RFC: Add support for ES256 algorithm

src/JWT.php

@@ -1,6 +1,7 @@
 <?php
 
 namespace Firebase\JWT;
+
 use \DomainException;
 use \InvalidArgumentException;
 use \UnexpectedValueException;
@@ -21,6 +22,9 @@
  */
 class JWT
 {
+    const ASN1_INTEGER = 0x02;
+    const ASN1_SEQUENCE = 0x10;
+    const ASN1_BIT_STRING = 0x03;
 
     /**
      * When checking nbf, iat or expiration times,
@@ -97,6 +101,11 @@ public static function decode($jwt, $key, array $allowed_algs = array())
         if (!in_array($header->alg, $allowed_algs)) {
             throw new UnexpectedValueException('Algorithm not allowed');
         }
+        if ($header->alg === 'ES256') {
+            // OpenSSL expects an ASN.1 DER sequence for ES256 signatures
+            $sig = self::signatureToDER($sig);
+        }
+
         if (is_array($key) || $key instanceof \ArrayAccess) {
             if (isset($header->kid)) {
                 if (!isset($key[$header->kid])) {
@@ -160,7 +169,7 @@ public static function encode($payload, $key, $alg = 'HS256', $keyId = null, $he
         if ($keyId !== null) {
             $header['kid'] = $keyId;
         }
-        if ( isset($head) && is_array($head) ) {
+        if (isset($head) && is_array($head)) {
             $header = array_merge($head, $header);
         }
         $segments = array();
@@ -192,7 +201,7 @@ public static function sign($msg, $key, $alg = 'HS256')
             throw new DomainException('Algorithm not supported');
         }
         list($function, $algorithm) = static::$supported_algs[$alg];
-        switch($function) {
+        switch ($function) {
             case 'hash_hmac':
                 return hash_hmac($algorithm, $msg, $key, true);
             case 'openssl':
@@ -201,6 +210,9 @@ public static function sign($msg, $key, $alg = 'HS256')
                 if (!$success) {
                     throw new DomainException("OpenSSL unable to sign data");
                 } else {
+                    if ($alg === 'ES256') {
+                        $signature = self::signatureFromDER($signature, 256);
+                    }
                     return $signature;
                 }
         }
@@ -226,7 +238,7 @@ private static function verify($msg, $signature, $key, $alg)
         }
 
         list($function, $algorithm) = static::$supported_algs[$alg];
-        switch($function) {
+        switch ($function) {
             case 'openssl':
                 $success = openssl_verify($msg, $signature, $key, $algorithm);
                 if ($success === 1) {
@@ -377,4 +389,126 @@ private static function safeStrlen($str)
         }
         return strlen($str);
     }
+
+    /**
+     * Convert an ECDSA signature to an ASN.1 DER sequence
+     *
+     * @param   string $sig The ECDSA signature to convert
+     * @return  string The encoded DER object
+     */
+    private static function signatureToDER($sig)
+    {
+        // Separate the signature into r-value and s-value
+        list($r, $s) = str_split($sig, (int) (strlen($sig) / 2));
+
+        // Trim leading zeros
+        $r = ltrim($r, "\x00");
+        $s = ltrim($s, "\x00");
+
+        // Convert r-value and s-value from unsigned big-endian integers to
+        // signed two's complement
+        if (ord($r[0]) > 0x7f) {
+            $r = "\x00" . $r;
+        }
+        if (ord($s[0]) > 0x7f) {
+            $s = "\x00" . $s;
+        }
+
+        return self::encodeDER(
+            self::ASN1_SEQUENCE,
+            self::encodeDER(self::ASN1_INTEGER, $r) .
+            self::encodeDER(self::ASN1_INTEGER, $s)
+        );
+    }
+
+    /**
+     * Encodes a value into a DER object.
+     *
+     * @param   int     $type DER tag
+     * @param   string  $value the value to encode
+     * @return  string  the encoded object
+     */
+    private static function encodeDER($type, $value)
+    {
+        $tag_header = 0;
+        if ($type === self::ASN1_SEQUENCE) {
+            $tag_header |= 0x20;
+        }
+
+        // Type
+        $der = chr($tag_header | $type);
+
+        // Length
+        $der .= chr(strlen($value));
+
+        return $der . $value;
+    }
+
+    /**
+     * Encodes signature from a DER object.
+     *
+     * @param   string  $der binary signature in DER format
+     * @param   int     $keySize the nubmer of bits in the key
+     * @return  string  the signature
+     */
+    private static function signatureFromDER($der, $keySize)
+    {
+        // OpenSSL returns the ECDSA signatures as a binary ASN.1 DER SEQUENCE
+        list($offset, $_) = self::readDER($der);
+        list($offset, $r) = self::readDER($der, $offset);
+        list($offset, $s) = self::readDER($der, $offset);
+
+        // Convert r-value and s-value from signed two's compliment to unsigned
+        // big-endian integers
+        $r = ltrim($r, "\x00");
+        $s = ltrim($s, "\x00");
+
+        // Pad out r and s so that they are $keySize bits long
+        $r = str_pad($r, $keySize / 8, "\x00", STR_PAD_LEFT);
+        $s = str_pad($s, $keySize / 8, "\x00", STR_PAD_LEFT);
+
+        return $r . $s;
+    }
+
+    /**
+     * Reads binary DER-encoded data and decodes into a single object
+     *
+     * @param string $der the binary data in DER format
+     * @param int $offset the offset of the data stream containing the object
+     * to decode
+     * @return array [$offset, $data] the new offset and the decoded object
+     */
+    private static function readDER($der, $offset = 0)
+    {
+        $pos = $offset;
+        $size = strlen($der);
+        $constructed = (ord($der[$pos]) >> 5) & 0x01;
+        $type = ord($der[$pos++]) & 0x1f;
+
+        // Length
+        $len = ord($der[$pos++]);
+        if ($len & 0x80) {
+            $n = $len & 0x1f;
+            $len = 0;
+            while ($n-- && $pos < $size) {
+                $len = ($len << 8) | ord($der[$pos++]);
+            }
+        }
+
+        // Value
+        if ($type == self::ASN1_BIT_STRING) {
+            $pos++; // Skip the first contents octet (padding indicator)
+            $data = substr($der, $pos, $len - 1);
+            if (!$ignore_bit_strings) {
+                $pos += $len - 1;
+            }
+        } elseif (!$constructed) {
+            $data = substr($der, $pos, $len);
+            $pos += $len;
+        } else {
+            $data = null;
+        }
+
+        return array($pos, $data);
+    }
 }

