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From: Peter Todd <pete@petertodd.org>
Date: Wed, 06 Aug 2014 10:20:25 -0700
To: Mark Friedenbach <mark@monetize.io>,
	Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Message-ID: <cafd8184-f589-4709-90f3-f3a38f2dd8d0@email.android.com>
Subject: Re: [Bitcoin-development] deterministic transaction expiration
Precedence: list

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On 6 August 2014 09:31:24 GMT-07:00, Mark Friedenbach <mark@monetize.io> wrote:
>I highly doubt that is the best approach.
>
>If this nExpiry field is a consensus rule, then the Merkle tree or the
>appropriate paths through needs to be included with the transaction as
>part of the network and on-disk data structures, so that proper
>validation can be done. This would be both more disruptive and less
>efficient than simply adding an nExpiry field to the transaction
>format,
>as we do in Freimarkets.

The general case doesn't require transmission of any merkle data; it is derived from the tx data. Equally changing a data format is certainly: note how Freimarkets has no third-party library support because you've made it incompatible with the standard Bitcoin data structures. Merkle radix tree formatting OTOH is just a cryptographically committed extension of the tag-value concept seen in protobuf, among others.

re: efficiency, we need fundamental improvements in efficiency, not little micro-optimisations everywhere done at high cost to maintainability.

re: validation, note how the merkle radix tree meets that need by allowing the absence of data to be proven.

>If the field is pre-consensus (a mempool gentleman's agreement), then
>it
>has no business in the transaction structure at all and should be
>packaged in some sort of envelope container.

It's also rather useless without consensus. Expiry is only useful if it is a guarantee, if not you might as well just implement tx replacement directly.

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