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<?php |
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namespace MadWizard\WebAuthn\Attestation\Verifier; |
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use MadWizard\WebAuthn\Attestation\Android\SafetyNetResponseParser; |
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use MadWizard\WebAuthn\Attestation\Android\SafetyNetResponseParserInterface; |
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use MadWizard\WebAuthn\Attestation\AttestationType; |
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use MadWizard\WebAuthn\Attestation\AuthenticatorData; |
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use MadWizard\WebAuthn\Attestation\Statement\AndroidSafetyNetAttestationStatement; |
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use MadWizard\WebAuthn\Attestation\Statement\AttestationStatementInterface; |
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use MadWizard\WebAuthn\Attestation\TrustPath\CertificateTrustPath; |
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use MadWizard\WebAuthn\Exception\VerificationException; |
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use MadWizard\WebAuthn\Pki\CertificateParser; |
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use MadWizard\WebAuthn\Pki\CertificateParserInterface; |
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use function base64_encode; |
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use function hash_equals; |
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use function microtime; |
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final class AndroidSafetyNetAttestationVerifier implements AttestationVerifierInterface |
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{ |
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private const ATTEST_HOSTNAME = 'attest.android.com'; |
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/** |
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* @var CertificateParserInterface |
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*/ |
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private $certificateParser; |
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/** |
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* @var SafetyNetResponseParserInterface |
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*/ |
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private $responseParser; |
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/** |
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* @var float|null |
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*/ |
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private $fixedTimestamp = null; |
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public function __construct(?CertificateParserInterface $certificateParser = null, ?SafetyNetResponseParserInterface $responseParser = null) |
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{ |
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$this->certificateParser = $certificateParser ?? new CertificateParser(); |
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$this->responseParser = $responseParser ?? new SafetyNetResponseParser(); |
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} |
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private function getMsTimestamp(): float |
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{ |
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if ($this->fixedTimestamp !== null) { |
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return $this->fixedTimestamp; |
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} |
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return microtime(true) * 1000; |
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} |
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/** |
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* @internal Used for testing only |
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*/ |
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public function useFixedTimestamp(float $time): void |
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{ |
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$this->fixedTimestamp = $time; |
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} |
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public function verify(AttestationStatementInterface $attStmt, AuthenticatorData $authenticatorData, string $clientDataHash): VerificationResult |
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{ |
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if (!($attStmt instanceof AndroidSafetyNetAttestationStatement)) { |
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throw new VerificationException('Expecting AndroidSafetyNetAttestationStatement'); |
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} |
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// Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding on it to extract the contained fields. |
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// -> this is done in AndroidSafetyNetAttestationStatement |
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// Verify that response is a valid SafetyNet response of version ver. |
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$response = $this->responseParser->parse($attStmt->getResponse()); |
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// Verify that the nonce in the response is identical to the Base64 encoding of the SHA-256 hash of the concatenation of authenticatorData and clientDataHash. |
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$expectedNonce = base64_encode(hash('sha256', $authenticatorData->getRaw()->getBinaryString() . $clientDataHash, true)); |
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if (!hash_equals($expectedNonce, $response->getNonce())) { |
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throw new VerificationException('Nonce is invalid.'); |
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} |
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// Let attestationCert be the attestation certificate. |
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$x5c = $response->getCertificateChain(); |
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if (!isset($x5c[0])) { |
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throw new VerificationException('No certificates in chain.'); |
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} |
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$attCert = $x5c[0]; |
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// Verify that attestationCert is issued to the hostname "attest.android.com" (see SafetyNet online documentation). |
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$certInfo = $this->certificateParser->parsePem($attCert->asPem()); |
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$cn = $certInfo->getSubjectCommonName(); |
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if ($cn !== self::ATTEST_HOSTNAME) { |
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throw new VerificationException(sprintf('Attestation certificate should be issued to %s.', self::ATTEST_HOSTNAME)); |
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} |
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// Verify that the ctsProfileMatch attribute in the payload of response is true. |
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if (!$response->isCtsProfileMatch()) { |
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throw new VerificationException('Attestation should have ctsProfileMatch set to true.'); |
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} |
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$diff = $this->getMsTimestamp() - $response->getTimestampMs(); |
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if ($diff < -60e3 || $diff > 60e3) { |
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throw new VerificationException('Timestamp is not within margin of one minute'); |
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} |
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// If successful, return implementation-specific values representing attestation type Basic and attestation trust path attestationCert. |
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return new VerificationResult(AttestationType::BASIC, new CertificateTrustPath($x5c)); |
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} |
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} |
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madwizard-org /
webauthn-server
