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<?php |
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namespace SimpleSAML\Module\webauthn\WebAuthn; |
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use Cose\Key\Ec2Key; |
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include_once 'AAGUID.php'; |
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/** |
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* FIDO2/WebAuthn Authentication Processing filter |
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* |
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* Filter for registering or authenticating with a FIDO2/WebAuthn token after |
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* having authenticated with the primary authsource. |
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* |
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* @author Stefan Winter <[email protected]> |
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* @package SimpleSAMLphp |
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*/ |
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class WebAuthnRegistrationEvent extends WebAuthnAbstractEvent |
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{ |
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/** |
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* Public key algorithm supported. This is -7 - ECDSA with curve P-256 |
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*/ |
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const PK_ALGORITHM = -7; |
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const AAGUID_ASSURANCE_LEVEL_NONE = 0; |
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const AAGUID_ASSURANCE_LEVEL_SELF = 1; |
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const AAGUID_ASSURANCE_LEVEL_BASIC = 2; |
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const AAGUID_ASSURANCE_LEVEL_ATTCA = 3; |
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/** |
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* the AAGUID of the newly registered authenticator |
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* @var string |
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*/ |
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public $AAGUID; |
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/** |
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* how sure are we about the AAGUID? |
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* @var int |
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*/ |
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public $AAGUIDAssurance; |
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/** |
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* Initialize the event object. |
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* |
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* Validates and parses the configuration. |
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* |
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* @param string $pubkeyCredType PublicKeyCredential.type |
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* @param string $scope the scope of the event |
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* @param string $challenge the challenge which was used to trigger this event |
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* @param string $idpEntityId the entity ID of our IdP |
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* @param string $attestationData the attestation data CBOR blob |
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* @param string $responseId the response ID |
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* @param string $clientDataJSON the client data JSON string which is present in all types of events |
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* @param bool $debugMode print debugging statements? |
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*/ |
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public function __construct( |
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string $pubkeyCredType, |
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string $scope, |
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string $challenge, |
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string $idpEntityId, |
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string $attestationData, |
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string $responseId, |
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string $clientDataJSON, |
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bool $debugMode = false |
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) { |
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$this->debugBuffer .= "attestationData raw: " . $attestationData . "<br/>"; |
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/** |
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* §7.1 STEP 9 : CBOR decode attestationData. |
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*/ |
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$attestationArray = $this->cborDecode($attestationData); |
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$authData = $attestationArray['authData']; |
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$this->eventType = "REG"; |
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parent::__construct($pubkeyCredType, $scope, $challenge, $idpEntityId, $authData, $clientDataJSON, $debugMode); |
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// this function extracts the public key |
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$this->validateAttestedCredentialData(substr($authData, 37), $responseId); |
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// this function may need the public key to have been previously extracted |
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$this->validateAttestationData($attestationData, $clientDataJSON); |
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// the following function sets the credential properties |
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$this->debugBuffer .= "Attestation Data (bin2hex): " . bin2hex(substr($authData, 37)) . "<br/>"; |
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} |
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/** |
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* validate the incoming attestation data CBOR blob and return the embedded authData |
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* @param string $attestationData |
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* @param string $clientDataJSON |
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* @return void |
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*/ |
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private function validateAttestationData(string $attestationData, string $clientDataJSON) : void |
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{ |
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/** |
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* STEP 9 of the validation procedure in § 7.1 of the spec: CBOR-decode the attestationObject |
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*/ |
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$attestationArray = $this->cborDecode($attestationData); |
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$this->debugBuffer .= "<pre>"; |
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$this->debugBuffer .= print_r($attestationArray, true); |
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$this->debugBuffer .= "</pre>"; |
