From: Sebastian Falbesoner <sebastian.falbesoner@gmail.com>
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
Subject: [bitcoindev] Re: BIP-352: Limiting the number of per-group recipients (K_max)
Date: Thu, 19 Feb 2026 12:39:15 -0800 (PST) [thread overview]
Message-ID: <ea67d9d0-3e3e-4906-9c47-495f8011468en@googlegroups.com> (raw)
In-Reply-To: <b8edb433-c7b8-4d79-b710-e89a578eb42cn@googlegroups.com>
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Thanks for all the feedback left on the secp256k1 issue [1].
As no objections were raised to the proposed K_max protocol change, I've
opened a corresponding PR in the BIPs repository, where the discussion can
be continued:
https://github.com/bitcoin/bips/pull/2106
Best, Sebastian
[1] https://github.com/bitcoin-core/secp256k1/issues/1799#issuecomment-3842046237
ff.
On Wednesday, February 4, 2026 at 6:21:09 PM UTC+1 Sebastian Falbesoner
wrote:
> Hi list,
>
> In the course of working on a Silent Payments module for libsecp256k1 [1],
> we
> discovered that the scanning approach suggested in BIP-352 [2] suffers from
> very poor performance for adversarial transactions [3].
>
> One more recent proposal to mitigate this issue is by introducing a "K_max"
> protocol limit. This effectively limits the number of per-group recipients
> within a single transaction, i.e. the number of recipients sharing the same
> scan public key. In theory this is a backwards incompatible protocol
> change,
> in practice we believe that none of the existing SP wallets would be
> affected,
> for a reasonably high K_max (the example value used is K_max=1000, but this
> can be seen as a placeholder).
>
> See the following BIP change draft for more details and motivation:
>
> https://github.com/theStack/bips/commit/961d1442139ceecd6c0cc5775ef911d69aabed4c
>
> The discussion is on-going at the following issue:
> https://github.com/bitcoin-core/secp256k1/issues/1799 [4]
>
> If you have any concerns or feedback for this change, either for currently
> existing wallets or potential future use-cases that you could think of,
> please
> comment there. Most SP wallet developers that we are aware of have already
> been
> pinged on the issue. We are posting this here to reach a wider audience
> and to
> provide an alternative opportunity to comment, in case anyone doesn't want
> to
> use GitHub.
>
> Best,
> Sebastian
>
> [1] https://github.com/bitcoin-core/secp256k1/pull/1765
> [2]
> https://github.com/bitcoin/bips/blob/5d0f70a5cf4cfc429267cd6cc246ba3bcb949cb3/bip-0352.mediawiki?plain=1#L330
> [3]
> https://github.com/bitcoin-core/secp256k1/pull/1698#pullrequestreview-3341766084
> [4]
> https://github.com/bitcoin-core/secp256k1/issues/1799#issuecomment-3842046237
> ff. in particular
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prev parent reply other threads:[~2026-02-19 23:36 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-04 17:20 [bitcoindev] " Sebastian Falbesoner
2026-02-19 20:39 ` Sebastian Falbesoner [this message]
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