Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
On Sat, Apr 26, 2014 at 6:08 AM, Thomas Voegtlin thoma...@gmx.de wrote: Perhaps the only thing that needs to be standardized is the order of public keys in the redeem script: I think they should be sorted, so that the p2sh address does not depend on the order of pubkeys. Yes. That solution is already implemented in a few wallets. -- Jeff Garzik Bitcoin core developer and open source evangelist BitPay, Inc. https://bitpay.com/ -- Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available. Simple to use. Nothing to install. Get started now for free. http://p.sf.net/sfu/SauceLabs ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
I'm not sure I understand why you need any special structure for this at all. The way I'd do it is just use regular HD wallets for everyone, of the regular form, and then swap the watching keys. Why do people need to be given a cosigner index at all, given that they all have unique root keys anyway? On Sat, Apr 26, 2014 at 12:27 AM, Manuel Araoz m...@bitpay.com wrote: Hi, I'm part of the team building copay https://github.com/bitpay/copay, a multisignature P2SH HD wallet. We've been following the discussion regarding standardizing the structure for branches both on this list and on github (1 https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki, 2 https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki, 3https://github.com/bitcoin/bips/blob/master/bip-0043.mediawiki, 4 https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki, 5https://github.com/bitcoin/bips/pull/52). Soon, we realized the assumptions in the discussions were not true for a multisig hd wallet, so we wanted to share our current approach to that, to get feedback and see if we can arrive to a new standard (and possibly a new BIP) These are our assumptions: - N parties want to share an m-of-n wallet. - Each party must generate their master private keys independently. - Use multisig P2SH for all addresses. - Use BIP32 to derive public keys, then create a multisig script, and use the P2SH address for that. - The address generation process should not require communicating with other parties. (Thus, all parties must be able to generate all public keys) - Transaction creation + signing requires communication between parties, of course. - Following BIP43, we're be using: m / purpose' / * where *purpose* is the hardened derivation scheme based on the new BIP number. We then define the following levels: m / purpose' / cosigner_index / change / address_index Each level has a special meaning detailed below: *cosigner_index* http://en.wikipedia.org/wiki/Co-signing: the index of the party creating this address. The indices can be determined independently by lexicographically sorting the master public keys of each cosigner. *change*: 0 for change, 1 for receive address. *address_index*: Addresses are numbered from index 0 in sequentially increasing manner. We're currently syncing the max used index for each branch between all parties when they connect, but we're open to considering removing the index sync and doing the more elegant used-address discovery via a gap limit, as discussed in BIP44https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki#address-gap-limit. We feel 20 might be too low though. *Wallet high-level description:* Each party generates their own extended master keypair and shares the extended purpose' public key with the others, which is stored encrypted. Each party can generate any of the other's derived public keys, but only his own private keys. *General address generation procedure:* When generating an address, each party can independently generate the N needed public keys. They do this by deriving the public key in each of the different trees, but using the same path. They can then generate the multisig script and the corresponding p2sh address. In this way, each path corresponds to an address, but the public keys for that address come from different trees. *Receive address case:* Each cosigner generates addresses only on his own branch. One of the n cosigners wants to receive a payment, and the others are offline. He knows the last used index in his own branch, because only he generates addresses there. Thus, he can generate the public keys for all of the others using the next index, and calculate the needed script for the address. *Example: *Cosigner #2 wants to receive a payment to the shared wallet. His last used index on his own branch is 4. Then, the path for the next receive address is m/$purpose/2/1/5. He uses this same path in all of the cosigners trees to generate a public key for each one, and from that he gets the new p2sh address. *Change address case:* Again, each cosigner generates addresses only on his own branch. One of the n cosigners wants to create an outgoing payment, for which he'll need a change address. He generates a new address using the same procedure as above, but using a separate index to track the used change addresses. *Example: *Cosigner #5 wants to send a payment from the shared wallet, for which he'll need a change address. His last used change index on his own branch is 11. Then, the path for the next change address is m/$purpose/5/0/12. He uses this same path in all of the cosigners trees to generate a public key for each one, and from that he gets the new p2sh address. *Transaction creation and signing:* When creating a transaction, first one of the parties creates a Transaction Proposal. This is a transaction
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
Le 26/04/2014 11:43, Mike Hearn a écrit : I'm not sure I understand why you need any special structure for this at all. The way I'd do it is just use regular HD wallets for everyone, of the regular form, and then swap the watching keys. Why do people need to be given a cosigner index at all, given that they all have unique root keys anyway? I agree with that. Perhaps the only thing that needs to be standardized is the order of public keys in the redeem script: I think they should be sorted, so that the p2sh address does not depend on the order of pubkeys. -- Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform ___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
