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From: Matt Corallo <lf-lists@mattcorallo.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Simplicity: An alternative to Script
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OK, fair enough, just wanted to make sure we were on the same page.
"Thorny issues there and there hasn't been a ton of effort put into what
Bitcoin integration and maintainability looks like" is a perfectly fair
response :)
Matt
On 10/30/17 18:32, Mark Friedenbach wrote:
> I was just making a factual observation/correction. This is Russell’s project and I don’t want to speak for him. Personally I don’t think the particulars of bitcoin integration design space have been thoroughly explored enough to predict the exact approach that will be used.
>
> It is possible to support a standard library of jets that are general purpose enough to allow the validation of new crypto primitives, like reusing sha2 to make Lamport signatures. Or use curve-agnostic jets to do Weil pairing validation. Or string manipulation and serialization jets to implement covenants. So I don’t think the situation is as dire as you make it sound.
>
>> On Oct 30, 2017, at 3:14 PM, Matt Corallo <lf-lists@mattcorallo.com> wrote:
>>
>> Are you anticipating it will be reasonably possible to execute more
>> complicated things in interpreted form even after "jets" are put in
>> place? If not its just a soft-fork to add new script operations and
>> going through the effort of making them compatible with existing code
>> and using a full 32 byte hash to represent them seems wasteful - might
>> as well just add a "SHA256 opcode".
>>
>> Either way it sounds like you're assuming a pretty aggressive soft-fork
>> cadence? I'm not sure if that's so practical right now (or are you
>> thinking it would be more practical if things were
>> drop-in-formally-verified-equivalent-replacements?).
>>
>> Matt
>>
>>> On 10/30/17 17:56, Mark Friedenbach wrote:
>>> Script versions makes this no longer a hard-fork to do. The script
>>> version would implicitly encode which jets are optimized, and what their
>>> optimized cost is.
>>>
>>>> On Oct 30, 2017, at 2:42 PM, Matt Corallo via bitcoin-dev
>>>> <bitcoin-dev@lists.linuxfoundation.org
>>>> <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>>>>
>>>> I admittedly haven't had a chance to read the paper in full details,
>>>> but I was curious how you propose dealing with "jets" in something
>>>> like Bitcoin. AFAIU, other similar systems are left doing hard-forks
>>>> to reduce the sigops/weight/fee-cost of transactions every time they
>>>> want to add useful optimized drop-ins. For obvious reasons, this seems
>>>> rather impractical and a potentially critical barrier to adoption of
>>>> such optimized drop-ins, which I imagine would be required to do any
>>>> new cryptographic algorithms due to the significant fee cost of
>>>> interpreting such things.
>>>>
>>>> Is there some insight I'm missing here?
>>>>
>>>> Matt
>>>>
>>>> On October 30, 2017 11:22:20 AM EDT, Russell O'Connor via bitcoin-dev
>>>> <bitcoin-dev@lists.linuxfoundation.org
>>>> <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>>>>
>>>> I've been working on the design and implementation of an
>>>> alternative to Bitcoin Script, which I call Simplicity. Today, I
>>>> am presenting my design at the PLAS 2017 Workshop
>>>> <http://plas2017.cse.buffalo.edu/> on Programming Languages and
>>>> Analysis for Security. You find a copy of my Simplicity paper at
>>>> https://blockstream.com/simplicity.pdf
>>>> <https://blockstream.com/simplicity.pdf>
>>>>
>>>> Simplicity is a low-level, typed, functional, native MAST language
>>>> where programs are built from basic combinators. Like Bitcoin
>>>> Script, Simplicity is designed to operate at the consensus layer.
>>>> While one can write Simplicity by hand, it is expected to be the
>>>> target of one, or multiple, front-end languages.
>>>>
>>>> Simplicity comes with formal denotational semantics (i.e.
>>>> semantics of what programs compute) and formal operational
>>>> semantics (i.e. semantics of how programs compute). These are both
>>>> formalized in the Coq proof assistant and proven equivalent.
>>>>
>>>> Formal denotational semantics are of limited value unless one can
>>>> use them in practice to reason about programs. I've used
>>>> Simplicity's formal semantics to prove correct an implementation
>>>> of the SHA-256 compression function written in Simplicity. I have
>>>> also implemented a variant of ECDSA signature verification in
>>>> Simplicity, and plan to formally validate its correctness along
>>>> with the associated elliptic curve operations.
>>>>
>>>> Simplicity comes with easy to compute static analyses that can
>>>> compute bounds on the space and time resources needed for
>>>> evaluation. This is important for both node operators, so that
>>>> the costs are knows before evaluation, and for designing
>>>> Simplicity programs, so that smart-contract participants can know
>>>> the costs of their contract before committing to it.
>>>>
>>>> As a native MAST language, unused branches of Simplicity programs
>>>> are pruned at redemption time. This enhances privacy, reduces the
>>>> block weight used, and can reduce space and time resource costs
>>>> needed for evaluation.
>>>>
>>>> To make Simplicity practical, jets replace common Simplicity
>>>> expressions (identified by their MAST root) and directly implement
>>>> them with C code. I anticipate developing a broad set of useful
>>>> jets covering arithmetic operations, elliptic curve operations,
>>>> and cryptographic operations including hashing and digital
>>>> signature validation.
>>>>
>>>> The paper I am presenting at PLAS describes only the foundation of
>>>> the Simplicity language. The final design includes extensions not
>>>> covered in the paper, including
>>>>
>>>> - full convent support, allowing access to all transaction data.
>>>> - support for signature aggregation.
>>>> - support for delegation.
>>>>
>>>> Simplicity is still in a research and development phase. I'm
>>>> working to produce a bare-bones SDK that will include
>>>>
>>>> - the formal semantics and correctness proofs in Coq
>>>> - a Haskell implementation for constructing Simplicity programs
>>>> - and a C interpreter for Simplicity.
>>>>
>>>> After an SDK is complete the next step will be making Simplicity
>>>> available in the Elements project <https://elementsproject.org/>
>>>> so that anyone can start experimenting with Simplicity in
>>>> sidechains. Only after extensive vetting would it be suitable to
>>>> consider Simplicity for inclusion in Bitcoin.
>>>>
>>>> Simplicity has a long ways to go still, and this work is not
>>>> intended to delay consideration of the various Merkelized Script
>>>> proposals that are currently ongoing.
>>>>
>>>> _______________________________________________
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>>>> bitcoin-dev@lists.linuxfoundation.org
>>>> <mailto:bitcoin-dev@lists.linuxfoundation.org>
>>>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>>
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