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|andytoshi: I wonder if it's possible to use this as just a 'devel time dependency' but make it easy to build without it? https://github.com/nrc/libhoare
|oh gmaxwell, i was just poking at that today
|the short answer is yes, there are debug_* variants of all the contracts
|the long answer is yes, rust will let you make any decorator conditional on the compilation mode :)
|i haven't had an opportuntity to play with it yet, my rust time has been spent on halfsleep (mutation testing) which requires a bunch of work since i need to build a namespace for all the identifiers to get their paths straight
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|hktud0: now we have a fluffybunny *and* a fluffypony here, oh dear!
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|gmaxwell: how exactly does the 'Build your own nHashType' proposal "result in a kind of limited covenant" ?
|* Luke-Jr thought we had given up on covenant-avoidence.
|AFAIK, covenants aren't exactly possible currently, so avoiding them is a given
|StephenM347: i think gmax is referring to his mechanism for getting the hash of [everything signed] onto the stack
|if you create a sighash flag which doesn't cover the output script it's spending in any way (including not using the txid) then you can force this to be specific values
|andytoshi: Right, he mentioned something about OP_MASKED_TRANSACTION_HASH_EQUALS, but my proposal didn't enable that, as far as I can tell.
|StephenM347: that's already in bitcoin
|it's just not useful for covenants because every sighash type covers the output itself
|StephenM347: you can get it by forcing the signature to some dummy value (1, 1) say, then there is one (easily-computable) pubkey which'll give you that signature for any message
|that pubkey is the "hash"
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|andytoshi: That sounds interesting, do you (or anyone else) know of a link where I could read more about this?
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|StephenM347: https://botbot.me/freenode/bitcoin-wizards/2014-09-04/?msg=21030748&page=5 is the only record of it i think
|i can't believe that was 7 months ago o.O i thought like 2 months
|StephenM347: If its possible to completely mask out the input transaction information you can use pubkey recovery to create a coin that can only be spent with by a specific masked transaction.
|That doesn't directly create a perpetual covenant; but I would be very unsurprised if it were possible to use a pair of coins with clever masking to get a perpetual one.
|The thing I was responding to was a person suggesting the replay vulnerable for for _all_ transactions as a "solution" to malleability; I think that suggestion is really really ill advised.
|"It just goes to where it went before" is not a good answer; where it went before may well be a total black hole now. Sure; I agree there are cases where a replay vulnerability is acceptable-- e.g. where you can be fairly sure the software will prevent replay, and where it happening will be recoverable-- but this is not the case for ordinary transactions.
|would it be better for a civilization to insist on only doing reversible economic transactions?
|i would imagine you'd have to leave out.. a lot.
|s/reversible/replayable (subtle difference i guess?)
|StephenM347: saying that it's not worse that txid mutation seems completely incohearent to me. Changing a txid can not result in funds loss in an even stronger sense than your argument that replay-with-value cannot result in loss.
|kanzure: for replay to be safe you must never reuse addresses; not reusing addresses is hard from an application perspective because maintaining state is hard. E.g. say you generate an address but then crash; when you recover you forgot that you already generated that address.
|It's not impossible; but it requires a lot of considerations.
|right, you should never generate addresses at run-time anyway
|and ideally you should never allocate addresses at run-time either
|whether you generate them at runtime or not is not relevant
|whether you mark them as used is
|gmaxwell: "but this is not the case for ordinary transactions" -- and ordinary transactions have no use for these types of sighash flags anyway. I'm not saying we should all start using these flags all the time, there would just be very specific use cases
|For example, when setting up a micropayment channel you have to establish the refund TX
|that could be done with SIGHASH_INPUT_WITHOUT_TXID
|That refund transaction is never meant to be broadcasted to be blockchain, it's just there as a back up
|And the refund transaction would be signing away a scriptPubKey that was sent to a 2-of-2 multisig address
|StephenM347: "and ordinary transactions have no use" please read the thread you were responding to.
|... the person there was basically arguing that BIP66 protections against third party malleability shouldn't be done because your flags proposal was a better solution.
|Which would mean using a replay vulnerable form on all transactions.
