neo-go/pkg/crypto/rfc6979/dsa.go

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2019-02-25 22:44:14 +00:00
package rfc6979
import (
"crypto/dsa"
"hash"
"math/big"
)
// SignDSA signs an arbitrary length hash (which should be the result of hashing
// a larger message) using the private key, priv. It returns the signature as a
// pair of integers.
//
// Note that FIPS 186-3 section 4.6 specifies that the hash should be truncated
// to the byte-length of the subgroup. This function does not perform that
// truncation itself.
func SignDSA(priv *dsa.PrivateKey, hash []byte, alg func() hash.Hash) (r, s *big.Int, err error) {
n := priv.Q.BitLen()
if n&7 != 0 {
err = dsa.ErrInvalidPublicKey
return
}
n >>= 3
generateSecret(priv.Q, priv.X, alg, hash, func(k *big.Int) bool {
inv := new(big.Int).ModInverse(k, priv.Q)
r = new(big.Int).Exp(priv.G, k, priv.P)
r.Mod(r, priv.Q)
if r.Sign() == 0 {
return false
}
z := new(big.Int).SetBytes(hash)
s = new(big.Int).Mul(priv.X, r)
s.Add(s, z)
s.Mod(s, priv.Q)
s.Mul(s, inv)
s.Mod(s, priv.Q)
return s.Sign() != 0
})
return
}