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<petertodd>
Taek: that's the thing, I suspect you can design a system where that's provable
<petertodd>
Taek: yeah, I had the merge avoidence idea ages ago; iiirc my treechains writeup mentions it as a possibility before mentioning linearization
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<petertodd>
Taek: note how one of my ideas here is to institutionalise that kind of fraud, by making it how miners earn a living
<kanzure>
instead of a subsidy rule?
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<petertodd>
kanzure: somethng like that; not clear exactly what would work yet
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<petertodd>
re: expected value, another concept would be to design the system such that the % of hashing power you would need to pull that off is ~100% - in that circumstance you have a big risk in addition to that type of fraud
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<kanzure>
probabilistic validation doesn't really solve all the bandwidth problems...
<petertodd>
my thinking as how to derive the random beacon is essentially to mix many differnt blocks together; via addition sems possible
<petertodd>
kanzure: hmm? it's a huge improvement over the exponential blowup
<petertodd>
kanzure: er, also, tx history linearization isn't the same as probabilistic validation
<kanzure>
is it more like: random beacon picks some keys from the k-v tree, and the miner has to supply some amount of information, and they might experience bad luck and have not put in any of the requested information and therefore their block is deemed invalid ?
<petertodd>
kanzure: oh, no, that's something very different than history linearization; I suspect prob validation can't be made to work reliably enough
<petertodd>
kanzure: otoh, proving you have posession of block contents via prob sampling is fine, because failure isn't a big deal
<kanzure>
what's the worst that can happen with no double spending protection in the consensus layer. you have to incentivize everyone to report double spends, right?
<petertodd>
if you're relying on people reporting double spends, I think you're doing it wrong
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<kanzure>
you end up with indefinitely hidden double spends i guess, which can be revealed at any time later -- but pruning should nix that i think?
<petertodd>
proof-of-publication schemes *are* double-spending protection, yet there's no reporting of double-spends
<kanzure>
hm? you have to report double spends somehow-- that's what the block contents are for, right?
<petertodd>
I mean, the worst case is to imagine a timestamping scheme w/o publication... and I don't see how that'd ever be reliable
<petertodd>
kanzure: no, there's no reporting - I prove to you there isn't a double-spend, but no-one else is able to find the double-spend
<petertodd>
kanzure: remember that you can (and should!) encrypt the actual stuff getting published to make it meaningless garbage to anyone w/o the key
<kanzure>
right, well, i mean the block ontents really. that's the source of the bandwidth issue. so removing it solves the problem. it introduces double spending though... no way for you to check.
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<kanzure>
*contents
<petertodd>
kanzure: well, lemme finish this next post... bandwidth isn[t as bad as you'd expect
<kanzure>
bandwidth is the entire bottleneck
<petertodd>
it'll nevre be worse than k*# of movements
<kanzure>
yeah but that's a terrible limitation
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<petertodd>
you're missing my point - no client-side validation scheme can do better than that anyway; reporting double-spends doesn't prove anything about the coin being valid, so is irrelevant to the bigger problem
<kanzure>
hm? reporting to the potential recipient, i mean. you basically go out and pay for block data and transaction history from your friends/peers and figure out what they have. if thy have anything that conflicts, then you don't accept the payment.
<petertodd>
I have to provide you with sufficient tx history proof to prove the coin is valid in the first place; even if I magically could eliminate doubelspends in that proof that's still a fair bit of data
<petertodd>
e.g. imagine if we had trusted computing that could implement a single-use-seal, but *not* attest to the validity of history - even with tx linearization you'd have k*#of-spends sized history proofs
<kanzure>
if you have two outputs in a merkle root in some block, you would never reveal both to me when you're making a payment
<kanzure>
*payment to me
<petertodd>
like I say, that's irrelevant to the bigger problem
<petertodd>
also, the idea that the blocks contain the outputs is wrong - blocks would contain spends
<kanzure>
so the worst case scenario of double spending here is that, you spend to two different people, and then 10 years later the two different sectors of society finally interact and they find out about your fraudulence
<petertodd>
yes, I get that - point is even if you solve that problem, you still have to pass around a lot of data!
<petertodd>
fortunately, there are ways to potentially make that data e the *same* data for every person
<petertodd>
with an economy that joins coins sufficiently often, everyone will converge towards having their coins have the same tx history proofs (if linearized)
<petertodd>
e.g. what my scaling bitcoin presentation examined (and found to be not applicable in bitcoin's current economy)
<petertodd>
anyway, bbl, breakfast!
<petertodd>
7am here, and we have a 8am bus to the conference venue... :/
<kanzure>
for what conference
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<JackH>
and its Python, sweet
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<petertodd>
JackH: it also has some reaslly powerful pruning mechanisms
<petertodd>
JackH: basically, you can prune a k:v tree, access a few keys, then extract from that tree *only* the data needed to prove those keys do (or do not!) exist in the tree
<petertodd>
JackH: behind the scenes this is done with a bunch of python getattr magic, and pruning-supporting serialization
<petertodd>
JackH: I think it's the most natural way to handle proof extraction that I've ever seen
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<waxwing>
huh, this is interesting, so you can prove non-membership of a key in the tree? how compact is that?
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<petertodd>
/away
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<petertodd>
waxwing: O(log2 n)
<petertodd>
waxwing: basically, you just need to show that when you go down the tree in the particular path defined by the key, that path doesn't end in that key
<petertodd>
that's why it's a k:v tree rather than just a merkle tree
<waxwing>
thanks, reading.
<JackH>
yeah what is interesting here is that its k:v based from my point of view
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<JackH>
how do you handle multiple attributes that Python offers with getattr
<JackH>
is that supported ?
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<petertodd>
JackH: what do you mean by multiple ttributes?
<JackH>
so for example
<JackH>
we create this:
<JackH>
a = ["bob", "alice"]
<JackH>
and then getattr(a, "append")("joe")
<JackH>
basically multiple values for a key
<petertodd>
how is that multiple values for a key? you're getting "append" - a function - and calling it with "joe"
<petertodd>
to be exact, I mean the magic is done with the special function __getattr__
<JackH>
ah no, so in this example I add joe
<petertodd>
*special classfunction
<JackH>
hmm I need to read up on this in Python
<petertodd>
yeah, I think you're misunderstanding something
<petertodd>
also read the source code for python-proofmarshal and how pruning works
<petertodd>
the unittests are good for understanding all this
<petertodd>
basically, what's going on under the hood with __getattr__ is a pruned object is just an object with all attributes removed, and as they are accessed, setattr is used to put them back one by one, marking them as needed (unpruned)
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<petertodd>
note that when I say attributes there, I'm referring to a pre-defined per-class list that defines the attribute name and type - aka how its serialized
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