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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Good morning ZmnSCPxj, Thank you for your answer. There is a position that fullnodes must be able to get a view of the UTXO s= et, and extension blocks (which are invisible to pre-extension-block fullno= des) means that fullnodes no longer have an accurate view of the UTXO set. I think old nodes don't need to know the CT part of the UTXO set. It would = be possible to move coins from normal address to CT address and the opposit= e, it would be written as "anyone-can-spend" transactions in the main block= so old nodes are fully aware of these transactions. Miners would enforce t= hat "anyone-can-spend" transactions are true. The full details of the trans= actions involving CT would be in the extension block. CT to CT transactions= don't need to be written in the main block. Maybe I'm missing some technic= al detail here but it looks good for me. > - Capacity increase: the CT signature is stored in the extension block, s= o 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 fullnod= es. Yes, there is an increase in block size and network usage but I think it wo= uld still be possible for people with regular computers to run a full node,= an people in developing countries could use light wallets. Regards ________________________________ From: ZmnSCPxj Sent: Monday, February 11, 2019 5:29 To: Kenshiro \[\]; Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Implementing Confidential Transactions in extens= ion blocks 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 s= et, and extension blocks (which are invisible to pre-extension-block fullno= des) 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, alt= hough pre-SegWit fullnodes could be convinced that a particular UTXO is any= one-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 int= ended 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 co= ins because the coins move from normal block to normal block as public tran= sactions I think more relevant here is the issue of a future quantum computing breac= h of the algorithms used to implement confidentiality. I believe this is also achievable with a non-extension-block approach by im= plementing 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 f= uture QC breach allows confidential transaction value commitments to be ope= ned 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, s= o 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 fullnod= es. Regards, ZmnSCPxj --_000_DB6PR10MB1832F0E339FD9B76E87BC64FA6640DB6PR10MB1832EURP_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Good morning ZmnSCPxj,

Thank you for your answer.

There is a position that fullnodes must be able to get a view of the UTX= O set, and extension blocks (which are invisible to pre-extension-block ful= lnodes) means that fullnodes no longer have an accurate view of the UTXO se= t.

I think old nodes don't need to know the CT part of the UTXO set. It would = be possible to move coins from normal address to CT address and the opposit= e, it would be written as "anyone-can-spend" transactions in the = main block so old nodes are fully aware of these transactions. Miners would enforce that "anyone-can-spend"= transactions are true. The full details of the transactions involving CT w= ould be in the extension block. CT to CT transactions don't need to be writ= ten in the main block. Maybe I'm missing some technical detail here but it looks good for me.


> - Capacity increase: the CT signature is stored in the extens= ion block, so CT transactions  increase the maximum number of transact= ions per block

This is not an unalloyed positive: block size increase, even via e= xtension block, translates to greater network capacity usage globally on al= l fullnodes.

Yes, there is an increase in block size and network usage but I think it wo= uld still be possible for people with regular computers to run a full node,= an people in developing countries could use light wallets.

Regards


From: ZmnSCPxj <ZmnSCPxj= @protonmail.com>
Sent: Monday, February 11, 2019 5:29
To: Kenshiro \[\]; Bitcoin Protocol Discussion
Subject: Re: [bitcoin-dev] Implementing Confidential Transactions in= extension blocks
 
Good morning Kenshiro,

> - Soft fork: old nodes see CT transactions as "sendtoany" tr= ansactions

There is a position that fullnodes must be able to get a view of the UTXO s= et, and extension blocks (which are invisible to pre-extension-block fullno= des) means that fullnodes no longer have an accurate view of the UTXO set.<= br> SegWit still provides pre-SegWit fullnodes with a view of the UTXO set, alt= hough pre-SegWit fullnodes could be convinced that a particular UTXO is any= one-can-spend even though they are no longer anyone-can-spend.

Under this point-of-view, then, extension block is "not" soft for= k.
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 t= ransactions

I think more relevant here is the issue of a future quantum computing breac= h of the algorithms used to implement confidentiality.

I believe this is also achievable with a non-extension-block approach by im= plementing 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 f= uture QC breach allows confidential transaction value commitments to be ope= ned 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<= br>
This is not an unalloyed positive: block size increase, even via extension = block, translates to greater network capacity usage globally on all fullnod= es.

Regards,
ZmnSCPxj
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