Received: from sog-mx-4.v43.ch3.sourceforge.com ([172.29.43.194] helo=mx.sourceforge.net) by sfs-ml-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1WhPU9-0002Ih-3l for bitcoin-development@lists.sourceforge.net; Mon, 05 May 2014 20:27:37 +0000 Received-SPF: pass (sog-mx-4.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.215.48 as permitted sender) client-ip=209.85.215.48; envelope-from=stanga@gmail.com; helo=mail-la0-f48.google.com; Received: from mail-la0-f48.google.com ([209.85.215.48]) by sog-mx-4.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1WhPU7-00034x-LM for bitcoin-development@lists.sourceforge.net; Mon, 05 May 2014 20:27:37 +0000 Received: by mail-la0-f48.google.com with SMTP id el20so3199639lab.7 for ; Mon, 05 May 2014 13:27:29 -0700 (PDT) X-Received: by 10.152.20.137 with SMTP id n9mr3301455lae.39.1399321648899; Mon, 05 May 2014 13:27:28 -0700 (PDT) MIME-Version: 1.0 Sender: stanga@gmail.com Received: by 10.112.46.203 with HTTP; Mon, 5 May 2014 13:27:08 -0700 (PDT) In-Reply-To: <5367EA43.1090308@certimix.com> References: <52CDA01B-13BF-4BB8-AC9A-5FBBB324FD15@sant.ox.ac.uk> <20140423150555.GE19430@savin> <53638616.2030009@certimix.com> <536388F9.3040607@certimix.com> <5367EA43.1090308@certimix.com> From: Ittay Date: Mon, 5 May 2014 16:27:08 -0400 X-Google-Sender-Auth: nT0wjhzI6TpxQ9PiXStCeASjTR4 Message-ID: To: Sergio Lerner Content-Type: multipart/alternative; boundary=089e01493df6cf2daa04f8acf550 X-Spam-Score: -0.5 (/) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (stanga[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 1.0 HTML_MESSAGE BODY: HTML included in message 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Headers-End: 1WhPU7-00034x-LM Cc: bitcoin-research@lists.cs.princeton.edu, "bitcoin-development@lists.sourceforge.net" , Joseph Bonneau , =?UTF-8?Q?Emin_G=C3=BCn_Sirer?= , Ittay Eyal Subject: Re: [Bitcoin-development] Block collision resolution using the DECOR protocol and Bonneau's Kickbacks problem X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 May 2014 20:27:37 -0000 --089e01493df6cf2daa04f8acf550 Content-Type: text/plain; charset=UTF-8 As far as I understand, the incentives Sergio suggests would work. So we can assume that the pruned uncle blocks would still win their creators at least partial revenue. As for selfish mining - I'm not sure how GHOST affects it. I don't think it does. The selfish miners just care about heaviest subtree rather than longest chain. DECOR changes revenue collection significantly, so it certainly affects selfish mining. I believe it changes the threshold at which selfish mining is profitable, but doesn't deter selfish mining completely: Selfish miners can still cause others to reduce their revenue by having them work on older blocks. Ittay On Mon, May 5, 2014 at 3:45 PM, Sergio Lerner wrote: > > On 02/05/2014 10:56 a.m., Joseph Bonneau wrote: > > This is an interesting idea Sergio. I have two concerns: > > > > You mention "50% of the block reward" going to the uncle block. Does > > this mean the parent gets 1, and the uncle 0.5, or both get 0.5? In > > the first interpretation (which I assumed was the design), mining is > > no longer a zero-sum game and this could have lots of unforeseen > > implications. For example, selfish mining might be more profitable, > > since you're less disincentivized to avoid conflicts. > The second interpretation is the correct one. > > In the second interpretation, there's pressure to have the next miner > > ignore the uncle to not share the reward. This would encourage > > kickback-style attacks and advantage large mining pools because they > > can mine on their own blocks and ignore colliding uncles. > Including an uncle can be done at any time before a coinbase matures > (100 blocks) (of course the term "uncle" is misleading in those cases) . > So, for example, the uncle can be included 50 blocks afterward. So it's > very difficult that a miner prevents other miners from including the > uncle and taking the reward given by uncle inclusion. > > Same ineffective attack: > A big miner could try to bribe all other miners not to include the > uncle, but this would be terribly costly. Suppose that I mine a block > ignoring an uncle Z and then I publish this message: "Every miner from > block number X to block number Y that does not include this uncle Z will > be given Q Bitcoins". How much would Q be? Since by including the uncle > the miner gets 5 BTC of reward (in the example case where block reward > is 50 BTC), then each bribery payment would have to be higher than 5 > BTC, totaling 500 BTC ! much more than the 25 BTC the miner will loose > by including the uncle. > > Just by sending a transaction with a lot of fees that depends on my > block does not prevent subsequent miners from including the supposedly > banned uncle. > > Then, I think there are no kickback-style attacks. > > > > > Also, I think this came up in the Princeton meet-up, but it's not > > ideal to just hash the blocks to decide the "winner" because this lets > > you know in advance your block's likelihood of winning a collision by > > looking at how high or low its hash is, in which case you can publish > > a weak block right away or withhold a strong one and do selfish > > mining. A better approach to break ties between blocks A and B is to > > see if H(A||B) < H(B||A). That way neither block holder can find out > > in advance if their block is likely to win a collision. > > > In the DECOR protocol, I think selfish miners cannot get any advantage, > because the blocks that loose the latency race will come back as uncles > and get their reward share anyway. Maybe Ittay Eyal and Emin Gun Sirer > can say more about this... > > Best regards, Sergio. > --089e01493df6cf2daa04f8acf550 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
As far as I understand, the incentives Sergio suggests wou= ld work. So=C2=A0
we can assume that the pruned uncle blocks would stil= l win their creators=C2=A0
at least partial revenue.=C2=A0
<= div>
As for selfish mining - I'm not sure how GHOST affects it. I don&#= 39;t think it=C2=A0
does. The selfish miners just care about heav= iest subtree rather than=C2=A0
longest chain. DECOR changes reven= ue collection significantly, so it=C2=A0
certainly affects selfish mining. I believe it changes the threshold a= t which=C2=A0
selfish mining is profitable, but doesn't deter= selfish mining completely:=C2=A0
Selfish miners can still cause = others to reduce their revenue by having=C2=A0
them work on older blocks.=C2=A0

