Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
On Thu, Jun 11, 2015 at 12:55 PM, Aaron Voisine vois...@gmail.com wrote: A Header-PoW-verifying client could still be given all transactions in a recent block, from which it can see the in-band fees directly. You don't know the fees paid by any given transaction unless you also have all it's inputs. Transaction inputs do not include an amount. You could however get the average fee-per-kb paid by all transactions in a block by looking at the coinbase transaction, subtracting the block reward, and dividing by the size of block minus the header. Excellent point and alternative proposal. You're right: to get the specifi fees, you'd need all transactions in a block, and all TxOuts with membership proofs. Your alternative seems like a much leaner trade-off for similar data. Aaron Voisine co-founder and CEO breadwallet.com On Thu, Jun 11, 2015 at 11:30 AM, Nathan Wilcox nat...@leastauthority.com wrote: On Wed, Jun 10, 2015 at 2:03 PM, Peter Todd p...@petertodd.org wrote: On Wed, Jun 10, 2015 at 02:00:27PM -0600, Nathan Wilcox wrote: On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine vois...@gmail.com wrote: It could be done by agreeing on a data format and encoding it in an op_return output in the coinbase transaction. If it catches on it could later be enforced with a soft fork. Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. (Until a softfork is activated, SPV clients should not rely on this encoding, since until that time the results can be fabricated by individual miners.) Fee stats can always be fabricated by individual miners because fees can be paid out-of-band. This is a point I hadn't considered carefully before. I don't understand the marketplace here or why miners would want to move fees outside of explicit inband fees. Implicit in this proposal is that the statistics only cover in-band data, because that's the scope of consensus rules, and thus the proposal is only as useful as the information of in-band fees is useful. I've also noticed a detracting technical argument given a particular tradeoff: A Header-PoW-verifying client could still be given all transactions in a recent block, from which it can see the in-band fees directly. The trade-off is the size of those transactions versus the need to alter any consensus rules or do soft forks. Notice how this trade-off's costs change with maximum block size. -- 'peter'[:-1]@petertodd.org 1245bd2f5c99379ee76836227ded9c08324894faabc0d27f -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
If we assume that transactions are being dropped in an unpredictable way when blocks are full, knowing the network congestion *right now* is critical, and even then you just have to hope that someone who wants that space more than you do doesn't show up after you disconnect. Yeah, my proposal is not intended to function correctly with full blocks, as Bitcoin cannot work at all in such a state. It assumes that fees only change slowly and that transactions are being cleared normally. -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
On 6/11/2015 6:10 AM, Peter Todd wrote: On Wed, Jun 10, 2015 at 02:18:30PM -0700, Aaron Voisine wrote: The other complication is that this will tend to be a lagging indicator based on network congestion from the last time you connected. If we assume that transactions are being dropped in an unpredictable way when blocks are full, knowing the network congestion *right now* is critical, and even then you just have to hope that someone who wants that space more than you do doesn't show up after you disconnect. Hence the need for ways to increase fees on transactions after initial broadcast like replace-by-fee and child-pays-for-parent. Re: dropped in an unpredictable way - transactions would be dropped lowest fee/KB first, a completely predictable way. Quite agreed. Also, transactions with unconfirmed inputs should be among the first to get dropped, as discussed in the Dropped-transaction spam thread. Like all policy rules, either of these works in proportion to its deployment. Be advised that pull request #6068 emphasizes the view that the network will never have consistent mempool/relay policies, and on the contrary needs a framework that supports and encourages pluggable, generally parameterized policies that could (some might say should) conflict wildly with each other. It probably doesn't matter that much. Deploying a new policy still wouldn't be much easier than deploying a patched version. I mean, nobody has proposed a policy rule engine yet (oops). -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
Re: dropped in an unpredictable way - transactions would be dropped lowest fee/KB first, a completely predictable way. Quite agreed. No, Aaron is correct. It's unpredictable from the perspective of the user sending the transaction, and as they are the ones picking the fees, that is what matters. -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
On Wed, Jun 10, 2015 at 2:03 PM, Peter Todd p...@petertodd.org wrote: On Wed, Jun 10, 2015 at 02:00:27PM -0600, Nathan Wilcox wrote: On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine vois...@gmail.com wrote: It could be done by agreeing on a data format and encoding it in an op_return output in the coinbase transaction. If it catches on it could later be enforced with a soft fork. Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. (Until a softfork is activated, SPV clients should not rely on this encoding, since until that time the results can be fabricated by individual miners.) Fee stats can always be fabricated by individual miners because fees can be paid out-of-band. This is a point I hadn't considered carefully before. I don't understand the marketplace here or why miners would want to move fees outside of explicit inband fees. Implicit in this proposal is that the statistics only cover in-band data, because that's the scope of consensus rules, and thus the proposal is only as useful as the information of in-band fees is useful. I've also noticed a detracting technical argument given a particular tradeoff: A Header-PoW-verifying client could still be given all transactions in a recent block, from which it can see the in-band fees directly. The trade-off is the size of those transactions versus the need to alter any consensus rules or do soft forks. Notice how this trade-off's costs change with maximum block size. -- 'peter'[:-1]@petertodd.org 1245bd2f5c99379ee76836227ded9c08324894faabc0d27f -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
