[Bitcoin-development] bloom filtering, privacy

Chris Pacia ctpacia at gmail.com
Sat Feb 21 18:38:05 UTC 2015

Yeah that overhead is pretty high. I wasn't thinking about 10 years out.

On Sat, Feb 21, 2015, 11:47 AM Mike Hearn <mike at plan99.net> wrote:

> Adam seems to be making sense to me. Only querying a single node when an
>> address in my wallet matches the block filter seems to be pretty efficient.
> No, I think it's less efficient (for the client).
> Quick sums:  blocks with 1500 transactions in them are common today. But
> Bitcoin is growing. Let's imagine a system 10x larger than today. Doesn't
> seem implausible to reach that in the next 5-10 years, so 15,000
> transactions. Each transaction has multiple elements we might want to match
> (addresses, keys, etc).
> Let's say the average tx contains 5 unique keys/elements. That's the base
> case of {1 input, 2 outputs} without address reuse, plus fudged up a bit
> for multi-sends then down a bit again for address reuse.
> 15,000*5=75,000 unique elements per block. With an FP rate of 0.1% we get:
> http://hur.st/bloomfilter?n=75000&p=0.001
> 131.63KB per block extra overhead.
> 144 blocks in a day, so that's 18mb of data per day's worth of sync to
> pull down over the network. If you don't start your wallet for a week
> that's 126 megabytes of data just to get started.
> Affordable, yes (in the west). Fast enough to be competitive? Doubtful. I
> don't believe that even in five years mobiles will be pulling down and
> processing that much data within a few seconds, not even in developed
> countries.
> But like I said, I don't see why it matters. Anyone who is watching the
> wire close to you learns which transactions are yours, still, so it doesn't
> stop intelligence agencies. Anyone who is running a node learns which
> transactions in the requested block were yours and thus can follow the tx
> chain to learn which other transactions might be yours too, no different to
> today. If you connect to a single node and say "give me the transactions
> sending money to key A in block N", it doesn't matter if you then don't
> request block N+6 from the same peer - they know you will request it
> eventually anyway, just by virtue of the fact that one of the transactions
> they gave you was spent in that block.
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