crypto, crypto/secp256k1: add CompressPubkey (#15626)

This adds the inverse to DecompressPubkey and improves a few minor
details in crypto/secp256k1.

1 files changed, 28 insertions, 8 deletions

diff --git a/crypto/secp256k1/secp256.go b/crypto/secp256k1/secp256.go
index 00a1f8aaa..eefbb99ee 100644
--- a/crypto/secp256k1/secp256.go
+++ b/crypto/secp256k1/secp256.go
@@ -115,7 +115,7 @@ func RecoverPubkey(msg []byte, sig []byte) ([]byte, error) {
 		sigdata = (*C.uchar)(unsafe.Pointer(&sig[0]))
 		msgdata = (*C.uchar)(unsafe.Pointer(&msg[0]))
 	)
-	if C.secp256k1_ecdsa_recover_pubkey(context, (*C.uchar)(unsafe.Pointer(&pubkey[0])), sigdata, msgdata) == 0 {
+	if C.secp256k1_ext_ecdsa_recover(context, (*C.uchar)(unsafe.Pointer(&pubkey[0])), sigdata, msgdata) == 0 {
 		return nil, ErrRecoverFailed
 	}
 	return pubkey, nil
@@ -130,22 +130,42 @@ func VerifySignature(pubkey, msg, signature []byte) bool {
 	sigdata := (*C.uchar)(unsafe.Pointer(&signature[0]))
 	msgdata := (*C.uchar)(unsafe.Pointer(&msg[0]))
 	keydata := (*C.uchar)(unsafe.Pointer(&pubkey[0]))
-	return C.secp256k1_ecdsa_verify_enc(context, sigdata, msgdata, keydata, C.size_t(len(pubkey))) != 0
+	return C.secp256k1_ext_ecdsa_verify(context, sigdata, msgdata, keydata, C.size_t(len(pubkey))) != 0
 }
 
 // DecompressPubkey parses a public key in the 33-byte compressed format.
 // It returns non-nil coordinates if the public key is valid.
-func DecompressPubkey(pubkey []byte) (X, Y *big.Int) {
+func DecompressPubkey(pubkey []byte) (x, y *big.Int) {
 	if len(pubkey) != 33 {
 		return nil, nil
 	}
-	buf := make([]byte, 65)
-	bufdata := (*C.uchar)(unsafe.Pointer(&buf[0]))
-	pubkeydata := (*C.uchar)(unsafe.Pointer(&pubkey[0]))
-	if C.secp256k1_decompress_pubkey(context, bufdata, pubkeydata) == 0 {
+	var (
+		pubkeydata = (*C.uchar)(unsafe.Pointer(&pubkey[0]))
+		pubkeylen  = C.size_t(len(pubkey))
+		out        = make([]byte, 65)
+		outdata    = (*C.uchar)(unsafe.Pointer(&out[0]))
+		outlen     = C.size_t(len(out))
+	)
+	if C.secp256k1_ext_reencode_pubkey(context, outdata, outlen, pubkeydata, pubkeylen) == 0 {
 		return nil, nil
 	}
-	return new(big.Int).SetBytes(buf[1:33]), new(big.Int).SetBytes(buf[33:])
+	return new(big.Int).SetBytes(out[1:33]), new(big.Int).SetBytes(out[33:])
+}
+
+// CompressPubkey encodes a public key to 33-byte compressed format.
+func CompressPubkey(x, y *big.Int) []byte {
+	var (
+		pubkey     = S256().Marshal(x, y)
+		pubkeydata = (*C.uchar)(unsafe.Pointer(&pubkey[0]))
+		pubkeylen  = C.size_t(len(pubkey))
+		out        = make([]byte, 33)
+		outdata    = (*C.uchar)(unsafe.Pointer(&out[0]))
+		outlen     = C.size_t(len(out))
+	)
+	if C.secp256k1_ext_reencode_pubkey(context, outdata, outlen, pubkeydata, pubkeylen) == 0 {
+		panic("libsecp256k1 error")
+	}
+	return out
 }
 
 func checkSignature(sig []byte) error {