Subject: Re: [bitcoin-dev] Uniquely identifying forked chains

From: Jorge Timón <[email-masked]>
Date: Fri, 28 Aug 2015 22:45:29 +0200

On Fri, Aug 28, 2015 at 10:15 PM, Matt Whitlock via bitcoin-dev
<[email-masked]> wrote:
> Why would you use a hash of hashes? Wouldn't it be simpler and just as effective to use either:
>
> 1) the genesis block hash, or

If it's a new chain, we're talking about a "spinoffs"
https://bitcointalk.org/index.php?topic=563972.0

> 2) the block hash of the first block in a fork?

Yes, this seems like the best solution in the schism hardfork case.
What both sides of a schism hardfork would want is to avoid hurting
bystander users who can't tell the difference between the old and the
new currency/chain.

I should extend BIP99's section on schism hardforks.
Anybody else is welcomed to propose changes to the BIP draft, just PR
to this branch:

https://github.com/jtimon/bips/tree/bip-forks

> Every block hash in a chain implicitly subsumes the genesis block hash of that chain, so there's no need to incorporate the genesis block hash again.
>
>
> On Saturday, 29 August 2015, at 1:27 am, gladoscc via bitcoin-dev wrote:
>> There has been discussion of using the genesis block hash to identify
>> chains in BIP 21 (bitcoin:// URI scheme). However, this does not allow
>> identification between blockchain forks building upon the same genesis
>> block. While many see this as undesirable, I think it is inevitable that
>> this will eventually happen at some point, and think it is best to build
>> systems redundantly.
>>
>> I propose identifying blockchains for BIP 21 and any other relevant needs
>> through:
>>
>> 1) the genesis block hash for a new chain, or
>> 2) a hash of the genesis block hash,  concatenated with block hash(es) of
>> fork point(s) for a fork chain
>>
>> This would support forks, forks of forks, forks of forks of forks, etc
>> while preserving a fixed length chain identifier.
>>
>> If a user wants to specify "whatever chain is the longest with PoW", they
>> would use (1). In times where multiple chains are coexisting and being
>> actively mined, a user can use (2) to specifically identify a chain.
>>
>> Thoughts?
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