A Header-PoW-verifying client could still be given all transactions in a recent block, from which it can see the in-band fees directly. You don't know the fees paid by any given transaction unless you also have all it's inputs. Transaction inputs do not include an amount. You could however get the average fee-per-kb paid by all transactions in a block by looking at the coinbase transaction, subtracting the block reward, and dividing by the size of block minus the header. Aaron Voisine co-founder and CEO breadwallet.com On Thu, Jun 11, 2015 at 11:30 AM, Nathan Wilcox nat...@leastauthority.com wrote: On Wed, Jun 10, 2015 at 2:03 PM, Peter Todd p...@petertodd.org wrote: On Wed, Jun 10, 2015 at 02:00:27PM -0600, Nathan Wilcox wrote: On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine vois...@gmail.com wrote: It could be done by agreeing on a data format and encoding it in an op_return output in the coinbase transaction. If it catches on it could later be enforced with a soft fork. Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. (Until a softfork is activated, SPV clients should not rely on this encoding, since until that time the results can be fabricated by individual miners.) Fee stats can always be fabricated by individual miners because fees can be paid out-of-band. This is a point I hadn't considered carefully before. I don't understand the marketplace here or why miners would want to move fees outside of explicit inband fees. Implicit in this proposal is that the statistics only cover in-band data, because that's the scope of consensus rules, and thus the proposal is only as useful as the information of in-band fees is useful. I've also noticed a detracting technical argument given a particular tradeoff: A Header-PoW-verifying client could still be given all transactions in a recent block, from which it can see the in-band fees directly. The trade-off is the size of those transactions versus the need to alter any consensus rules or do soft forks. Notice how this trade-off's costs change with maximum block size. -- 'peter'[:-1]@petertodd.org 1245bd2f5c99379ee76836227ded9c08324894faabc0d27f -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
On Wed, Jun 10, 2015 at 02:00:27PM -0600, Nathan Wilcox wrote: On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine vois...@gmail.com wrote: It could be done by agreeing on a data format and encoding it in an op_return output in the coinbase transaction. If it catches on it could later be enforced with a soft fork. Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. (Until a softfork is activated, SPV clients should not rely on this encoding, since until that time the results can be fabricated by individual miners.) Fee stats can always be fabricated by individual miners because fees can be paid out-of-band. -- 'peter'[:-1]@petertodd.org 1245bd2f5c99379ee76836227ded9c08324894faabc0d27f signature.asc Description: Digital signature -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine vois...@gmail.com wrote: It could be done by agreeing on a data format and encoding it in an op_return output in the coinbase transaction. If it catches on it could later be enforced with a soft fork. Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. (Until a softfork is activated, SPV clients should not rely on this encoding, since until that time the results can be fabricated by individual miners.) For real up-to-the-minute fee calculations you're also going to want to look at the current mempool, how many transactions are waiting, what fees they're paying, etc, but of course that information is susceptible to sybil attack. Hm, when you mention Sybil attack, I don't quite follow. When a client relies on any report of a mempool [*], this is already outside the realm of locally-verifiable SPV information, so they are already susceptible to the service making false claims. If that's acceptable (and in many cases it may be) then this whole mechanism is moot, because the client can ask the service for fee statistics for past blocks. In practice what we're doing for now is using services like blockcypher who's business is improving reliability of zero-conf to tell us what fee-per-kb is needed, and then putting a hard coded range around it to protect against the service being compromised. This is interesting for me, because I had previously believed fees were fairly static presently, and also because I like hearing about real life wallet implementations. So if this SPV Fee Stats feature were added, a wallet might rely on an API for timely stats (aka block height 1) then verify that the API isn't lying after doing SPV verification of fee stats for confirmed blocks. This is also the kind of thing being done for exchange rate data which is probably the bigger security risk until bitcoin becomes the standard unit of account for the planet. That makes sense, although there's no SPV equivalent for exchange data. Aaron Voisine co-founder and CEO breadwallet.com On Wed, Jun 10, 2015 at 10:37 AM, Nathan Wilcox nat...@leastauthority.com wrote: [I'm currently wading through bitcoin-development. I'm still about a month behind, so I apologize in advance for any noisy redundancy in this post.] While reading about blocksize, I've just finished Mike Hearn's blog post describing expected systemic behavior as actual blocks approach the current limit (with or without non-protocol-changing implementation improvements): https://medium.com/@octskyward/crash-landing-f5cc19908e32 One detail Mike uses to argue against the fee's will save us line of reasoning is that wallets have no good way to learn fee information. So, here's a proposal to fix that: put fee and (and perhaps block size, UTXO, etc...) statistics into the locally-verifiable data available to SPV clients (ie: block headers). It's easy to imagine a hard fork that places details like per-block total fees, transaction count, fee variance, UTXO delta, etc... in a each block header. This would allow SPV clients to rely on this data with the same PoW-backed assurances as all other header data. This mechanism seems valuable regardless of the outcome of blocksize debate. So long as fees are interesting or important, SPV clients should know about them. (Same for other stats such as UTXO count.) Upgrading the protocol without a hard-fork may be possible and is left as an exercise for the reader. ;-) -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