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/** |
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* STEP 15 of the validation procedure in § 7.1 of the spec: verify attStmt values |
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*/ |
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switch ($attestationArray['fmt']) { |
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case "none": |
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$this->validateAttestationFormatNone($attestationArray); |
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break; |
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case "packed": |
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$this->validateAttestationFormatPacked($attestationArray, $clientDataJSON); |
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break; |
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case "fido-u2f": |
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$this->validateAttestationFormatFidoU2F($attestationArray); |
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break; |
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case "android-safetynet": |
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$this->validateAttestationFormatAndroidSafetyNet($attestationArray); |
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break; |
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case "tpm": |
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case "android-key": |
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$this->fail("Attestation format " . $attestationArray['fmt'] . " validation not supported right now."); |
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break; |
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default: |
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$this->fail("Unknown attestation format."); |
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break; |
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} |
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} |
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/** |
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* @param array $attestationArray |
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* @return void |
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*/ |
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private function validateAttestationFormatNone(array $attestationArray) : void |
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{ |
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// § 8.7 of the spec |
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/** |
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* § 7.1 Step 16 && §8.7 Verification Procedure: stmt must be an empty array |
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* § 7.1 Step 17+18 are a NOOP if the format was "none" (which is acceptable as per this RPs policy) |
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*/ |
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if (count($attestationArray['attStmt']) == 0) { |
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$this->pass("Attestation format and statement as expected, and no attestation authorities to retrieve."); |
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$this->AAGUIDAssurance = WebAuthnRegistrationEvent::AAGUID_ASSURANCE_LEVEL_NONE; |
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return; |
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} else { |
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$this->fail("Non-empty attestation authorities are not expected with 'attestationFormat = none'."); |
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} |
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} |
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/** |
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* @param array $attestationArray |
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* @param string $clientDataJSON |
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* @return void |
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*/ |
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private function validateAttestationFormatPacked(array $attestationArray, string $clientDataJSON) : void |
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{ |
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$stmtDecoded = $attestationArray['attStmt']; |
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$this->debugBuffer .= "AttStmt: " . print_r($stmtDecoded, true) . "<br/>"; |
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/** |
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* §7.1 Step 16: attestation is either done with x5c or ecdaa. |
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*/ |
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if (isset($stmtDecoded['x5c'])) { |
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/** |
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* §8.2 Step 2: check x5c attestation |
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*/ |
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$sigdata = $attestationArray['authData'] . hash("sha256", $clientDataJSON, true); |
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$keyResource = openssl_pkey_get_public($this->der2pem($stmtDecoded['x5c'][0])); |
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if ($keyResource === false) { |
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$this->fail("Unable to construct public key resource from PEM."); |
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} |
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/** |
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* §8.2 Step 2 Bullet 1: check signature |
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*/ |
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if (openssl_verify($sigdata, $stmtDecoded['sig'], $keyResource, OPENSSL_ALGO_SHA256) != 1) { |
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$this->fail("x5c attestation failed."); |
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} |
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$this->pass("x5c sig check passed."); |
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// still need to perform sanity checks on the attestation certificate |
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/** |
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* §8.2 Step 2 Bullet 2: check certificate properties listed in §8.2.1 |
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*/ |
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$certProps = openssl_x509_parse($this->der2pem($stmtDecoded['x5c'][0])); |
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$this->debugBuffer .= "Attestation Certificate:" . print_r($certProps, true) . "<br/>"; |
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if ($certProps['version'] != 2 || /** §8.2.1 Bullet 1 */ |
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$certProps['subject']['OU'] != "Authenticator Attestation" || /** §8.2.1 Bullet 2 [Subject-OU] */ |
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!isset($certProps['subject']['CN']) || /** §8.2.1 Bullet 2 [Subject-CN] */ |
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!isset($certProps['extensions']['basicConstraints']) || |
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strstr("CA:FALSE", $certProps['extensions']['basicConstraints']) === false /** §8.2.1 Bullet 4 */ |
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) { |
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$this->fail("Attestation certificate properties are no good."); |
