Re: [bitcoin-dev] Safer NOINPUT with output tagging

2019-01-31 Thread Anthony Towns via bitcoin-dev
On Mon, Dec 24, 2018 at 11:47:38AM +, ZmnSCPxj via bitcoin-dev wrote:
> A boutique protocol would reduce the number of existing onchain wallets that 
> could be integrated in such UI.

Seems like PSBT would be a sufficient protocol:

 0) lightning node generates a PSBT for a new channel,
with no inputs and a single output of the 2-of-2 address

 1) wallet funds the PSBT but doesn't sign it, adding a change address
if necessary, and could combine with other tx's bustapay style

 2) lightning determines txid from PSBT, and creates update/settlement
tx's for funding tx so funds can be recovered

 3) wallet signs and publishes the PSBT

 4) lightning sees tx on chain and channel is open

That's a bit more convoluted than "(0) lightning generates an address and
value, and creates NOINPUT update/settlement tx's for that address/value;
(1) wallet funds address to exactly that value; (2) lightning monitors
blockchain for payment to that address" of course.

But it avoids letting users get into the habit of passing NOINPUT
addresses around, or the risk of a user typo'ing the value and losing
money immediately, and it has the benefit that the wallet can tweak the
value if (eg) that avoids a change address or enhances privacy (iirc,
c-lightning tweaks payment values for that reason). If the channel's
closed cooperatively, it also avoids ever needing to publish a NOINPUT
sig (or NOINPUT tagged output).

Does that seem a fair trade off?


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Re: [bitcoin-dev] bustapay BIP :: a practical sender/receiver coinjoin protocol

2019-01-31 Thread James MacWhyte via bitcoin-dev
On Tue, Jan 29, 2019 at 6:46 PM  wrote:

> If the sender refuses to sign the final transaction, the receiver just
> propagates the template transaction which pays the receiver! So it's a
> pretty weak attack.
> The only real attack is that the sender could double-spend the
> template-transaction before it's propagated, but the cost of doing this
> isn't free, as at the very least you need to pay the transaction fees of
> creating a double spend. It's not an amazingly good defence, but it's good
> enough that it's unlikely to get abused (and an attacker would only learn a
> single utxo of the receiver) .

Okay, I see what you mean. I better understand the weaknesses you've
identified, and I can't really think of a better solution than what you've
proposed. I also realized that implementors who aren't capable of
integrating signing and UTXO validation wouldn't be the ones trying to
implement this feature, so my concerns there are also moot. Carry on ;)
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Re: [bitcoin-dev] Contribution

2019-01-31 Thread Marco Falke via bitcoin-dev
This mailing list is for the development of the Bitcoin protocol (see
Code changes to Bitcoin Core can be discussed on or
preferably be submitted to

-- Marco
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