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70 lines
2.2 KiB
70 lines
2.2 KiB
// +build !libsecp256k1
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package secp256k1
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import (
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"math/big"
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secp256k1 "github.com/btcsuite/btcd/btcec"
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"github.com/tendermint/tendermint/crypto"
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)
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// used to reject malleable signatures
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// see:
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// - https://github.com/ethereum/go-ethereum/blob/f9401ae011ddf7f8d2d95020b7446c17f8d98dc1/crypto/signature_nocgo.go#L90-L93
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// - https://github.com/ethereum/go-ethereum/blob/f9401ae011ddf7f8d2d95020b7446c17f8d98dc1/crypto/crypto.go#L39
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var secp256k1halfN = new(big.Int).Rsh(secp256k1.S256().N, 1)
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// Sign creates an ECDSA signature on curve Secp256k1, using SHA256 on the msg.
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// The returned signature will be of the form R || S (in lower-S form).
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func (privKey PrivKey) Sign(msg []byte) ([]byte, error) {
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priv, _ := secp256k1.PrivKeyFromBytes(secp256k1.S256(), privKey[:])
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sig, err := priv.Sign(crypto.Sha256(msg))
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if err != nil {
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return nil, err
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}
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sigBytes := serializeSig(sig)
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return sigBytes, nil
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}
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// VerifyBytes verifies a signature of the form R || S.
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// It rejects signatures which are not in lower-S form.
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func (pubKey PubKey) VerifySignature(msg []byte, sigStr []byte) bool {
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if len(sigStr) != 64 {
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return false
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}
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pub, err := secp256k1.ParsePubKey(pubKey[:], secp256k1.S256())
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if err != nil {
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return false
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}
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// parse the signature:
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signature := signatureFromBytes(sigStr)
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// Reject malleable signatures. libsecp256k1 does this check but btcec doesn't.
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// see: https://github.com/ethereum/go-ethereum/blob/f9401ae011ddf7f8d2d95020b7446c17f8d98dc1/crypto/signature_nocgo.go#L90-L93
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if signature.S.Cmp(secp256k1halfN) > 0 {
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return false
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}
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return signature.Verify(crypto.Sha256(msg), pub)
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}
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// Read Signature struct from R || S. Caller needs to ensure
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// that len(sigStr) == 64.
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func signatureFromBytes(sigStr []byte) *secp256k1.Signature {
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return &secp256k1.Signature{
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R: new(big.Int).SetBytes(sigStr[:32]),
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S: new(big.Int).SetBytes(sigStr[32:64]),
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}
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}
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// Serialize signature to R || S.
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// R, S are padded to 32 bytes respectively.
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func serializeSig(sig *secp256k1.Signature) []byte {
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rBytes := sig.R.Bytes()
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sBytes := sig.S.Bytes()
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sigBytes := make([]byte, 64)
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// 0 pad the byte arrays from the left if they aren't big enough.
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copy(sigBytes[32-len(rBytes):32], rBytes)
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copy(sigBytes[64-len(sBytes):64], sBytes)
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return sigBytes
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}
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