simple-totp

simple-totp.go

package main

import (
	"crypto/hmac"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"crypto/subtle"
	"encoding/binary"
	"fmt"
	prf "hash"
	"math"
)

func main() {
	key := []byte("1234567890123456789012345678901234567890123456789012345678901234")

	for _, unixtime := range []int64{59, 1111111109, 1111111111, 1234567890, 2000000000, 20000000000} {
		fmt.Printf("%08d \n", Criar(sha1.New, key[0:20], unixtime, 30, 0, 8))
		fmt.Printf("%08d \n", Criar(sha256.New, key[0:32], unixtime, 30, 0, 8))
		fmt.Printf("%08d \n", Criar(sha512.New, key[0:64], unixtime, 30, 0, 8))
	}
}

func Criar(h func() prf.Hash, chave []byte, tempo, intervalo, inicio int64, comprimento int) uint32 {
	tempo = (tempo - inicio) / intervalo

	derivacao := hmac.New(h, chave)
	binary.Write(derivacao, binary.BigEndian, tempo)

	hash := derivacao.Sum(nil)
	posicao := hash[len(hash)-1] & 0x0F
	hash = hash[posicao:posicao+4]

	codigo := binary.BigEndian.Uint32(hash) & 0x7FFFFFFF

	return codigo % uint32(math.Pow10(comprimento))
}

func Comparar(x, y uint32) int {
	var xb, yb = make([]byte, 8), make([]byte, 8)

	binary.LittleEndian.PutUint32(xb, x)
	binary.LittleEndian.PutUint32(yb, y)

	return subtle.ConstantTimeCompare(xb, yb)
}