Listing: TOTP im Detail

# Laden der Otp.NET-Bibliothek
Add-Type -Path .\lib\Otp.NET.dll
# 1. Konvertieren des Base32-kodierten Seed zu einem Byte-Array
$base32Seed = "M5K6Z7MDJ6KJ2LHC‘
$bytesSeed = [OtpNet.Base32Encoding]::ToBytes($base32Seed)
# 2. Zeitgeber berechnen
$unixTime = [DateTimeOffset]::UtcNow.ToUnixTimeSeconds()
$timeCounter = [Math]::Floor($unixTime / 30)
# 3. Counter zu Byte-Array (Big-Endian)
$counterBytes = [BitConverter]::GetBytes([int64]$timeCounter)
[Array]::Reverse($counterBytes)
# 4. HMAC berechnen
$hmac = [System.Security.Cryptography.HMACSHA1]::new($bytesSeed)
$hash = $hmac.ComputeHash($counterBytes)
# 5. Dynamische Trunkierung
$offset = $hash[$hash.Length - 1] -band 0x0F
$binary = (($hash[$offset] -band 0x7F) -shl 24) -bor
(($hash[$offset + 1] -band 0xFF) -shl 16) -bor
(($hash[$offset + 2] -band 0xFF) -shl 8) -bor
($hash[$offset + 3] -band 0xFF)
# 6. Ausgabe des 6-stelligen OTP-Code
($binary % 1000000).ToString("D6‘)