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From: Mark Friedenbach <mark@friedenbach.org>
To: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: [bitcoin-dev] Merkle branch verification & tail-call semantics for generalized MAST
Date: Wed, 6 Sep 2017 17:38:55 -0700	[thread overview]
Message-ID: <5B6756D0-6BEF-4A01-BDB8-52C646916E29@friedenbach.org> (raw)

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


             reply	other threads:[~2017-09-07  0:39 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-07  0:38 Mark Friedenbach [this message]
2017-09-08  9:21 ` [bitcoin-dev] Merkle branch verification & tail-call semantics for generalized MAST 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
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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