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<?php |
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namespace MadWizard\WebAuthn\Attestation\Verifier; |
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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\Fido\FidoAaguidExtension; |
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use MadWizard\WebAuthn\Attestation\Registry\AttestationFormatInterface; |
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use MadWizard\WebAuthn\Attestation\Registry\BuiltInAttestationFormat; |
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use MadWizard\WebAuthn\Attestation\Statement\AttestationStatementInterface; |
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use MadWizard\WebAuthn\Attestation\Statement\PackedAttestationStatement; |
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use MadWizard\WebAuthn\Attestation\TrustPath\CertificateTrustPath; |
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use MadWizard\WebAuthn\Attestation\TrustPath\EmptyTrustPath; |
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use MadWizard\WebAuthn\Exception\ParseException; |
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use MadWizard\WebAuthn\Exception\UnsupportedException; |
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use MadWizard\WebAuthn\Exception\VerificationException; |
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use MadWizard\WebAuthn\Exception\WebAuthnException; |
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use MadWizard\WebAuthn\Format\ByteBuffer; |
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use MadWizard\WebAuthn\Pki\CertificateDetails; |
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use MadWizard\WebAuthn\Pki\CertificateDetailsInterface; |
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use MadWizard\WebAuthn\Pki\X509Certificate; |
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final class PackedAttestationVerifier implements AttestationVerifierInterface |
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{ |
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public function verify(AttestationStatementInterface $attStmt, AuthenticatorData $authenticatorData, string $clientDataHash): VerificationResult |
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{ |
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// Verification procedure from https://www.w3.org/TR/webauthn/#packed-attestation |
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if (!($attStmt instanceof PackedAttestationStatement)) { |
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throw new VerificationException('Expecting PackedAttestationStatement'); |
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} |
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// 1. Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding on it |
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// to extract the contained fields. |
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// -> This is done in PackedAttestationStatement |
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// 2. If x5c is present, this indicates that the attestation type is not ECDAA. |
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$x5c = $attStmt->getCertificates(); |
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if ($x5c !== null) { |
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return $this->verifyX5C($x5c, $attStmt->getSignature(), $attStmt->getAlgorithm(), $authenticatorData, $clientDataHash); |
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} |
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// 3. If ecdaaKeyId is present, then the attestation type is ECDAA. |
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$ecdaaKeyId = $attStmt->getEcdaaKeyId(); |
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if ($ecdaaKeyId !== null) { |
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throw new UnsupportedException('ECDAA is not supported by this library and is removed in later WebAuthn specifications.'); |
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} |
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// 4. If neither x5c nor ecdaaKeyId is present, self attestation is in use. |
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return $this->verifySelf($attStmt->getSignature(), $attStmt->getAlgorithm(), $authenticatorData, $clientDataHash); |
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} |
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/** |
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* @param X509Certificate[] $x5c |
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*/ |
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private function verifyX5c(array $x5c, ByteBuffer $signature, int $signatureAlgorithm, AuthenticatorData $authenticatorData, string $clientDataHash): VerificationResult |
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{ |
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// Verify that sig is a valid signature over the concatenation of authenticatorData and clientDataHash using |
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// the attestation public key in attestnCert with the algorithm specified in alg. |
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if (!isset($x5c[0])) { |
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throw new VerificationException('Empty X5C in attestation.'); |
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} |
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try { |
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$cert = CertificateDetails::fromPem($x5c[0]->asPem()); |
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$verificationData = $authenticatorData->getRaw()->getBinaryString() . $clientDataHash; |
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$valid = $cert->verifySignature($verificationData, $signature->getBinaryString(), $signatureAlgorithm); |
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} catch (WebAuthnException $e) { |
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throw new VerificationException('Failed to process attestation certificate.', 0, $e); |
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} |
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if (!$valid) { |
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throw new VerificationException('Attestation signature is invalid.'); |
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} |
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// Verify that attestnCert meets the requirements in §8.2.1 Packed attestation statement certificate requirements. |
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$this->checkCertRequirements($cert); |
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// If attestnCert contains an extension with OID 1.3.6.1.4.1.45724.1.1.4 (id-fido-gen-ce-aaguid) verify that the value of this extension matches the aaguid in authenticatorData. |
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FidoAaguidExtension::checkAaguidExtension($cert, $authenticatorData->getAaguid()); |
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// If successful, return attestation type Basic and attestation trust path x5c. |