The other complication is that this will tend to be a lagging indicator based on network congestion from the last time you connected. If we assume that transactions are being dropped in an unpredictable way when blocks are full, knowing the network congestion *right now* is critical, and even then you just have to hope that someone who wants that space more than you do doesn't show up after you disconnect. Aaron Voisine co-founder and CEO breadwallet.com On Wed, Jun 10, 2015 at 1:26 PM, Mike Hearn m...@plan99.net wrote: I described an alternative way for SPV wallets to learn about fees some time ago. It requires a new transaction version that embeds output values into the signed data. Then an upgrade to the P2P protocol to send UTXO data along with transactions when they are relayed. The idea is that the wallet sets a Bloom filter with an FP rate that ensures it will see some random subset of all transactions being broadcast on the network, and with the extra data, it can calculate the fee paid. Once a transaction broadcast is observed the wallet includes that tx hash in its next Bloom filter, thus it can see which block the tx confirmed in. By measuring the amount of time that passed between a broadcast and it appearing in a block, it can calculate its own tables of fee paid:time taken. This has the advantage that you don't have to trust miners to publish data accurately. However it requires some protocol upgrades and of course, a lot of new code in SPV wallets. The way Bitcoin Wallet for Android handles fees currently is to just update a hard coded value every so often. -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism
Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. Yes you'd either need a way to add those transactions to the bloom filter, or add/modify a p2p message to request it specifically. when you mention Sybil attack, I don't quite follow. I just mean that someone could spin up a bunch of malicious p2p nodes that lied about mempool data. It's a bit worse for SPV clients since they can't verify that unconfirmed transactions are valid. I had previously believed fees were fairly static presently, I actually just added it the other day after getting blockcypher to include it in their api. The current release is still using a hard coded fee rate. Aaron Voisine co-founder and CEO breadwallet.com On Wed, Jun 10, 2015 at 1:00 PM, Nathan Wilcox nat...@leastauthority.com wrote: On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine vois...@gmail.com wrote: It could be done by agreeing on a data format and encoding it in an op_return output in the coinbase transaction. If it catches on it could later be enforced with a soft fork. Sounds plausible, except SPV protocols would need to include this coinbase txn if it's going to help SPV clients. (Until a softfork is activated, SPV clients should not rely on this encoding, since until that time the results can be fabricated by individual miners.) For real up-to-the-minute fee calculations you're also going to want to look at the current mempool, how many transactions are waiting, what fees they're paying, etc, but of course that information is susceptible to sybil attack. Hm, when you mention Sybil attack, I don't quite follow. When a client relies on any report of a mempool [*], this is already outside the realm of locally-verifiable SPV information, so they are already susceptible to the service making false claims. If that's acceptable (and in many cases it may be) then this whole mechanism is moot, because the client can ask the service for fee statistics for past blocks. In practice what we're doing for now is using services like blockcypher who's business is improving reliability of zero-conf to tell us what fee-per-kb is needed, and then putting a hard coded range around it to protect against the service being compromised. This is interesting for me, because I had previously believed fees were fairly static presently, and also because I like hearing about real life wallet implementations. So if this SPV Fee Stats feature were added, a wallet might rely on an API for timely stats (aka block height 1) then verify that the API isn't lying after doing SPV verification of fee stats for confirmed blocks. This is also the kind of thing being done for exchange rate data which is probably the bigger security risk until bitcoin becomes the standard unit of account for the planet. That makes sense, although there's no SPV equivalent for exchange data. Aaron Voisine co-founder and CEO breadwallet.com On Wed, Jun 10, 2015 at 10:37 AM, Nathan Wilcox nat...@leastauthority.com wrote: [I'm currently wading through bitcoin-development. I'm still about a month behind, so I apologize in advance for any noisy redundancy in this post.] While reading about blocksize, I've just finished Mike Hearn's blog post describing expected systemic behavior as actual blocks approach the current limit (with or without non-protocol-changing implementation improvements): https://medium.com/@octskyward/crash-landing-f5cc19908e32 One detail Mike uses to argue against the fee's will save us line of reasoning is that wallets have no good way to learn fee information. So, here's a proposal to fix that: put fee and (and perhaps block size, UTXO, etc...) statistics into the locally-verifiable data available to SPV clients (ie: block headers). It's easy to imagine a hard fork that places details like per-block total fees, transaction count, fee variance, UTXO delta, etc... in a each block header. This would allow SPV clients to rely on this data with the same PoW-backed assurances as all other header data. This mechanism seems valuable regardless of the outcome of blocksize debate. So long as fees are interesting or important, SPV clients should know about them. (Same for other stats such as UTXO count.) Upgrading the protocol without a hard-fork may be possible and is left as an exercise for the reader. ;-) -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 / AAAC 5675 E3F7 514C 67ED E9C9 3BFE 5263 1116 9993 -- ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development -- Nathan Wilcox Least Authoritarian email: nat...@leastauthority.com twitter: @least_nathan PGP: 11169993 /
