Re: [Bitcoin-development] Bait for reusable addresses
brittleness. The real world experience is that users, or to be exact wallet authors, turn down SPV privacy parameters until bloom filters have almost no privacy in exchange for little bandwidth usage. That's not fundamental though, it just reflects that the only implementation of this is used on a wide range of devices and doesn't yet have any notion of bandwidth modes or monitoring. It can and will be resolved at some point. -- CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431iu=/4140/ostg.clktrk___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Bait for reusable addresses
On Fri, Jan 24, 2014 at 12:26:19PM +, Mike Hearn wrote: brittleness. The real world experience is that users, or to be exact wallet authors, turn down SPV privacy parameters until bloom filters have almost no privacy in exchange for little bandwidth usage. That's not fundamental though, it just reflects that the only implementation of this is used on a wide range of devices and doesn't yet have any notion of bandwidth modes or monitoring. It can and will be resolved at some point. Resolved for some users, not for all. The underlying trade-off will always be there; less bandwidth makes it harder, more addresses to check makes it harder; an HD wallet used properly without re-using addresses will quickly lead to a fairly full bloom filter unless addresses are expired, and expiration leads to scenarios where funds can be lost. I think we need to provide users with better options than that. -- 'peter'[:-1]@petertodd.org 64ddd387d7548c97c4d42f4df1008d180f306c59e0440f4f signature.asc Description: Digital signature -- CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431iu=/4140/ostg.clktrk___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Bait for reusable addresses
I think prefix has analysis side effects. There are (at least) 4 things that link payments: the graph of payment flows, timing, precise amounts, IP addresses, but with prefix a 5th: the prefix allows public elmination of candidates connections, I think that may make network flow analysis even more effective than it has been. So SPV can be tuned as Mike just said, and as Greg pointed out somewhere bloom is more private than prefix because its a wallet to node connection, not a node broadcast, and Mike mentioned embedded Tor in another post to boost node-capture issues with hostile network. So reusable addresses are cool for full node recipients (0-bit prefix) or trusted server offload (your own desktop, VPS, or trusted service provider node, and solve real problems for the use case of static and donation addresses particularly with this second delegatable key for no-funds at risk search (which is even good as Jeremey said for your own node, in a offline wallet use case). Now while it would be clearly a very nice win if reusable addresses could be made SPV-like in network characteristics and privacy, but we dont have a plausible mechanism yet IMO. Close as we got was Greg's enhancement of my/your bloom bait/prefix concept to make multiple candidate baits to provide some ambiguity (still allows elimination, just slightly less of it). If we can find some efficient crypto to solve that last one, we could even adopt them generally if it was efficient enough without needing interactive one-use address release. Maybe we should ask some math/theoretical crypto people if there is anything like public key watermarking or something that could solve this problem efficiently. For the related but different case of transaction level authenticity I like Alan's server derived but communicated scalar base to allow the client to do at least TOFU. Payment protocol may add another level of identity framework on top of TOFU addresses (at a lower level than the payment messages defined now), and without then needing a batch upload of offline signed secondary address sigature that Mike described a while back, at least in person, maybe online somewhere (an add on with similar purpose and effect to Alan's TOFU, but then with revocation, identity and certification for merchants). I have not talked about payment protocols main app level function I think we all understand and agree on the purpose and use of the server and optional client certs in that. People may wish to add other cert types later (eg PGP, SSH etc) but this version covers the common merchant tech, and allows client-side certs to be experimented with for identity also (eg imagine as a way to enrol with regulated entities like exchanges.) Tell me if I am misunderstanding anything :) Adam On Fri, Jan 24, 2014 at 12:26:19PM +, Mike Hearn wrote: brittleness. The real world experience is that users, or to be exact wallet authors, turn down SPV privacy parameters until bloom filters have almost no privacy in exchange for little bandwidth usage. That's not fundamental though, it just reflects that the only implementation of this is used on a wide range of devices and doesn't yet have any notion of bandwidth modes or monitoring. It can and will be resolved at some point. -- CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431iu=/4140/ostg.clktrk ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] Bait for reusable addresses
