Content-Type: text/plain;
	charset=us-ascii
Mime-Version: 1.0 (1.0)
From: Eric Voskuil <eric@voskuil.org>
In-Reply-To: <20160628201447.GA1148@fedora-21-dvm>
Date: Tue, 28 Jun 2016 22:29:54 +0200
Content-Transfer-Encoding: quoted-printable
Message-Id: <4DCF7DD2-6533-4F79-8CA1-871B67C01BDA@voskuil.org>
References: <87h9cecad5.fsf@rustcorp.com.au>
	<1E86A00F-0609-4DBC-9543-94AE04CC13C9@voskuil.org>
	<577234A4.3030808@jonasschnelli.ch>
	<360EF9B8-A174-41CA-AFDD-2BC2C0B4DECB@voskuil.org>
	<20160628182202.GA5519@fedora-21-dvm>
	<D40F9E9D-DB6C-4083-A9E8-C5EBC363DB30@voskuil.org>
	<20160628201447.GA1148@fedora-21-dvm>
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 10:14 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 incre=
ases 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 ke=
ys,

PGP requires a secure side channel for transmission of public keys. How does=
 one "check" a key of an anonymous peer? I know you well enough to know you w=
ouldn't trust a PGP key received over an insecure channel.

All you can prove is that you are talking to a peer and that communications i=
n the session remain with that peer. The peer can be the attacker. As Jonas h=
as acknowledged, authentication is required to actually guard against MITM a=
ttacks.

> so an attacker won't have a hard time MITM attacking those users. But some=

> users do check keys, a labor intensive manual process, but not a process t=
hat
> requires any real cryptographic sophistication, let alone writing any code=
.
> It's very difficult for widescale attackers to distinguish the users who d=
o
> check keys from the ones that don't, so if you MITM attack _any_ user you r=
un
> the risk of running into one of the few that does check, and those users c=
an
> alert everyone else.
>=20
> The key thing, is we need to get everyones communications encrypted first:=
 if
> we don't the MITM attacker can intercept 99% of the communications with 0%=
 risk
> of detection, because the non-sophisticated users are trivially distinguis=
hable from the sophisticated users: just find the users with unencrypted
> communications!
>=20
> --=20
> https://petertodd.org 'peter'[:-1]@petertodd.org