Subject: Re: [Bitcoin-development] alternate proposal opt-in miner takes double-spend (Re: replace-by-fee v0.10.0rc4)

From: Natanael <[email-masked]>
Date: Sun, 22 Feb 2015 15:44:30 +0100

Den 22 feb 2015 14:29 skrev "Natanael" <[email-masked]>:
>
>
> Den 22 feb 2015 13:36 skrev "Peter Todd" <[email-masked]>:
>
> > Implementing it as a general purpose scripting language improvement has
> > a lot of advantages, not least of which is that you no longer need to
> > rely entirely on inherently unreliable P2P networking: Promise to never
> > create two signatures for a specific BIP32 root pubkey and make
> > violating that promise destroy and/or reallocate a fidelity bond whose
> > value is locked until some time into the future. Since the fidelity bond
> > is a separate pool of funds, detection of the double-spend can happen
> > later.
>
> Somebody sent me a zero-confirmation transaction, or one that got
orphaned after one block. I created a transaction spending that UTXO, and
another.
>
> So at that point I have UTXO_orphaned based on the sender's UTXO_origin
and my UTXO_old (because I've had it unspent for a long time), both in one
transaction, creating UTXO_new.
>
> Now he doublespend UTXO_origin to create a UTXO_doublespend (which
conflicts with UTXO_orphaned). He conspires with a miner to get it into a
block.
>
> Now what? Can my UTXO_old effectively be tainted forever because UTXO_new
got invalidated together with UTXO_orphaned? Will that transaction be a
valid proof of doublespend against a new UTXO_replacement I created?
>
> Or otherwise, if only transactions where all UTXO's are currently valid
works as doublespend proofs, aren't you still just left without protection
against any one miner that conspires with doublespend attempting thieves?
>
> In other words, you are unprotected and potentially at greater risk if
you create a transaction depending on another zero-confirmation transaction.

Additional comments:

If you punish the creation of UTXO_replacement, you will punish people who
was lead to think zero-confirmation transactions were safe and thus that
chains of zero-confirmation transactions also were safe.

If you don't, but STILL accept chains of zero-confirmation transactions
were not all of them are covered by fidelity bonds, then you failed to
protect yourself against thieves who creates chains of unconfirmed
transactions.

Another question: if all transactions in the chain are covered by fidelity
bonds for their own value, which one pays out to who? Does only the first
one pay out, and only to the last party in the chain? Or to every
subsequent party after him? In full or just a fraction? Why, why not? You
might not know which of these serviced their customers in full without
getting full value back in exchange due to the doublespend.

What if the fidelity bond is too small, do you stop accepting it as a
zero-confirmation transaction?

Do you even accept chains of unconfirmed transactions at all?