As a long term silent reader of this list, I felt compelled to comment on this address expiration topic. I don't believe that address expiration should be part of the protocol. I think instead that the "sending" feature should by default offer guidance to request a fresh address from the recipient. Also allow the receiver of funds to be able to generate an "invoice" that the sender acts on. I also think that re-directs are fraught with privacy issues. At the end of the day, the ultimate burden is on the sender (with much self interest from the receiver) that the correct address is being used. ________________________________ From: bitcoin-dev-bounces@lists.linuxfoundation.org on behalf of Chris Priest via bitcoin-dev Sent: Wednesday, September 27, 2017 3:35 PM To: Peter Todd; Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Address expiration times should be added to BIP-173 A better solution is to just have the sending wallet check to see if the address you are about to send to has been used before. If it's a fresh address, it sends it through without any popup alert. If the address has history going back a certain amount of time, then a popup comes up and notifies the sender that they are sending to a non-fresh address that may no longer be controlled by the receiver anymore. Also, an even better idea is to set up an "address expiration service". When you delete a wallet, you first send off an "expiration notice" which is just a message (signed with the private key) saying "I am about to delete this address, here is my new address". When someone tries to send to that address, they first consult the address expiration service, and the service will either tell them "this address is not expired, proceed", or "this address has been expired, please send to this other address instead...". Basically like a 301 redirect, but for addresses. I don't think address expiration should be part of the protocol. On Wed, Sep 27, 2017 at 10:06 AM, 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? -- https://petertodd.org 'peter'[:-1]@petertodd.org _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev -- Chris Priest 786-531-5938