To: bitcoin-dev@lists.linuxfoundation.org
From: Andreas Schildbach <andreas@schildbach.de>
Date: Thu, 28 Sep 2017 12:09:59 +0200
Message-ID: <oqihpf$5gc$1@blaine.gmane.org>
References: <20170927160654.GA12492@savin.petertodd.org>
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In-Reply-To: <20170927160654.GA12492@savin.petertodd.org>
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Subject: Re: [bitcoin-dev] Address expiration times should be added to
	BIP-173
Precedence: list

This feels redundant to me; the payment protocol already has an
expiration time.


On 09/27/2017 06:06 PM, Peter Todd via bitcoin-dev wrote:
> Re-use of old addresses is a major problem, not only for privacy, but also
> operationally: services like exchanges frequently have problems with users
> sending funds to addresses whose private keys have been lost or stolen; there
> are multiple examples of exchanges getting hacked, with users continuing to
> lose funds well after the actual hack has occured due to continuing deposits.
> This also makes it difficult operationally to rotate private keys. I personally
> have even lost funds in the past due to people sending me BTC to addresses that
> I gave them long ago for different reasons, rather than asking me for fresh
> one.
> 
> To help combat this problem, I suggest that we add a UI-level expiration time
> to the new BIP173 address format. Wallets would be expected to consider
> addresses as invalid as a destination for funds after the expiration time is
> reached.
> 
> Unfortunately, this proposal inevitably will raise a lot of UI and terminology
> questions. Notably, the entire notion of addresses is flawed from a user point
> of view: their experience with them should be more like "payment codes", with a
> code being valid for payment for a short period of time; wallets should not be
> displaying addresses as actually associated with specific funds. I suspect
> we'll see users thinking that an expired address risks the funds themselves;
> some thought needs to be put into terminology.
> 
> Being just an expiration time, seconds-level resolution is unnecessary, and
> may give the wrong impression. I'd suggest either:
> 
> 1) Hour resolution - 2^24 hours = 1914 years
> 2) Month resolution - 2^16 months = 5458 years
> 
> Both options have the advantage of working well at the UI level regardless of
> timezone: the former is sufficiently short that UI's can simply display an
> "exact" time (though note different leap second interpretations), while the
> latter is long enough that rounding off to the nearest day in the local
> timezone is fine.
> 
> Supporting hour-level (or just seconds) precision has the advantage of making
> it easy for services like exchanges to use addresses with relatively short
> validity periods, to reduce the risks of losses after a hack. Also, using at
> least hour-level ensures we don't have any year 2038 problems.
> 
> Thoughts?
> 
> 
> 
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