> I’m confident that we could work with the miners who we have good relationships with to start including the root hash of the (lagging) UTXO set in their coinbase transactions, in order to begin transforming this idea into reality.

By itself, this wouldn't work without a way for a new node to differentiate between a false history and a true one.

>  We could also issue regular transactions from “semi-trusted” addresses controlled by known people that include the same root hash in an OP_RETURN output, which would allow cross-checking against the miners’ UTXO commitments, as part of this initial “prototype”

This might work, but I fail to understand how a new node could verify an address / transaction without a blockchain to back it.  Even if it could, it becomes dependent upon those addresses not being compromised, and the owners of those addresses would become targets for potential government operations.

Having the software silently attempt to resolve the problem is risky unless it is foolproof.  Otherwise, users will assume their software is showing them the correct history/numbers implicitly, and if the change the utxo attacker made was small, the users might be able to follow the main chain totally until it was too late and the attacker struck with an address that otherwise never transacted.  Sudden, bizarre, hard to debug fork and potentially double spend against people who picked up the fraudulent utxo.  

Users already treat wallet software with some level of suspicion, asking if they can trust x or y or z, or like the portion of the BU community convinced that core has been compromised by blockstream bigwigs.  Signed releases could provide the same thing but would encourage both open-source security checks of the signed utxo's and potentially of users to check download signatures.

Either approach is better than what we have now though, so I'd support anything.

On Wed, Mar 29, 2017 at 1:28 PM, Peter R via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
I believe nearly everyone at Bitcoin Unlimited would be supportive of a UTXO check-pointing scheme.  I’d love to see this happen, as it would greatly reduce the time needed to get a new node up-and-running, for node operators who are comfortable trusting these commitments.  

I’m confident that we could work with the miners who we have good relationships with to start including the root hash of the (lagging) UTXO set in their coinbase transactions, in order to begin transforming this idea into reality.  We could also issue regular transactions from “semi-trusted” addresses controlled by known people that include the same root hash in an OP_RETURN output, which would allow cross-checking against the miners’ UTXO commitments, as part of this initial “prototype” system.

This would "get the ball rolling" on UTXO commitments in a permissionless way (no one can stop us from doing this). If the results from this prototype commitment scheme were positive, then perhaps there would be support from the community and miners to enforce a new rule which requires the (lagging) root hashes be included in new blocks.  At that point, the UTXO commitment scheme is no longer a prototype but a trusted feature of the Bitcoin network.    

On that topic, are there any existing proposals detailing a canonical ordering of the UTXO set and a scheme to calculate the root hash?

Best regards,
Peter


On Mar 29, 2017, at 12:33 PM, Daniele Pinna via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

What about periodically committing the entire UTXO set to a special checkpoint block which becomes the new de facto Genesis block? 

Daniele 

------------------------------

Message: 5
Date: Wed, 29 Mar 2017 16:41:29 +0000
From: Andrew Johnson <andrew.johnson83@gmail.com>
To: David Vorick <david.vorick@gmail.com>
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Hard fork proposal from last week's meeting
Message-ID:
        <CAAy62_+JtoAuM-RsrAAp5eiGiO+OHLDjzqgbnF2De7TUU7TyYg@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

I believe that as we continue to add users to the system by scaling
capacity that we will see more new nodes appear, but I'm at a bit of a loss
as to how to empirically prove it.

I do see your point on increasing load on archival nodes, but the majority
of that load is going to come from new nodes coming online, they're the
only ones going after very old blocks.   I could see that as a potential
attack vector, overwhelm the archival nodes by spinning up new nodes
constantly, therefore making it difficult for a "real" new node to get up
to speed in a reasonable amount of time.

Perhaps the answer there would be a way to pay an archival node a small
amount of bitcoin in order to retrieve blocks older than a certain cutoff?
Include an IP address for the node asking for the data as metadata in the
transaction...  Archival nodes could set and publish their own policy, let
the market decide what those older blocks are worth.  Would also help to
incentivize running archival node, which we do need.  Of course, this isn't
very user friendly.

We can take this to bitcoin-discuss, if we're getting too far off topic.


On Wed, Mar 29, 2017 at 11:25 AM David Vorick <david.vorick@gmail.com>
wrote:

>
> On Mar 29, 2017 12:20 PM, "Andrew Johnson" <andrew.johnson83@gmail.com>
> wrote:
>
> What's stopping these users from running a pruned node?  Not every node
> needs to store a complete copy of the blockchain.
>
>
> Pruned nodes are not the default configuration, if it was the default
> configuration then I think you would see far more users running a pruned
> node.
>
> But that would also substantially increase the burden on archive nodes.
>
>
> Further discussion about disk space requirements should be taken to
> another thread.
>
>
> --
Andrew Johnson
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