Subject: Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism

From: Aaron Voisine <[email-masked]>
Date: Wed, 10 Jun 2015 12:19:36 -0700

It could be done by agreeing on a data format and encoding it in an
op_return output in the coinbase transaction. If it catches on it could
later be enforced with a soft fork.

For real up-to-the-minute fee calculations you're also going to want to
look at the current mempool, how many transactions are waiting, what fees
they're paying, etc, but of course that information is susceptible to sybil
attack.

In practice what we're doing for now is using services like blockcypher
who's business is improving reliability of zero-conf to tell us what
fee-per-kb is needed, and then putting a hard coded range around it to
protect against the service being compromised. This is also the kind of
thing being done for exchange rate data which is probably the bigger
security risk until bitcoin becomes the standard unit of account for the
planet.

Aaron Voisine
co-founder and CEO
breadwallet.com

On Wed, Jun 10, 2015 at 10:37 AM, Nathan Wilcox <[email-masked]>
wrote:

> [I'm currently wading through bitcoin-development. I'm still about a month
> behind, so I apologize in advance for any noisy redundancy in this post.]
>
> While reading about blocksize, I've just finished Mike Hearn's blog post
> describing expected systemic behavior as actual blocks approach the current
> limit (with or without non-protocol-changing implementation improvements):
>
> https://medium.com/@octskyward/crash-landing-f5cc19908e32
>
>
> One detail Mike uses to argue against the "fee's will save us" line of
> reasoning is that wallets have no good way to learn fee information.
>
> So, here's a proposal to fix that: put fee and (and perhaps block size,
> UTXO, etc...) statistics into the locally-verifiable data available to SPV
> clients (ie: block headers).
>
>
> It's easy to imagine a hard fork that places details like per-block total
> fees, transaction count, fee variance, UTXO delta, etc... in a each block
> header. This would allow SPV clients to rely on this data with the same
> PoW-backed assurances as all other header data.
>
> This mechanism seems valuable regardless of the outcome of blocksize
> debate. So long as fees are interesting or important, SPV clients should
> know about them. (Same for other stats such as UTXO count.)
>
> Upgrading the protocol without a hard-fork may be possible and is left as
> an exercise for the reader. ;-)
>
> --
> Nathan Wilcox
> Least Authoritarian
>
> email: [email-masked]
> twitter: @least_nathan
> PGP: 11169993 / AAAC 5675 E3F7 514C 67ED  E9C9 3BFE 5263 1116 9993
>
>
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