From: "Luke-Jr" <luke@dashjr.org>
To: bitcoin-development@lists.sourceforge.net
Date: Tue, 6 Dec 2011 16:10:39 -0500
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Subject: [Bitcoin-development] Version bytes "2.0"
Precedence: list

sipa made a nice specification for version numbers a while back, that seemed 
great at the time. However, there are concerns that it has overlooked a very 
important factor: usability in base58 encoding. The version currently chosen 
for script-based addresses (2) makes this excessively complicated for end 
users-- these addresses, once encoded, may begin with ANY of the following 
characters: 2opqrstuvwxyz

Taking this into account, as well as sipa's original goals, I have come up 
with the following proposal:
* Bits 128/64 define network class
** 0 = main network
** 64,128 = reserved
** 192 = test network
* Bits 32/16 define network
** 0 = Bitcoin
** 16,32 = reserved
** 48 = OTHER (next octet)
* Bits 8/4/2 define data class
** 0 = Public key hash
** 2 = Public key (raw)
** 4 = Script hash
** 6 = reserved
** 8 = Private key (raw)
** 10 = Signature
** 12 = reserved
** 14 = OTHER (next octet)
* Bit 1 is freely chosen (for aesthetic assignment)

Unlike sipa's proposal, however, I have (intentionally) neglected to consider 
the versions currently in use other than the widespread Bitcoin addresses. 
That means this reassigns the versions used by Namecoin and testnets, and 
probably messes with the (unmerged) key export format and signature formats.

It "wastes" 2 bits (64 and 1) to accomplish aesthetic norms. Bit 64 *could* be 
assigned in the future if we ever have a "crunch". By using the high bit (128) 
to designate test networks, all testnet addresses will now begin with '2'. 
Bitcoin script-hash (aka OP_EVAL) addresses are assigned version 5 (using the 
aesthetic +1), which means they always begin with '3'. Signatures are on 
version 10 and/or 11, beginning with '5'.

We get two first-class "networks" besides Bitcoin, addresses starting with '7' 
and 'E' (pubkey), and '9' and 'F' (script). I propose these should be assigned 
sparingly, only when a network has significant adoption-- the only one I would 
even *consider* might fit the requirement today is Namecoin. I would also 
suggest making merged mining support a requirement except for networks that 
have a proven-better proof-of-work (ie, NOT scrypt). Other networks can use 
the "other" value (thus beginning with 'L' and 'N') and a second octet (which 
can be divided up later).

Thoughts?

Luke