Content-Type: text/plain;
	charset=us-ascii
Mime-Version: 1.0 (1.0)
From: Eric Voskuil <eric@voskuil.org>
In-Reply-To: <20160629111728.GO13338@dosf1.alfie.wtf>
Date: Thu, 30 Jun 2016 13:56:42 +0200
Content-Transfer-Encoding: quoted-printable
Message-Id: <2981A919-4550-4807-8ED9-F8C51B2DC061@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>
	<20160629111728.GO13338@dosf1.alfie.wtf>
To: Alfie John <alfie@alfie.wtf>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP 151
Precedence: list

Hi Alfie,

Yes, this is exactly what I meant. The complexity of the proposed constructi=
on is comparable to that of Bitcoin itself. This is not itself prohibitive, b=
ut it is clearly worthy of consideration.

A question we should ask is whether decentralized anonymous credentials is a=
pplicable to the authentication problem posed by BIP151. I propose that it i=
s not.

The core problem posed by BIP151 is a MITM attack. The implied solution (BIP=
151 + authentication) requires that a peer trusts that another is not an att=
acker.=20

Authentication of an anonymous peer cannot achieve this objective, since the=
 peer may be anyone and an attack on privacy can be undetectable. The identi=
ty of a peer must be known to the relying peer, either directly or transitiv=
ely.

DAC is applicable in cases where identity is never required.  The prime exam=
ple in the paper is that of first-come-first-served name registration. No id=
entity is required in that scenario, just proof that a party in question is t=
he original registrant. All participants are presumed to be "good".

I believe that a distributed anonymous system is fundamentally at odds with i=
solation of "good" vs. "bad" participants who comply with protocol rules (Do=
S considerations aside), and that any attempt to resolve this conflict will r=
esult in the system no longer allowing anonymous participation.

I may be mistaken, but I haven't found a way out of this realization.

e

> On Jun 29, 2016, at 1:17 PM, Alfie John <alfie@alfie.wtf> wrote:
>=20
> On Tue, Jun 28, 2016 at 06:45:58PM +0200, Eric Voskuil via bitcoin-dev wro=
te:
>>> then we should definitively use a form of end-to-end encryption between
>>> nodes. Built into the network layer.
>>=20
>> Widespread application of this model is potentially problematic. It is a
>> non-trivial problem to design a distributed system that requires authenti=
cation
>> but without identity and without central control. In fact this may be mor=
e
>> challenging than Bitcoin itself. Trust on first use (TOFU) does not solve=
 this
>> problem.
>=20
> Maybe the following paper can feed into this discussion:
>=20
> "Decentralized Anonymous Credentials" by Christina Garman, Matthew Green, I=
an Miers
>   https://eprint.iacr.org/2013/622.pdf
>=20
> Alfie
>=20
> --=20
> Alfie John
> https://www.alfie.wtf