fix: add key length validation for ec keys (#615)

Author: bshaffer

src/JWT.php

@@ -270,6 +270,8 @@ public static function sign(
                 }
                 if (str_starts_with($alg, 'RS')) {
                     self::validateRsaKeyLength($key);
+                } elseif (str_starts_with($alg, 'ES')) {
+                    self::validateEcKeyLength($key, $alg);
                 }
                 $success = \openssl_sign($msg, $signature, $key, $algorithm);
                 if (!$success) {
@@ -330,11 +332,13 @@ private static function verify(
         list($function, $algorithm) = static::$supported_algs[$alg];
         switch ($function) {
             case 'openssl':
-                if (str_starts_with($algorithm, 'RS')) {
-                    if (!$key = openssl_pkey_get_private($keyMaterial)) {
-                        throw new DomainException('OpenSSL unable to validate key');
-                    }
+                if (!$key = openssl_pkey_get_public($keyMaterial)) {
+                    throw new DomainException('OpenSSL unable to validate key');
+                }
+                if (str_starts_with($alg, 'RS')) {
                     self::validateRsaKeyLength($key);
+                } elseif (str_starts_with($alg, 'ES')) {
+                    self::validateEcKeyLength($key, $alg);
                 }
                 $success = \openssl_verify($msg, $signature, $keyMaterial, $algorithm);
                 if ($success === 1) {
@@ -721,4 +725,24 @@ private static function validateRsaKeyLength(#[\SensitiveParameter] OpenSSLAsymm
             throw new DomainException('Provided key is too short');
         }
     }
+
+    /**
+     * Validate RSA key length
+     *
+     * @param OpenSSLAsymmetricKey $key RSA key material
+     * @param string $algorithm The algorithm
+     * @throws DomainException Provided key is too short
+     */
+    private static function validateEcKeyLength(
+        #[\SensitiveParameter] OpenSSLAsymmetricKey $key,
+        string $algorithm
+    ): void {
+        if (!$keyDetails = openssl_pkey_get_details($key)) {
+            throw new DomainException('Unable to validate key');
+        }
+        $minKeyLength = (int) \str_replace('ES', '', $algorithm);
+        if ($keyDetails['bits'] < $minKeyLength) {
+            throw new DomainException('Provided key is too short');
+        }
+    }
 }

tests/JWTTest.php

@@ -678,6 +678,65 @@ public function provideHmac()
         ];
     }
 
+    /** @dataProvider provideEcKeyInvalidLength */
+    public function testEcKeyLengthValidationThrowsExceptionEncode(string $keyFile, string $alg): void
+    {
+        $this->expectException(DomainException::class);
+        $this->expectExceptionMessage('Provided key is too short');
+
+        $tooShortEcKey = file_get_contents(__DIR__ . '/data/' . $keyFile);
+        $payload = ['message' => 'abc'];
+
+        JWT::encode($payload, $tooShortEcKey, $alg);
+    }
+
+    public function testEcKeyLengthValidationThrowsExceptionDecode(): void
+    {
+        $this->expectException(DomainException::class);
+        $this->expectExceptionMessage('Provided key is too short');
+
+        $payload = ['message' => 'abc'];
+
+        $validEcKeyBytes = file_get_contents(__DIR__ . '/data/ecdsa384-private.pem');
+        $encoded = JWT::encode($payload, $validEcKeyBytes, 'ES256');
+
+        $tooShortEcKey = file_get_contents(__DIR__ . '/data/ecdsa192-public.pem');
+        JWT::decode($encoded, new Key($tooShortEcKey, 'ES256'));
+    }
+
+    /** @dataProvider provideEcKey */
+    public function testEcKeyLengthValidationPassesWithCorrectLength(
+        string $privateKeyFile,
+        string $publicKeyFile,
+        string $alg
+    ): void {
+        $payload = ['message' => 'test hmac length'];
+
+        // Test with a key that is the required length
+        $privateKeyBytes = file_get_contents(__DIR__ . '/data/' . $privateKeyFile);
+        $encoded48 = JWT::encode($payload, $privateKeyBytes, $alg);
+
+        $publicKeyBytes = file_get_contents(__DIR__ . '/data/' . $publicKeyFile);
+        $decoded48 = JWT::decode($encoded48, new Key($publicKeyBytes, $alg));
+        $this->assertEquals($payload['message'], $decoded48->message);
+    }
+
+    public function provideEcKeyInvalidLength()
+    {
+        return [
+            ['ecdsa192-private.pem', 'ES256'],
+            ['ecdsa-private.pem', 'ES384'],
+        ];
+    }
+
+    public function provideEcKey()
+    {
+        return [
+            ['ecdsa-private.pem', 'ecdsa-public.pem', 'ES256'],
+            ['ecdsa384-private.pem', 'ecdsa384-public.pem', 'ES384'],
+        ];
+    }
+
     private function generateHmac256(): Key
     {
         return new Key(random_bytes(32), 'HS256');

tests/data/ecdsa192-private.pem

@@ -0,0 +1,5 @@
+-----BEGIN EC PRIVATE KEY-----
+MF8CAQEEGPRkK7lK/9FuZ3BE8ZX+dlHavL22Q9CN2KAKBggqhkjOPQMBAaE0AzIA
+BL4pM50YcLq/I9Y8T+C+fwoOtwRW8zdV6yQmG9fD8zWaAs28+UxHeK8VD7THatbp
+wg==
+-----END EC PRIVATE KEY-----

tests/data/ecdsa192-public.pem

@@ -0,0 +1,4 @@
+-----BEGIN PUBLIC KEY-----
+MEkwEwYHKoZIzj0CAQYIKoZIzj0DAQEDMgAEvikznRhwur8j1jxP4L5/Cg63BFbz
+N1XrJCYb18PzNZoCzbz5TEd4rxUPtMdq1unC
+-----END PUBLIC KEY-----