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From: Leo Wandersleb <leo@LeoWandersleb.de>
To: bitcoin-dev@lists.linuxfoundation.org
Subject: Re: [bitcoin-dev] Committed bloom filters for improved wallet performance and SPV security
Date: Thu, 28 Jul 2016 23:07:29 +0200	[thread overview]
Message-ID: <307a1ca0-5554-a14e-fd3b-aace7d7c2233@LeoWandersleb.de> (raw)
In-Reply-To: <20160511202933.GR20063@mcelrath.org>

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gmaxwell just made me aware of this mail thread [0]. Some days ago I had
independently and naively started implementing "something similar" [1].

My version totally ignored the commitment and signing part but I'm pretty sure
that 12GB is overkill. My code is currently broken and I have no time to work on
it much but I thought it might be helpful to chime in.

At this point in time the difference between 80GB and 3GB (as my current 1.5GB
of only outputs would suggest if I had covered the inputs) or even 12GB makes
the difference of being able to store it on a phone, vs. not being able to. 80GB
"compressed" to 3GB is not that bad at all. Unfortunately, with segWit this will
be worse, with the higher transaction count per MB.

Regards,

Leo

[0]
https://www.reddit.com/r/Bitcoin/comments/4v28jl/how_have_fungiblity_problems_affected_you_in/d5ux6aq
[1] https://github.com/Giszmo/TransactionFinder

On 05/11/2016 10:29 PM, Bob McElrath via bitcoin-dev wrote:
> Eerrrr....let me revise that last paragraph.  That's 12 *GB* of filters at
> today's block height (at fixed false-positive rate 1e-6.  Compared to block
> headers only which are about 33 MB today.  So this proposal is not really
> compatible with such a wallet being "light"...
>
> Damn units...
>
> Bob McElrath via bitcoin-dev [bitcoin-dev@lists.linuxfoundation.org] wrote:
>> I like this idea, but let's run some numbers...
>>
>> bfd--- via bitcoin-dev [bitcoin-dev@lists.linuxfoundation.org] wrote:
>>> A Bloom Filter Digest is deterministically created of every block
>> Bloom filters completely obfuscate the required size of the filter for a desired
>> false-positive rate.  But, an optimal filter is linear in the number of elements
>> it contains for fixed false-positive rate, and logarithmic in the false-positive
>> rate.  (This comment applies to a RLL encoded Bloom filter Greg mentioned, but
>> that's not the only way)  That is for N elements and false positive rate
>> \epsilon:
>>
>>     filter size = - N \log_2 \epsilon
>>
>> Given that the data that would be put into this particular filter is *already*
>> hashed, it makes more sense and is faster to use a Cuckoo[1] filter, choosing a
>> fixed false-positive rate, given expected wallet sizes.  For Bloom filters,
>> multiply the above formula by 1.44.
>>
>> To prevent light clients from downloading more blocks than necessary, the
>> false-positive rate should be roughly less than 1/(block height).  If we take
>> the false positive rate to be 1e-6 for today's block height ~ 410000, this is
>> about 20 bits per element.  So for todays block's, this is a 30kb filter, for a
>> 3% increase in block size, if blocks commit to the filter.  Thus the required
>> size of the filter commitment is roughly:
>>
>>     filter size = N \log_2 H
>>
>> where H is the block height.  If bitcoin had these filters from the beginning, a
>> light client today would have to download about 12MB of data in filters.  My
>> personal SPV wallet is using 31MB currently.  It's not clear this is a bandwidth
>> win, though it's definitely a win for computing load on full nodes.
>>
>>
>> [1] https://www.cs.cmu.edu/~dga/papers/cuckoo-conext2014.pdf
>>
>> --
>> Cheers, Bob McElrath
>>
>> "For every complex problem, there is a solution that is simple, neat, and wrong."
>>     -- H. L. Mencken 
>>
>>
>>
>> !DSPAM:5733934b206851108912031!
>
>
>> _______________________________________________
>> bitcoin-dev mailing list
>> bitcoin-dev@lists.linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>
>>
>> !DSPAM:5733934b206851108912031!
> --
> Cheers, Bob McElrath
>
> "For every complex problem, there is a solution that is simple, neat, and wrong."
>     -- H. L. Mencken 
>
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev



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  reply	other threads:[~2016-07-28 21:16 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-09  8:26 [bitcoin-dev] Committed bloom filters for improved wallet performance and SPV security bfd
2016-05-09  8:57 ` Gregory Maxwell
2016-05-11 20:06 ` Bob McElrath
2016-05-11 20:29   ` Bob McElrath
2016-07-28 21:07     ` Leo Wandersleb [this message]
2017-01-06 22:07       ` Erik Aronesty
2017-01-03 20:24     ` bfd
     [not found] ` <77b6dd25-0603-a0bd-6a9e-38098e5cb19d@jonasschnelli.ch>
2017-01-03 20:18   ` bfd
2017-01-03 22:18     ` Aaron Voisine
2017-01-03 22:28       ` bfd
2017-01-03 23:06       ` adiabat
2017-01-03 23:46         ` Aaron Voisine
2017-01-04  0:10           ` bfd
2017-01-04  0:36             ` Aaron Voisine
2017-01-04  6:06               ` Eric Voskuil
2017-01-04 16:13         ` Leo Wandersleb
2017-01-04  7:47       ` Jonas Schnelli
2017-01-04  8:56         ` Aaron Voisine
2017-01-04 10:13           ` Jorge Timón
2017-01-04 11:00             ` Adam Back
2017-01-06  2:15           ` bfd
2017-01-06  7:07             ` Aaron Voisine
2017-01-05  7:06         ` Chris Priest
2017-01-05  7:45           ` Eric Voskuil
2017-01-05 14:48             ` Christian Decker
2017-01-06 20:15             ` Chris Priest
2017-01-06 21:35               ` James MacWhyte
2017-01-06 21:50                 ` Eric Voskuil
2017-01-06  2:04           ` bfd
2017-03-15 22:36             ` Tom Harding
2017-03-16  0:25               ` bfd
2017-03-16 15:05                 ` Tom Harding
2017-02-17  0:28 ` Chris Belcher
2017-04-01 23:49   ` bfd

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