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Date: Thu, 17 Apr 2025 18:52:34 +0000
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
From: "'Antoine Poinsot' via Bitcoin Development Mailing List" <bitcoindev@googlegroups.com>
Subject: [bitcoindev] Relax OP_RETURN standardness restrictions
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Hi,
Standardness rules exist for 3 mains reasons: mitigate DoS vectors, provide=
upgrade hooks, or as a nudge to deter some usages.
Bitcoin Core will by default only relay and mine transactions with at most =
a single OP_RETURN output, with a scriptPubKey no larger than 83 bytes. Thi=
s standardness rule falls into the third category: it aims to mildly deter =
data storage while still allowing a less harmful alternative than using non=
-provably-unspendable outputs.
Developers are now designing constructions that work around these limitatio=
ns. An example is Clementine, the recently-announced Citrea bridge, which u=
ses unspendable Taproot outputs to store data in its "WatchtowerChallenge" =
transaction due to the standardness restrictions on the size of OP_RETURNs[=
^0]. Meanwhile, we have witnessed in recent years that the nudge is ineffec=
tive to deter storing data onchain.
Since the restrictions on the usage of OP_RETURN outputs encourage harmful =
practices while being ineffective in deterring unwanted usage, i propose to=
drop them. I suggest to start by lifting the restriction on the size of th=
e scriptPubKey for OP_RETURN outputs, as a first minimal step to stop encou=
raging harmful behaviour, and to then proceed to lift the restriction on th=
e number of OP_RETURN outputs per transactions.
Antoine Poinsot
[^0]: See section 6.1 of their whitepaper here https://citrea.xyz/clementin=
e_whitepaper.pdf
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Hi,<br>
<br>
Standardness rules exist for 3 mains reasons: mitigate DoS vectors, provide=
upgrade hooks, or as a nudge to deter some usages.</div><div style=3D"font=
-family: Arial, sans-serif; font-size: 14px;"><br></div><div style=3D"font-=
family: Arial, sans-serif; font-size: 14px;">Bitcoin Core will by default o=
nly relay and mine transactions with at most a single OP_RETURN output, wit=
h a scriptPubKey no larger than 83 bytes. <span>This standardness rule fall=
s into the third category: it aims to mildly deter data storage while still=
allowing a less harmful alternative than using non-provably-unspendable ou=
tputs.</span></div><div style=3D"font-family: Arial, sans-serif; font-size:=
14px;"><span><br></span></div><div style=3D"font-family: Arial, sans-serif=
; font-size: 14px;">Developers are now designing constructions that work ar=
ound these limitations. An example is Clementine, the recently-announced Ci=
trea bridge, which uses unspendable Taproot outputs to store data in its "W=
atchtowerChallenge" transaction due to the standardness restrictions on the=
size of OP_RETURNs[^0]. Meanwhile, we have witnessed in recent years that =
the nudge is ineffective to deter storing data onchain.</div><div style=3D"=
font-family: Arial, sans-serif; font-size: 14px;"><br></div><div style=3D"f=
ont-family: Arial, sans-serif; font-size: 14px;">Since the restrictions on =
the usage of OP_RETURN outputs encourage harmful practices while being inef=
fective in deterring unwanted usage, i propose to drop them. I suggest to s=
tart by lifting the restriction on the size of the scriptPubKey for OP_RETU=
RN outputs, as a first minimal step to stop encouraging harmful behaviour, =
and to then proceed to lift the restriction on the number of OP_RETURN outp=
uts per transactions.<br></div><div style=3D"font-family: Arial, sans-serif=
; font-size: 14px;"><br></div><div style=3D"font-family: Arial, sans-serif;=
font-size: 14px;">Antoine Poinsot<br></div><div style=3D"font-family: Aria=
l, sans-serif; font-size: 14px;"><br></div><div style=3D"font-family: Arial=
, sans-serif; font-size: 14px;">[^0]: See section 6.1 of their whitepaper h=
ere <span><a target=3D"_blank" rel=3D"noreferrer nofollow noopener" href=3D=
"https://citrea.xyz/clementine_whitepaper.pdf">https://citrea.xyz/clementin=
e_whitepaper.pdf</a></span><br></div>
<p></p>
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