?) scripts based on block height and/or > block timestamp. > > The OP_CHECKLOCKTIMEVERIFY can still be easily implemented, by using > > nLockTimeThatWouldBeInTx OP_CHECKLOCKTIME OP_VERIFY
Then the scripts validity isn't a pure function of the the transaction, and once valid transactions could become invalid while in the mempool. This breaks existing invariants and would make the coins potentially less fungible because they wouldn't be reorg safe. That locktime validity is basically monotonic is a useful intentional property. :)
The things you're suggesting were all carefully designed out of the proposal, perhaps the BIP text needs some more clarification to make this more clear.
On 27 November 2014 18:46:23 GMT-05:00, Gregory Maxwell <gmaxwell@gmail•com> wrote:
<snip 100% accurate commentary from gmaxwell>
Quoted text (3 lines)
>The things you're suggesting were all carefully designed out of the >proposal, perhaps the BIP text needs some more clarification to make >this more clear.
It does; it is still a draft. That said I think writing up some actual working examples, in code, of CHECKLOCKTIMEVERIFY using protocols is a bigger priority. Micropayment channels comes to mind, as well as a greenaddress-style wallet.
When I get a chance I'm going to rebase the initial implementation and add to it a command-line-flag to verify CHECKLOCKTIMEVERIFY as an IsStandard() rule for testing purposes.
Quoted text (1 line)
> This breaks existing invariants and would make the coins potentially less
fungible because they wouldn't be reorg safe.
I'm not sure coins are ever reorg safe. All it takes is a double spend in the history of your coins for them to become invalid after a reorg. Because of that, there are already less fungible coins. This is why we recommend 6 confirmations for important payments.
On Fri, Nov 28, 2014 at 3:18 AM, Peter Todd <pete@petertodd•org> wrote:
Quoted text (50 lines)
> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > > > On 27 November 2014 18:46:23 GMT-05:00, Gregory Maxwell < > gmaxwell@gmail•com> wrote: > > <snip 100% accurate commentary from gmaxwell> > > >The things you're suggesting were all carefully designed out of the > >proposal, perhaps the BIP text needs some more clarification to make > >this more clear. > > It does; it is still a draft. That said I think writing up some actual > working examples, in code, of CHECKLOCKTIMEVERIFY using protocols is a > bigger priority. Micropayment channels comes to mind, as well as a > greenaddress-style wallet. > > When I get a chance I'm going to rebase the initial implementation and add > to it a command-line-flag to verify CHECKLOCKTIMEVERIFY as an IsStandard() > rule for testing purposes. > -----BEGIN PGP SIGNATURE----- > Version: APG v1.1.1 > > iQFQBAEBCAA6BQJUd+luMxxQZXRlciBUb2RkIChsb3cgc2VjdXJpdHkga2V5KSA8 > cGV0ZUBwZXRlcnRvZGQub3JnPgAKCRAZnIM7qOfwhWmcB/0UK030Q6TSpi95x0Gh > hGYaSAInUWpbZzZtP+1AFrGDGRdGo0glFFf8xggI+U5kuc0woPYrn/VEGcprPhvs > KQFZrirXVr7Q09TVlHiPDen5v3Y7xwL5kQDUrBPP71Pe3R2o6IbfdwxsZ8+yYso8 > hY6WQmImQpKJd4gEd76w1QrF8Btl1Jz/PGh4EE3GSPGlflvBwA6igSiRoD/czb1x > 63y4AsPEil2hrmIjTZHqwnl40BqnmZ8qpNLWeIEjE++pbkxLTjvUcPy03/wtTWZA > 5dCGeY5WavgZsPazhSdaTtM5/7wPSQQ0PDXNHdHgmewkvbyBpy78orV/3bEG+xFz > 2SWi > =4OmI > -----END PGP SIGNATURE----- > > > > ------------------------------------------------------------------------------ > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > with Interactivity, Sharing, Native Excel Exports, App Integration & more > Get technology previously reserved for billion-dollar corporations, FREE > > http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk > _______________________________________________ > Bitcoin-development mailing list > Bitcoin-development@lists•sourceforge•net > https://lists.sourceforge.net/lists/listinfo/bitcoin-development >
On Fri, Nov 28, 2014 at 11:45 AM, Flavien Charlon <flavien.charlon@coinprism•com> wrote:
Quoted text (7 lines)
>> This breaks existing invariants and would make the coins potentially less >> fungible because they wouldn't be reorg safe. > > I'm not sure coins are ever reorg safe. All it takes is a double spend in > the history of your coins for them to become invalid after a reorg. Because > of that, there are already less fungible coins. This is why we recommend 6 > confirmations for important payments.
I used the word 'less' intentionally. A double spend requires an active action. Roughly 1% of blocks are lost to reorganizations by chance, longer otherwise harmless reorgs as we've had in the past could forever destroy large chunks of coins if descendants had the unwelcome properties of having additional constraints on them. Past instances where the network had a dozen block reorganization which were harmless and simply confirmed the same transactions likely would have caused substantial losses if it reorganizations precluded the recovery of many transactions which were valid when placed earlier in the chain.
Additionally your '6 confirmations' is a uniform rule. The recommendation is just a count, it's tidy. It's not a "traverse the recent history of each coin you receive to determine if its script conditions make it unusually fragile and subject to irrecoverable loss", which is the space you can get into with layering violations and transaction validity depending on arbitrary block data.