On Apr 26, 2014 6:43 AM, Mike Hearn m...@plan99.net wrote: I'm not sure I understand why you need any special structure for this at all. The way I'd do it is just use regular HD wallets for everyone, of the regular form, and then swap the watching keys. Why do people need to be given a cosigner index at all, given that they all have unique root keys anyway? I tried to explain that here: The reason for using separate branches for each cosigner is we don't want two of them generating the same address and receiving simultaneous payments to it. The ideal case is that each address receives at most one payment, requested by the corresponding cosigner. To clarify, the problem the cosigner_index is trying to solve is race conditions when receiving payments. Remember that we can't assume all cosigners to be online at all times. Let's assume we use one shared branch for everyone. Then two cosigners could need a new receiving address at the same time, and get the next unused address on that branch. They then each pass the same address to their payers, and we can get two payments to the same address. Monitoring balances is not enough in this case because a cosigner can never know when the others are generating a new address. Separating branches and having each cosigner only use one branch makes this problem go away. -- Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
Let's assume we use one shared branch for everyone. Then two cosigners could need a new receiving address at the same time, and get the next unused address on that branch. This is the part I struggle to understand. There is no shared branch because each user/cosigner has their own unique seed and thus unique key hierarchy, right? What you described above could be an issue if all co-signers shared the same seed but then the scheme wouldn't work. -- Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
On 04/26/2014 04:33 PM, Mike Hearn wrote: Let's assume we use one shared branch for everyone. Then two cosigners could need a new receiving address at the same time, and get the next unused address on that branch. This is the part I struggle to understand. There is no shared branch because each user/cosigner has their own unique seed and thus unique key hierarchy, right? What you described above could be an issue if all co-signers shared the same seed but then the scheme wouldn't work. Consider two people with phones, using 2-of-2, using private seeds k1 and k2. Every address generated by either party is: 2-of-2(K1/a'/b/c, K2/a'/b/c) So for any a, b and c you end up with a 2-of-2 address. The seeds/branches will not be used for single-sig receiving... it's always a multisig 2-of-2. In fact it behaves much like a regular wallet, you give an a, b, and c value, and you get an address -- it's just that this wallet always gives you a P2SH multisig address. The problem is that if you follow BIP32 in the the most obvious way, both devices will generate receiving addresses along the last index, i.e. K/a'/b/0, K/a'/b/1, K/a'/b/2,... If I am at one store and my wife at another, we might both give out 2-of-2(K1/a'/b/382, K2/a'/b/382) at the same time not realizing the other one has distributed that address. There's not a good way to coordinate the devices well enough to avoid it. But we don't have to. The solution is to use two separate branches -- both phones will follow/watch both branches, but each only only distributes payment addresses from one such branch. The original proposal here suggested adding a level to the tree using the cosigner index as a branch point for doing this... I recommended simply having 2*N values for b, so that each participant has a receiving line and change line, that won't conflict with other devices. However, all devices will still watch all 2*N branches to know the total balance of the wallet, and will use UTXOs from those branches when constructing spending transactions/proposals. -- Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
Ah, I see now. Thanks. And actually now I re-read it, Manuel's explanation was clear, it just didn't sink in for some reason. -- Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform___ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
[Bitcoin-development] New BIP32 structure for P2SH multisig wallets
Hi, I'm part of the team building copay https://github.com/bitpay/copay, a multisignature P2SH HD wallet. We've been following the discussion regarding standardizing the structure for branches both on this list and on github (1 https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki, 2 https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki, 3https://github.com/bitcoin/bips/blob/master/bip-0043.mediawiki, 4 https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki, 5https://github.com/bitcoin/bips/pull/52). Soon, we realized the assumptions in the discussions were not true for a multisig hd wallet, so we wanted to share our current approach to that, to get feedback and see if we can arrive to a new standard (and possibly a new BIP) These are our assumptions: - N parties want to share an m-of-n wallet. - Each party must generate their master private keys independently. - Use multisig P2SH for all addresses. - Use BIP32 to derive public keys, then create a multisig script, and use the P2SH address for that. - The address generation process should not require communicating with other parties. (Thus, all parties must be able to generate all public keys) - Transaction creation + signing requires communication between parties, of course. - Following BIP43, we're be using: m / purpose' / * where *purpose* is the hardened derivation scheme based on the new BIP number. We then define the following levels: m / purpose' / cosigner_index / change / address_index Each level has a special meaning detailed below: *cosigner_index* http://en.wikipedia.org/wiki/Co-signing: the index of the party creating this address. The indices can be determined independently by lexicographically sorting the master public keys of each cosigner. *change*: 0 for change, 1 for receive address. *address_index*: Addresses are numbered from index 0 in sequentially increasing manner. We're currently syncing the max used index for each branch between all parties when they connect, but we're open to considering removing the index sync and doing the more elegant used-address discovery via a gap limit, as discussed in BIP44https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki#address-gap-limit. We feel 20 might be too low though. *Wallet high-level description:* Each party generates their own extended master keypair and shares the extended purpose' public key with the others, which is stored encrypted. Each party can generate any of the other's derived public keys, but only his own private keys. *General address generation procedure:* When generating an address, each party can independently generate the N needed public keys. They do this by deriving the public key in each of the different trees, but using the same path. They can then generate the multisig script and the corresponding p2sh address. In this way, each path corresponds to an address, but the public keys for that address come from different trees. *Receive address case:* Each cosigner generates addresses only on his own branch. One of the n cosigners