From james.chiangwu at gmail.com  Fri Jul 13 14:54:18 2018
From: james.chiangwu at gmail.com (James Chiang)
Date: Fri, 13 Jul 2018 16:54:18 +0200
Subject: [Lightning-dev] Lightning-dev Digest, Vol 35,
	Issue 13 (sighash_noinput & watchtowers)
Message-ID: <CAHT-rsTPKv9i2vVntEp3jYaqiUL9BmAmNr7n1YV4LLj6t=b-3w@mail.gmail.com>

Hello everyone,
 I understand sighash_noinput allows us to reduce the number of stored
signatures, as it can spend any uxto with the respective one-use pub key
script.
In the case of watchtowers, are we not trading off privacy, as we are
revealing which states are related, right?

I'm trying to catch up my understanding on the various models here. The
txid_half + encrypted blob guarantees nothing is learned about each state
and how they relate unless a revocation must happen (but doesn't scale, one
blob per outsourced state). Once signatures are reused for multiple states
with sighash_noinput, how do we minimise information being disclosed to 3rd
party?

Many thanks in advance!

James


On Fri, Jul 13, 2018 at 2:00 PM, <
lightning-dev-request at lists.linuxfoundation.org> wrote:

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>    1. Re: [bitcoin-dev] BIP sighash_noinput (Rusty Russell)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 13 Jul 2018 09:34:14 +0930
> From: Rusty Russell <rusty at rustcorp.com.au>
> To: DING FENG <dingfeng12345 at gmail.com>, Luke Dashjr <luke at dashjr.org>
> Cc: Bitcoin Protocol Discussion
>         <bitcoin-dev at lists.linuxfoundation.org>,
>         lightning-dev at lists.linuxfoundation.org, Gregory Maxwell
>         <greg at xiph.org>
> Subject: Re: [Lightning-dev] [bitcoin-dev] BIP sighash_noinput
> Message-ID: <878t6gxapt.fsf at rustcorp.com.au>
> Content-Type: text/plain
>
> DING FENG <dingfeng12345 at gmail.com> writes:
> > Hi,
> >
> > I'm a junior developer and a bitcoin user.
> > And I have read this thread carefully.
> >
> > I'm very worried about "SIGHASH_NOINPUT".
> >
> > Because "SIGHASH_NOINPUT" looks will be widely used, and it makes reuse
> > address more dangerous.
>
> No.
>
> A wallet should *never* create a SIGHASH_NOINPUT to spend its own UTXOs.
> SIGHASH_NOINPUT is useful for smart contracts which have unique
> conditions, such as a pair of peers rotating keys according to an agreed
> schedule (eg. lightning).
>
> Cheers,
> Rusty.
>
>
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>
> End of Lightning-dev Digest, Vol 35, Issue 13
> *********************************************
>
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