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return new VerificationResult(AttestationType::BASIC, new CertificateTrustPath(...$x5c)); |
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} |
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private function verifySelf(ByteBuffer $signature, int $algorithm, AuthenticatorData $authenticatorData, string $clientDataHash): VerificationResult |
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{ |
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// Validate that alg matches the algorithm of the credentialPublicKey in authenticatorData. |
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if (!$authenticatorData->hasKey()) { |
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throw new VerificationException('No key in authenticator data.'); |
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} |
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$key = $authenticatorData->getKey(); |
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if ($key->getAlgorithm() !== $algorithm) { |
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throw new VerificationException(sprintf('Algorithm in packed attestation statement (%d) should match public key algorithm (%d)', $algorithm, $key->getAlgorithm())); |
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} |
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// Verify that sig is a valid signature over the concatenation of authenticatorData and clientDataHash using the credential public key with alg. |
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try { |
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$verificationData = $authenticatorData->getRaw()->getBinaryString() . $clientDataHash; |
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$valid = $key->verifySignature(new ByteBuffer($verificationData), $signature); |
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} catch (WebAuthnException $e) { |
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throw new VerificationException('Error while verifying signature for packed attestation', 0, $e); |
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} |
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// If successful, return attestation type Self and empty attestation trust path. |
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if ($valid) { |
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return new VerificationResult(AttestationType::SELF, new EmptyTrustPath()); |
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} |
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throw new VerificationException('Signature for self attestation could not be verified.'); |
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} |
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private function checkCertRequirements(CertificateDetailsInterface $cert): void |
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{ |
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// 8.2.1. Packed attestation statement certificate requirements |
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// The attestation certificate MUST have the following fields/extensions: |
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// Version MUST be set to 3 (which is indicated by an ASN.1 INTEGER with value 2). |
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$version = $cert->getCertificateVersion(); |
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if ($version !== CertificateDetails::VERSION_3) { |
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throw new VerificationException(sprintf('Attestation certificate version value is %s but should be %s (version 3).', $version ?? 'null', CertificateDetails::VERSION_3)); |
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} |
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// Subject field MUST be set to: |
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// [... Most fields are vendor specific, only subject-OU is specified in the spec ...] |
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// Subject-OU Literal string "Authenticator Attestation" (UTF8String) |
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try { |
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$ou = $cert->getOrganizationalUnit(); |
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if ($ou !== 'Authenticator Attestation') { |
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throw new VerificationException(sprintf("Subject-OU is '%s' but expecting 'Authenticator Attestation'.", $ou)); |
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} |
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} catch (ParseException $e) { |
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throw new VerificationException('Failed to parse Subject-OU in attestation certificate.', 0, $e); |
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} |
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// If the related attestation root certificate is used for multiple authenticator models, the Extension OID |
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// 1.3.6.1.4.1.45724.1.1.4 (id-fido-gen-ce-aaguid) MUST be present, containing the AAGUID as a 16-byte OCTET |
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// STRING. The extension MUST NOT be marked as critical. |
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// -> this is already verified in checkAaguidExtension |
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// The Basic Constraints extension MUST have the CA component set to false. |
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if ($cert->isCA() !== false) { |
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throw new VerificationException('Attestation certificate should not the CA basic constraint set to false.'); |
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} |
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// An Authority Information Access (AIA) extension with entry id-ad-ocsp and a CRL Distribution Point extension |
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// [RFC5280] are both OPTIONAL as the status of many attestation certificates is available through authenticator |
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// metadata services. See, for example, the FIDO Metadata Service [FIDOMetadataService]. |
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// -> not handled here. |
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} |
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public function getSupportedFormat(): AttestationFormatInterface |
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{ |
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return new BuiltInAttestationFormat( |
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PackedAttestationStatement::FORMAT_ID, |
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PackedAttestationStatement::class, |
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$this |
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); |
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} |
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} |
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madwizard-org /
webauthn-server
