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To: Mike Brooks <m@ib.tc>,
Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] PubRef - Script OP Code For Public Data References
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Good morning Mike,
> PubRef is not susceptible to malleability attacks because the blockchain =
is immutable.
This is not quite accurate.
While very old blocks are indeed immutable-in-practice, chain tips are not,=
and are often replaced.
At least specify that such data can only be referred to if buried under 100=
blocks.
--
There are a number of other issues:
* It strongly encourages pubkey reuse, reducing privacy.
* There is a design-decision wherein a SCRIPT can only access data in the t=
ransaction that triggers its execution.
In particular, it cannot access data in the block the transaction is in, =
or in past blocks.
For example, `OP_CHECKLOCKTIMEVERIFY` does not check the blockheight of t=
he block that the transaction is confirmed in, but instead checks only `nLo=
ckTime`, a field in the transaction.
* This lets us run SCRIPT in isolation on a transaction, exactly one time=
, when the transaction is about to be put into our mempool.
When a new block arrives, transactions in our mempool that are in the b=
lock do not need to have their SCRIPTs re-executed or re-validated.
> In order for a client to make use of the PUBREF operations they=E2=80=
=99ll need access to a database that look up public-keys and resolve their =
PUBREF index.=C2=A0 A value can be resolved to an index with a hash-table l=
ookup in O(1) constant time. Additionally, all instances of PUSHDATA can be=
indexed as an ordered list, resolution of a PUBREF index to the intended v=
alue would be an O(1) array lookup.=C2=A0 Although the data needed to build=
and resolve public references is already included with every full node, ad=
ditional computational effort is needed to build and maintain these indices=
- a tradeoff which provides smaller transaction sizes and relieving the ne=
ed to store repetitive data on the blockchain.
This is not only necessary at the creator of the transaction --- it is also=
necessary at every validator.
In particular, consider existing pruning nodes, which cannot refer to previ=
ous block data.
We would need to have another new database containing every `PUSHDATA` in e=
xistence.
And existing pruning nodes would need to restart from genesis, as this data=
base would not exist yet.
Regards,
ZmnSCPxj
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