Re: [Bitcoin-development] BIP0039: Final call
On Tue, Jan 21, 2014 at 01:00:43AM +0100, Thomas Voegtlin wrote: Hi slush, Thank you for your new proposal; it seems to be a compromise. @Christophe Biocca: If the wordlist becomes part of the standard, then we will run into problems of collisions once users ask for wordlists in every language. IMO the right approach is to implement checksums that do not depend on the wordlist (eg the 'brute force' method, Hash(mnemonic||1) mod 2^k == 0 ) this would also allow us to implement sipa's variable stretching proposal. I understand this is not possible because of the computational requirements of devices such as trezor. Is it? Surely the trezor can bruteforce, say, 8 bits == 0. How many SHA256/sec can the trezor hardware do? Generating your seed is a one-time thing after all - that taking 10-30s doesn't seem like a big deal to me. Even a 1/256th checksum will really cut down on the number of mistakes made and money lost. -- 'peter'[:-1]@petertodd.org 0001d8b9d438c18e856735ddae5b1d918416010350d19794aab6 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] unlinakble static address? spv-privacy (Re: Stealth Addresses)
On Mon, Jan 20, 2014 at 08:00:05PM -0800, Jeremy Spilman wrote: Let's say the payee's reusable address is 'version prefix Q1 Q2 ...', where prefix is 2 bytes. Without any length indicator. What's the payer going to put on the blockchain? How would they know what the 'rest of the space' is? They would have to put the whole prefix verbatim into the OP_RETURN without knowing how many bits of prefix the payee actually wants to see there. If instead, the address is 'version prefix prefixLen Q1 Q2 ...' where prefix is 2 bytes, and prefixLen is 1 byte, representing number of bits of prefix that should be fixed. Then payer will know how much of prefix from the address should be taken verbatim, and the rest of the two bytes would be replaced with random data, and exactly two bytes would be put in the OP_RETURN. If prefixLen was zero, the 2 byte prefix in the reusable address must be ignored, and an entirely random 2 byte prefix would be put into the OP_RETURN. I'm a bit worried about broken implementations copying the prefix from the reusable address into OP_RETURN when prefixLen is 0, and ending up basically identifying the payee. That's the only reason I can think of to make 'prefix prefixLen' optional in the reusable address, to prevent the opportunity to screw it up. You would *still* put a 2-byte random prefix in the OP_RETURN, even if the fields weren't in the address at all. It's just a minor concern though. Something to keep in mind is that it's quite likely that the indexes available will be over H(scriptPubKey). There's really good engineering reasons for doing this: you need to be able to create succinct proofs of fraud in indexes, miner committed and otherwise, and the only way they are succinct is if you limit the length. Hashes naturally do that because it's so expensive to generate partial collisions. If you don't do this on the other hand now you have a situation where the usual case - max 16 level deep tree - and worst case - hundreds or even thousands of levels deep - are vastly different. That's hard to test for and likely to reveal implementation-specific limits in nasty ways. Anyway, grinding nonces isn't much of a burden given it's fast hash functions. The prefixes in question are fairly small and will be small for the forseeable future. As I said elsewhere in this thread, even Javascript has performance that's perfectly adequate for the task. -- 'peter'[:-1]@petertodd.org 3590a8a20ec9ff5b1c1af3f046a1f62dc1ac9a464721fd8f 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
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] BIP0039: Final call
Le 24/01/2014 10:05, Peter Todd a écrit : On Tue, Jan 21, 2014 at 01:00:43AM +0100, Thomas Voegtlin wrote: Hi slush, Thank you for your new proposal; it seems to be a compromise. @Christophe Biocca: If the wordlist becomes part of the standard, then we will run into problems of collisions once users ask for wordlists in every language. IMO the right approach is to implement checksums that do not depend on the wordlist (eg the 'brute force' method, Hash(mnemonic||1) mod 2^k == 0 ) this would also allow us to implement sipa's variable stretching proposal. I understand this is not possible because of the computational requirements of devices such as trezor. Is it? Surely the trezor can bruteforce, say, 8 bits == 0. How many SHA256/sec can the trezor hardware do? Generating your seed is a one-time thing after all - that taking 10-30s doesn't seem like a big deal to me. Even a 1/256th checksum will really cut down on the number of mistakes made and money lost. slush, correct me if I'm wrong, but I don't think that's the only reason: They want to generate a seed by combining entropy from the trezor device and from the user's computer; In addition, they want the computer to be able to check that the seed actually was derived from the entropy it provided, using only a master public key (the computer does not have access to the seed) This is why they designed bip39 that way. I think the new bip39 proposal could be used in Electrum as an option for trezor, but I am reluctant to make it default, because it imposes its own dictionary. -- 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 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
