generate nonce value in golang

package main

import (

"fmt"

"crypto/aes"

"crypto/cipher"

"crypto/rand"

"encoding/base64"

"math/big"

)

const nonceLen = 40

func main() {

nonce := make([]byte, 12)

for i := 0; i < 4; i++ {

nonce[i] = 0

}

if _, err := rand.Read(nonce[4:]); err != nil {

panic("Failure in NewCipher: " + err.Error())

}

// Encode counter to plaintext

pt := make([]byte, 16)

ctr := big.NewInt(11)

pad := 8 - len(ctr.Bytes())

fmt.Printf("pad = %d\n", pad)

copy(pt[pad:], ctr.Bytes())

fmt.Printf("pt = %d\n", pt)

// Encrypt AES256

key := make([]byte, 32)

if _, err := rand.Read(key); err != nil {

panic("Failure in NewCipher: " + err.Error())

}

c, err := aes.NewCipher(key)

if err != nil {

panic("Failure in NewCipher: " + err.Error())

}

gcm, err := cipher.NewGCM(c)

if err != nil {

panic("Failure in NewGCM: " + err.Error())

}

ret := make([]byte, nonceLen)

ct := gcm.Seal(nil, nonce, pt, nil)

copy(ret, nonce[4:])

copy(ret[8:], ct)

fmt.Println(base64.RawURLEncoding.EncodeToString(ret))

}