tests/JWTTest.php

@@ -282,6 +282,22 @@ public function testVerifyError()
         self::$opensslVerifyReturnValue = -1;
         JWT::decode($msg, $pkey, array('RS256'));
     }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testEncodeAndDecodeEcdsaToken()
+    {
+        $privateKey = file_get_contents(__DIR__ . '/ecdsa-private.pem');
+        $payload = array('foo' => 'bar');
+        $encoded = JWT::encode($payload, $privateKey, 'ES256');
+
+        // Verify decoding succeeds
+        $publicKey = file_get_contents(__DIR__ . '/ecdsa-public.pem');
+        $decoded = JWT::decode($encoded, $publicKey, array('ES256'));
+
+        $this->assertEquals('bar', $decoded->foo);
+    }
 }
 
 /*

tests/ecdsa-private.pem

@@ -0,0 +1,18 @@
+-----BEGIN EC PARAMETERS-----
+MIH3AgEBMCwGByqGSM49AQECIQD/////AAAAAQAAAAAAAAAAAAAAAP//////////
+/////zBbBCD/////AAAAAQAAAAAAAAAAAAAAAP///////////////AQgWsY12Ko6
+k+ez671VdpiGvGUdBrDMU7D2O848PifSYEsDFQDEnTYIhucEk2pmeOETnSa3gZ9+
+kARBBGsX0fLhLEJH+Lzm5WOkQPJ3A32BLeszoPShOUXYmMKWT+NC4v4af5uO5+tK
+fA+eFivOM1drMV7Oy7ZAaDe/UfUCIQD/////AAAAAP//////////vOb6racXnoTz
+ucrC/GMlUQIBAQ==
+-----END EC PARAMETERS-----
+-----BEGIN EC PRIVATE KEY-----
+MIIBaAIBAQQgyP9e7yS1tjpXa0l6o+80dbSxuMcqx3lUg0n2OT9AmiuggfowgfcC
+AQEwLAYHKoZIzj0BAQIhAP////8AAAABAAAAAAAAAAAAAAAA////////////////
+MFsEIP////8AAAABAAAAAAAAAAAAAAAA///////////////8BCBaxjXYqjqT57Pr
+vVV2mIa8ZR0GsMxTsPY7zjw+J9JgSwMVAMSdNgiG5wSTamZ44ROdJreBn36QBEEE
+axfR8uEsQkf4vOblY6RA8ncDfYEt6zOg9KE5RdiYwpZP40Li/hp/m47n60p8D54W
+K84zV2sxXs7LtkBoN79R9QIhAP////8AAAAA//////////+85vqtpxeehPO5ysL8
+YyVRAgEBoUQDQgAE2klp6aX6y5kAir3EWQt0QAeapTW+db/9fD65KAoDzVajtThx
+PVLEf1CufcfTxMQAQPM3wkZhu0NjlWFetcMdcQ==
+-----END EC PRIVATE KEY-----

tests/ecdsa-public.pem

@@ -0,0 +1,9 @@
+-----BEGIN PUBLIC KEY-----
+MIIBSzCCAQMGByqGSM49AgEwgfcCAQEwLAYHKoZIzj0BAQIhAP////8AAAABAAAA
+AAAAAAAAAAAA////////////////MFsEIP////8AAAABAAAAAAAAAAAAAAAA////
+///////////8BCBaxjXYqjqT57PrvVV2mIa8ZR0GsMxTsPY7zjw+J9JgSwMVAMSd
+NgiG5wSTamZ44ROdJreBn36QBEEEaxfR8uEsQkf4vOblY6RA8ncDfYEt6zOg9KE5
+RdiYwpZP40Li/hp/m47n60p8D54WK84zV2sxXs7LtkBoN79R9QIhAP////8AAAAA
+//////////+85vqtpxeehPO5ysL8YyVRAgEBA0IABNpJaeml+suZAIq9xFkLdEAH
+mqU1vnW//Xw+uSgKA81Wo7U4cT1SxH9Qrn3H08TEAEDzN8JGYbtDY5VhXrXDHXE=
+-----END PUBLIC KEY-----