Hi ZmnSCPxj. > There is a position that fullnodes must be able to get a view of the UTXO set, and extension blocks (which are invisible to pre-extension-block fullnodes) means that fullnodes no longer have an accurate view of the UTXO set. > SegWit still provides pre-SegWit fullnodes with a view of the UTXO set, although pre-SegWit fullnodes could be convinced that a particular UTXO is anyone-can-spend even though they are no longer anyone-can-spend. > Under this point-of-view, then, extension block is "not" soft fork.
There's a way to do CT without an extension block and while still maintaining a correct UTXO set for old nodes. Perhaps it is similar what you meant with this comment (I believe you don't need to do a hardfork though) > Then it becomes impossible to move from confidential to public transactions with a value more than this counter, thus preventing inflation even if a future QC breach allows confidential transaction value commitments to be opened to any value. > (do note that a non-extension-block approach is a definite hardfork) Anyway, the method goes like this: Funds that go in to CT-mode are placed in a consensus/miner controlled reserve pool. To go out from CT back to normal, funds are then transferred back to the user from this pool. CT transactions seen from a non-upgraded node will be a transaction with 0 sat outputs. The actual rangeproof commitment could be placed in the script output or perhaps somewhere else. To enter CT-mode, you'll need to make a commitment. The transaction contains two outputs, one to the reserve pool containing the funds that can only be reclaimed when you go back to normal and one CT-output that you can start doing CT transactions from. I believe this could be made seamlessly with just a new bech32 address specifically for CT. Sending to a CT address could be done as easily as sending to a P2SH. In other words, it doesn't have to be two steps to send to someone over at CT space. > It is "evil" soft fork since older nodes are forced to upgrade as their intended functionality becomes impossible. > In this point-of-view, it is no better than a hard fork, which at least is very noisy about how older fullnode versions will simply stop working. Regarding normal extension blocks, I think it is definitely better than a hardfork since there's no way to be derailed from the network, even though you do not understand the rules fully. Sidenote, I think Trey Del Bonis is right regarding the terminology here, evil softforks/soft hardforks usually mean that you abandon the old chain to force all nodes to upgrade (https://petertodd.org/2016/forced-soft-forks ). Best Hampus Den tis 12 feb. 2019 kl 13:49 skrev ZmnSCPxj via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org>: > Good morning Kenshiro, > > > - Soft fork: old nodes see CT transactions as "sendtoany" transactions > > There is a position that fullnodes must be able to get a view of the UTXO > set, and extension blocks (which are invisible to pre-extension-block > fullnodes) means that fullnodes no longer have an accurate view of the UTXO > set. > SegWit still provides pre-SegWit fullnodes with a view of the UTXO set, > although pre-SegWit fullnodes could be convinced that a particular UTXO is > anyone-can-spend even though they are no longer anyone-can-spend. > > Under this point-of-view, then, extension block is "not" soft fork. > It is "evil" soft fork since older nodes are forced to upgrade as their > intended functionality becomes impossible. > In this point-of-view, it is no better than a hard fork, which at least is > very noisy about how older fullnode versions will simply stop working. > > > - Safe: if there is a software bug in CT it's impossible to create new > coins because the coins move from normal block to normal block as public > transactions > > I think more relevant here is the issue of a future quantum computing > breach of the algorithms used to implement confidentiality. > > I believe this is also achievable with a non-extension-block approach by > implementing a globally-verified publicly-visible counter of the total > amount in all confidential transaction outputs. > Then it becomes impossible to move from confidential to public > transactions with a value more than this counter, thus preventing inflation > even if a future QC breach allows confidential transaction value > commitments to be opened to any value. > > (do note that a non-extension-block approach is a definite hardfork) > > > - Capacity increase: the CT signature is stored in the extension block, > so CT transactions increase the maximum number of transactions per block > > This is not an unalloyed positive: block size increase, even via extension > block, translates to greater network capacity usage globally on all > fullnodes. > > Regards, > ZmnSCPxj > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >
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