Ittay=C2=A0<= /div>



On Mon, May 5, 2014 at 3:45 PM, Sergio Lerner <sergio= lerner@certimix.com> wrote:

On 02/05/2014 10:56 a.m., Joseph Bonneau wrote:
> This is an interesting idea Sergio. I have two concerns:
>
> You mention "50% of the block reward" going to the uncle blo= ck. Does
> this mean the parent gets 1, and the uncle 0.5, or both get 0.5? In > the first interpretation (which I assumed was the design), mining is > no longer a zero-sum game and this could have lots of unforeseen
> implications. For example, selfish mining might be more profitable, > since you're less disincentivized to avoid conflicts.
The second interpretation is the correct one.
> In the second interpretation, there's pressure to = have the next miner
> ignore the uncle to not share the reward. This would encourage
> kickback-style attacks and advantage large mining pools because they > can mine on their own blocks and ignore colliding uncles.
Including an uncle can be done at any time before a coinbase matures<= br> (100 blocks) (of course the term "uncle" is misleading in those c= ases) .
So, for example, the uncle can be included 50 blocks afterward. So it's=
very difficult that a miner prevents other miners from including the
uncle and taking the reward given by uncle inclusion.

Same ineffective attack:
A big miner could try to bribe all other miners not to include the
uncle, but this would be terribly costly. Suppose that I mine a block
ignoring an uncle Z and then I publish this message: "Every miner from=
block number X to block number Y that does not include this uncle Z will be given Q Bitcoins". How much would Q be? Since by including the uncl= e
the miner gets 5 BTC of reward (in the example case where block reward
is 50 BTC), then each bribery payment would have to be higher than 5
BTC, totaling 500 BTC ! much more than the 25 BTC the miner will loose
by including the uncle.

Just by sending a transaction with a lot of fees that depends on my
block does not prevent subsequent miners from including the supposedly
banned uncle.

Then, I think there are no kickback-style attacks.

>
> Also, I think this came up in the Princeton meet-up, but it's not<= br> > ideal to just hash the blocks to decide the "winner" because= this lets
> you know in advance your block's likelihood of winning a collision= by
> looking at how high or low its hash is, in which case you can publish<= br> > a weak block right away or withhold a strong one and do selfish
> mining. A better approach to break ties between blocks A and B is to > see if H(A||B) < H(B||A). That way neither block holder can find ou= t
> in advance if their block is likely to win a collision.
>
In the DECOR protocol, I think selfish miners cannot get any advantag= e,
because the blocks that loose the latency race will come back as uncles
and get their reward share anyway. Maybe Ittay Eyal and Emin Gun Sirer
can say more about this...

Best regards, Sergio.

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