add libsecp256k1 wrapper for sign/verify.

libsecp256k1/bip340.go

@@ -0,0 +1,58 @@
+package libsecp256k1
+
+/*
+#cgo LDFLAGS: -lsecp256k1
+#include <secp256k1.h>
+#include <secp256k1_schnorrsig.h>
+#include <secp256k1_extrakeys.h>
+*/
+import "C"
+
+import (
+	"crypto/rand"
+	"errors"
+	"unsafe"
+)
+
+type Context struct {
+	ctx *C.secp256k1_context
+}
+
+func NewContext() (*Context, error) {
+	ctx := C.secp256k1_context_create(C.SECP256K1_CONTEXT_SIGN | C.SECP256K1_CONTEXT_VERIFY)
+	if ctx == nil {
+		return nil, errors.New("failed to create secp256k1 context")
+	}
+	return &Context{ctx: ctx}, nil
+}
+
+func (c *Context) Destroy() {
+	C.secp256k1_context_destroy(c.ctx)
+}
+
+func (c *Context) Sign(msg [32]byte, sk [32]byte) ([64]byte, error) {
+	var sig [64]byte
+
+	var keypair C.secp256k1_keypair
+	if C.secp256k1_keypair_create(c.ctx, &keypair, (*C.uchar)(unsafe.Pointer(&sk[0]))) != 1 {
+		return sig, errors.New("failed to parse private key")
+	}
+
+	var random [32]byte
+	rand.Read(random[:])
+
+	if C.secp256k1_schnorrsig_sign32(c.ctx, (*C.uchar)(unsafe.Pointer(&sig[0])), (*C.uchar)(unsafe.Pointer(&msg[0])), &keypair, (*C.uchar)(unsafe.Pointer(&random[0]))) != 1 {
+		return sig, errors.New("failed to sign message")
+	}
+
+	return sig, nil
+}
+
+func (c *Context) Verify(msg [32]byte, sig [64]byte, pk [32]byte) bool {
+	var xonly C.secp256k1_xonly_pubkey
+	if C.secp256k1_xonly_pubkey_parse(c.ctx, &xonly, (*C.uchar)(unsafe.Pointer(&pk[0]))) != 1 {
+		return false
+	}
+
+	return C.secp256k1_schnorrsig_verify(c.ctx, (*C.uchar)(unsafe.Pointer(&sig[0])), (*C.uchar)(unsafe.Pointer(&msg[0])), 32, &xonly) == 1
+}