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} |
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if (isset(AAGUID::AAGUID_DICTIONARY[strtolower($this->AAGUID)])) { |
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if ($certProps['subject']['O'] != AAGUID::AAGUID_DICTIONARY[strtolower($this->AAGUID)]['O'] || /** §8.2.1 Bullet 2 [Subject-O] */ |
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$certProps['subject']['C'] != AAGUID::AAGUID_DICTIONARY[strtolower($this->AAGUID)]['C']) { /** §8.2.1 Bullet 2 [Subject-C] */ |
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$this->fail("AAGUID does not match vendor data."); |
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} |
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if (AAGUID::AAGUID_DICTIONARY[strtolower($this->AAGUID)]['multi'] === true) { // need to check the OID |
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if (!isset($certProps['extensions']['1.3.6.1.4.1.45724.1.1.4'])) { /** §8.2.1 Bullet 3 */ |
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$this->fail("This vendor uses one cert for multiple authenticator model attestations, but lacks the AAGUID OID."); |
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} |
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/** |
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* §8.2 Step 2 Bullet 3: compare AAGUID values |
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*/ |
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$AAGUIDFromOid = substr(bin2hex($certProps['extensions']['1.3.6.1.4.1.45724.1.1.4']), 4); |
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$this->debugBuffer .= "AAGUID from OID = $AAGUIDFromOid<br/>"; |
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if (strtolower($AAGUIDFromOid) != strtolower($this->AAGUID)) { |
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$this->fail("AAGUID mismatch between attestation certificate and attestation statement."); |
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} |
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} |
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// we would need to verify the attestation certificate against a known-good root CA certificate to get more than basic |
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/* |
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* §7.1 Step 17 is to look at AAGUID::AAGUID_DICTIONARY[strtolower($this->AAGUID)]['RootPEMs'] |
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*/ |
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/* |
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* §7.1 Step 18 is skipped, and we unconditionally return "only" Basic. |
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*/ |
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$this->AAGUIDAssurance = WebAuthnRegistrationEvent::AAGUID_ASSURANCE_LEVEL_BASIC; |
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} else { |
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$this->warn("Unknown authenticator model found: " . $this->AAGUID . "."); |
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// unable to verify all cert properties, so this is not enough for BASIC. |
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// but it's our own fault, we should add the device to our DB. |
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$this->AAGUIDAssurance = WebAuthnRegistrationEvent::AAGUID_ASSURANCE_LEVEL_SELF; |
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} |
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$this->pass("x5c attestation passed."); |
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return; |
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} |
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if (isset($stmtDecoded['ecdaa'])) { |
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$this->fail("ecdaa attestation not supported right now."); |
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} |
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// if we are still here, we are in the "self" type. |
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/** |
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* §8.2 Step 4 Bullet 1: check algorithm |
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*/ |
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if ($stmtDecoded['alg'] != WebAuthnRegistrationEvent::PK_ALGORITHM) { |
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$this->fail("Unexpected algorithm type in packed basic attestation: " . $stmtDecoded['alg'] . "."); |
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} |
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$keyObject = new Ec2Key($this->cborDecode(hex2bin($this->credential))); |
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$keyResource = openssl_pkey_get_public($keyObject->asPEM()); |
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if ($keyResource === false) { |
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$this->fail("Unable to construct public key resource from PEM."); |
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} |
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$sigdata = $attestationArray['authData'] . $this->clientDataHash; |
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/** |
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* §8.2 Step 4 Bullet 2: verify signature |
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*/ |
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if (openssl_verify($sigdata, $stmtDecoded['sig'], $keyResource, OPENSSL_ALGO_SHA256) == 1) { |
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$this->pass("Self-Attestation veried."); |
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/** |
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* §8.2 Step 4 Bullet 3: return Self level |
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*/ |
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$this->AAGUIDAssurance = WebAuthnRegistrationEvent::AAGUID_ASSURANCE_LEVEL_SELF; |
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} else { |
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$this->fail("Self-Attestation failed."); |
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} |
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248
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} |
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250
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/** |
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251
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* support legacy U2F tokens |
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252
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* |
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253
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* @param array $attestationData the incoming attestation data |
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254
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*/ |
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255
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private function validateAttestationFormatFidoU2F($attestationData) { |
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256
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257
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} |
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258
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259
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/** |
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260
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* support Android authenticators (fingerprint etc.) |
