Date: Sun, 3 Nov 2013 01:41:11 -0500
From: Timo Hanke <timo.hanke@web.de>
To: Thomas Voegtlin <thomasv1@gmx.de>
Message-ID: <20131103064111.GI16611@crunch>
References: <trinity-ba3941a0-f758-4372-b431-c64e9b44328a-1382635758149@3capp-gmx-bs09>
	<CAJna-HjgpRhLdVGh+prx54VezHaH1vXGpPotW1Xkz2tiAiWrbg@mail.gmail.com>
	<526BDEC2.2090709@gmx.de>
	<CAJna-HgH1g8iiSvxXrJuga808SQJ6DKo4AYw4fxpwTRCsL+EyQ@mail.gmail.com>
	<CAPg+sBiuLJJV3pB-EF3O9sgB_Z3tuLhEg9k=A9mcxJvgy3UQSw@mail.gmail.com>
	<52721F47.30206@gmx.de>
	<CAJna-Hj+q7oyTj8SWiVESPt5Web-mLuDhv7yA8zF5wRD81aBXA@mail.gmail.com>
	<5274C99A.8060304@gmx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5274C99A.8060304@gmx.de>
User-Agent: Mutt/1.5.21 (2010-09-15)
Cc: bitcoin-development@lists.sourceforge.net
Subject: Re: [Bitcoin-development] Proposal to replace BIP0039
Precedence: list
Reply-To: timo.hanke@web.de

On Sat, Nov 02, 2013 at 10:44:58AM +0100, Thomas Voegtlin wrote:
> 
> >To be specific, we (in cooperation with / inspired by Timo Hanke)
> >developed method how to prove that the seed generated by Trezor
> >has been created using combination of computer-provided entropy
> >and device-provided entropy, without leaking full private
> >information to other computer, just because we want Trezor to be
> >blackbox-testable and fully deterministic (seed generation is
> >currently the only operation which uses any source of RNG).
> >
> 
> Thanks for the explanation. Here is how I understand how it works,
> please correct me if I'm wrong:
> 
> The user's computer picks a random number a, the Trezor picks a
> random number b.
> Trezor adds a and b in the secp256k1 group, and this creates a
> master private key k.
> Trezor sends the corresponding master public key K to the computer.
> Thus, the computer can check that K was derived from a, without knowing b.

No. You mean the computer would use B for this check? 
(k,K) could be rigged by Trezor, who computes b as k-a.

Timo

> This also allows the computer to check that any bitcoin address
> derived from K is derived from a, without leaking b. (and
> reciprocally)
> 
> However, it seems to me that this property will work only with bip32
> public derivations; if a private derivation is used, don't you need
> to know k?
> 
> 
> 

-- 
Timo Hanke
PGP 1EFF 69BC 6FB7 8744 14DB  631D 1BB5 D6E3 AB96 7DA8