WIP

Author: bshaffer

src/ECPublicKey.php

@@ -0,0 +1,161 @@
+<?php
+
+namespace Firebase\JWT;
+
+class ECPublicKey
+{
+    const ASN1_INTEGER = 0x02;
+    const ASN1_BIT_STRING = 0x03;
+    const ASN1_OBJECT_IDENTIFIER = 0x06;
+    const ASN1_SEQUENCE = 0x10;
+    const OID = '1.2.840.10045.2.1';
+
+    private $data;
+
+    private static $curves = [
+        'P-256' => '1.2.840.10045.3.1.7', // Len: 64
+        // 'P-384' => '1.3.132.0.34', // Len: 96 (not yet supported)
+        // 'P-521' => '1.3.132.0.35', // Len: 132 (not supported)
+    ];
+
+    public function __construct(array $data)
+    {
+        if (isset($data['d'])) {
+            // The key is actually a private key
+            throw new \Exception('Key data must be for a public key');
+        }
+
+        if (empty($data['crv'])) {
+            throw new \Exception('crv not set');
+        }
+
+        if (!isset(self::$curves[$data['crv']])) {
+            throw new \Exception('Unrecognised or unsupported EC curve');
+        }
+
+        $this->data = $data;
+    }
+
+    public function toPEM()
+    {
+        $oid = self::$curves[$this->data['crv']];
+        $pem =
+            self::encodeDER(
+                self::ASN1_SEQUENCE,
+                self::encodeDER(
+                    self::ASN1_SEQUENCE,
+                    self::encodeDER(
+                        self::ASN1_OBJECT_IDENTIFIER,
+                        self::encodeOID(self::OID)
+                    )
+                    . self::encodeDER(
+                        self::ASN1_OBJECT_IDENTIFIER,
+                        self::encodeOID($oid)
+                    )
+                ) .
+                self::encodeDER(
+                    self::ASN1_BIT_STRING,
+                    chr(0x00) . chr(0x04)
+                    . JWT::urlsafeB64Decode($this->data['x'])
+                    . JWT::urlsafeB64Decode($this->data['y'])
+                )
+            );
+
+        return sprintf(
+            "-----BEGIN PUBLIC KEY-----\n%s\n-----END PUBLIC KEY-----\n",
+            wordwrap(base64_encode($pem), 64, "\n", true)
+        );
+    }
+
+    /**
+     * Convert an ECDSA signature to an ASN.1 DER sequence
+     *
+     * @param   string $sig The ECDSA signature to convert
+     * @return  string The encoded DER object
+     */
+    public static function encodeSignature($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 a string into a DER-encoded OID.
+     *
+     * @param   string $oid the OID string
+     * @return  string the binary DER-encoded OID
+     */
+    private static function encodeOID($oid)
+    {
+        $octets = explode('.', $oid);
+
+        // Get the first octet
+        $oid = chr(array_shift($octets) * 40 + array_shift($octets));
+
+        // Iterate over subsequent octets
+        foreach ($octets as $octet) {
+            if ($octet == 0) {
+                $oid .= chr(0x00);
+                continue;
+            }
+            $bin = '';
+
+            while ($octet) {
+                $bin .= chr(0x80 | ($octet & 0x7f));
+                $octet >>= 7;
+            }
+            $bin[0] = $bin[0] & chr(0x7f);
+
+            // Convert to big endian if necessary
+            if (pack('V', 65534) == pack('L', 65534)) {
+                $oid .= strrev($bin);
+            } else {
+                $oid .= $bin;
+            }
+        }
+
+        return $oid;
+    }
+}

src/JWT.php

@@ -97,6 +97,11 @@ 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
+            $sig = ECPublicKey::encodeSignature($sig);
+        }
+
         if (is_array($key) || $key instanceof \ArrayAccess) {
             if (isset($header->kid)) {
                 if (!isset($key[$header->kid])) {