Subject: Re: [bitcoin-dev] BIP 151

From: Eric Voskuil <[email-masked]>
Date: Wed, 29 Jun 2016 00:07:45 +0200

Hi Cameron, good to hear from you!

> On Jun 28, 2016, at 11:40 PM, Cameron Garnham <[email-masked]> wrote:
> 
> Unauthenticated link level encryption is wonderful! MITM attacks are overrated; as they require an active attacker.

This is not really the case with Bitcoin. A MITM attack does not require that the attacker find a way to inject traffic into the communication between nodes. Peers will connect to the attacker directly, or accept connections directly from it. Such attacks can be easier than even passive attacks.

> Stopping passive attacks is the low hanging fruit. This should be taken first.
> 
> Automated and secure peer authentication in a mesh network is a huge topic. One of the unsolved problems in computer science.
> 
> A simple 'who is that' by asking for the fingerprint of your peers from your other peers is a very simple way to get 'some' authentication.  Semi-trusted index nodes also is a low hanging fruit for authentication.

It is the implication of widespread authentication that is at issue. Clearly there are ways to implement it using a secure side channels.

> However, let's first get unauthenticated encryption. Force the attackers to use active attacks. (That are thousands times more costly to couduct).
> 
> Sent from my iPhone
> 
>> On 29 Jun 2016, at 00:36, Gregory Maxwell via bitcoin-dev <[email-masked]> wrote:
>> 
>> On Tue, Jun 28, 2016 at 9:22 PM, Eric Voskuil via bitcoin-dev
>> <[email-masked]> wrote:
>>> An "out of band key check" is not part of BIP151.
>> 
>> It has a session ID for this purpose.
>> 
>>> It requires a secure channel and is authentication. So BIP151 doesn't provide the tools to detect an attack, that requires authentication. A general requirement for authentication is the issue I have raised.
>> 
>> One might wonder how you ever use a Bitcoin address, or even why we
>> might guess these emails from "you" aren't actually coming from the
>> NSA.
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