From: Matt Whitlock <bip@mattwhitlock.name>
To: Tamas Blummer <tamas@bitsofproof.com>
Date: Sat, 29 Mar 2014 04:54:03 -0400
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Cc: bitcoin-development@lists.sourceforge.net
Subject: Re: [Bitcoin-development] Presenting a BIP for Shamir's Secret
	Sharing of Bitcoin private keys
Precedence: list

On Saturday, 29 March 2014, at 4:51 am, Matt Whitlock wrote:
> On Saturday, 29 March 2014, at 9:44 am, Tamas Blummer wrote:
> > I used Shamir's Secret Sharing to decompose a seed for a BIP32 master key, that is I think more future relevant than a single key.
> > Therefore suggest to adapt the BIP for a length used there typically 16 or 32 bytes and have a magic code to indicate its use as key vs. seed.
> 
> Master keys of 32 bytes would work as-is, as ordinary private keys are also 32 bytes. Secrets of other lengths could be supported if the function that generates a[i] from a[i-1] (which is presently SHA-256) were replaced with a function having parameterized output length, such as scrypt.

Actually, secrets with value greater than secp256k1_N cannot be supported because the modular arithmetic would destroy them. But any secret smaller than 256 bits would be fine.