<?php
declare(strict_types=1);
/*
* The MIT License (MIT)
*
* Copyright (c) 2014-2021 Spomky-Labs
*
* This software may be modified and distributed under the terms
* of the MIT license. See the LICENSE file for details.
*/
namespace Webauthn\AttestationStatement;
use Assert\Assertion;
use CBOR\Decoder;
use CBOR\OtherObject\OtherObjectManager;
use CBOR\Tag\TagObjectManager;
use Cose\Algorithms;
use Cose\Key\Ec2Key;
use Cose\Key\Key;
use Cose\Key\RsaKey;
use function count;
use FG\ASN1\ASNObject;
use FG\ASN1\ExplicitlyTaggedObject;
use FG\ASN1\Universal\OctetString;
use FG\ASN1\Universal\Sequence;
use function Safe\hex2bin;
use function Safe\openssl_pkey_get_public;
use function Safe\sprintf;
use Webauthn\AuthenticatorData;
use Webauthn\CertificateToolbox;
use Webauthn\StringStream;
use Webauthn\TrustPath\CertificateTrustPath;
final class AndroidKeyAttestationStatementSupport implements AttestationStatementSupport
{
/**
* @var Decoder
*/
private $decoder;
public function __construct()
{
$this->decoder = new Decoder(new TagObjectManager(), new OtherObjectManager());
}
public function name(): string
{
return 'android-key';
}
/**
* @param mixed[] $attestation
*/
public function load(array $attestation): AttestationStatement
{
Assertion::keyExists($attestation, 'attStmt', 'Invalid attestation object');
foreach (['sig', 'x5c', 'alg'] as $key) {
Assertion::keyExists($attestation['attStmt'], $key, sprintf('The attestation statement value "%s" is missing.', $key));
}
$certificates = $attestation['attStmt']['x5c'];
Assertion::isArray($certificates, 'The attestation statement value "x5c" must be a list with at least one certificate.');
Assertion::greaterThan(count($certificates), 0, 'The attestation statement value "x5c" must be a list with at least one certificate.');
Assertion::allString($certificates, 'The attestation statement value "x5c" must be a list with at least one certificate.');
$certificates = CertificateToolbox::convertAllDERToPEM($certificates);
return AttestationStatement::createBasic($attestation['fmt'], $attestation['attStmt'], new CertificateTrustPath($certificates));
}
public function isValid(string $clientDataJSONHash, AttestationStatement $attestationStatement, AuthenticatorData $authenticatorData): bool
{
$trustPath = $attestationStatement->getTrustPath();
Assertion::isInstanceOf($trustPath, CertificateTrustPath::class, 'Invalid trust path');
$certificates = $trustPath->getCertificates();
//Decode leaf attestation certificate
$leaf = $certificates[0];
$this->checkCertificateAndGetPublicKey($leaf, $clientDataJSONHash, $authenticatorData);
$signedData = $authenticatorData->getAuthData().$clientDataJSONHash;
$alg = $attestationStatement->get('alg');
return 1 === openssl_verify($signedData, $attestationStatement->get('sig'), $leaf, Algorithms::getOpensslAlgorithmFor((int) $alg));
}
private function checkCertificateAndGetPublicKey(string $certificate, string $clientDataHash, AuthenticatorData $authenticatorData): void
{
$resource = openssl_pkey_get_public($certificate);
$details = openssl_pkey_get_details($resource);
Assertion::isArray($details, 'Unable to read the certificate');
//Check that authData publicKey matches the public key in the attestation certificate
$attestedCredentialData = $authenticatorData->getAttestedCredentialData();
Assertion::notNull($attestedCredentialData, 'No attested credential data found');
$publicKeyData = $attestedCredentialData->getCredentialPublicKey();
Assertion::notNull($publicKeyData, 'No attested public key found');
$publicDataStream = new StringStream($publicKeyData);
$coseKey = $this->decoder->decode($publicDataStream)->getNormalizedData(false);
Assertion::true($publicDataStream->isEOF(), 'Invalid public key data. Presence of extra bytes.');
$publicDataStream->close();
$publicKey = Key::createFromData($coseKey);
Assertion::true(($publicKey instanceof Ec2Key) || ($publicKey instanceof RsaKey), 'Unsupported key type');
Assertion::eq($publicKey->asPEM(), $details['key'], 'Invalid key');
/*---------------------------*/
$certDetails = openssl_x509_parse($certificate);
//Find Android KeyStore Extension with OID “1.3.6.1.4.1.11129.2.1.17” in certificate extensions
Assertion::isArray($certDetails, 'The certificate is not valid');
Assertion::keyExists($certDetails, 'extensions', 'The certificate has no extension');
Assertion::isArray($certDetails['extensions'], 'The certificate has no extension');
Assertion::keyExists($certDetails['extensions'], '1.3.6.1.4.1.11129.2.1.17', 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is missing');
$extension = $certDetails['extensions']['1.3.6.1.4.1.11129.2.1.17'];
$extensionAsAsn1 = ASNObject::fromBinary($extension);
Assertion::isInstanceOf($extensionAsAsn1, Sequence::class, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
$objects = $extensionAsAsn1->getChildren();
//Check that attestationChallenge is set to the clientDataHash.
Assertion::keyExists($objects, 4, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
Assertion::isInstanceOf($objects[4], OctetString::class, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
Assertion::eq($clientDataHash, hex2bin(($objects[4])->getContent()), 'The client data hash is not valid');
//Check that both teeEnforced and softwareEnforced structures don’t contain allApplications(600) tag.
Assertion::keyExists($objects, 6, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
$softwareEnforcedFlags = $objects[6];
Assertion::isInstanceOf($softwareEnforcedFlags, Sequence::class, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
$this->checkAbsenceOfAllApplicationsTag($softwareEnforcedFlags);
Assertion::keyExists($objects, 7, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
$teeEnforcedFlags = $objects[6];
Assertion::isInstanceOf($teeEnforcedFlags, Sequence::class, 'The certificate extension "1.3.6.1.4.1.11129.2.1.17" is invalid');
$this->checkAbsenceOfAllApplicationsTag($teeEnforcedFlags);
}
private function checkAbsenceOfAllApplicationsTag(Sequence $sequence): void
{
foreach ($sequence->getChildren() as $tag) {
Assertion::isInstanceOf($tag, ExplicitlyTaggedObject::class, 'Invalid tag');
/* @var ExplicitlyTaggedObject $tag */
Assertion::notEq(600, (int) $tag->getTag(), 'Forbidden tag 600 found');
}
}
}