[bitcoin-dev] Alternative chain support for payment protocol

[Ross Nicoll <jrn@jrn.me.uk>]

BIP 70 currently lists two networks, main and test (inferred as 
testnet3) for payment protocol requests. This means that different 
testnets cannot be supported trivially, and the protocol cannot be used 
for alternative coins (or, lacks context to indicate which coin the 
request applies to, which is particularly dangerous in cases where coins 
share address prefixes).

I propose adding a new optional "genesis" field as a 16 byte sequence 
containing the SHA-256 hash of the genesis block of the network the 
request belongs to, uniquely identifying chains without any requirement 
for a central registry. For backwards compatibility, the "network" field 
would contain "main" for Bitcoin main net, "test" for Bitcoin testnet3, 
and "other" for other networks apart from those two.

I'd appreciate initial feedback on the idea, and if there's no major 
objections I'll raise this as a BIP.

Ross