Hur TOTP fungerar: Implementering av RFC 6238-algoritmen i Python, JavaScript & Go

import base64
import hashlib
import hmac
import struct
import time
def generate_totp(secret_base32: str, timestamp: int = None, step: int = 30, digits: int = 6) -> str:
"""
Generera en RFC 6238-kompatibel TOTP-kod.
:param secret_base32: Delad hemlig nyckel i Base32-format (t.ex. ‘JBSWY3DPEHPK3PXP’)
:param timestamp: Unix-epoktidsstämpel i sekunder. Standard är time.time()
:param step: Tidsfönster i sekunder (standard: 30)
:param digits: Antal utdatasiffror (standard: 6)
:return: Nollutfylld OTP-sträng (t.ex. ‘045812’)
"""
if timestamp is None:
timestamp = int(time.time())
# 1. Normalisera Base32-strängen och lägg till '=' som utfyllnad
normalized_secret = secret_base32.replace(" ", "").upper()
padding_needed = (8 - len(normalized_secret) % 8) % 8
normalized_secret += "=" * padding_needed
key_bytes = base64.b32decode(normalized_secret)

# 2. Beräkna 64-bitars big-endian tidsstegsräknare T
time_counter = timestamp // step
time_bytes = struct.pack(">Q", time_counter)  # 8 bytes big-endian unsigned long long

# 3. Beräkna HMAC-SHA1-digest (20 bytes)
hmac_digest = hmac.new(key_bytes, time_bytes, hashlib.sha1).digest()

# 4. Utför dynamisk trunkering
offset = hmac_digest[-1] & 0x0F  # Lägre 4 bitar av 20:e byten
# Packa upp 4 bytes vid offset och rensa MSB-teckenbiten
binary_code = struct.unpack(">I", hmac_digest[offset : offset + 4])[0] & 0x7FFFFFFF

# 5. Modulo-aritmetik och formatering med nollutfyllnad
otp_code = binary_code % (10 ** digits)
return str(otp_code).zfill(digits)

if name == “main”:
test_secret = “JBSWY3DPEHPK3PXP”
print(f”Genererad TOTP-kod: {generate_totp(test_secret)}”)

const crypto = require('crypto');
// RFC 4648 Base32-avkodare i ren JavaScript
function base32Decode(base32Str) {
const alphabet = ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ234567’;
const cleaned = base32Str.replace(/=+$/, ”).toUpperCase().replace(/\s+/g, ”);
let bits = 0, value = 0, index = 0;
const output = new Uint8Array(Math.floor((cleaned.length * 5) / 8));
for (let i = 0; i < cleaned.length; i++) {
const val = alphabet.indexOf(cleaned[i]);
if (val === -1) continue;
value = (value << 5) | val;
bits += 5;
if (bits >= 8) {
output[index++] = (value >>> (bits - 8)) & 255;
bits -= 8;
}
}
return Buffer.from(output.buffer, 0, index);
}
function generateTOTP(secretBase32, timestamp = Math.floor(Date.now() / 1000), step = 30, digits = 6) {
const key = base32Decode(secretBase32);
const counter = Math.floor(timestamp / step);
// Allokera 8-byte buffert i Big-Endian-format
const buffer = Buffer.alloc(8);
buffer.writeBigUInt64BE(BigInt(counter), 0);
// Beräkna HMAC-SHA1
const hmac = crypto.createHmac(‘sha1’, key).update(buffer).digest();
// Dynamisk trunkering
const offset = hmac[hmac.length - 1] & 0x0f;
const binary = ((hmac[offset] & 0x7f) << 24) |
((hmac[offset + 1] & 0xff) << 16) |
((hmac[offset + 2] & 0xff) << 8) |
(hmac[offset + 3] & 0xff);
const otp = binary % (10 ** digits);
return otp.toString().padStart(digits, ‘0’);
}
console.log(“Beräknad TOTP:”, generateTOTP(“JBSWY3DPEHPK3PXP”));

async function generateBrowserTOTP(secretBase32, timestamp = Math.floor(Date.now() / 1000)) {
  const keyBytes = base32Decode(secretBase32);
  const counter = Math.floor(timestamp / 30);
// 1. Importera rå hemlig nyckel till SubtleCrypto
const cryptoKey = await window.crypto.subtle.importKey(
“raw”,
keyBytes,
{ name: “HMAC”, hash: { name: “SHA-1” } },
false,
[“sign”]
);
// 2. Koda 8-byte Big-Endian räknarbuffert
const buffer = new ArrayBuffer(8);
const view = new DataView(buffer);
view.setBigUint64(0, BigInt(counter), false); // false = Big-Endian
// 3. Utför kryptografisk HMAC-signering
const signature = await window.crypto.subtle.sign(“HMAC”, cryptoKey, buffer);
const hmacResult = new Uint8Array(signature);
// 4. Dynamisk trunkering
const offset = hmacResult[hmacResult.length - 1] & 0x0f;
const binary = ((hmacResult[offset] & 0x7f) << 24) |
((hmacResult[offset + 1] & 0xff) << 16) |
((hmacResult[offset + 2] & 0xff) << 8) |
(hmacResult[offset + 3] & 0xff);
const otp = binary % 1000000;
return otp.toString().padStart(6, ‘0’);
}

package main
import (
“crypto/hmac”
“crypto/sha1”
“encoding/base32”
“encoding/binary”
“fmt”
“math”
“strings”
“time”
)
// GenerateTOTP beräknar standardiserade RFC 6238-tidsbaserade koder
func GenerateTOTP(secretBase32 string, timestamp int64, step int64, digits int) (string, error) {
// 1. Rensa Base32-nyckeln och avkoda
cleaned := strings.ToUpper(strings.ReplaceAll(secretBase32, ” ”, ""))
key, err := base32.StdEncoding.WithPadding(base32.NoPadding).DecodeString(cleaned)
if err != nil {
key, err = base32.StdEncoding.DecodeString(cleaned)
if err != nil {
return "", err
}
}
// 2. Koda 64-bitars Big-Endian tidsstegsräknare
counter := uint64(timestamp / step)
buf := make([]byte, 8)
binary.BigEndian.PutUint64(buf, counter)

// 3. Beräkna HMAC-SHA1
mac := hmac.New(sha1.New, key)
mac.Write(buf)
hash := mac.Sum(nil)

// 4. Dynamisk trunkering
offset := hash[len(hash)-1] & 0x0f
binaryCode := binary.BigEndian.Uint32(hash[offset:offset+4]) & 0x7fffffff

// 5. Modulo-aritmetik
mod := uint32(math.Pow10(digits))
otp := binaryCode % mod

format := fmt.Sprintf("%%0%dd", digits)
return fmt.Sprintf(format, otp), nil

}
func main() {
code, err := GenerateTOTP(“JBSWY3DPEHPK3PXP”, time.Now().Unix(), 30, 6)
if err != nil {
panic(err)
}
fmt.Printf(“Golang beräknad TOTP: %s\n”, code)
}