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

-- 
You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group.
To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/ea67d9d0-3e3e-4906-9c47-495f8011468en%40googlegroups.com.