// Sign creates a signature on the hash under the given secret key.
func Sign(sk *eckey.SecretKey, hash []byte) (*Signature, error) {
// Generate random nonce
nonce:
k, kG, err := eckey.GenerateKeyPair()
if err != nil {
return nil, err
}
// Try again if kG is nil (point at infinity)
if kG == nil {
goto nonce
}
// Clear nonce after completion
defer k.Zero()
// Compute non-interactive challenge
e := util.Hash256d(append([]byte(hash), kG[:]...))
kInt := new(big.Int).SetBytes(k[:])
eInt := new(big.Int).SetBytes(e[:])
rInt := new(big.Int).SetBytes(sk[:])
// Compute s = k - er
s := new(big.Int)
s.Mul(eInt, rInt)
s.Sub(kInt, s)
s.Mod(s, eckey.S256.N)
// Serialize signature
sig := new(Signature)
copy(sig[:SignatureSize/2], e[:])
util.PaddedCopy(sig[SignatureSize/2:], s.Bytes(), SignatureSize/2)
return sig, nil
}
func BenchmarkSign(b *testing.B) {
for i := 0; i < b.N; i++ {
msg := []byte("Super short message")
sk, _, _ := eckey.GenerateKeyPair()
b.StartTimer()
Sign(sk, msg)
b.StopTimer()
}
}
