Subject: Re: [Bitcoin-development] [RFC] [BIP proposal] Dealing with malleability

From: Natanael <[email-masked]>
Date: Thu, 20 Feb 2014 08:50:51 +0100

You could pregenerate entire "trees" of alternative outcomes where you pick
one branch / chain to broadcast based on the real world events as they
happen.

But I see another problem regarding use of oracles, if you have a P2SH
address with 2-of-3 signatures or similar in the chain, amd some
transactions following it, then the oracle needs to pregenerate both
transactions for both outcomes in advance. But the oracle probably don't
want to actually share it in advance to any third party before the event
happened.

This can be solved if the oracle only shares the transaction hash in
advance and then hands out a Zero-knowledge proof of that transaction with
the given hash is following the agreed upon rules, so you can trust the
transaction chain anyway and still being able to pregenerate a full tree of
transactions.

And then the oracle will release one of the possible transactions after the
event in question has happened, so you can broadcast the chain of choice.

This unfortunately breaks down if the number of possible outcomes becomes
too many as you would need to both generate and store a tree of possible
outcomes that is massive.

- Sent from my phone
Den 20 feb 2014 02:29 skrev "Allen Piscitello" <[email-masked]>:

> This is somewhat problematic in my use case since some parts need to be in
> the chain earlier than others and have the same ID as expected.
>
> https://bitcointalk.org/index.php?topic=260898.10
>
> I haven't gone back to see if there are any ways around it, but the main
> problem here is I need the Contract TX to be in the chain much earlier than
> redeeming, but I need the refund transaction to be in the chain much
> earlier.  Perhaps there are some tricks to pull off to get it to work, but
> I haven't been working on this for a while so I'm a bit rusty in that area.
>
> This might be helpful enough to help a lot of use cases, but shouldn't be
> final.
>
> -Allen
>
> On Wed, Feb 19, 2014 at 6:22 PM, Natanael <[email-masked]> wrote:
>
>> Regarding chains of transactions intended to be published at once
>> together, wouldn't it be easier to add a "only-mine-with-child flag"?
>>
>> That way the parent transactions aren't actually valid unless spent
>> together with the transaction that depends on it, and only the original
>> will have a child referencing it.
>>
>> Then malleability is not an issue at all for transaction chains if you
>> only need to broadcast your full transaction chain once, and don't need to
>> extend it in two or more occasions, *after* broadcasting subchains to the
>> network, from the same set of pregenerated transactions.
>>
>> If you need to broadcast pregenerated subchains separately, then you need
>> the last child in the chain to be non-malleable.
>>
>> This would require all miners to start to respect it at once in order to
>> avoid forking the network.
>>
>> - Sent from my phone
>> Den 19 feb 2014 22:13 skrev "Pieter Wuille" <[email-masked]>:
>>
>> On Wed, Feb 19, 2014 at 9:28 PM, Michael Gronager <[email-masked]>
>>> wrote:
>>> > I think that we could guarantee fewer incidents by making version 1
>>> transactions unmalleable and then optionally introduce a version 3 that
>>> supported the malleability feature. That way most existing problematic
>>> implementations would be fixed and no doors were closed for people
>>> experimenting with other stuff - tx v 3 would probably then be called
>>> experimental transactions.
>>>
>>> Just to be clear: this change is not directly intended to avoid
>>> "incidents". It will take way too long to deploy this. Software should
>>> deal with malleability. This is a longer-term solution intended to
>>> provide non-malleability guarantees for clients that a) are upgraded
>>> to use them  b) willing to restrict their functionality. As there are
>>> several intended use cases for malleable transactions (the sighash
>>> flags pretty directly are a way to signify what malleabilities are
>>> *wanted*), this is not about outlawing malleability.
>>>
>>> While we could right now make all these rules non-standard, and
>>> schedule a soft fork in a year or so to make them illegal, it would
>>> mean removing potential functionality that can only be re-enabled
>>> through a hard fork. This is significantly harder, so we should think
>>> about it very well in advance.
>>>
>>> About new transaction and block versions: this allows implementing and
>>> automatically scheduling a softfork without waiting for wallets to
>>> upgrade. The non-DER signature change was discussed for over two
>>> years, and implemented almost a year ago, and we still notice wallets
>>> that don't support it. We can't expect every wallet to be instantly
>>> modified (what about hardware wallets like the Trezor, for example?
>>> they may not just be able to be upgraded). Nor is it necessary: if
>>> your software only spends confirmed change, and tracks all debits
>>> correctly, there is no need.
>>>
>>> --
>>> Pieter
>>>
>>>
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