wants to receive a payment, and the others are offline. He knows the last used index in his own branch, because only he generates addresses there. Thus, he can generate the public keys for all of the others using the next index, and calculate the needed script for the address. *Example: *Cosigner #2 wants to receive a payment to the shared wallet. His last used index on his own branch is 4. Then, the path for the next receive address is m/$purpose/2/1/5. He uses this same path in all of the cosigners trees to generate a public key for each one, and from that he gets the new p2sh address. *Change address case:* Again, each cosigner generates addresses only on his own branch. One of the n cosigners wants to create an outgoing payment, for which he'll need a change address. He generates a new address using the same procedure as above, but using a separate index to track the used change addresses. *Example: *Cosigner #5 wants to send a payment from the shared wallet, for which he'll need a change address. His last used change index on his own branch is 11. Then, the path for the next change address is m/$purpose/5/0/12. He uses this same path in all of the cosigners trees to generate a public key for each one, and from that he gets the new p2sh address. *Transaction creation and signing:* When creating a transaction, first one of the parties creates a Transaction Proposal. This is a transaction that spends some output stored in any of the p2sh multisig addresses (corresponding to any of the copayers' branches). This proposal is sent to the other parties, who decide if they want to sign. If they approve the proposal, they can generate their needed private key for that specific address (using the same path that generated the public key in that address, but deriving the private key instead), and sign it. Once the proposal reaches m signatures, any
Re: [Bitcoin-development] New BIP32 structure for P2SH multisig wallets
I will just chime in that I've been working on a similar spec for Armory to implement P2SH multisig and I came up with basically an identical scheme. I think you covered most of what is needed. The one thing I did differently was try to match the BIP 32 structure, by keeping the original 3 levels (wallet, chain, addresses), and use 2*N chains to handle the N different parties generating receiving and change addresses. It's not necessary, but it follows more closely the three-level scheme that BIP 32 originally envisioned. I also concluded that the chain indices are ordered by lexicographical sorting of root public keys, but resorting each individual address. There are use cases where it will be necessary for parties to know how to combine public keys into a multi-sig address without knowing the root keys. Also, for the purposes of one-off types of escrow multi-sig, we have included a wallet locator field in the transaction that must be passed around. This wallet locator is stored with each key (perhaps at the time public keys are collected and merged), and passed around with transactions to be signed. This allows lightweight devices like hardware wallets, to recognize their own keys. It would encoded in a VAR_STR, and doesn't have to be meaningful to the other participants -- each device would look at all signing slots in a transaction (either singlesig or each key in a multisig) and would generate a public key along each path, and see if the result matches. If so, it can sign it. If not, it must be someone else's. I bring this up, because this multisig wallet structure you're talking about has a very simple wallet locator scheme -- all parties will use the same locator for a given receiving address. But that field should remain part of the data structure for each key, to accommodate all types of multisig, not just linked/parallel tree schemes. -Alan On 04/25/2014 06:27 PM, Manuel Araoz wrote: Hi, I'm part of the team building copay https://github.com/bitpay/copay, a multisignature P2SH HD wallet. We've been following the discussion regarding standardizing the structure for branches both on this list and on github (1 https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki, 2 https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki, 3 https://github.com/bitcoin/bips/blob/master/bip-0043.mediawiki, 4 https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki, 5 https://github.com/bitcoin/bips/pull/52). Soon, we realized the assumptions in the discussions were not true for a multisig hd wallet, so we wanted to share our current approach to that, to get feedback and see if we can arrive to a new standard (and possibly a new BIP) These are our assumptions: - N parties want to share an m-of-n wallet. - Each party must generate their master private keys independently. - Use multisig P2SH for all addresses. - Use BIP32 to derive public keys, then create a multisig script, and use the P2SH address for that. - The address generation process should not require communicating with other parties. (Thus, all parties must be able to generate all public keys) - Transaction creation + signing requires communication between parties, of course. - Following BIP43, we're be using: m / purpose' / * where /purpose/ is the hardened derivation scheme based on the new BIP number. We then define the following levels: m / purpose' / cosigner_index / change / address_index Each level has a special meaning detailed below: /cosigner_index/ http://en.wikipedia.org/wiki/Co-signing: the index of the party creating this address. The indices can be determined independently by lexicographically sorting the master public keys of each cosigner. /change/: 0 for change, 1 for receive address. /address_index/: Addresses are numbered from index 0 in sequentially increasing manner. We're currently syncing the max used index for each branch between all parties when they connect, but we're open to considering removing the index sync and doing the more elegant used-address discovery via a gap limit, as discussed in BIP44 https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki#address-gap-limit. We feel 20 might be too low though. *Wallet high-level description:* Each party generates their own extended master keypair and shares the extended purpose' public key with the others, which is stored encrypted. Each party can generate any of the other's derived public keys, but only his own private keys. *General address generation procedure:* When generating an address, each party can independently generate the N needed public keys. They do this by deriving the public key in each of the different trees, but using the same path. They can then generate the multisig script and the corresponding p2sh address. In this way, each path corresponds to an address, but the public keys for that address come
