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From: Mark Friedenbach <mark@friedenbach.org>
To: Bitcoin Protocol Discussion
	<bitcoin-dev@lists.linuxfoundation.org>,
	Luke Dashjr <luke@dashjr.org>
Subject: Re: [bitcoin-dev] Merkle branch verification & tail-call semantics for generalized MAST
Date: Fri, 27 Oct 2017 21:40:01 -0700	[thread overview]
Message-ID: <3FE16880-868C-40BA-BCC5-954B15478FB2@friedenbach.org> (raw)
In-Reply-To: <5B6756D0-6BEF-4A01-BDB8-52C646916E29@friedenbach.org>

I have completed updating the three BIPs with all the feedback that I have received so far. In short summary, here is an incomplete list of the changes that were made:

* Modified the hashing function fast-SHA256 so that an internal node cannot be interpreted simultaneously as a leaf.
* Changed MERKLEBRANCHVERIFY to verify a configurable number of elements from the tree, instead of just one.
* Changed MERKLEBRANCHVERIFY to have two modes: one where the inputs are assumed to be hashes, and one where they are run through double-SHA256 first.
* Made tail-call eval compatible with BIP141’s CLEANSTACK consensus rule by allowing parameters to be passed on the alt-stack.
* Restricted tail-call eval to segwit scripts only, so that checking sigop and opcode limits of the policy script would not be necessary.

There were a bunch of other small modifications, typo fixes, and optimizations that were made as well.

I am now ready to submit these BIPs as a PR against the bitcoin/bips repo, and I request that the BIP editor assign numbers.

Thank you,
Mark Friedenbach

> On Sep 6, 2017, at 5:38 PM, Mark Friedenbach <mark@friedenbach.org> wrote:
> 
> I would like to propose two new script features to be added to the
> bitcoin protocol by means of soft-fork activation. These features are
> a new opcode, MERKLE-BRANCH-VERIFY (MBV) and tail-call execution
> semantics.
> 
> In brief summary, MERKLE-BRANCH-VERIFY allows script authors to force
> redemption to use values selected from a pre-determined set committed
> to in the scriptPubKey, but without requiring revelation of unused
> elements in the set for both enhanced privacy and smaller script
> sizes. Tail-call execution semantics allows a single level of
> recursion into a subscript, providing properties similar to P2SH while
> at the same time more flexible.
> 
> These two features together are enough to enable a range of
> applications such as tree signatures (minus Schnorr aggregation) as
> described by Pieter Wuille [1], and a generalized MAST useful for
> constructing private smart contracts. It also brings privacy and
> fungibility improvements to users of counter-signing wallet/vault
> services as unique redemption policies need only be revealed if/when
> exceptional circumstances demand it, leaving most transactions looking
> the same as any other MAST-enabled multi-sig script.
> 
> I believe that the implementation of these features is simple enough,
> and the use cases compelling enough that we could BIP 8/9 rollout of
> these features in relatively short order, perhaps before the end of
> the year.
> 
> I have written three BIPs to describe these features, and their
> associated implementation, for which I now invite public review and
> discussion:
> 
> Fast Merkle Trees
> BIP: https://gist.github.com/maaku/41b0054de0731321d23e9da90ba4ee0a
> Code: https://github.com/maaku/bitcoin/tree/fast-merkle-tree
> 
> MERKLEBRANCHVERIFY
> BIP: https://gist.github.com/maaku/bcf63a208880bbf8135e453994c0e431
> Code: https://github.com/maaku/bitcoin/tree/merkle-branch-verify
> 
> Tail-call execution semantics
> BIP: https://gist.github.com/maaku/f7b2e710c53f601279549aa74eeb5368
> Code: https://github.com/maaku/bitcoin/tree/tail-call-semantics
> 
> Note: I have circulated this idea privately among a few people, and I
> will note that there is one piece of feedback which I agree with but
> is not incorporated yet: there should be a multi-element MBV opcode
> that allows verifying multiple items are extracted from a single
> tree. It is not obvious how MBV could be modified to support this
> without sacrificing important properties, or whether should be a
> separate multi-MBV opcode instead.
> 
> Kind regards,
> Mark Friedenbach



  parent reply	other threads:[~2017-10-28  4:40 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-07  0:38 [bitcoin-dev] Merkle branch verification & tail-call semantics for generalized MAST Mark Friedenbach
2017-09-08  9:21 ` Johnson Lau
2017-09-12  2:03   ` Mark Friedenbach
2017-09-12  2:13     ` Bryan Bishop
2017-09-12  8:55     ` Johnson Lau
2017-09-12 19:57       ` Mark Friedenbach
2017-09-12 23:27         ` Karl Johan Alm
2017-09-13  9:41           ` Peter Todd
2017-09-11 20:37 ` Adán Sánchez de Pedro Crespo
2017-09-19  0:46 ` Mark Friedenbach
2017-09-19  3:09   ` [bitcoin-dev] cleanstack alt stack & softfork improvements (Was: Merkle branch verification & tail-call semantics for generalized MAST) Luke Dashjr
2017-09-19  7:33     ` Mark Friedenbach
2017-09-22 20:32       ` Sergio Demian Lerner
2017-09-22 21:11         ` Mark Friedenbach
2017-09-22 21:32           ` Sergio Demian Lerner
2017-09-22 21:39             ` Mark Friedenbach
2017-09-22 21:54               ` Sergio Demian Lerner
2017-09-22 22:07                 ` Mark Friedenbach
2017-09-22 22:09                 ` Pieter Wuille
2021-04-09  8:15                   ` [bitcoin-dev] maximum block height on transaction Erik Aronesty
2021-04-09 11:39                     ` Russell O'Connor
2021-04-09 15:54                       ` Jeremy
2021-04-12 20:04                         ` Billy Tetrud
2021-04-16  4:24                           ` ZmnSCPxj
2021-05-03  2:30                             ` ZmnSCPxj
2017-09-20  5:13     ` [bitcoin-dev] cleanstack alt stack & softfork improvements (Was: Merkle branch verification & tail-call semantics for generalized MAST) Johnson Lau
2017-09-20 19:29       ` Mark Friedenbach
2017-09-21  3:58         ` Johnson Lau
2017-09-21  4:11       ` Luke Dashjr
2017-09-21  8:02         ` Johnson Lau
2017-09-21 16:33           ` Luke Dashjr
2017-09-21 17:38             ` Johnson Lau
2017-09-30 23:23 ` [bitcoin-dev] Merkle branch verification & tail-call semantics for generalized MAST Luke Dashjr
2017-09-30 23:51   ` Mark Friedenbach
2017-10-02 17:15     ` Russell O'Connor
2017-10-28  4:40 ` Mark Friedenbach [this message]
2017-11-01  8:43   ` Luke Dashjr
2017-11-01 15:08     ` Mark Friedenbach
2017-11-04  7:59       ` Luke Dashjr

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