More clarity in threshold sign comments#30
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jordanschalm
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Jul 10, 2025
| // For safety, the function attemps the reconstruction and only returns a signature that is valid against the group public key. | ||
| // This is done by first reconstructing the signature and then validating it against the group public key. | ||
| // The reconstructed may fail the validation if at least one signature share added via `TrustedAdd` is invalid. | ||
| // The threshold signature is reconstructed only once and is cached for subsequent calls. |
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A literal reading of this comment implies it, but I assume we don't cache reconstructed signatures that fail validation? 😄
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Yes an invalid reconstructed signature isn't cached, I'll update the wording. However, your question raises a useful point: Since the invalid signature isn't cached, the function would attempt a reconstruction each time it is called, which is useless because there is no way currently to update the internal state of signature shares, once we reach the threshold of shares. All reconstructed signatures in the current code are computed from the same internal state and are equal.
There are two ways to improve this:
- cache the invalidity of the reconstructed signature so that we don't attempt a new reconstruction each time. Once set, this flag is immutable (because the internal state is immutable).
- add a new API to remove signature shares, which is useful to remove invalid shares. This allows to continue updating the internal state and not have it fixed at some point.
I can update this in a subsequent PR, my preference is the second option.
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