Issue 14, OpenSSL RC4

.gitignore

@@ -1,3 +1,4 @@
 vendor
 .idea
 composer.phar
+.DS_Store

src/FpdiProtection.php

@@ -193,24 +193,33 @@ class FpdiProtection extends \setasign\Fpdi\Fpdi
      */
     protected $fileIdentifier;
 
+    /**
+     * @var bool
+     */
+    protected $useArcfourFallback;
+
     /**
      * FpdiProtection constructor.
      *
      * @param string $orientation
      * @param string $unit
      * @param string $size
      */
-    public function __construct($orientation = 'P', $unit = 'mm', $size = 'A4')
+    public function __construct($orientation = 'P', $unit = 'mm', $size = 'A4', $useArcfourFallback = false)
     {
         parent::__construct($orientation, $unit, $size);
 
+        // PHP 7.1-8.0 requires OpenSSL >= 1.0.1, < 3.0
+        $isOpensslCompatibleWithPhp7 = PHP_VERSION_ID < 70100 || PHP_VERSION_ID > 80100 || OPENSSL_VERSION_NUMBER >= 0x10001010 && OPENSSL_VERSION_NUMBER < 0x30000000;
         $randomBytes = function_exists('random_bytes') ? \random_bytes(32) : \mt_rand();
         $this->fileIdentifier = md5(__FILE__ . PHP_SAPI . PHP_VERSION . $randomBytes, true);
+        $this->useArcfourFallback = $useArcfourFallback;
 
-        if (!function_exists('openssl_encrypt') || !in_array('rc4-40', openssl_get_cipher_methods(), true)) {
+        if (!$useArcfourFallback && (!function_exists('openssl_encrypt') || !in_array('rc4-40', openssl_get_cipher_methods(), true) || !$isOpensslCompatibleWithPhp7)) {
             throw new \RuntimeException(
-                'OpenSSL with RC4 supported is required. In case you use OpenSSL 3 make sure that ' .
-                'legacy providers are loaded (see https://wiki.openssl.org/index.php/OpenSSL_3.0#Providers).'
+                'OpenSSL with RC4 supported is required if $useArcfourFallback is false.' .
+                'If using OpenSSL 3 make sure that legacy providers are loaded ' .
+                '(see https://wiki.openssl.org/index.php/OpenSSL_3.0#Providers).'
             );
         }
     }
@@ -509,7 +518,39 @@ protected function computeUValue($encryptionKey)
      */
     protected function arcfour($key, $data)
     {
-        return openssl_encrypt($data, 'RC4-40', $key, OPENSSL_RAW_DATA, '');
+        if (!$this->useArcfourFallback) {
+            return openssl_encrypt($data, 'rc4-40', $key,  OPENSSL_RAW_DATA, '');
+        }
+
+        static $_lastRc4Key = null, $_lastRc4KeyValue = null;
+
+        if ($_lastRc4Key !== $key) {
+            $k = str_repeat($key, (int)(256 / strlen($key) + 1));
+            $rc4 = range(0, 255);
+            $j = 0;
+            for ($i = 0; $i < 256; $i++) {
+                $rc4[$i] = $rc4[$j = ($j + ($t = $rc4[$i]) + ord($k[$i])) % 256];
+                $rc4[$j] = $t;
+            }
+            $_lastRc4Key = $key;
+            $_lastRc4KeyValue = $rc4;
+
+        } else {
+            $rc4 = $_lastRc4KeyValue;
+        }
+
+        $len = strlen($data);
+        $newData = '';
+        $a = 0;
+        $b = 0;
+        for ($i = 0; $i < $len; $i++) {
+            $b = ($b + ($t = $rc4[$a = ($a + 1) % 256])) % 256;
+            $rc4[$a] = $rc4[$b];
+            $rc4[$b] = $t;
+            $newData .= chr(ord($data[$i]) ^ $rc4[($rc4[$a] + $rc4[$b]) % 256]);
+        }
+
+        return $newData;
     }
 
     /**
@@ -646,4 +687,31 @@ protected function _puttrailer()
             $this->_put('/ID [<' . $fileIdentifier . '><' . $fileIdentifier . '>]');
         }
     }
+
+    protected function getOpensslVersionNumber($patchAsNumber = false, $opensslVersionNumber = null) {
+        if (is_null($opensslVersionNumber)) $opensslVersionNumber = OPENSSL_VERSION_NUMBER;
+        $opensslNumericIdentifier = str_pad((string)dechex($opensslVersionNumber),8,'0',STR_PAD_LEFT);
+
+        $opensslVersionParsed = array();
+        $preg = '/(?<major>[[:xdigit:]])(?<minor>[[:xdigit:]][[:xdigit:]])(?<fix>[[:xdigit:]][[:xdigit:]])';
+        $preg.= '(?<patch>[[:xdigit:]][[:xdigit:]])(?<type>[[:xdigit:]])/';
+        preg_match_all($preg, $opensslNumericIdentifier, $opensslVersionParsed);
+        $opensslVersion = false;
+        if (!empty($opensslVersionParsed)) {
+            $alphabet = array(1=>'a',2=>'b',3=>'c',4=>'d',5=>'e',6=>'f',7=>'g',8=>'h',9=>'i',10=>'j',11=>'k',
+                                           12=>'l',13=>'m',14=>'n',15=>'o',16=>'p',17=>'q',18=>'r',19=>'s',20=>'t',21=>'u',
+                                           22=>'v',23=>'w',24=>'x',25=>'y',26=>'z');
+            $opensslVersion = intval($opensslVersionParsed['major'][0]).'.';
+            $opensslVersion.= intval($opensslVersionParsed['minor'][0]).'.';
+            $opensslVersion.= intval($opensslVersionParsed['fix'][0]);
+            $patchlevelDec = hexdec($opensslVersionParsed['patch'][0]);
+            if (!$patchAsNumber && array_key_exists($patchlevelDec, $alphabet)) {
+                $opensslVersion.= $alphabet[$patchlevelDec]; // ideal for text comparison
+            }
+            else {
+                $opensslVersion.= '.'.$patchlevelDec; // ideal for version_compare
+            }
+        }
+        return $opensslVersion;
+    }
 }