Subject: Re: [Bitcoin-development] Presenting a BIP for Shamir's Secret Sharing of Bitcoin private keys

From: Jeff Garzik <[email-masked]>
Date: Sat, 29 Mar 2014 10:19:20 -0400

On Sat, Mar 29, 2014 at 10:10 AM, Matt Whitlock <[email-masked]> wrote:
> Multisig does not allow for the topology I described. Say the board has seven directors, meaning the majority threshold is four. This means the organization needs the consent of six individuals in order to sign a transaction: the president, the CFO, and any four of the board members. A 6-of-9 multisig would not accomplish the same policy, as then any six board members could successfully sign a transaction without the consent of the president or CFO. Of course the multi-signature scheme could be expanded to allow for hierarchical threshold topologies, or Shamir's Secret Sharing can be used to distribute keys at the second level (and further, if desired).

Disagree with "does not allow"  Review bitcoin's script language.

Bitcoin script can handle the use case you describe.  Add conditionals
to the bitcoin script, OP_IF etc.  You can do 'multisig AND multisig'
type boolean logic entirely in script, and be far more flexible than a
single CHECKMULTISIG affords.

-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/