On 21 May 2013 01:59, Mark Friedenbach <mark@monetize.io> 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.

This is essentially name spacing. As registries grow namespaces become more important. In bitcoin's quest for decentrality there's also the question of who maintains the registry.

Some out of band algo/hash could work so long as there was a one to one relationship between the described object and the UUID. In this case the gensis block may not uniquely identify a coin.

The normal way to namespace a registry on the internet is to allow it to be a URI. In this case an http style uri has the added bonus side effect that it can be dereferencable and both human and machine readable. So yes something like org.bitcoin.* is good, just simply growing things to http style uris is cleaner, imho

Kind regards,
Mark Friedenbach

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