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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\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\FidoU2fAttestationStatement; |
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use MadWizard\WebAuthn\Attestation\TrustPath\CertificateTrustPath; |
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use MadWizard\WebAuthn\Crypto\Ec2Key; |
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use MadWizard\WebAuthn\Exception\VerificationException; |
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use function openssl_free_key; |
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use function openssl_pkey_get_details; |
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use function openssl_verify; |
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use const OPENSSL_ALGO_SHA256; |
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final class FidoU2fAttestationVerifier implements AttestationVerifierInterface |
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{ |
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public function verify(AttestationStatementInterface $attStmt, AuthenticatorData $authenticatorData, string $clientDataHash): VerificationResult |
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{ |
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if (!($attStmt instanceof FidoU2fAttestationStatement)) { |
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throw new VerificationException('Expecting FidoU2fAttestationStatement'); |
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} |
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// AAGUID for U2F should be zeroes (not in WebAuthn spec but in FIDO2 CTAP specs and FIDO conformance tools) |
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if (!$authenticatorData->getAaguid()->isZeroAaguid()) { |
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throw new VerificationException('AAGUID should be zeroed for U2F attestations.'); |
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} |
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// 1. Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding |
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// on it to extract the contained fields. |
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// -> This is done in FidoU2fAttestationStatement |
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// 2 |
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$key = $this->checkAttCertKey($attStmt); |
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try { |
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// 3. Extract the claimed rpIdHash from authenticatorData, and the claimed credentialId and credentialPublicKey |
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// from authenticatorData.attestedCredentialData. |
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$rpIdHash = $authenticatorData->getRpIdHash(); |
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$credentialId = $authenticatorData->getCredentialId(); |
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if ($credentialId === null) { |
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throw new VerificationException('No credential id available.'); |
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} |
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// 4 |
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$publicKeyU2f = $this->getPublicKeyU2f($authenticatorData); |
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// 5. Let verificationData be the concatenation of (0x00 || rpIdHash || clientDataHash || credentialId || publicKeyU2F) |
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$verificationData = "\x00" . $rpIdHash->getBinaryString() . $clientDataHash . $credentialId->getBinaryString() . $publicKeyU2f; |
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// 6. Verify the sig using verificationData and certificate public key per [SEC1]. |
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$result = openssl_verify( |
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$verificationData, |
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$attStmt->getSignature()->getBinaryString(), |
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$key, |
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OPENSSL_ALGO_SHA256 |
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); |
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if ($result === 1) { |
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// 7. If successful, return attestation type Basic with the attestation trust path set to x5c. |
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return new VerificationResult(AttestationType::BASIC, new CertificateTrustPath(...$attStmt->getCertificates())); |
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} |
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if ($result === 0) { |
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throw new VerificationException('Signature invalid.'); |
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} |
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throw new VerificationException('Failed to check signature'); |
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} finally { |
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if (PHP_VERSION_ID < 80000) { |
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openssl_free_key($key); |
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} |
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} |
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} |
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/** |
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* @return resource |
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* |
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* @throws VerificationException |
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*/ |
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private function checkAttCertKey(FidoU2fAttestationStatement $attStmt) |
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{ |
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// 2. Check that x5c has exactly one element and let attCert be that element. Let certificate public key |
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// be the public key conveyed by attCert. If certificate public key is not an Elliptic Curve (EC) public |
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// key over the P-256 curve, terminate this algorithm and return an appropriate error. |
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$certificates = $attStmt->getCertificates(); |
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if (count($certificates) === 0) { |
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throw new VerificationException('FIDO-U2F statements should contain exactly one certificate.'); |
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} |
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$attCert = $certificates[0]; |
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$x509 = openssl_pkey_get_public($attCert->asPem()); |
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if ($x509 === false) { |
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throw new VerificationException('Failed to parse x509 public key.'); |
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} |
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$details = openssl_pkey_get_details($x509); |
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if ($details === false || ($details['ec']['curve_name'] ?? null) !== 'prime256v1') { |
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throw new VerificationException('Expecting first certificate to have P-256 EC key.'); |
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} |
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return $x509; |
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} |
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private function getPublicKeyU2f(AuthenticatorData $authData): string |
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{ |
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// 4. Convert the COSE_KEY formatted credentialPublicKey (see Section 7 of [RFC8152]) to Raw ANSI X9.62 public |
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// key format (see ALG_KEY_ECC_X962_RAW in Section 3.6.2 Public Key Representation Formats of [FIDO-Registry]). |
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// |
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// Let x be the value corresponding to the "-2" key (representing x coordinate) in credentialPublicKey, |
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// and confirm its size to be of 32 bytes. If size differs or "-2" key is not found, terminate this algorithm |
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// |
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// Let y be the value corresponding to the "-3" key (representing y coordinate) in credentialPublicKey, |
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// and confirm its size to be of 32 bytes. If size differs or "-3" key is not found, terminate this algorithm |
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// and return an appropriate error. |
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// |
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$credentialPublicKey = $authData->getKey(); |
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if (!($credentialPublicKey instanceof Ec2Key)) { |
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throw new VerificationException('Public key is not EC2 key.'); |
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} |
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$x = $credentialPublicKey->getX(); |
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$y = $credentialPublicKey->getY(); |
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if ($x->getLength() !== 32 || $y->getLength() !== 32) { |
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throw new VerificationException('Unexpected key size.'); |
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} |
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// Let publicKeyU2F be the concatenation 0x04 || x || y. This signifies uncompressed ECC key format. |
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return "\x04" . $x->getBinaryString() . $y->getBinaryString(); |
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} |
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public function getSupportedFormat(): AttestationFormatInterface |
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{ |
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return new BuiltInAttestationFormat( |
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FidoU2fAttestationStatement::FORMAT_ID, |
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FidoU2fAttestationStatement::class, |
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$this |
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); |
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} |
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} |
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madwizard-org /
webauthn-server
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