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Recover() didn't check whether the share ID is zero, which allows one manipulated share to determine the final recovered secret. The applicability is rather narrow: the Verify() function that checks secret commitments already did check whether the share ID is zero. Without calling Verify(), an attacker can already manipulate the shared secret already to a certain degree. Arguably, we wouldn't need to check it here, but it's cheap to do so.
lukevalenta
reviewed
Jul 15, 2026
| attackerValue := g.RandomScalar(rand.Reader) | ||
| tampered := make([]secretsharing.Share, 0, t+1) | ||
| tampered = append(tampered, secretsharing.Share{ | ||
| ID: g.NewScalar(), |
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Optional, to make it a little more clear that this is the zero ID.
Suggested change
| ID: g.NewScalar(), | |
| ID: g.NewScalar(), // a zero-valued scalar, the tampered share |
lukevalenta
approved these changes
Jul 15, 2026
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Recover() didn't check whether the share ID is zero, which allows one manipulated share to determine the final recovered secret. The applicability is rather narrow: the Verify() function that checks secret commitments already did check whether the share ID is zero. Without calling Verify(), an attacker can already manipulate the shared secret already to a certain degree. Arguably, we wouldn't need to check it here, but it's cheap to do so.