|gmaxwell: Oh, right. As I said in the email chain, I don't think this should be seen as a replacement for that BIP at all, they are complementary
|gmaxwell: only transactions with address reuse?
|also, do you mean BIP 62? 66 is just strict DER…
|he means bip62 i think :)
|StephenM347: Well my response was specific to that subject, not a general opposition to more flexible masking; as far as the point that "better to build in a more flexible solution now than to wish we had more flexible nHashTypes later"; there is a straight forward counterargument that every piece of additional complexity has high cost; not just for the system itself but for many of its users (th
|ere are applications that become insecure if you're not minding sighash flags set by third party software); Functionality is basically impossible to take away (since removing functionality might confiscate coins), but possible to add; so great care and consideration must be applied.
|Though, I'm also not a great fan of the bag-of-flags approach, I'd rather a more programmtic approach to powerful masking, one which is demonstratively fully general. Even though it would likely be somewhat more complex it would not have te outcome of having a lot of complexity that turned out to not be useful.
|(which is something we suffer from in the system today; lots of options almost no one uses; missing a few options people really want)
|gmaxwell: Makes sense :) And if you're software isn't paying attention to sighash flags set by third party software, then it probably already has vulnerabilities just with the set of sighash flags we use now.
|How could you be more general with a programatic approach? It seems like the so-called bag-of-flags approach general and compact
|Things like OP_FEELESSTHANVERIFY should probably be done programmatically, though, rather than in sighash flags
|ehh, that sounds like a crappy opcode to have :P
|especially since fees are possible underdetectably
|StephenM347: e.g. An op_code that pushes a full parse tree of the transaction onto the stack; and an opcode that pushes elements onto a tagged signature stack for signing.
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|I am going to be in SF 14th-16th of May if anyone is interested in grabbing lunch or a drink.
|mm_1 is now known as mm_0
|sipa: I think I have a ~log(height) computation, O(1) communication algorithim for selecting and signaling random subsets of the block history.
|sipa: History is divided into ranges of some number of blocks for locality purposes, e.g. say 100 or 1000 or whatever. For now I'll pretend the range size is 1 for simplicity, but you'd just substitude range for block in the below.
|sipa: Each peer signals a 32-bit seed (which they select uniformly, and a count of the number of blocks they'll store.
|When you want to figure out what blocks your peers have, for each peer you pick a random index out of their nr_blocks range. You then compute key = index||seed, and query a jump-consistent hash  JCH(key, height), the result is what block they're storing in that slot.
|After doing this with all peers, if you've found adequate sources for the block you want, you're done. Otherwise, go back and for peers with more slots, determine what block they have in that slot.
| A candidate JCH() is http://arxiv.org/pdf/1406.2294v1.pdf which is better than log(height) in runtime.
|I don't think I can do better than this, but I think this is actually good enough to use. Some simulation would be needed, and perhaps some preprocessing of the key to avoid pathological behavior in the JCH due to poor distribution of the nr_blocks index.
|gmaxwell: that's good enough for finding what to ask from which peer
|gmaxwell: but perhaps not for deciding who to connect to
|I'm assuming an extended addr message that includes these seed,nr values.
|though ... one could hijack the existing addr messages by using your external IP as the seed, and talking a couple service bits to signal nr. 0_o I'm not a huge fan of that.
|(I assume the extended messages would also include a range or flag for how near to the tip do you keep, e.g. 288 vs 2016 vs all blocks.)
|In any case, I think this is a pretty big improvement over my prior best approach of using reservoir sampling, which had O(height) complexity. The downside is that you the heights of the blocks you hold are not monotonic increasing. :( At a future height you may find yourself needing to replace a slot with older blocks. :(
|Which wasn't a problem the reservoir sampling had.
|Though there may be some choice of a consistent hash that would just be monotonically increasing.
|[Totally OT but will be of interest to some here]: http://bbcomp.ini.rub.de/ with only 4 days left I'm just going to phone in some pre-fabbed optimization code of mine.
|hi there, are there any /r/bitcoin mods here?
|/r/bitcoin is probably a better place to ask, I don't know of any who hang out here