Convert Kyber.Point to Byte or Extract Byte from Using Kyber.Point

How to convert Kyber.Point type to Byte or Extract bytes from in Golang ?

I want the secret key (ECDH) to use with HMAC has hash key.

Code:

package main

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"math/big"

	"go.dedis.ch/kyber/v3/group/edwards25519"
	"go.dedis.ch/kyber/v3/util/random"
)

var rng = random.New()

func GenerateRandomASCIIString(length int) (string, error) {
	result := ""
	for {
		if len(result) >= length {
			return result, nil
		}
		num, err := rand.Int(rand.Reader, big.NewInt(int64(127)))
		if err != nil {
			return "", err
		}
		n := num.Int64()
		if n > 32 && n < 127 {
			result += string(n)
		}
	}
}
func main() {

	suite := edwards25519.NewBlakeSHA256Ed25519()

	X := suite.Point().Pick(rng)
	Y := suite.Point().Pick(rng)
	a := suite.Scalar().Pick(suite.RandomStream())
	b := suite.Scalar().Pick(suite.RandomStream())

	fmt.Printf("Titik yang disepakati Alice dan Bob :\n X:\t%s\n Y:\t%s\n\n", X, Y)
	fmt.Printf("Kunci Private Alice:\n %s\n\n", a)
	fmt.Printf("Kunci Private Bob:\n %s\n\n", b)

	aX := suite.Point().Mul(a, X)
	aY := suite.Point().Mul(a, Y)

	bX := suite.Point().Mul(b, X)
	bY := suite.Point().Mul(b, Y)

	//Punya Alice
	abX := suite.Point().Mul(a, bX)
	abY := suite.Point().Mul(a, bY)

	//Punya Bob
	baX := suite.Point().Mul(b, aX)
	baY := suite.Point().Mul(b, aY)

	fmt.Printf("Kunci Rahasia Alice:\n abX : %s\n abY : %s\n\n", abX, abY)
	fmt.Printf("Kunci Rahasia Bob:\n baX : %s\n baY : %s\n", baX, baY)

	data := "data"

	h := hmac.New(sha256.New, abX)

	h.Write([]byte(data))

	sha := hex.EncodeToString(h.Sum(nil))

	fmt.Println("Hasil Hash Alice: " + sha)

	g := hmac.New(sha256.New, baY)

	g.Write([]byte(data))

	sha2 := hex.EncodeToString(g.Sum(nil))

	fmt.Println("Hasil Hash Bob: " + sha2)
}

I am getting below errors when running the code:

./prog.go:77:15: cannot use abX (type kyber.Point) as type []byte in argument to hmac.New
./prog.go:90:15: cannot use baY (type kyber.Point) as type []byte in argument to hmac.New

I want abX/abY and baX/baY to Byte type.

If you are referring to kyber

Point interface of this library has a Data method which returns embedded byte data.

> Method Signature: Data() ([]byte, error).

Since abX and baY are both Point type you can directly call Data method on it to retrieve bytes.

package main

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"math/big"

	"go.dedis.ch/kyber/v3/group/edwards25519"
	"go.dedis.ch/kyber/v3/util/random"
)

var rng = random.New()

func GenerateRandomASCIIString(length int) (string, error) {
	result := ""
	for {
		if len(result) >= length {
			return result, nil
		}
		num, err := rand.Int(rand.Reader, big.NewInt(int64(127)))
		if err != nil {
			return "", err
		}
		n := num.Int64()
		if n > 32 && n < 127 {
			result += string(n)
		}
	}
}
func main() {

	suite := edwards25519.NewBlakeSHA256Ed25519()

	X := suite.Point().Pick(rng)
	Y := suite.Point().Pick(rng)
	a := suite.Scalar().Pick(suite.RandomStream())
	b := suite.Scalar().Pick(suite.RandomStream())

	fmt.Printf("Titik yang disepakati Alice dan Bob :\n X:\t%s\n Y:\t%s\n\n", X, Y)
	fmt.Printf("Kunci Private Alice:\n %s\n\n", a)
	fmt.Printf("Kunci Private Bob:\n %s\n\n", b)

	aX := suite.Point().Mul(a, X)
	aY := suite.Point().Mul(a, Y)

	bX := suite.Point().Mul(b, X)
	bY := suite.Point().Mul(b, Y)

	//Punya Alice
	abX := suite.Point().Mul(a, bX)
	abY := suite.Point().Mul(a, bY)

	//Punya Bob
	baX := suite.Point().Mul(b, aX)
	baY := suite.Point().Mul(b, aY)

	fmt.Printf("Kunci Rahasia Alice:\n abX : %s\n abY : %s\n\n", abX, abY)
	fmt.Printf("Kunci Rahasia Bob:\n baX : %s\n baY : %s\n", baX, baY)

    data, err := abX.Data()
    if err != nil {
      fmt.Println("Someting went wrong while extracting bytes")
    }
    fmt.Printf("DATA: %+v", data);

	h := hmac.New(sha256.New, data)

	h.Write([]byte(data))

	sha := hex.EncodeToString(h.Sum(nil))

	fmt.Println("Hasil Hash Alice: " + sha)

    data, err = baY.Data()
    if err != nil {
      fmt.Println("Someting went wrong while extracting bytes")
    }
    fmt.Printf("DATA: %+v", data);

	g := hmac.New(sha256.New, data)

	g.Write([]byte(data))

	sha2 := hex.EncodeToString(g.Sum(nil))

	fmt.Println("Hasil Hash Bob: " + sha2)
}