From: "Luke-Jr" <luke@dashjr.org>
To: bitcoin-development@lists.sourceforge.net
Date: Tue, 21 May 2013 04:04:28 +0000
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Subject: Re: [Bitcoin-development] UUID to identify chains (payment protocol
	and elsewhere)
Precedence: list

Bitcoin currently uses raw hashes extensively as UUIDs; whether the payment 
protocol should be influence by that or not, I've not given thought to yet.

Some alt coins may share a blockchain, or even merely the genesis block (two 
currently do; despite one of those being a scamcoin, I think the possibility 
should not be dismissed). Because of this, requiring a 1:1 mapping between 
genesis block and chain or coin seems non-ideal.

On Monday, May 20, 2013 11:59:39 PM Mark Friedenbach wrote:
> At the developer round-table it was asked if the payment protocol would
> alt-chains, and Gavin noted that it has a UTF-8 encoded string
> identifying the network ("main" or "test"). As someone with two
> proposals in the works which also require chain/coin identification (one
> for merged mining, one for colored coins), I am opinionated on this. I
> believe that we need a standard mechanism for identifying chains, and
> one which avoids the trap of maintaining a standard registry of
> string-to-chain mappings.
> 
> Any chain can be uniquely identified by its genesis block, 122 random
> bits is more than sufficient for uniquely tagging chains/colored assets,
> and the low-order 16-bytes of the block's hash are effectively random.
> With these facts in mind, I propose that we identify chains by UUID.
> 
> So as to remain reasonably compliant with RFC 4122, I recommend that we
> use Version 4 (random) UUIDs, with the random bits extracted from the
> double-SHA256 hash of the genesis block of the chain. (For colored
> coins, the colored coin definition transaction would be used instead,
> but I will address that in a separate proposal and will say just one
> thing about it: adopting this method for identifying chains/coins will
> greatly assist in adopting the payment protocol to colored coins.)
> 
> The following Python code illustrates how to construct the chain
> identifier from the serialized genesis block:
> 
>      from hashlib import sha256
>      from uuid import UUID
>      def chain_uuid(serialized_genesis_block):
>          h = sha256(serialized_genesis_block).digest()
>          h = sha256(h).digest()
>          h = h[:16]
>          h = ''.join([
>              h[:6],
>              chr(0x40 | ord(h[6]) & 0x0f),
>              h[7],
>              chr(0x80 | ord(h[8]) & 0x3f),
>              h[9:]
>          ])
>          return UUID(bytes=h)
> 
> And some example chain identifiers:
> 
>      mainnet:  UUID('6fe28c0a-b6f1-4372-81a6-a246ae63f74f')
>      testnet3: UUID('43497fd7-f826-4571-88f4-a30fd9cec3ae')
>      namecoin: UUID('70c7a9f0-a2fb-4d48-a635-a70d5b157c80')
> 
> As for encoding the chain identifier, the simplest method is to give
> "network" the "bytes" type, but defining a "UUID" message type is also
> possible. In either case bitcoin mainnet would be the default, so the
> extra 12 bytes (vs: "main" or "test") would only be an issue for
> alt-chains or colored coins.
> 
> Kind regards,
> Mark Friedenbach
> 
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