我们如何在 PHP 中创建一个相当安全的密码哈希?

• Do NOT use a single salt for all passwords. Use a randomly generated salt per password.
• Do NOT rehash an unmodified hash (collision issue, see my previous answer, you need infinite input for hashing).
• Do NOT attempt to create your own hashing algorithm or mix-matching algorithms into a complex operation.
• If stuck with broken/unsecure/fast hash primitives, use key strengthening. This increases the time required for the attacker to compute a rainbow table. Example:

function strong_hash($input, $salt = null, $algo = 'sha512', $rounds = 20000) {
  if($salt === null) {
    $salt = crypto_random_bytes(16);
  } else {
    $salt = pack('H*', substr($salt, 0, 32));
  }

  $hash = hash($algo, $salt . $input);

  for($i = 0; $i < $rounds; $i++) {
    // $input is appended to $hash in order to create
    // infinite input.
    $hash = hash($algo, $hash . $input);
  }

  // Return salt and hash. To verify, simply
  // passed stored hash as second parameter.
  return bin2hex($salt) . $hash;
}

function crypto_random_bytes($count) {
  static $randomState = null;

  $bytes = '';

  if(function_exists('openssl_random_pseudo_bytes') &&
      (strtoupper(substr(PHP_OS, 0, 3)) !== 'WIN')) { // OpenSSL slow on Win
    $bytes = openssl_random_pseudo_bytes($count);
  }

  if($bytes === '' && is_readable('/dev/urandom') &&
     ($hRand = @fopen('/dev/urandom', 'rb')) !== FALSE) {
    $bytes = fread($hRand, $count);
    fclose($hRand);
  }

  if(strlen($bytes) < $count) {
    $bytes = '';

    if($randomState === null) {
      $randomState = microtime();
      if(function_exists('getmypid')) {
        $randomState .= getmypid();
      }
    }

    for($i = 0; $i < $count; $i += 16) {
      $randomState = md5(microtime() . $randomState);

      if (PHP_VERSION >= '5') {
        $bytes .= md5($randomState, true);
      } else {
        $bytes .= pack('H*', md5($randomState));
      }
    }

    $bytes = substr($bytes, 0, $count);
  }

  return $bytes;
}

<小时>

与其部署您自己的(固有缺陷)哈希/盐算法，为什么不使用由安全专业人员开发的算法?

class Bcrypt {
  private $rounds;
  public function __construct($rounds = 12) {
    if(CRYPT_BLOWFISH != 1) {
      throw new Exception("bcrypt not supported in this installation. See http://php.net/crypt");
    }

    $this->rounds = $rounds;
  }

  public function hash($input) {
    $hash = crypt($input, $this->getSalt());

    if(strlen($hash) > 13)
      return $hash;

    return false;
  }

  public function verify($input, $existingHash) {
    $hash = crypt($input, $existingHash);

    return $hash === $existingHash;
  }

  private function getSalt() {
    $salt = sprintf('$2a$%02d$', $this->rounds);

    $bytes = $this->getRandomBytes(16);

    $salt .= $this->encodeBytes($bytes);

    return $salt;
  }

  private $randomState;
  private function getRandomBytes($count) {
    $bytes = '';

    if(function_exists('openssl_random_pseudo_bytes') &&
        (strtoupper(substr(PHP_OS, 0, 3)) !== 'WIN')) { // OpenSSL slow on Win
      $bytes = openssl_random_pseudo_bytes($count);
    }

    if($bytes === '' && is_readable('/dev/urandom') &&
       ($hRand = @fopen('/dev/urandom', 'rb')) !== FALSE) {
      $bytes = fread($hRand, $count);
      fclose($hRand);
    }

    if(strlen($bytes) < $count) {
      $bytes = '';

      if($this->randomState === null) {
        $this->randomState = microtime();
        if(function_exists('getmypid')) {
          $this->randomState .= getmypid();
        }
      }

      for($i = 0; $i < $count; $i += 16) {
        $this->randomState = md5(microtime() . $this->randomState);

        if (PHP_VERSION >= '5') {
          $bytes .= md5($this->randomState, true);
        } else {
          $bytes .= pack('H*', md5($this->randomState));
        }
      }

      $bytes = substr($bytes, 0, $count);
    }

    return $bytes;
  }

  private function encodeBytes($input) {
    return strtr(rtrim(base64_encode($input), '='), '+', '.');
  }
}

$bcrypt = new Bcrypt(15);

$hash = $bcrypt->hash('password');
$isGood = $bcrypt->verify('password', $hash);