Saman Bank TOTP implementation

saman_totp.go

package main

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha1"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"time"
)
func main() {
	token := "6D436B6A54FF6916E7611CA8168C4E94210790F4"
	pin := "123456"
	keyHex := []byte(token+pin)
	key := make([]byte, len(keyHex)/2)
	_, err := hex.Decode(key, keyHex)
	if err != nil {
		panic(err)
	}

	now := time.Now().UnixNano() / int64(60*time.Second)

	buffer := new(bytes.Buffer)
	binary.Write(buffer, binary.BigEndian, now)

	mac := hmac.New(sha1.New, key)
	mac.Write(buffer.Bytes())
	sum := mac.Sum(nil)

	b := sum[len(sum)-1] & 15
	fmt.Println(b)
	fmt.Println(binary.BigEndian.Uint32(sum[b:b+4]) % 100000000)
}