Re: [bitcoin-dev] Committed bloom filters for improved wallet performance and SPV security

[adiabat <rx@awsomnet.org>]

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Mempool transactions have their place, but "unconfirmed" and "SPV" don't
belong together.  Only a full node can tell if a transaction may get
confirmed, or is nonsense.  Unfortunately all the light / SPV wallets I
know of show mempool transactions, which makes it hard to go back... (e.g.
"why doesn't your software show 0-conf! your wallet is broken!", somewhat
akin to people complaining about RBF)

So, this is easy, just don't worry about mempool filtering.  Why are light
clients looking at the mempool anyway?  Maybe if there were some way to
provide SPV proofs of all inputs, but that's a bit of a mess for full nodes
to do.

Without mempool filtering, I think the committed bloom filters would be a
great improvement over the current bloom filter setup, especially for
lightning network use cases (with lightning, not finding out about a
transaction can make you lose money).  I want to work on it and may be able
to at some point as it's somewhat related to lightning.

Also, if you're running a light client, and storing the filters the way you
store block headers, there's really no reason to go all the way back to
height 0.  You can start grabbing headers at some point a while ago, before
your set of keys was generated.  I think it'd be very worth it even with
GB-scale disk usage.

-Tadge


On Tue, Jan 3, 2017 at 5:18 PM, Aaron Voisine via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Unconfirmed transactions are incredibly important for real world use.
> Merchants for instance are willing to accept credit card payments of
> thousands of dollars and ship the goods despite the fact that the
> transaction can be reversed up to 60 days later. There is a very large cost
> to losing the ability to have instant transactions in many or even most
> situations. This cost is typically well above the fraud risk.
>
> It's important to recognize that bitcoin serves a wide variety of use
> cases with different profiles for time sensitivity and fraud risk.
>
> Aaron
>
> On Tue, Jan 3, 2017 at 12:41 PM bfd--- via bitcoin-dev <bitcoin-dev@lists.
> linuxfoundation.org> wrote:
>
>> The concept combined with the weak blocks system where miners commit
>>
>> to potential transaction inclusion with fractional difficulty blocks
>>
>> is possible. I'm not personally convinced that unconfirmed transaction
>>
>> display in a wallet is worth the privacy trade-off. The user has very
>>
>> little to gain from this knowledge until the txn is in a block.
>>
>>
>>
>>
>>
>> On 2017-01-01 13:01, Jonas Schnelli via bitcoin-dev wrote:
>>
>> > Hi
>>
>> >> We introduce several concepts that rework the lightweight Bitcoin
>>
>> >> client model in a manner which is secure, efficient and privacy
>>
>> >> compatible.
>>
>> >>
>>
>> >> The BFD can be used verbatim in replacement of BIP37, where the filter
>>
>> >> can be cached between clients without needing to be recomputed. It can
>>
>> >> also be used by normal pruned nodes to do re-scans locally of their
>>
>> >> wallet without needing to have the block data available to scan, or
>>
>> >> without reading the entire block chain from disk.
>>
>> > I started exploring the potential of BFD after this specification.
>>
>> >
>>
>> > What would be the preferred/recommended way to handle 0-conf/mempool
>>
>> > filtering – if & once BDF would have been deployed (any type,
>>
>> > semi-trusted oracles or protocol-level/softfork)?
>>
>> >
>>
>> > From the user-experience perspective, this is probably pretty important
>>
>> > (otherwise the experience will be that incoming funds can take serval
>>
>> > minutes to hours until they appear).
>>
>> > Using BIP37 bloom filters just for mempool filtering would obviously
>>
>> > result in the same unwanted privacy-setup.
>>
>> >
>>
>> > </jonas>
>>
>> >
>>
>> >
>>
>> > _______________________________________________
>>
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>>
>> > bitcoin-dev@lists.linuxfoundation.org
>>
>> > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>
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>>
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