| 00:05:31 | gmaxwell: | https://bitcointalk.org/index.php?topic=949942.0 kind of disappointing that the author seems to have been somehow unaware of the state of the art in development (e.g. that Bitcoin core has validated off a utxo database for years now) |
| 00:05:42 | gmaxwell: | roconnor: perhaps of particular interest to you ^ |
| 00:10:27 | kanzure: | .title |
| 00:10:27 | yoleaux: | Ledger Theory Coq Development |
| 00:12:06 | gwillen: | interesting that they're working in Coq though |
| 00:13:26 | kanzure: | i have been meaning to pay a coq person to show up in here |
| 00:13:41 | kanzure: | perhaps i will pay him to review (and/or fix?) that work instead |
| 00:15:51 | gmaxwell: | there are coq people in here. (thus my bringing that to roconnor's attention) |
| 00:16:16 | kanzure: | oh good |
| 02:10:41 | roconnor: | cute |
| 02:11:39 | gmaxwell: | post by the author here: https://bitcointalk.org/index.php?topic=949880.0 |
| 02:14:13 | roconnor: | I'll have to read this later |
| 02:14:27 | kanzure: | .title |
| 02:14:27 | yoleaux: | Lightweight Cryptos without Block Chain Bloat (Coq Development and Paper) |
| 02:19:26 | phantomcircuit: | gmaxwell, it's not exactly SPV security |
| 02:19:48 | phantomcircuit: | you can take the UTXO from 2 weeks ago and replay the full blocks until now |
| 02:19:57 | phantomcircuit: | which gets you better than spv, but worse than a full node |
| 02:20:43 | gmaxwell: | phantomcircuit: it's strictly weaker SPV security with an equal block confirmation count. It's not 1:1 but the places where it's a win aren't super clear to me. |
| 02:21:40 | phantomcircuit: | " equal block confirmation count" hum? |
| 02:22:34 | gmaxwell: | e.g. if you'd take a utxo set from 2016 blocks back, then waiting 2016 blocks on a payment is strictly more secure. As in there is no attack where a 2016 block reorg would trick a SPV wallet there but couldn't just be used for your UTXO set syncers. |
| 02:24:02 | gmaxwell: | It complicates if you are using 'what miners could have gotten out of their attack' (e.g. an economic security assumption) rather than just "I'm assuming most hashpower will be honest no matter what". |
| 02:25:06 | phantomcircuit: | gmaxwell, possibly we're talking about different modes of spv operation, a trivial spv client would not trace the graph for it's transactions back to a coinbase |
| 02:25:22 | phantomcircuit: | for such a client the utxo commitment is of substantial benefit |
| 02:25:27 | phantomcircuit: | well... |
| 02:25:31 | phantomcircuit: | it's of benefit |
| 02:25:33 | gmaxwell: | phantomcircuit: huh. nope not at all. |
| 02:25:40 | gmaxwell: | read what I wrote again. |
| 02:26:29 | gmaxwell: | If you just accept the commitment at height X then it could (possibly) contain _anything_. You're just trusting it. Okay, well you could also just trust a regular old SPV transaction at that height. You're trusting height X completely. |
| 02:26:53 | phantomcircuit: | gmaxwell, oh |
| 02:26:58 | phantomcircuit: | yes we agree there |
| 02:27:32 | phantomcircuit: | im saying that the ability to walk from the trusted point many blocks ago to the tip provides a benefit over spv |
| 02:27:44 | gmaxwell: | Right, and the tracing example shows that you can also get 'in between' with a 'tracing SPV' |
| 02:27:51 | phantomcircuit: | k |
| 02:28:09 | phantomcircuit: | it's difficult to discuss this stuff |
| 02:28:21 | phantomcircuit: | easy with a whiteboard :/ |
| 02:28:39 | gmaxwell: | Sure I'm not saying it's useless, but at the limit it's the SPV security model; it's not free from a security perspective. And if you were really happy with SPV you could just use that. So I'm unsure of the utility. |
| 02:29:26 | gmaxwell: | esp since a committed UTXO set comes with a (say) 20 fold IO increase for full nodes in additional cost updating the utxo set hashes. |
| 02:31:39 | phantomcircuit: | wouldn't the normal full node only have to calculate the utxo set hash once when the block was checked? |
| 02:31:50 | phantomcircuit: | oh right that actually is a huge cost |
| 02:32:11 | phantomcircuit: | gmaxwell, utxo commitments every 2016 blocks? :P |
| 02:34:24 | gmaxwell: | if the UTXO set is large compared to the transaction count in N blocks, then the gain from batching is small; and of course it's not nice to have a big burst of cost all at once. |
| 02:38:33 | phantomcircuit: | true |
| 03:45:04 | everettForth: | when is that bitcoin roundtable thing? |
| 03:46:05 | sipa: | #bitcoin |
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| 15:15:06 | maaku: | gmaxwell: would be 2x, not 20x no? |
| 15:15:37 | maaku: | a balanced tree has twice as many nodes as leafs |
| 15:17:03 | sipa: | in a binary tree yes |
| 15:17:05 | tromp__: | any binary tree, balanced or not, has 1 fewer internal nodes than leafs, so total nodes = 2* leafs - 1 |
| 15:17:16 | sipa: | but leveldb is not a binary tree |
| 15:17:48 | sipa: | while any db commitment pretty much has to at least semantically impose a bimary tree structure |
| 15:17:59 | sipa: | plus uodate all parents for every write |
| 15:18:15 | maaku: | oh right. an update hits log(N) |
| 15:18:33 | sipa: | you can merge the top tree updates |
| 15:18:45 | sipa: | but those are only small in number anyway |
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| 23:02:22 | ryan-c: | maaku: still want to talk to you about the status of your utxo work |