Date: Thu, 7 Sep 2017 14:09:02 -0400
From: Peter Todd <pete@petertodd.org>
To: Jonas Schnelli <dev@jonasschnelli.ch>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <20170907180902.GC13727@fedora-23-dvm>
References: <0d405f5d-c0a4-bad7-b6c3-08ba4424bf17@satoshilabs.com>
	<A806D2EB-744F-41A9-91C1-603F89E9005B@jonasschnelli.ch>
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In-Reply-To: <A806D2EB-744F-41A9-91C1-603F89E9005B@jonasschnelli.ch>
User-Agent: Mutt/1.5.23 (2014-03-12)
Subject: Re: [bitcoin-dev] Proposal: Extended serialization format for
 BIP-32 wallets
Precedence: list


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On Thu, Sep 07, 2017 at 09:47:16AM -0700, Jonas Schnelli via bitcoin-dev wr=
ote:
> Thanks for the proposal.
>=20
> Three points it could see as possible improvements:
>=20
> 1.
> From what I know, the exact birthday in seconds doesn=E2=80=99t matter th=
at much therefore it may be possible to just use 13 or 16bits to create a r=
epresentation in week from 2009-01-09 00:00 UTC. 13bits would give you 157 =
years.
> Always round down to the beginning of the week when the key was created.
> But not sure if it=E2=80=99s worth to save ~two bytes for that.
> Also not sure if the key-birthday in seconds could have a security or pri=
vacy implication (week maybe better).

Note how private key birthday is a potential privacy issue in certain cases.
Rare of course, because usually you don't release your private keys! But us=
ers
will on occasion have those keys be compromised.

Personally, I'd advocate rounding down to month-level resolution, as that
should be both enough to handle any likely reorg scenario, and it's still a
precision that won't add much extra scanning ot any reasonably old (~1yr)
wallet.

Note also how if transactions created with private keys in a seed use
nLockTime, you can ensure coins won't exist in a block older than the seed
birthday by simply ensuring that nLockTime is set to a more recent date then
that birthday under all circumstances.

--=20
https://petertodd.org 'peter'[:-1]@petertodd.org

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