Add support for apple verification format

README.md

@@ -683,13 +683,13 @@ Due to an inability to generate responses with all formats, not all are supporte
 
 | Format | Supported | Spec | Notes |
 | --- | --- | --- | --- |
-| `packed` | ✅⚠️ | 8.2 | Parses fine, attestation trust path support is limited. |
+| `packed` | ✅⚠️[^limited-trust-path] | 8.2 | |
 | `tpm` | ❌ | 8.3 | |
 | `android-key` | ❌ | 8.4 | |
 | `android-safetynet` | ❌ | 8.5 | |
 | `fido-u2f` | ✅ | 8.6 | YubiKeys and similar U2F stateless devices. |
 | `none` | ✅ | 8.7 | Used by Apple in Safari when using Passkeys (even when direct attestation is requested) |
-| `apple` | ❌ | 8.8 | Apple does not appear to use this format, instead providing non-attested credentials. |
+| `apple` | ✅⚠️ [^ext-vec], [^limited-trust-path] | 8.8 | Apple no longer appears to use this format, instead providing non-attested credentials (fmt=none). |
 | `compound` | ❌ | 8.9 | This format only appears in the editor's draft of the spec and is not yet on the official registry. |
 
 If you receive an `UnhandledMatchError` from the library pertaining to a format, please file an issue.
@@ -716,3 +716,6 @@ General quickstart guide:
 
 Intro to passkeys:
 - https://developer.apple.com/videos/play/wwdc2021/10106/
+
+[^ext-vec]: Support is based on [unofficial test vectors](https://github.com/w3c/webauthn/issues/1633).
+[^limited-trust-path]: Handling of attestation trust path is limited.

src/Attestations/Apple.php

@@ -0,0 +1,109 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Firehed\WebAuthn\Attestations;
+
+use Exception;
+use Firehed\CBOR\Decoder;
+use Firehed\WebAuthn\AuthenticatorData;
+use Firehed\WebAuthn\BinaryString;
+use Firehed\WebAuthn\Certificate;
+use Firehed\WebAuthn\PublicKey\EllipticCurve;
+use OpenSSLCertificate;
+
+class Apple implements AttestationStatementInterface
+{
+    private const OID = '1.2.840.113635.100.8.2';
+
+    /**
+     * @param array{
+     *   x5c: string[],
+     * } $data
+     */
+    public function __construct(
+        private array $data,
+    ) {
+    }
+
+    // 8.8
+    public function verify(AuthenticatorData $data, BinaryString $clientDataHash): VerificationResult
+    {
+        // ¶2
+        $nonceToHash = new BinaryString(
+            $data->getRaw()->unwrap() . $clientDataHash->unwrap()
+        );
+        // ¶3
+        $nonce = hash('sha256', $nonceToHash->unwrap(), binary: true);
+
+        // ¶4 - there's a whole lot of validation and data extraction that the
+        // spec glosses over.
+        $certs = array_map(self::parseDer(...), $this->data['x5c']);
+        assert(count($certs) >= 1);
+        $credCert = array_shift($certs);
+        $info = openssl_x509_parse($credCert);
+        if ($info === false) {
+            throw new Exception('Invalid certificate');
+        }
+        if (!array_key_exists('extensions', $info)) {
+            throw new Exception('No extensions in credential cert');
+        }
+        $certExt = $info['extensions'];
+        if (!array_key_exists(self::OID, $certExt)) {
+            throw new Exception('Expected OID not present in cert extensions');
+        }
+        $nonceInCert = $certExt[self::OID];
+        // This isn't clear in the spec, but the value arrives ASN.1-encoded.
+        // Manually verify some length assumptions instead of doing some
+        // full-on parsing.
+        if (strlen($nonceInCert) !== 38) {
+            throw new Exception("Malformed nonce in cert");
+        }
+        // 0x3024 SEQUENCE (constructed) legnth 36
+        //   0xA122 Element 1, length 34
+        //     0x0420 OCTET STRING length 32
+        if (!str_starts_with(needle: "\x30\x24\xA1\x22\x04\x20", haystack: $nonceInCert)) {
+            throw new Exception("Cert nonce has weird encoding");
+        }
+        // (finally, the actual verification procedure)
+        $decodedNonceInCert = substr($nonceInCert, 6);
+        if (!hash_equals($nonce, $decodedNonceInCert)) {
+            throw new Exception('Nonce mismatch of expected value');
+        }
+
+        // ¶5
+        $pubKey = openssl_pkey_get_public($credCert);
+        if ($pubKey === false) {
+            throw new Exception('Could not read pubkey of certificate');
+        }
+        $pkd = openssl_pkey_get_details($pubKey);
+        if ($pkd === false) {
+            throw new Exception('Could not extract public key info');
+        }
+        $credPK = $data->getAttestedCredentialData()->coseKey;
+        $credPKPem = $credPK->getPublicKey()->getPemFormatted();
+        // ¶6
+        if (trim($pkd['key']) !== trim($credPKPem)) {
+            throw new Exception('Credential public key does not match cert subject');
+        }
+        return new VerificationResult(
+            AttestationType::AnonymizationCA,
+            // trustPath: rest of x5c
+        );
+    }
+
+    private static function parseDer(string $certificate): OpenSSLCertificate
+    {
+        // Convert DER to PEM format
+        $certificate = "-----BEGIN CERTIFICATE-----\n"
+            . chunk_split(base64_encode($certificate), 64, "\n")
+            . "-----END CERTIFICATE-----";
+
+        // Read and parse the certificate
+        $certResource = openssl_x509_read($certificate);
+        if ($certResource === false) {
+            throw new Exception('Certiticate parsing error');
+        }
+        return $certResource;
+    }
+}

src/Attestations/AttestationObject.php

@@ -30,6 +30,7 @@ public function __construct(
         assert(array_key_exists('authData', $decoded));
 
