Constant-time alternative to strtok()

src/Keys/Version4/AsymmetricPublicKey.php

@@ -14,7 +14,7 @@
 use ParagonIE\Paseto\ProtocolInterface;
 use ParagonIE\Paseto\Util;
 use TypeError;
-use function str_replace, strlen, strtok, substr;
+use function str_replace, strlen, substr;
 
 /**
  * Class AsymmetricPublicKey
@@ -88,21 +88,15 @@ public static function importPem(string $pem, ?ProtocolInterface $protocol = nul
     {
         $formattedKey = str_replace('-----BEGIN PUBLIC KEY-----', '', $pem);
         $formattedKey = str_replace('-----END PUBLIC KEY-----', '', $formattedKey);
-
         /**
          * @psalm-suppress DocblockTypeContradiction
          * PHP 8.4 updated the docblock return for str_replace, which makes this check required
          */
         if (!is_string($formattedKey)) {
             throw new PasetoException('Invalid PEM format', ExceptionCode::UNSPECIFIED_CRYPTOGRAPHIC_ERROR);
         }
-
-        $tokenizedKey = strtok($formattedKey, "\n");
-        if ($tokenizedKey === false) {
-            throw new PasetoException('Invalid PEM format', ExceptionCode::UNSPECIFIED_CRYPTOGRAPHIC_ERROR);
-        }
-
-        $key = Base64::decode($tokenizedKey);
+        $formattedKey = Util::stripNewlines($formattedKey);
+        $key = Base64::decode($formattedKey);
         $prefix = Hex::decode(self::PEM_ENCODE_PREFIX);
 
         return new self(substr($key, strlen($prefix)));

src/Keys/Version4/AsymmetricSecretKey.php

@@ -14,7 +14,7 @@
 use ParagonIE\Paseto\ProtocolInterface;
 use ParagonIE\Paseto\Util;
 use TypeError;
-use function str_replace, strlen, strtok, substr;
+use function str_replace, strlen, substr;
 
 /**
  * Class AsymmetricSecretKey
@@ -109,13 +109,8 @@ public static function importPem(string $pem, ?ProtocolInterface $protocol = nul
         if (!is_string($formattedKey)) {
             throw new PasetoException('Invalid PEM format', ExceptionCode::UNSPECIFIED_CRYPTOGRAPHIC_ERROR);
         }
-
-        $tokenizedKey = strtok($formattedKey, "\n");
-        if ($tokenizedKey === false) {
-            throw new PasetoException('Invalid PEM format', ExceptionCode::UNSPECIFIED_CRYPTOGRAPHIC_ERROR);
-        }
-
-        $key = Base64::decode($tokenizedKey);
+        $formattedKey = Util::stripNewlines($formattedKey);
+        $key = Base64::decode($formattedKey);
         $prefix = Hex::decode(self::PEM_ENCODE_PREFIX);
 
         return new self(substr($key, strlen($prefix)));

src/Util.php

@@ -24,6 +24,7 @@
     preg_match_all,
     sodium_memzero,
     str_replace;
+use ParagonIE_Sodium_Core_Util as SodiumUtil;
 
 /**
  * Class Util
@@ -173,6 +174,46 @@ public static function removeFooter(string $payload): string
         return $payload;
     }
 
+    /**
+     * Strip all newlines (CR, LF) characters from a string.
+     *
+     * @param string $input
+     * @return string
+     */
+    public static function stripNewlines(string $input): string
+    {
+        $bytes = SodiumUtil::stringToIntArray($input);
+        $length = count($bytes);
+
+        // First value is a dummy value, to overwrite it in constant-time
+        $return = array_fill(0, $length + 1, 0);
+        // Output index:
+        $j = 1;
+
+        // Now let's strip:
+        for ($i = 0; $i < $length; ++$i) {
+            $char = ($bytes[$i]);
+
+            // Determine if we're stripping this character or not?
+            $isCR = ((($char ^ 0x0d) - 1) >> 8) & 1;
+            $isLF = ((($char ^ 0x0a) - 1) >> 8) & 1;
+            $isNewline = $isCR | $isLF;
+
+            // Set destination index: 0 if $isNewLine, $j otherwise
+            $swap = -$isNewline;
+
+            // if ($isNewLine), $dest === 0, else $dest === $j
+            $dest = (~$swap & $j) ^ $swap;
+
+            // Now let's overwrite the index (0 or $j) with $char:
+            $return[$dest] = $char;
+
+            // We only advance $j if we didn't encounter a newline:
+            $j += 1 - $isNewline;
+        }
+        return SodiumUtil::intArrayToString(array_slice($return, 1, $j - 1));
+    }
+
     /**
      * If a footer was included with the message, first verify that
      * it's equivalent to the one we expect, then remove it from the

tests/UtilTest.php

@@ -8,6 +8,7 @@
 };
 use ParagonIE\Paseto\Exception\EncodingException;
 use ParagonIE\Paseto\Util;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use TypeError;
 
@@ -123,6 +124,23 @@ public function testPreAuthEncode()
         );
     }
 
+    public static function newlineProvider(): array
+    {
+        return [
+            ["abc\ndef", 'abcdef'],
+            ["abc\r\ndef", 'abcdef'],
+            ["abc \r\ndef", 'abc def'],
+            ["\n", ''],
+            ["\r\n", ''],
+        ];
+    }
+
+    #[DataProvider('newlineProvider')]
+    public function testStripNewliens(string $input, string $output): void
+    {
+        $this->assertSame($output, Util::stripNewlines($input));
+    }
+
     /**
      * @covers Util::validateAndRemoveFooter()
      */