On Fri, Jan 24, 2014 at 04:42:35PM +0100, Adam Back wrote: I think prefix has analysis side effects. There are (at least) 4 things that link payments: the graph of payment flows, timing, precise amounts, IP addresses, but with prefix a 5th: the prefix allows public elmination of candidates connections, I think that may make network flow analysis even more effective than it has been. You know, we've made this discussion rather confusing because we're using the term prefix for both prefix filters - which are equivalent to bloom filters but with better scalability - and the act of forcing a scriptPubKey to match some given prefix. I suggest we call the latter concept 'wallet clustering' as it can just as easily be applied to bloom filters, as well as Gregory Maxwell's candidate bait scheme, and for that matter, prefix filters with a tweak option, e.g. H(scriptPubKey | nTweak) So yeah, clustering schemes make network flow analysis easier if the attacker only has blockchain data to work from. But they can also make network flow analysis significantly harder for attackers that have query logs from attackers running nodes, and as we know sybiling the network to get query logs is very easy. I'd rather develop systems that don't fail catastrophically against sybil attack. So SPV can be tuned as Mike just said, and as Greg pointed out somewhere bloom is more private than prefix because its a wallet to node connection, not a node broadcast, and Mike mentioned embedded Tor in another post to boost node-capture issues with hostile network. The hostile network is likely to have a significant percentage of hostile, query-logging nodes. For one thing, running nodes is expensive and would be even more so in a blocksize limit raising scenario, and a easy way to pay those costs is by selling query data. So reusable addresses are cool for full node recipients (0-bit prefix) or trusted server offload (your own desktop, VPS, or trusted service provider node, and solve real problems for the use case of static and donation addresses particularly with this second delegatable key for no-funds at risk search (which is even good as Jeremey said for your own node, in a offline wallet use case). Sure, in some cases you can use zero-length prefixes with trusted nodes; not many users have access to such nodes. Now while it would be clearly a very nice win if reusable addresses could be made SPV-like in network characteristics and privacy, but we dont have a plausible mechanism yet IMO. Close as we got was Greg's enhancement of my/your bloom bait/prefix concept to make multiple candidate baits to provide some ambiguity (still allows elimination, just slightly less of it). If we can find some efficient crypto to solve that last one, we could even adopt them generally if it was efficient enough without needing interactive one-use address release. Conversely, it'd be interesting if someone can dig up a proof showing that doing much better than Gregory's ambiguity tradeoff is impossible. My gut feeling is that it is, especially if you take into account the desire for scalability - if we're to make the blocksize bigger assuming all nodes have all data for every block just isn't going to happen. Maybe we should ask some math/theoretical crypto people if there is anything like public key watermarking or something that could solve this problem efficiently. Yes, and I think such schemes should be pursued. But in the near-term what can we offer users? Remember that making stealth addresses and similar clustering-using schemes capable of backward compatible upgrades isn't hard; if the crypto is found later it can be adopted. What is harder is that people want miners to commit to various types of indexes - changing those indexes would require a soft-fork and there's much pressure for those indexes to have very good performance properties. For the related but different case of transaction level authenticity I like Alan's server derived but communicated scalar base to allow the client to do at least TOFU. Payment protocol may add another level of identity framework on top of TOFU addresses (at a lower level than the payment messages defined now), and without then needing a batch upload of offline signed secondary address sigature that Mike described a while back, at least in person, maybe online somewhere (an add on with similar purpose and effect to Alan's TOFU, but then with revocation, identity and certification for merchants). Note how well the OpenPGP + bitcoin address UID ideas I and others have been talking about meshes with TOFU: the logic for Do I trust this address to send money? and Do I trust this PGP key to send more encrypted mail/verify signatures? is just different questions about the same human identity, so combining the two is synergistic. For instance I might want to communicate securely with a friend via email and also send funds to them securely. An interesting nuance is
Re: [Bitcoin-development] Bait for reusable addresses
I think we need to provide users with better options than that. Perfect privacy without extraordinary computational overhead today means downloading everything. But we could provide better tools to *shift* bandwidth requirements rather than try to reduce them. I've been thinking about a setup where user runs a UTXO only, and maybe even outbound-connect only (like bitcoinj), full node at home. Then using Tor, mostly for tunneling, they host a hidden service they can connect back to from their smartphone to see balances, manage receive addresses, send funds, etc. The smartphone is not doing SPV, it's like a web client for the wallet running at home. The initial connection between the smartphone and home wallet has the phone learn two codes, one is the hidden service name, another is an access token which is revocable. You may require further authentication from that point. With fast bootstrapping / checkpointing of the UTXO I think usability could be as good as SPV, and you would get push-notification of relevant transactions with zero privacy trade-off. I wonder if people would want to run such an app, if they would run it on their desktop, a dedicated machine, or an old smartphone or other cheap ARM device. -- CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431iu=/4140/ostg.clktrk ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
