Unfortunately a non validating SPV wallet has absolutely no idea if
the information about an unconfirmed transaction they are seeing is
anything but properly formatted. They are connecting to an easily
manipulated, sybil attacked, and untrusted network and then asking
them for financial information. Seeing an unconfirmed transaction in a
wallet that's not also fully validating is at best meaningless.


On 2017-01-03 15:46, Aaron Voisine wrote:

If the sender doesn't control the receiver's network connection, then
the information the receiver gains by watching the mempool is if the
transaction has propagated across the bitcoin network. This is useful
to know in all kinds of situations.

Aaron Voisine
co-founder and CEO
breadwallet [2]

On Tue, Jan 3, 2017 at 3:06 PM, adiabat <rx@awsomnet.org> wrote:

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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