package main

import (
	"crypto/ecdh"
	"crypto/ecdsa"
	"crypto/elliptic"
	"fmt"
	"math/big"
)

func main() {
	k1 := []byte{42, 154, 0, 223, 84, 8, 55, 162, 117, 24, 142, 136, 128, 33, 143, 69, 194, 175, 251, 116, 183, 49, 190, 0, 228, 232, 21, 229, 203, 187, 226, 96}
	k2 := []byte{195, 5, 124, 117, 229, 83, 2, 62, 251, 203, 46, 195, 218, 215, 152, 7, 226, 64, 180, 63, 19, 183, 198, 37, 234, 194, 188, 222, 158, 85, 230, 191}

	privECDH, _ := ecdh.P256().NewPrivateKey(k1)
	privECDH2, _ := ecdh.P256().NewPrivateKey(k2)
	secretECDHE, _ := privECDH.ECDH(privECDH2.PublicKey())

	privECDSA := ecdhToECDSAPrivKey(privECDH)
	pubECDSA := ecdhToECDSAPublicKey(privECDH2.PublicKey())
	x, _ := privECDSA.Curve.ScalarMult(pubECDSA.X, pubECDSA.Y, privECDSA.D.Bytes())
	secretScalarMult := x.Bytes()
	secretMultFillBytes := make([]byte, 32)
	secretMultFillBytes = x.FillBytes(secretMultFillBytes)

	fmt.Printf("len:%d %x\n", len(secretECDHE), secretECDHE)                 // len:32 005363f5f75762476c04d7f32385629501368593df7e89aea4cdaebe4ae6c217
	fmt.Printf("len:%d %x\n", len(secretScalarMult), secretScalarMult)       // len:31 5363f5f75762476c04d7f32385629501368593df7e89aea4cdaebe4ae6c217
	fmt.Printf("len:%d %x\n", len(secretMultFillBytes), secretMultFillBytes) // len:32 005363f5f75762476c04d7f32385629501368593df7e89aea4cdaebe4ae6c217
}

func ecdhToECDSAPrivKey(key *ecdh.PrivateKey) *ecdsa.PrivateKey {
	return &ecdsa.PrivateKey{
		PublicKey: *ecdhToECDSAPublicKey(key.PublicKey()),
		D:         big.NewInt(0).SetBytes(key.Bytes()),
	}
}

func ecdhToECDSAPublicKey(key *ecdh.PublicKey) *ecdsa.PublicKey {
	rawKey := key.Bytes()
	return &ecdsa.PublicKey{
		Curve: elliptic.P256(),
		X:     big.NewInt(0).SetBytes(rawKey[1:33]),
		Y:     big.NewInt(0).SetBytes(rawKey[33:]),
	}
}