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btcec: check if recovered pk is at point of infinity #1750

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merged 2 commits into from Sep 13, 2021
Merged

btcec: check if recovered pk is at point of infinity #1750

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74f1360
btcec: check if recovered pk is at point of infinity
MariusVanDerWijden Sep 13, 2021
1ff14ef
btcec: added testcase for point at infinity
MariusVanDerWijden Sep 13, 2021
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4 changes: 4 additions & 0 deletions btcec/signature.go
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Expand Up @@ -353,6 +353,10 @@ func recoverKeyFromSignature(curve *KoblitzCurve, sig *Signature, msg []byte,
// step to prevent the jacobian conversion back and forth.
Qx, Qy := curve.Add(sRx, sRy, minuseGx, minuseGy)

if Qx.Sign() == 0 && Qy.Sign() == 0 {
return nil, errors.New("point (Qx, Qy) equals the point at infinity")
}

return &PublicKey{
Curve: curve,
X: Qx,
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6 changes: 6 additions & 0 deletions btcec/signature_test.go
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Expand Up @@ -549,6 +549,12 @@ var recoveryTests = []struct {
sig: "0100b1693892219d736caba55bdb67216e485557ea6b6af75f37096c9aa6a5a75f00b940b1d03b21e36b0e47e79769f095fe2ab855bd91e3a38756b7d75a9c4549",
err: fmt.Errorf("invalid square root"),
},
{
// Point at infinity recovered
msg: "6b8d2c81b11b2d699528dde488dbdf2f94293d0d33c32e347f255fa4a6c1f0a9",
sig: "0079be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f817986b8d2c81b11b2d699528dde488dbdf2f94293d0d33c32e347f255fa4a6c1f0a9",
err: fmt.Errorf("point (Qx, Qy) equals the point at infinity"),
},
{
// Low R and S values.
msg: "ba09edc1275a285fb27bfe82c4eea240a907a0dbaf9e55764b8f318c37d5974f",
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