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From: "Russell O'Connor" <roconnor@blockstream.com>
To: Tim Ruffing <crypto@timruffing.de>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Overview of anti-covert-channel signing techniques
Date: Sun, 22 Mar 2020 11:30:34 -0400	[thread overview]
Message-ID: <CAMZUoKkNvdegQFzosD-_DHZuu+qiCS6dKXvW7vDTpuB+T_j7dg@mail.gmail.com> (raw)
In-Reply-To: <c14db3d600c0c60bbf06ea832fc438a5c9fd97da.camel@timruffing.de>

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On Sun, Mar 22, 2020 at 5:43 AM Tim Ruffing <crypto@timruffing.de> wrote:

> On Sat, 2020-03-21 at 12:59 -0400, Russell O'Connor wrote:
> > Public keys are deterministic and can be spot checked.  In fact,
> > AFAIU if hardened HD key derivations are not used, then spot checking
> > is very easy.
> >
> > While spot checking isn't ideal, my original concern with the
> > synthetic none standard proposal was that it is inherently non-
> > deterministic and cannot ever be spot checked.  This is why anti-
> > covert signing protocols are so important if we are going to use
> > synthetic nonces.
>
> If spot checking means checking a few instances, then I think this is a
> pretty weak defense. What if the device starts to behave differently
> after a year?
>

I agree, which is why there perhaps is merit in using a non-hardered
derivation path so that the software side of a hardware wallet can check
the pubkey. Though I understand there are some disadvantages to the
non-hardened paths.

However, spot checking can even be done retroactively (and thoroughly).
Again, I agree that this is less than ideal, but does let you take some
action once you notice a deviation.

Your claim is that if we don't fix the pubkey issue there is no point in
fixing the signature issue.  I disagree.  While I think both issues need to
be fully addressed, the issues around the original proposed
non-deterministic signature scheme are far more severe. The proposal would
move us from a deterministic scheme, where spot checks are possible, with
all the caveats that entails, to a non-deterministic scheme where spot
checks are impossible.  My hope is that we can standardise a scheme that
has the advantages of non-determinism without the threat of covert channels.

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  reply	other threads:[~2020-03-22 15:30 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-03 21:35 [bitcoin-dev] Overview of anti-covert-channel signing techniques Pieter Wuille
2020-03-21 13:34 ` Tim Ruffing
2020-03-21 16:59   ` Russell O'Connor
2020-03-22  9:43     ` Tim Ruffing
2020-03-22 15:30       ` Russell O'Connor [this message]
2020-03-22 15:38         ` Tim Ruffing
2020-03-21 20:29   ` Marko Bencun
2020-03-23 14:38 ` Dustin Dettmer
2020-03-24  7:49   ` Tim Ruffing
2020-03-24 14:51     ` Dustin Dettmer

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