<p>Compact block filters do not index nulldata outputs. Therefore, a different mechanism would need to be used to retrieve notification outputs. Since BIP351 notification outputs have a distinct label, they could e.g. be provided as a set of Merkle branches for download, or via a new network service. All participants in BIP351 would need to retrieve the complete set, since discovery of ownership requires use of a private key and can only be performed client-side.</p>

CC BY-SA 4.0
2023-01-18T17:00:16.547Z
Even if BIP158 filters contained OP_RETURNs, it wouldn't be usable for BIP351 notification outputs, because filters by definition don't contain the full scriptPubKeys (if they did, it wouldn't have false positives), and as you say, the full notifications are needed for scanning.
Pieter Wuille
CC BY-SA 4.0
2023-01-18T16:23:07.453Z
2023-01-18T16:34:11.120Z
2023-01-18T16:34:11.120Z
Murch
<p>I have been reading a bit about BIP351 Private Payments. BIP351 uses nulldata outputs (<code>OP_RETURN</code>) to create shared secrets on the blockchain. Could these notification outputs be monitored client-side using compact block filters?</p>

<op-return><compact-client-side-block-filters>
Can BIP351 notification transactions be discovered via compact client-side block filters?
Murch
# Can BIP351 notification transactions be discovered via compact client-side block filters?

(Asked by: username_0 on 2023-01-18)

I have been reading a bit about BIP351 Private Payments. BIP351 uses nulldata outputs (`OP_RETURN`) to create shared secrets on the blockchain. Could these notification outputs be monitored client-side using compact block filters?

**Tags:** op-return, compact-client-side-block-filters


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## 1 answers

### Answer by username_0 on 2023-01-18. Score: 1 | Accepted answer

Compact block filters do not index nulldata outputs. Therefore, a different mechanism would need to be used to retrieve notification outputs. Since BIP351 notification outputs have a distinct label, they could e.g. be provided as a set of Merkle branches for download, or via a new network service. All participants in BIP351 would need to retrieve the complete set, since discovery of ownership requires use of a private key and can only be performed client-side.

> **Comments:**
> **username_1**: Even if BIP158 filters contained OP_RETURNs, it wouldn't be usable for BIP351 notification outputs, because filters by definition don't contain the full scriptPubKeys (if they did, it wouldn't have false positives), and as you say, the full notifications are needed for scanning.  

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