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<?php
namespace PragmaRX\Google2FA\Support;
use ParagonIE\ConstantTime\Base32 as ParagonieBase32;
use PragmaRX\Google2FA\Exceptions\IncompatibleWithGoogleAuthenticatorException;
use PragmaRX\Google2FA\Exceptions\InvalidCharactersException;
use PragmaRX\Google2FA\Exceptions\SecretKeyTooShortException;
trait Base32
{
/**
* Enforce Google Authenticator compatibility.
*/
protected $enforceGoogleAuthenticatorCompatibility = true;
/**
* Calculate char count bits.
*
* @param string $b32
*
* @return int
*/
protected function charCountBits($b32)
{
return strlen($b32) * 8;
}
/**
* Generate a digit secret key in base32 format.
*
* @param int $length
* @param string $prefix
*
* @throws \Exception
* @throws \PragmaRX\Google2FA\Exceptions\InvalidCharactersException
* @throws \PragmaRX\Google2FA\Exceptions\SecretKeyTooShortException
* @throws \PragmaRX\Google2FA\Exceptions\IncompatibleWithGoogleAuthenticatorException
*
* @return string
*/
public function generateBase32RandomKey($length = 16, $prefix = '')
{
$secret = $prefix ? $this->toBase32($prefix) : '';
$secret = $this->strPadBase32($secret, $length);
$this->validateSecret($secret);
return $secret;
}
/**
* Decodes a base32 string into a binary string.
*
* @param string $b32
*
* @throws \PragmaRX\Google2FA\Exceptions\InvalidCharactersException
* @throws \PragmaRX\Google2FA\Exceptions\SecretKeyTooShortException
* @throws \PragmaRX\Google2FA\Exceptions\IncompatibleWithGoogleAuthenticatorException
*
* @return string
*/
public function base32Decode($b32)
{
$b32 = strtoupper($b32);
$this->validateSecret($b32);
return ParagonieBase32::decodeUpper($b32);
}
/**
* Check if the string length is power of two.
*
* @param string $b32
*
* @return bool
*/
protected function isCharCountNotAPowerOfTwo($b32)
{
return (strlen($b32) & (strlen($b32) - 1)) !== 0;
}
/**
* Pad string with random base 32 chars.
*
* @param string $string
* @param int $length
*
* @throws \Exception
*
* @return string
*/
private function strPadBase32($string, $length)
{
for ($i = 0; $i < $length; $i++) {
$string .= substr(
Constants::VALID_FOR_B32_SCRAMBLED,
$this->getRandomNumber(),
1
);
}
return $string;
}
/**
* Encode a string to Base32.
*
* @param string $string
*
* @return string
*/
public function toBase32($string)
{
$encoded = ParagonieBase32::encodeUpper($string);
return str_replace('=', '', $encoded);
}
/**
* Get a random number.
*
* @param int $from
* @param int $to
*
* @throws \Exception
*
* @return int
*/
protected function getRandomNumber($from = 0, $to = 31)
{
return random_int($from, $to);
}
/**
* Validate the secret.
*
* @param string $b32
*
* @throws \PragmaRX\Google2FA\Exceptions\InvalidCharactersException
* @throws \PragmaRX\Google2FA\Exceptions\SecretKeyTooShortException
* @throws \PragmaRX\Google2FA\Exceptions\IncompatibleWithGoogleAuthenticatorException
*/
protected function validateSecret($b32)
{
$this->checkForValidCharacters($b32);
$this->checkGoogleAuthenticatorCompatibility($b32);
$this->checkIsBigEnough($b32);
}
/**
* Check if the secret key is compatible with Google Authenticator.
*
* @param string $b32
*
* @throws IncompatibleWithGoogleAuthenticatorException
*/
protected function checkGoogleAuthenticatorCompatibility($b32)
{
if (
$this->enforceGoogleAuthenticatorCompatibility &&
$this->isCharCountNotAPowerOfTwo($b32) // Google Authenticator requires it to be a power of 2 base32 length string
) {
throw new IncompatibleWithGoogleAuthenticatorException();
}
}
/**
* Check if all secret key characters are valid.
*
* @param string $b32
*
* @throws \PragmaRX\Google2FA\Exceptions\InvalidCharactersException
*/
protected function checkForValidCharacters($b32)
{
if (
preg_replace('/[^'.Constants::VALID_FOR_B32.']/', '', $b32) !==
$b32
) {
throw new InvalidCharactersException();
}
}
/**
* Check if secret key length is big enough.
*
* @param string $b32
*
* @throws \PragmaRX\Google2FA\Exceptions\SecretKeyTooShortException
*/
protected function checkIsBigEnough($b32)
{
// Minimum = 128 bits
// Recommended = 160 bits
// Compatible with Google Authenticator = 256 bits
if (
$this->charCountBits($b32) < 128
) {
throw new SecretKeyTooShortException();
}
}
}
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