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From: Eric Voskuil <eric@voskuil.org>
In-Reply-To: <20160628203605.GA1328@fedora-21-dvm>
Date: Tue, 28 Jun 2016 23:22:23 +0200
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To: Peter Todd <pete@petertodd.org>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP 151
Precedence: list


> On Jun 28, 2016, at 10:36 PM, Peter Todd <pete@petertodd.org> wrote:
>=20
>> On Tue, Jun 28, 2016 at 10:29:54PM +0200, Eric Voskuil wrote:
>>=20
>>=20
>>>> On Jun 28, 2016, at 10:14 PM, Peter Todd <pete@petertodd.org> wrote:
>>>>=20
>>>> On Tue, Jun 28, 2016 at 08:35:26PM +0200, Eric Voskuil wrote:
>>>> Hi Peter,
>>>>=20
>>>> What in this BIP makes a MITM attack easier (or easy) to detect, or inc=
reases the probability of one being detected?
>>>=20
>>> BIP151 gives users the tools to detect a MITM attack.
>>>=20
>>> It's kinda like PGP in that way: lots of PGP users don't properly check k=
eys,
>>=20
>> PGP requires a secure side channel for transmission of public keys. How d=
oes one "check" a key of an anonymous peer? I know you well enough to know y=
ou wouldn't trust a PGP key received over an insecure channel.
>>=20
>> All you can prove is that you are talking to a peer and that communicatio=
ns in the session remain with that peer. The peer can be the attacker. As Jo=
nas has acknowledged, authentication is required to actually guard against M=
ITM attacks.
>=20
> Easy: anonymous peers aren't always actually anonymous.
>=20
> A MITM attacker can't easily distinguish communications between two nodes t=
hat
> randomly picked their peers, and nodes that are connected because their op=
erators manually used -addnode to peer; in the latter case the operators can=

> check whether or not they're being attacked with an out-of-band key check.=


An "out of band key check" is not part of BIP151. It requires a secure chann=
el and is authentication. So BIP151 doesn't provide the tools to detect an a=
ttack, that requires authentication. A general requirement for authenticatio=
n is the issue I have raised.

e=