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fix vss #324

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fix vss #324

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2 changes: 1 addition & 1 deletion crypto/vss/feldman_vss.go
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Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,7 @@ func (share *Share) Verify(ec elliptic.Curve, threshold int, vs Vs) bool {
}

func (shares Shares) ReConstruct(ec elliptic.Curve) (secret *big.Int, err error) {
if shares != nil && shares[0].Threshold > len(shares) {
if shares != nil && shares[0].Threshold+1 > len(shares) {
return nil, ErrNumSharesBelowThreshold
}
modN := common.ModInt(ec.Params().N)
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6 changes: 4 additions & 2 deletions crypto/vss/feldman_vss_test.go
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Expand Up @@ -103,15 +103,17 @@ func TestReconstruct(t *testing.T) {
_, shares, err := Create(tss.EC(), threshold, secret, ids, rand.Reader)
assert.NoError(t, err)

secret2, err2 := shares[:threshold-1].ReConstruct(tss.EC())
secret2, err2 := shares[:threshold].ReConstruct(tss.EC())
assert.Error(t, err2) // not enough shares to satisfy the threshold
assert.Nil(t, secret2)

secret3, err3 := shares[:threshold].ReConstruct(tss.EC())
secret3, err3 := shares[:threshold+1].ReConstruct(tss.EC())
assert.NoError(t, err3)
assert.NotZero(t, secret3)
assert.Zero(t, secret.Cmp(secret3))

secret4, err4 := shares[:num].ReConstruct(tss.EC())
assert.NoError(t, err4)
assert.NotZero(t, secret4)
assert.Zero(t, secret.Cmp(secret4))
}
4 changes: 2 additions & 2 deletions ecdsa/keygen/local_party_test.go
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Expand Up @@ -279,9 +279,9 @@ keygen:

// fails if threshold cannot be satisfied (bad share)
{
badShares := pShares[:threshold]
badShares := pShares[:threshold+1]
badShares[len(badShares)-1].Share.Set(big.NewInt(0))
uj, err := pShares[:threshold].ReConstruct(tss.S256())
uj, err := pShares[:threshold+1].ReConstruct(tss.S256())
assert.NoError(t, err)
assert.NotEqual(t, parties[j].temp.ui, uj)
BigXjX, BigXjY := tss.EC().ScalarBaseMult(uj.Bytes())
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4 changes: 2 additions & 2 deletions eddsa/keygen/local_party_test.go
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Expand Up @@ -147,9 +147,9 @@ keygen:

// fails if threshold cannot be satisfied (bad share)
{
badShares := pShares[:threshold]
badShares := pShares[:threshold+1]
badShares[len(badShares)-1].Share.Set(big.NewInt(0))
uj, err := pShares[:threshold].ReConstruct(tss.Edwards())
uj, err := pShares[:threshold+1].ReConstruct(tss.Edwards())
assert.NoError(t, err)
assert.NotEqual(t, parties[j].temp.ui, uj)
BigXjX, BigXjY := tss.Edwards().ScalarBaseMult(uj.Bytes())
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