From: Matt Whitlock <bip@mattwhitlock.name>
To: Tamas Blummer <tamas@bitsofproof.com>,
	bitcoin-development@lists.sourceforge.net
Date: Sat, 29 Mar 2014 12:54:11 -0400
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Subject: Re: [Bitcoin-development] Presenting a BIP for Shamir's Secret
	Sharing of Bitcoin private keys
Precedence: list

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.

I have expanded the BIP so that it additionally applies to BIP32 master seeds of sizes 128, 256, and 512 bits.

https://github.com/whitslack/btctool/blob/bip/bip-xxxx.mediawiki

The most significant change versus the previous version is how the coefficients of the polynomials are constructed. Previously they were SHA-256 digests. Now they are SHA-512 digests, modulo a prime number that is selected depending on the size of the secret.