Re: [bitcoin-dev] Chain width expansion

[Braydon Fuller <braydon@purse.io>]

On 10/15/19 8:50 AM, Joachim Strömbergson wrote:

>>>>> [...] to generate much longer chain with superslow timestamp increase (~5 blocks in 1 second) without increasing difficulty (i.e. staying at min. diff.). [...]
>>>>> In that case, it would take about 7 minutes of block time seconds for
>>>>> the next retarget period, every 2016 blocks, and the difficulty would
>>>>> adjust. The difficulty would adjust in that case as if 2 weeks of blocks
>>>>> had been mined in 7 minutes. For the difficulty to remain the same the
>>>>> time between blocks needs to be 10 minutes.
>>>>> This calculation does not apply under time warp attack. You can fake timestamps of all blocks except for those relevant to the retarget calculation. Those are only the first and the last block in the 2016 block window.
>> This must be in reference to the non-overlapping difficulty calculation
>> and off-by-one bug?
> Indeed.
>
Yeah, limiting the width of the chain would not be effective unless the
timewarp off-by-one bug is resolved — the height can be extended instead.

Rate limiting based on chainwork would slow down a timewarped low work
header chain. There would be a maximum rate at which the headers could
be sent. It would be around 32KB/s. It would take about a month to send
100GB.