Subject: Re: [bitcoin-dev] We need to fix the block withholding attack

From: Dave Scotese <[email-masked]>
Date: Tue, 29 Dec 2015 10:59:58 -0800

There have been no decent objections to altering the block-selection
mechanism (when two block solutions appear at nearly the same time) as
described at

http://bitcoin.stackexchange.com/questions/39226

Key components are:

   - Compute BitcoinDaysDestroyed using only transactions that have been in
   your mempool for some time as oBTCDD ("old BTCDD").
   - Use "nearly the same time" to mean separated in time by your guess of
   the average duration of block propagation times.
   - When two block solutions come in at nearly the same time, build on the
   one that has the most oBTCDD, rather than the one that came in first.

The goal of this change is to reduce the profitability of withholding block
solutions by severely reducing the chances that a block solved a while ago
can orphan one solved recently.  "Came in first" seems more easily gamed
than "most oBTCDD".  As I wrote there, "*old coins* is always a dwindling
resource and *global nodes willing to help cheat* is probably a growing
one."

I will write a BIP if anyone agrees it's a good idea.

On Mon, Dec 28, 2015 at 12:26 PM, Ivan Brightly via bitcoin-dev <
[email-masked]> wrote:

> On Mon, Dec 28, 2015 at 2:12 PM, Peter Todd via bitcoin-dev <
>> [email-masked]> wrote:
>> Far more concerning is network propagation effects between large and
>> small miners. For that class of issues, if you are in an environemnt
>> where selfish mining is possible - a fairly flat, easily DoS/sybil
>> attacked network topology - the profitability difference between small
>> and large miners even *without* attacks going on is a hugely worrying
>> problem. OTOH, if you're blocksize is small enough that propagation time
>> is negligable to profitability, then selfish mining attacks with <30%
>> hashing power aren't much of a concern - they'll be naturally defeated
>> by anti-DoS/anti-sybil measures.
>>
>
> Let's agree that one factor in mining profitability is bandwidth/network
> reliability/stability. Why focus on that vs electricity contracts or
> vertically integrated chip manufacturers? Surely, sufficient network
> bandwidth is a more broadly available commodity than <$0.02/kwh
> electricity, for example. I'm not sure that your stranded hydroelectric
> miner is any more desirable than thousands of dorm room miners with access
> to 10gbit university connections and free electricity.
>
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