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From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
To: Christopher Gilliard <christopher.gilliard@gmail.com>,
	Bitcoin Protocol Discussion
	<bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP - limiting OP_RETURN / HF
Date: Fri, 16 Apr 2021 23:52:48 +0000	[thread overview]
Message-ID: <iU2J5dWMIgqAf312ZCNmx38_hcYsKrcuqx84kniWeEdb0wP8jPZPvwHK3P-q1yvmQ5OtdMCwMFqPgwmsL7BUfE8PGUlrxW4rOM3slwHun3E=@protonmail.com> (raw)
In-Reply-To: <CAK=nyAz5+yMUA=XDcunA1eeachSisaJoYE2_yzTLj=B0r4=w5A@mail.gmail.com>

Good morning Christopher,

> >> But more importantly, adding limitations on OP_RETURN transactions is not helpful.  Users who want to embed arbitrary data in their transactions can always do so by encoding their data inside the values of legacy multi-signature scriptpubkeys (pubkeys can be generated without knowing the private key in order to encode non-key related data).  Not only can users do this, users have done this in the past.  However, this behaviour is problematic because such multi-signature "data" scriptpubkeys are indistinguishable from "real" multisignature scriptpubkeys, and thus must be kept in the UTXO set.  This differs from outputs using OP_RETURN which are provably unspendable, and therefore can be safely omitted from the UTXO set.
>
> This sounds like a good justification to remove the legacy multi-signature capabilities as well.

The same technique can be used on P2PKH as well --- the "pubkey hash" need not be a hash of a public key, it can be a 20-byte commitment, or even an ASCII message like "ZmnSCPxj is the best" (20 characters, I counted).
There is nothing that *can* check if the hash of a public key is indeed the hash of a public key unless you actually reveal the public key.

If you need a 32-byte commitment, a P2WSH would work --- again the "script hash" need not be a hash of a script, it can be any 32-byte commitment.

In all these cases you have to waste 547 satoshi, but that tends to be small compared to tx fees currently.

Regards,
ZmnSCPxj


  parent reply	other threads:[~2021-04-16 23:53 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16  7:45 [bitcoin-dev] BIP - limiting OP_RETURN / HF Christopher Gilliard
2021-04-16 13:56 ` Russell O'Connor
2021-04-16 15:34   ` Christopher Gilliard
2021-04-16 15:55     ` Andrew Poelstra
2021-04-16 23:52     ` ZmnSCPxj [this message]
2021-04-17  3:57       ` Christopher Gilliard
2021-04-17 15:50         ` Peter Todd
2021-04-17 16:57           ` Christopher Gilliard
2021-04-16 13:59 ` Clark Moody
2021-04-16 15:33   ` Christopher Gilliard
2021-04-16 16:32 ` Jeremy
2021-04-16 17:05   ` Christopher Gilliard
2021-04-16 18:00     ` Jeremy
2021-04-16 19:15 ` Kostas Karasavvas
2021-04-16 20:12   ` Christopher Gilliard
2021-04-17  7:41     ` Kostas Karasavvas
2021-04-16 20:30   ` Ruben Somsen
2021-04-16 21:09     ` Christopher Gilliard
2021-04-20  1:23     ` yanmaani
2021-04-20  8:45       ` Zach Greenwood
2021-04-20 17:12         ` Christopher Gilliard
2021-04-20 19:07       ` Ruben Somsen
2021-05-03  5:17         ` ZmnSCPxj
2021-05-04 12:51           ` Ruben Somsen
2021-04-20  1:22 ` yanmaani

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