         $stmt = match (Format::tryFrom($decoded['fmt'])) { // @phpstan-ignore-line
+            Format::Apple => new Apple($decoded['attStmt']),
             Format::None => new None($decoded['attStmt']),
             Format::Packed => new Packed($decoded['attStmt']),
             Format::U2F => new FidoU2F($decoded['attStmt']),

tests/IntegrationTest.php

@@ -11,6 +11,7 @@
  * Performs general integration testing with known-good data covering various
  * formats, attestation requirements, etc.
  *
+ * @covers \Firehed\WebAuthn\Attestations\Apple
  * @covers \Firehed\WebAuthn\Attestations\FidoU2F
  * @covers \Firehed\WebAuthn\Attestations\None
  * @covers \Firehed\WebAuthn\Attestations\Packed

tests/integration/1633-ios/metadata.json

@@ -0,0 +1,4 @@
+{
+  "id": "f25BX23OovR-Ti84WI6lQcp_qfc",
+  "origin": "https://mobilepki.org"
+}

tests/integration/1633-ios/reg-req.json

@@ -0,0 +1,5 @@
+{
+  "publicKey": {
+    "challenge": "1Z4m-O7Lmi762WffOu5jSXSnJfF93HHwWd52BhNhrUQ"
+  }
+}

tests/integration/1633-ios/reg-res.json

@@ -0,0 +1,11 @@
+{
+  "id": "f25BX23OovR-Ti84WI6lQcp_qfc",
+  "rawId": "f25BX23OovR-Ti84WI6lQcp_qfc",
+  "response": {
+    "clientDataJSON": "eyJ0eXBlIjoid2ViYXV0aG4uY3JlYXRlIiwiY2hhbGxlbmdlIjoiMVo0bS1PN0xtaTc2MldmZk91NWpTWFNuSmZGOTNISHdXZDUyQmhOaHJVUSIsIm9yaWdpbiI6Imh0dHBzOi8vbW9iaWxlcGtpLm9yZyJ9",
+    "attestationObject": "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-MjNLS0p5nz8v5bGI3kXR6C1FeJzzXx7nU7cOfprQ_o1UwUzAMBgNVHRMBAf8EAjAAMA4GA1UdDwEB_wQEAwIE8DAzBgkqhkiG92NkCAIEJjAkoSIEIHcxH4L2XBi_OttASQZ8wqaTnb6PnGlh5mOwNfQGktYqMAoGCCqGSM49BAMCA2cAMGQCMHNr9RnVEWfKNtrG5ovjBic8WSEQE2T-CWmZ3nSO740N41kkQ6q5kx3iW-qThQ4_nwIwAyM4XCTtmH-AB_UmqN2AbPqvb0N57vVyQpey7Yxj9fKIJ6ALDOux0T1c9F-HteYrWQI4MIICNDCCAbqgAwIBAgIQViVTlcen-0Dr4ijYJghTtjAKBggqhkjOPQQDAzBLMR8wHQYDVQQDDBZBcHBsZSBXZWJBdXRobiBSb290IENBMRMwEQYDVQQKDApBcHBsZSBJbmMuMRMwEQYDVQQIDApDYWxpZm9ybmlhMB4XDTIwMDMxODE4MzgwMVoXDTMwMDMxMzAwMDAwMFowSDEcMBoGA1UEAwwTQXBwbGUgV2ViQXV0aG4gQ0EgMTETMBEGA1UECgwKQXBwbGUgSW5jLjETMBEGA1UECAwKQ2FsaWZvcm5pYTB2MBAGByqGSM49AgEGBSuBBAAiA2IABIMuhy8mFJGBAiW59fzWu2N4tfVfP8sEW8c1mTR1_VSQRN-b_hkhF2XGmh3aBQs41FCDQBpDT7JNES1Ww-HPv8uYkf7AaWCBvvlsvHfIjd2vRqWu4d1RW1r6q5O-nAsmkaNmMGQwEgYDVR0TAQH_BAgwBgEB_wIBADAfBgNVHSMEGDAWgBQm12TZxXjCWmfRp95rEtAbY_HG1zAdBgNVHQ4EFgQU666CxP-hrFtR1M8kYQUAvmO9d4gwDgYDVR0PAQH_BAQDAgEGMAoGCCqGSM49BAMDA2gAMGUCMQDdixo0gaX62du052V7hB4UTCe3W4dqQYbCsUdXUDNyJ-_lVEV-9kiVDGMuXEg-cMECMCyKYETcIB_P5ZvDTSkwwUh4Udlg7Wp18etKyr44zSW4l9DIBb7wx_eLB6VxxugOB2hhdXRoRGF0YViYKSqtX-Wo3JpWQpsrCGT2kSTRHZYWuoNy4MTSFTN75b1FAAAAAAAAAAAAAAAAAAAAAAAAAAAAFH9uQV9tzqL0fk4vOFiOpUHKf6n3pQECAyYgASFYIKxuaQlc65MIQK3GlRXyEild12w5QUOVXp5xCrE4F2tjIlggz4yM0tLSnmfPy_lsYjeRdHoLUV4nPNfHudTtw5-mtD8",
+    "transports": []
+  },
+  "authenticatorAttachment": "",
+  "type": "public-key"
+}