feat: Add ES256 support to JWK (#399)

Author: bshaffer

src/JWK.php

@@ -20,6 +20,16 @@
  */
 class JWK
 {
+    private const OID = '1.2.840.10045.2.1';
+    private const ASN1_OBJECT_IDENTIFIER = 0x06;
+    private const ASN1_SEQUENCE = 0x10; // also defined in JWT
+    private const ASN1_BIT_STRING = 0x03;
+    private const EC_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)
+    ];
+
     /**
      * Parse a set of JWK keys
      *
@@ -114,6 +124,26 @@ public static function parseKey(array $jwk, string $defaultAlg = null): ?Key
                     );
                 }
                 return new Key($publicKey, $jwk['alg']);
+            case 'EC':
+                if (isset($jwk['d'])) {
+                    // The key is actually a private key
+                    throw new UnexpectedValueException('Key data must be for a public key');
+                }
+
+                if (empty($jwk['crv'])) {
+                    throw new UnexpectedValueException('crv not set');
+                }
+
+                if (!isset(self::EC_CURVES[$jwk['crv']])) {
+                    throw new DomainException('Unrecognised or unsupported EC curve');
+                }
+
+                if (empty($jwk['x']) || empty($jwk['y'])) {
+                    throw new UnexpectedValueException('x and y not set');
+                }
+
+                $publicKey = self::createPemFromCrvAndXYCoordinates($jwk['crv'], $jwk['x'], $jwk['y']);
+                return new Key($publicKey, $jwk['alg']);
             default:
                 // Currently only RSA is supported
                 break;
@@ -122,6 +152,45 @@ public static function parseKey(array $jwk, string $defaultAlg = null): ?Key
         return null;
     }
 
+    /**
+     * Converts the EC JWK values to pem format.
+     *
+     * @param   string  $crv The EC curve (only P-256 is supported)
+     * @param   string  $x   The EC x-coordinate
+     * @param   string  $y   The EC y-coordinate
+     *
+     * @return  string
+     */
+    private static function createPemFromCrvAndXYCoordinates(string $crv, string $x, string $y): string
+    {
+        $pem =
+            self::encodeDER(
+                self::ASN1_SEQUENCE,
+                self::encodeDER(
+                    self::ASN1_SEQUENCE,
+                    self::encodeDER(
+                        self::ASN1_OBJECT_IDENTIFIER,
+                        self::encodeOID(self::OID)
+                    )
+                    . self::encodeDER(
+                        self::ASN1_OBJECT_IDENTIFIER,
+                        self::encodeOID(self::EC_CURVES[$crv])
+                    )
+                ) .
+                self::encodeDER(
+                    self::ASN1_BIT_STRING,
+                    chr(0x00) . chr(0x04)
+                    . JWT::urlsafeB64Decode($x)
+                    . JWT::urlsafeB64Decode($y)
+                )
+            );
+
+        return sprintf(
+            "-----BEGIN PUBLIC KEY-----\n%s\n-----END PUBLIC KEY-----\n",
+            wordwrap(base64_encode($pem), 64, "\n", true)
+        );
+    }
+
     /**
      * Create a public key represented in PEM format from RSA modulus and exponent information
      *
@@ -188,4 +257,68 @@ private static function encodeLength(int $length): string
 
         return \pack('Ca*', 0x80 | \strlen($temp), $temp);
     }
+
+    /**
+     * Encodes a value into a DER object.
+     * Also defined in Firebase\JWT\JWT
+     *
+     * @param   int     $type DER tag
+     * @param   string  $value the value to encode
+     * @return  string  the encoded object
+     */
+    private static function encodeDER(int $type, string $value): string
+    {
+        $tag_header = 0;
+        if ($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(string $oid): string
+    {
+        $octets = explode('.', $oid);
+
+        // Get the first octet
+        $first = (int) array_shift($octets);
+        $second = (int) array_shift($octets);
+        $oid = chr($first * 40 + $second);
+
+        // Iterate over subsequent octets
+        foreach ($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;
+    }
 }

tests/JWKTest.php

@@ -127,19 +127,33 @@ public function testDecodeByJwkKeySetTokenExpired()
     }
 
     /**
-     * @depends testParseJwkKeySet
+     * @dataProvider provideDecodeByJwkKeySet
      */
-    public function testDecodeByJwkKeySet()
+    public function testDecodeByJwkKeySet($pemFile, $jwkFile, $alg)
     {
-        $privKey1 = file_get_contents(__DIR__ . '/data/rsa1-private.pem');
+        $privKey1 = file_get_contents(__DIR__ . '/data/' . $pemFile);
         $payload = ['sub' => 'foo', 'exp' => strtotime('+10 seconds')];
-        $msg = JWT::encode($payload, $privKey1, 'RS256', 'jwk1');
+        $msg = JWT::encode($payload, $privKey1, $alg, 'jwk1');
 
-        $result = JWT::decode($msg, self::$keys);
+        $jwkSet = json_decode(
+            file_get_contents(__DIR__ . '/data/' . $jwkFile),
+            true
+        );
+
+        $keys = JWK::parseKeySet($jwkSet);
+        $result = JWT::decode($msg, $keys);
 
         $this->assertEquals('foo', $result->sub);
     }
 
+    public function provideDecodeByJwkKeySet()
+    {
+        return [
+            ['rsa1-private.pem', 'rsa-jwkset.json', 'RS256'],
+            ['ecdsa256-private.pem', 'ec-jwkset.json', 'ES256'],
+        ];
+    }
+
     /**
      * @depends testParseJwkKeySet
      */

tests/data/ec-jwkset.json

@@ -0,0 +1,22 @@
+{
+    "keys": [
+        {
+            "kty": "EC",
+            "use": "sig",
+            "crv": "P-256",
+            "kid": "jwk1",
+            "x": "ALXnvdCvbBx35J2bozBkIFHPT747KiYioLK4JquMhZU",
+            "y": "fAt_rGPqS95Ytwdluh4TNWTmj9xkcAbKGBRpP5kuGBk",
+            "alg": "ES256"
+        },
+        {
+            "kty": "EC",
+            "use": "sig",
+            "crv": "P-256",
+            "kid": "jwk2",
+            "x": "mQa0q5FvxPRujxzFazQT1Mo2YJJzuKiXU3svOJ41jhw",
+            "y": "jAz7UwIl2oOFk06kj42ZFMOXmGMFUGjKASvyYtibCH0",
+            "alg": "ES256"
+        }
+    ]
+}

tests/data/ecdsa256-private.pem

@@ -0,0 +1,4 @@
+-----BEGIN PRIVATE KEY-----
+MEECAQAwEwYHKoZIzj0CAQYIKoZIzj0DAQcEJzAlAgEBBCD0KvVxLJEzRBQmcEXf
+D2okKCNoUwZY8fc1/1Z4aJuJdg==
+-----END PRIVATE KEY-----