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261
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* |
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262
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* @param array $attestationData the incoming attestation data |
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263
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*/ |
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264
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private function validateAttestationFormatAndroidSafetyNet($attestationData) { |
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265
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266
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} |
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267
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268
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/** |
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269
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* The registration contains the actual credential. This function parses it. |
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270
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* @param string $attData the attestation data binary blob |
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271
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* @param string $responseId the response ID |
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272
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* @return void |
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273
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*/ |
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274
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private function validateAttestedCredentialData(string $attData, string $responseId) : void |
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275
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{ |
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276
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$aaguid = substr($attData, 0, 16); |
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277
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$credIdLenBytes = substr($attData, 16, 2); |
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278
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$credIdLen = intval(bin2hex($credIdLenBytes), 16); |
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279
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$credId = substr($attData, 18, $credIdLen); |
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280
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$this->debugBuffer .= "AAGUID (hex) = " . bin2hex($aaguid) . "</br/>"; |
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281
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$this->AAGUID = bin2hex($aaguid); |
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282
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$this->debugBuffer .= "Length Raw = " . bin2hex($credIdLenBytes) . "<br/>"; |
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283
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$this->debugBuffer .= "Credential ID Length (decimal) = " . $credIdLen . "<br/>"; |
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284
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$this->debugBuffer .= "Credential ID (hex) = " . bin2hex($credId) . "<br/>"; |
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285
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if (bin2hex(WebAuthnAbstractEvent::base64url_decode($responseId)) == bin2hex($credId)) { |
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286
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$this->pass("Credential IDs in authenticator response and in attestation data match."); |
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287
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} else { |
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$this->fail("Mismatch of credentialId (" . bin2hex($credId) . ") vs. response ID (" . bin2hex(WebAuthnAbstractEvent::base64url_decode($responseId)) . ")."); |
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289
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} |
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// so far so good. Now extract the actual public key from its COSE |
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// encoding. |
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// finding out the number of bytes to CBOR decode appears non-trivial. |
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// The simple case is if no ED is present as the CBOR data then goes to |
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// the end of the byte sequence. |
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// Since we made sure above that no ED is in the sequence, take the rest |
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// of the sequence in its entirety. |
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$pubKeyCBOR = substr($attData, 18 + $credIdLen); |
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$arrayPK = $this->cborDecode($pubKeyCBOR); |
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$this->debugBuffer .= "pubKey in canonical form: <pre>" . print_r($arrayPK, true) . "</pre>"; |
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/** |
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* STEP 13 of the validation procedure in § 7.1 of the spec: is the algorithm the expected one? |
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*/ |
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if ($arrayPK['3'] == WebAuthnRegistrationEvent::PK_ALGORITHM) { // we requested -7, so want to see it here |
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$this->pass("Public Key Algorithm is the expected one (-7, ECDSA)."); |
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} else { |
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$this->fail("Public Key Algorithm mismatch!"); |
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} |
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$this->credentialId = bin2hex($credId); |
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$this->credential = bin2hex($pubKeyCBOR); |
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} |
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/** |
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* transform DER formatted certificate to PEM format |
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* |
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* @param string $derData blob of DER data |
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* @return string the PEM representation of the certificate |
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*/ |
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private function der2pem(string $derData) : string |
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{ |
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$pem = chunk_split(base64_encode($derData), 64, "\n"); |
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$pem = "-----BEGIN CERTIFICATE-----\n" . $pem . "-----END CERTIFICATE-----\n"; |
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return $pem; |
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} |
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} |
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simplesamlphp /
simplesamlphp-module-webauthn
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