I needed to implemented TOTP two-factor authentication in a project.
Time based one time password works based on current timestamp.
If you face problem time problem in your maching, you can fetch timestamp from ntp server.
class TOTP {
const keyRegeneration = 30; // Interval between key regeneration
const otpLength = 6; // Length of the Token generated
private static $lut = array( // Lookup needed for Base32 encoding
"A" => 0, "B" => 1,
"C" => 2, "D" => 3,
"E" => 4, "F" => 5,
"G" => 6, "H" => 7,
"I" => 8, "J" => 9,
"K" => 10, "L" => 11,
"M" => 12, "N" => 13,
"O" => 14, "P" => 15,
"Q" => 16, "R" => 17,
"S" => 18, "T" => 19,
"U" => 20, "V" => 21,
"W" => 22, "X" => 23,
"Y" => 24, "Z" => 25,
"2" => 26, "3" => 27,
"4" => 28, "5" => 29,
"6" => 30, "7" => 31
);
/**
* Generates a 16 digit secret key in base32 format
* @return string
**/
public static function generate_secret_key($length = 16) {
$b32 = "234567QWERTYUIOPASDFGHJKLZXCVBNM";
$s = "";
for ($i = 0; $i < $length; $i++)
$s .= $b32[rand(0,31)];
return $s;
}
/**
* Returns the current Unix Timestamp devided by the keyRegeneration
* period.
* @return integer
**/
public static function get_timestamp() {
return floor( (microtime(true) + 10) /self::keyRegeneration);
}
/**
* Decodes a base32 string into a binary string.
**/
public static function base32_decode($b32) {
$b32 = strtoupper($b32);
if (!preg_match('/^[ABCDEFGHIJKLMNOPQRSTUVWXYZ234567]+$/', $b32, $match))
throw new Exception('Invalid characters in the base32 string.');
$l = strlen($b32);
$n = 0;
$j = 0;
$binary = "";
for ($i = 0; $i < $l; $i++) {
$n = $n << 5; // Move buffer left by 5 to make room
$n = $n + self::$lut[$b32[$i]]; // Add value into buffer
$j = $j + 5; // Keep track of number of bits in buffer
if ($j >= 8) {
$j = $j - 8;
$binary .= chr(($n & (0xFF << $j)) >> $j);
}
}
return $binary;
}
/**
* Takes the secret key and the timestamp and returns the one time
* password.
*
* @param binary $key - Secret key in binary form.
* @param integer $counter - Timestamp as returned by get_timestamp.
* @return string
**/
public static function oath_hotp($key, $counter)
{
if (strlen($key) < 8)
throw new Exception('Secret key is too short. Must be at least 16 base 32 characters');
$bin_counter = pack('N*', 0) . pack('N*', $counter); // Counter must be 64-bit int
$hash = hash_hmac ('sha1', $bin_counter, $key, true);
return str_pad(self::oath_truncate($hash), self::otpLength, '0', STR_PAD_LEFT);
}
/**
* Verifys a user inputted key against the current timestamp. Checks $window
* keys either side of the timestamp.
*
* @param string $b32seed
* @param string $key - User specified key
* @param integer $window
* @param boolean $useTimeStamp
* @return boolean
**/
public static function verify_key($b32seed, $key, $window = 4, $useTimeStamp = true) {
$timeStamp = self::get_timestamp();
if ($useTimeStamp !== true) $timeStamp = (int)$useTimeStamp;
$binarySeed = self::base32_decode($b32seed);
for ($ts = $timeStamp - $window; $ts <= $timeStamp + $window; $ts++)
if (self::oath_hotp($binarySeed, $ts) == $key)
return true;
return false;
}
/**
* Extracts the OTP from the SHA1 hash.
* @param binary $hash
* @return integer
**/
public static function oath_truncate($hash)
{
$offset = ord($hash[19]) & 0xf;
return (
((ord($hash[$offset+0]) & 0x7f) << 24 ) |
((ord($hash[$offset+1]) & 0xff) << 16 ) |
((ord($hash[$offset+2]) & 0xff) << 8 ) |
(ord($hash[$offset+3]) & 0xff)
) % pow(10, self::otpLength);
}
}
$InitalizationKey = "M5UIUKQBTRCU7IQG"; // Set the inital key
$TimeStamp = TOTP::get_timestamp();
$secretkey = TOTP::base32_decode($InitalizationKey); // Decode it into binary
$otp = TOTP::oath_hotp($secretkey, $TimeStamp); // Get current token
echo("Init key: $InitalizationKey\n");
echo("Timestamp: $TimeStamp\n");
echo("One time password: $otp\n");
// Use this to verify a key as it allows for some time drift.
$result = TOTP::verify_key($InitalizationKey, "123456");
var_dump($result);
