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Date: Wed, 15 Jan 2014 17:32:31 -0800
Message-ID: <CAAS2fgTRKgkO15VUvVgttP-iEBNF4=G+++Xo-XsaRBmOxyXXKA@mail.gmail.com>
From: Gregory Maxwell <gmaxwell@gmail.com>
To: Jeremy Spilman <jeremy@taplink.co>
Content-Type: text/plain; charset=UTF-8
Cc: "bitcoin-development@lists.sourceforge.net"
	<bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] unlinakble static address? & spv-privacy
 (Re: Stealth Addresses)
Precedence: list

On Wed, Jan 15, 2014 at 5:02 PM, Jeremy Spilman <jeremy@taplink.co> wrote:
> Choosing how many bits to put in the prefix may be difficult, particularly
> if transaction load changes dramatically over time. 0 or 1 bits may be
> just fine for a single user running their own node, whereas a central
> service might want 4 or 5 bits to keep their computation costs scalable.

Ignoring prefixes the cost for each reusable address is only a small
percentage of the full node cost (rational: each transaction has one
or more ECDSA signatures, and the derivation is no more expensive), so
I would only expect computation to be an issue for large centralized
services. (non-full nodes suffer more from just the bandwidth impact).

I'd point out that regardless of how long the desired prefix is, the
encoded prefix should probably always be constant length in all
reusable addresses. If you don't want a particular prefix then the
sender should just pick random data for the rest of the space. There
is no need to publish any additional distinguishing data in the form
of how long the prefix is.