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schnorr: Accept sig type in internal verify func.

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This modifies the internal schnorrVerify function to accept the
signature as a type instead of its raw serialized form.  This will
ultimately facilitate making it easier to switch over to more efficient
types for the r and s components.
This commit is contained in:
Dave Collins 2020-03-19 17:50:07 -05:00
parent 97294f5b41
commit 7542fa5268
No known key found for this signature in database
GPG Key ID: B8904D9D9C93D1F2
2 changed files with 13 additions and 22 deletions
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33
dcrec/secp256k1/schnorr/signature.go
View File

@ -86,7 +86,7 @@ func (sig Signature) IsEqual(otherSig *Signature) bool {
// schnorrVerify is the internal function for verification of a secp256k1
// Schnorr signature. A secure hash function may be passed for the calculation
// of r.
func schnorrVerify(sig []byte, pubkey *secp256k1.PublicKey, msg []byte, hashFunc func([]byte) []byte) (bool, error) {
func schnorrVerify(sig *Signature, pubkey *secp256k1.PublicKey, msg []byte, hashFunc func([]byte) []byte) (bool, error) {
curve := secp256k1.S256()
if len(msg) != scalarSize {
str := fmt.Sprintf("wrong size for message (got %v, want %v)",
@ -94,11 +94,6 @@ func schnorrVerify(sig []byte, pubkey *secp256k1.PublicKey, msg []byte, hashFunc
return false, schnorrError(ErrBadInputSize, str)
}
if len(sig) != SignatureSize {
str := fmt.Sprintf("wrong size for signature (got %v, want %v)",
len(sig), SignatureSize)
return false, schnorrError(ErrBadInputSize, str)
}
if pubkey == nil {
str := fmt.Sprintf("nil pubkey")
return false, schnorrError(ErrInputValue, str)
@ -109,11 +104,10 @@ func schnorrVerify(sig []byte, pubkey *secp256k1.PublicKey, msg []byte, hashFunc
return false, schnorrError(ErrPointNotOnCurve, str)
}
sigR := sig[:32]
sigS := sig[32:]
sigRCopy := make([]byte, scalarSize)
copy(sigRCopy, sigR)
toHash := append(sigRCopy, msg...)
rBytes := bigIntToEncodedBytes(sig.r)
toHash := make([]byte, 0, len(msg)+scalarSize)
toHash = append(toHash, rBytes[:]...)
toHash = append(toHash, msg...)
h := hashFunc(toHash)
hBig := new(big.Int).SetBytes(h)
@ -128,25 +122,22 @@ func schnorrVerify(sig []byte, pubkey *secp256k1.PublicKey, msg []byte, hashFunc
return false, schnorrError(ErrSchnorrHashValue, str)
}
// Convert s to big int.
sBig := encodedBytesToBigInt(copyBytes(sigS))
// We also can't have s greater than the order of the curve.
if sBig.Cmp(curve.N) >= 0 {
if sig.s.Cmp(curve.N) >= 0 {
str := fmt.Sprintf("s value is too big")
return false, schnorrError(ErrInputValue, str)
}
// r can't be larger than the curve prime.
rBig := encodedBytesToBigInt(copyBytes(sigR))
if rBig.Cmp(curve.P) == 1 {
if sig.r.Cmp(curve.P) == 1 {
str := fmt.Sprintf("given R was greater than curve prime")
return false, schnorrError(ErrBadSigRNotOnCurve, str)
}
// r' = hQ + sG
sBytes := bigIntToEncodedBytes(sig.s)
lx, ly := curve.ScalarMult(pubkey.X(), pubkey.Y(), h)
rx, ry := curve.ScalarBaseMult(sigS)
rx, ry := curve.ScalarBaseMult(sBytes[:])
rlx, rly := curve.Add(lx, ly, rx, ry)
if rly.Bit(0) == 1 {
@ -160,7 +151,7 @@ func schnorrVerify(sig []byte, pubkey *secp256k1.PublicKey, msg []byte, hashFunc
rlxB := bigIntToEncodedBytes(rlx)
// r == r' --> valid signature
if !bytes.Equal(sigR, rlxB[:]) {
if !bytes.Equal(rBytes[:], rlxB[:]) {
str := fmt.Sprintf("calculated R point was not given R")
return false, schnorrError(ErrUnequalRValues, str)
}
@ -170,8 +161,8 @@ func schnorrVerify(sig []byte, pubkey *secp256k1.PublicKey, msg []byte, hashFunc
// Verify is the generalized and exported function for the verification of a
// secp256k1 Schnorr signature. BLAKE256 is used as the hashing function.
func (sig Signature) Verify(msg []byte, pubkey *secp256k1.PublicKey) bool {
ok, _ := schnorrVerify(sig.Serialize(), pubkey, msg, chainhash.HashB)
func (sig *Signature) Verify(msg []byte, pubkey *secp256k1.PublicKey) bool {
ok, _ := schnorrVerify(sig, pubkey, msg, chainhash.HashB)
return ok
}

2
dcrec/secp256k1/schnorr/signature_test.go
View File

@ -237,7 +237,7 @@ func TestSchnorrSignAndVerify(t *testing.T) {
// Ensure the produced signature verifies as well.
pubKey := secp256k1.NewPrivateKey(hexToModNScalar(test.key)).PubKey()
ok, err := schnorrVerify(gotSigBytes, pubKey, hash, chainhash.HashB)
ok, err := schnorrVerify(gotSig, pubKey, hash, chainhash.HashB)
if err != nil {
t.Errorf("%s: signature failed to verify with error: %v", test.name,
err)