Subject: [bitcoindev] Standard Unstructured Annex

From: Peter Todd <[email-masked]>
Date: Thu, 20 Mar 2025 00:27:36 +0000

I'm working on adding support for the taproot annex to Libre Relay:

https://github.com/petertodd/bitcoin/commit/04c8e449a34e74e048bf5751d13592a22763ff7e

I'm basing this on Joost Jager's pull-req: https://github.com/bitcoin/bitcoin/pull/27926

Specifically, transactions containing taproot annexes will be standard
if:

1) All non-empty annexes start with the byte 0x00, to distinguish them
   from consensus-relevant annexes. This ensures that any use of the
   annex will not conflict with future soft-forks that may assign
   meaning to the annex.

2) All inputs have an annex. This ensures that use of the annex is
   opt-in, preventing transaction pinning attacks in multi-party
   protocols. This requirement may be relaxed in the future, eg to allow
   spends of keyless outputs, and/or if RBF for witness-only
   replacements is implemented.

An example of a transaction meeting these requirements is:

010000000001011a559447098aaa14dec0c62ea55f43f9ce6bda07d1759f11b634334ab9da939b0000000000ffffffff010000000000000000076a05616e6e657802406840b6fa27a00ba001cc92797ce4f3ab7b7a32c21d1fce49e893b42e506bd92e8db187966a84ef799915cf671334cc59779915b192bfb66b2afcf384bb61d0f422500049276d20616e20616e6e6578212041726520796f7520616e20616e6e65783f0000000000

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org

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