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From: Jeff Garzik <jgarzik@bitpay.com>
Date: Mon, 23 Feb 2015 20:11:26 -0500
Message-ID: <CAJHLa0Orx7KD1R8ijdZHQS1+S=nuD9G4X_bkdRqUk44U-+OPbg@mail.gmail.com>
To: Eric Lombrozo <elombrozo@gmail.com>
Content-Type: text/plain; charset=UTF-8
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] replace-by-fee v0.10.0rc4
Precedence: list

On Sun, Feb 22, 2015 at 6:29 PM, Eric Lombrozo <elombrozo@gmail.com> wrote:
> As for 0-conf security, there are instances where 0-conf transactions make a
> lot of sense - i.e. paying for utilities, ISP, web hosting, or other such
> services which could be immediately shut off upon detection of a
> double-spend.

Indeed.  0-conf risk calculus must include business conditions.

Business cases such as placing an order for a physical good, making an
in-person purchase at a brick-n-mortar store, or subscriptions already
have countermeasures in place if funds go astray.  Order fulfilment
can be stopped, subscriptions cancelled, photos handed to police.

A thief wants to maximize return, which usually means either stealing
a few large amounts or many small amounts.  Double-spending against a
SatoshiDICE clone is easy to automate.  Many other purchase situations
are difficult to repeat without getting caught, or the level of effort
(cost) is greater than the payout of double-spending a small amount.
0-conf is typically only used for small amounts, where useful theft
relies on high repetition.

Purely online, mostly anonymous services like SatoshiDICE will be
easily attacked if they accept 0-conf transactions as there is little
customer/reputation relationship to leverage.  However, that
observation cannot be easily applied to most other businesses.

-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/