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From: Jeff Garzik <jgarzik@bitpay.com>
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Subject: [Bitcoin-development] On OP_RETURN in upcoming 0.9 release
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An update in forthcoming 0.9 release includes a change to make
OP_RETURN standard, permitted a small amount of metadata to be
attached to a transaction:
https://github.com/bitcoin/bitcoin/pull/2738

There was always going to be some level of controversy attached to
this.  However, some issues, perceptions and questions are bubbling
up, and it seemed fair to cover them on the list, not just IRC.

1) FAQ:  Why 80 bytes of data?  This is the leading programmer
question, and it was not really documented well at all.  Simple
answer:  2x SHA256 or 1x SHA512, plus some tiny bit of metadata.  Some
schemes are of the nature "BOND<hash>" rather than just plain hash.
A common IRC proposal seems to lean towards reducing that from 80.
I'll leave it to the crowd to argue about size from there. I do think
regular transactions should have the ability to include some metadata.

2) Endorsement of chain data storage.  Listening to bitcoin conference
corridor discussions, reading forum posts and the occasional article
have over-simplified the situation to "core devs endorse data storage
over blockchain!  let me start uploading my naughty movie collection!
IM over blockchain, woo hoo!"

Nothing could be further from the truth.  It's a way to make data
/less damaging/, not an endorsement of data storage in chain as a good
idea.  MasterCoin and other projects were doing -even worse- things,
such as storing data in forever-unspendable TX outputs, bloating the
UTXO for eternity.

It seems reasonable to have a release note to this effect in the 0.9
release announcement, IMO.

-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/