Subject: Re: [bitcoin-dev] Amend the BIP 123 process to include buried deployments

From: Marco Falke <[email-masked]>
Date: Sun, 18 Feb 2018 13:57:03 -0500

> They also do not require software coordination. Therefore, why should there be
> BIPs at all? Seems to me that we should instead add these documents to
> https://github.com/bitcoin-core/docs

Consensus is not trivial. I think documentation is important, even if
it seems simple to some.
Personally, I don't care too much where to place the documentation,
but the BIPs repo seems a good place, since it also hosts other
informational documents.

To prevent "two BIPs for every protocol change", related buried
deployments could be bundled. E.g. the ISM BIP 90 change.

On Wed, Feb 14, 2018 at 6:57 PM, Eric Voskuil <[email-masked]> wrote:
> On 02/14/2018 02:01 PM, Marco Falke via bitcoin-dev wrote:
>> I define a buried deployment as a consensus rule change that affects
>> validity of blocks that are buried by a sufficiently large number of
>> blocks in the current valid most-work chain,
>
> Sufficient for what, specifically?

Sufficiently large to prevent potential bike-shedding. The expected
number of blocks in two weeks could be considered a lower bound. Then
multiply that by 10 or 20.

>
>> but the current block (and all its parents) remain valid.
>
> Remain valid in the case where the depth assumption is "sufficient" to
> ensure that a chain split is not possible?
>
> If this was true (which it is not), it would imply that there is no
> reason to validate any block deeper than the most recent 25,000.
> Presumably this means that people may continuously rely on some
> authority (like Bitcoin Core?) to determine the checkpoint for tip-25,000.
>

Note that a checkpoint *freezes* the chain completely at a given
height. Buried deployments are *not* checkpoints.

Also note that buried deployments only make sense after a protocol
upgrade has happened (i.e. a soft fork or hard fork). If a miner has
the resources to cause a chain split, they could trivially do that
even in the complete absence of buried deployments. Buried deployments
are *not* a solution to 50% attacks.

>> BIP 123 suggests that BIPs in the consensus layer should be assigned a
>> label "soft fork" or "hard fork". However, I think the differentiation
>> into soft fork or hard fork should not be made for BIPs that document
>> buried deployments. In contrast to soft forks and hard forks, buried
>> deployments do not require community and miner coordination for a safe
>> deployment.
>
> They can only avoid this requirement based on the assumption that the
> hard fork cannot result in a chain split. This is not the case.
>
>> For a chain fork to happen due to a buried deployment, a massive chain
>> reorganization must be produced off of a block in the very past.
>
> In other words a "buried deployment" is a hard fork that is not likely
> to cause a chain split. This is a subjective subcategory of hard fork,
> not an independent category - unless maybe you can show that there is
> the 25,000 blocks number is an objective threshold.

Please note that a buried deployment can very well be a soft fork. I
think this makes it even clearer, that such a label makes no sense for
buried deployments.

>> In the extremely unlikely event of such a large chain reorganization,
>> Bitcoin's general security assumptions would be violated regardless of
>> the presence of a buried deployment.
>
> This is untrue. The "security assumptions" of Bitcoin do not preclude
> deep reorganizations.
> e
>