Subject: Re: [bitcoin-dev] "Compressed" headers stream

From: Greg Sanders <[email-masked]>
Date: Mon, 28 Aug 2017 12:26:48 -0400

Well, if anything my question may bolster your use-case. If there's a
heavier chain that is invalid, I kind of doubt it matters for timestamping
reasons.

/digression

On Mon, Aug 28, 2017 at 12:25 PM, Riccardo Casatta <
[email-masked]> wrote:

>
> 2017-08-28 18:13 GMT+02:00 Greg Sanders <[email-masked]>:
>
>> Is there any reason to believe that you need Bitcoin "full security" at
>> all for timestamping?
>>
>
> This is a little bit out of the main topic of the email which is the
> savings in bandwidth in transmitting headers, any comment about that?
>
>
> P.S. As a personal experience timestamping is nowadays used to prove date
> and integrity of private databases containing a lot of value, so yes, in
> that cases I will go with Bitcoin "full security"
>
>
>>
>> On Mon, Aug 28, 2017 at 11:50 AM, Riccardo Casatta via bitcoin-dev <
>> [email-masked]> wrote:
>>
>>> Hi everyone,
>>>
>>> the Bitcoin headers are probably the most condensed and important piece
>>> of data in the world, their demand is expected to grow.
>>>
>>> When sending a stream of continuous block headers, a common case in IBD
>>> and in disconnected clients, I think there is a possible optimization of
>>> the transmitted data:
>>> The headers after the first could avoid transmitting the previous hash
>>> cause the receiver could compute it by double hashing the previous header
>>> (an operation he needs to do anyway to verify PoW).
>>> In a long stream, for example 2016 headers, the savings in bandwidth are
>>> about 32/80 ~= 40%
>>> without compressed headers 2016*80=161280 bytes
>>> with compressed headers 80+2015*48=96800 bytes
>>>
>>> What do you think?
>>>
>>>
>>> In OpenTimestamps calendars we are going to use this compression to give
>>> lite-client a reasonable secure proofs (a full node give higher security
>>> but isn't feasible in all situations, for example for in-browser
>>> verification)
>>> To speed up sync of a new client Electrum starts with the download of a
>>> file <https://headers.electrum.org/blockchain_headers> ~36MB containing
>>> the first 477637 headers.
>>> For this kind of clients could be useful a common http API with fixed
>>> position chunks to leverage http caching. For example /headers/2016/0
>>> returns the headers from the genesis to the 2015 header included while
>>> /headers/2016/1 gives the headers from the 2016th to the 4031.
>>> Other endpoints could have chunks of 20160 blocks or 201600 such that
>>> with about 10 http requests a client could fast sync the headers
>>>
>>>
>>> --
>>> Riccardo Casatta - @RCasatta <https://twitter.com/RCasatta>
>>>
>>> _______________________________________________
>>> bitcoin-dev mailing list
>>> [email-masked]
>>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>>
>>>
>>
>
>
> --
> Riccardo Casatta - @RCasatta <https://twitter.com/RCasatta>
>