> On 6 Apr 2017, at 01:43, Christopher Jeffrey <c...@purse.io> wrote: > > >> This hits the biggest question I asked in my January post: do you want >> to allow direct exit payment to legacy addresses? As a block reorg >> will almost guarantee changing txid of the resolution tx, that will >> permanently invalidate all the child txs based on the resolution tx. >> This is a significant change to the current tx model. To fix this, you >> need to make exit outputs unspendable for up to 100 blocks. Doing >> this, however, will make legacy wallet users very confused as they do >> not anticipate funding being locked up for a long period of time. So >> you can’t let the money sent back to a legacy address directly, but >> sent to a new format address that only recognized by new wallet, which >> understands the lock up requirement. This way, however, introduces >> friction and some fungibility issues, and I’d expect people using >> cross chain atomic swap to exchange bitcoin and xbitcoin > > Yes, this issue is probably the biggest edge case in the proposal. > > I think there's two possible solutions: > > First solution: > > Like you said, add a maturity requirement for exiting outputs. Likely > lower than coinbase's 100 block requirement. To solve the issue of > non-upgraded wallets not being aware of this rule and spending early, > have upgraded mempool implementations accept/relay txs that contain > early spends of exits, but not mine them until they are mature. This way > non-upgraded wallets do not end up broadcasting transactions that are > considered invalid to the rest of the network.
This won’t solve the problem. Think about the following conversation: Alice (not upgraded): Please pay 1 BTC to my address 1ALicExyz Bob (upgraded): ok, paid, please check 10 minutes later Alice: received and confirmed, thanks! 5 minutes later: Carol (not upgraded): Please pay 0.5BTC to my address 3CaroLXXX Alice: paid, please check 1 hour later: Carol: it’s not confirmed. Have you paid enough fees? Alice: ok, I’ll RBF/CPFP it 2 hours later: Carol: it’s still not confirmed. Alice: I have already paid double fees. Maybe the network is congested and I need to pay more….. Repeat until the lock up period ends. So this so-called “softfork” actually made non-upgraded wallet totally unusable. If failed to meet the very important requirement of a softfork: backward compatibility More discussion: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-April/013985.html <https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-April/013985.html> > > Depending on how wallets handle reorgs, a non-upgraded wallet may put > reorg'd spend chains from exits back into an unconfirmed state, when in > reality they should probably delete them or mark them conflicted in some > way. This may be an acceptable compromise as the wallet will still see > the funds as unconfirmed when they really don't exist anymore, but maybe > unconfirmed is good enough. Users are pretty used to dropping > non-confirming txs from their wallet, and this is much better than > legacy wallets seeing there funds as confirmed when they could be > permanently reorged out at any moment. > > Second solution: > > Move all exiting outputs to the coinbase. This will enforce a 100 block > maturity requirement and non-upgraded wallets will be aware of this. This is also unacceptable. When someone says "Please pay 1 BTC to my address 1ALicExyz”, no one anticipates being paid by a coinbase output. Some exchanges like btc-e explicitly reject coinbase payment. Such deterioration in user experience is unacceptable. It basically forces everyone to upgrade, i.e. a hardfork with soft fork’s skin > > The first solution might require more implementation, but allows more > flexibility with the maturity requirement. The second solution is > possibly simpler, but sticks to a hard 100 block limit. > >> 1. Is it acceptable to have massive txid malleability and transaction >> chain invalidation for every natural happening reorg? Yes: the >> current spec is ok; No: next question (I’d say no) > > Answered above. > >> 2. Is locking up exit outputs the best way to deal with the problem? >> (I tried really hard to find a better solution but failed) > > You've probably thought about this more than anyone, so I'd say yes, it > may be the only way. Painful, but necessary. > >> 3. How long the lock-up period should be? Answer could be anywhere >> from 1 to 100 > > I imagine having something lower than 100 would be preferable to users, > maybe somewhere in the 5 to 15 range. A 15 block reorg on mainnet is > seriously unlikely unless something strange is happening. A 5 block > reorg is still pretty unlikely, but possible. The coinbase solution only > allows for 100 blocks though. > >> 4. With a lock-up period, should it allow direct exit to legacy >> address? (I think it’s ok if the lock-up is short, like 1-2 block. But >> is that safe enough?) > > I think so. Adding a kind of special address probably creates more > issues than it solves. As I explained above, no legacy wallet would anticipate a lock up. If you want to make a softfork, all burden of incompatibility must be taken by the upgraded system. Only allow exit to a new address guarantees that only upgraded wallet will see the locked-up tx: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-January/013490.html <https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-January/013490.html> > >> 5. Due to the fungibility issues, it may need a new name for the >> tokens in the ext-block > > I suppose the market will decide whether that's the case. > > It's worth noting, if segwit is not activated on the mainchain, it > creates a much bigger incentive to use the extension block, and > potentially ensures that users will have less of a reason to exit. > I think it’s unacceptable if malleability is not fixed in main chain, for 3 reasons: 1. a solution is *already* available and tested for > 1 year. 2. the deactivation design (which I think is an interesting idea) makes the ext block unsuitable for long-term storage of value. 3. LN over main chain allows instant exchange of main coin and xcoin without going through the ugly 2-way-peg process.
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