Subject: Re: [Bitcoin-development] New standard transaction types: time to schedule a blockchain split?

From: Gregory Maxwell <[email-masked]>
Date: Wed, 24 Aug 2011 11:45:09 -0400

On Wed, Aug 24, 2011 at 11:12 AM, Gavin Andresen
<[email-masked]> wrote:
> It seems to me the fastest path to very secure, very-hard-to-lose
> bitcoin wallets is multi-signature transactions.
>
> To organize this discussion: first, does everybody agree?

It's a good tool which we should have in our tool-belt.

Though it's a bit of when you are a hammer all problems are nails.
This issue can also be addressed by things like external private key
protectors.  But someone would have to build one.

Someone might be more inclined to build such a thing if the software
had good support for tracking public keys without private keys, and
generating unsigned transactions for export to the device for signing.

> ByteCoin pointed to a research paper that gives a scheme for splitting
> a private key between two people, neither of which every knows the
[snip]
> So I'm assuming that is NOT the fastest way to solving the problem.

Regardless, it might be useful to contact the authors.

> I still think it is a good idea to enable a set of new 'standard'
> multisignature transactions, so they get relayed and included into
> blocks.  I don't want to let "the perfect become the enemy of the
> good" -- does anybody disagree?

I agree.

> The arguments against are that if the proposed standard transactions
> are accepted, then the next step is to define a new kind of bitcoin
> address that lets coins be deposited into a multisignature-protected
> wallet.
>
> And those new as-yet-undefined bitcoin addresses will have to be 2 or
> 3 times as big as current bitcoin addresses, and will be incompatible
> with old clients.
>
> So, if we are going to have new releases that are incompatible with
> old clients why not do things right in the first place, implement or
> enable opcodes so the new bitcoin addresses can be small, and schedule
> a block chain split for N months from now.

One way of doing this would be to have an address which hashes an
ordered concatenation of many addresses (perhaps plus a length
argument). To redeem you provide the public keys which are signing,
plus the addresses which aren't signing, and the receiver validates.

If it can be done, then yes, I agree it would be worth forking the chain.

This _feels_ like something which could and should be done with the
existing (but disabled opcodes).

It's not exclusive, however, with a long N-address address type for
multisig destinations.  We could support that _now_ and defer the
'compressed version' until after people have experience with this
usage.  The only cost would be supporting this address type forever,
which isn't that bad.

It's also important to note that incompatibility wouldn't be complete:
The only limit is that old clients couldn't send funds to escrow
addresses— which is an issue no matter how you encode the information.