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<?php
namespace CodeLts\U2F\U2FServer;
class U2FServer
{
/** Constant for the version of the u2f protocol */
const VERSION = "U2F_V2";
/** @internal */
const PUBKEY_LEN = 65;
/*
* NOTE: If you are lucky and can match this CNs to the hashes please also add it to
* the existing test case provider
* "CN=Yubico U2F EE Serial 776137165",
* "CN=Yubico U2F EE Serial 1086591525",
* "CN=Yubico U2F EE Serial 1973679733",
* "CN=Yubico U2F EE Serial 13503277888",
* "CN=Yubico U2F EE Serial 14803321578"
*/
/**
* @internal
* @see https://books.google.fr/books?id=SF68CwAAQBAJ&lpg=PT96&ots=PCLmrWyu2F&hl=fr&pg=PT96#v=onepage&q&f=false
* @see https://github.com/Yubico/python-u2flib-server/issues/15#issue-107916981
*/
private static $FIXCERTS = [
'349bca1031f8c82c4ceca38b9cebf1a69df9fb3b94eed99eb3fb9aa3822d26e8',
'dd574527df608e47ae45fbba75a2afdd5c20fd94a02419381813cd55a2a3398f', // "CN=Yubico U2F EE Serial 13831167861"
'1d8764f0f7cd1352df6150045c8f638e517270e8b5dda1c63ade9c2280240cae',
'd0edc9a91a1677435a953390865d208c55b3183c6759c9b5a7ff494c322558eb',
'6073c436dcd064a48127ddbf6032ac1a66fd59a0c24434f070d4e564c124c897',
'ca993121846c464d666096d35f13bf44c1b05af205f9b4a1e00cf6cc10c5e511'
];
/**
* @throws U2FException If OpenSSL older than 1.0.0 is used
*/
public static function checkOpenSSLVersion()
{
if(OPENSSL_VERSION_NUMBER < 0x10000000) {
throw new U2FException(
'OpenSSL has to be at least version 1.0.0, this is ' . OPENSSL_VERSION_TEXT,
U2FException::OLD_OPENSSL
);
}
return true;
}
/**
* Called to get a registration request to send to a user.
* Returns an array of one registration request and a array of sign requests.
*
* @param string $appId Application id for the running application, Basically the app's URL
* @param stdClass[] $registrations List of current registrations for this
* user, to prevent the user from registering the same authenticator several
* times.
* @return array<string,RegistrationRequest|SignRequest[]> An array of two elements, the first containing a
* RegisterRequest the second being an array of SignRequest
* @throws U2FException
*/
public static function makeRegistration($appId, array $registrations = [])
{
$request = new RegistrationRequest(static::createChallenge(), $appId);
$signatures = static::makeAuthentication($registrations, $appId);
return [
"request" => $request,
"signatures" => $signatures
];
}
/**
* Called to verify and unpack a registration message.
*
* @param RegistrationRequest $request this is a reply to
* @param object $response response from a user
* @param string|null $attestDir The folder to use where trusted CA files are stored (optional)
* @param bool $includeCert set to true if the attestation certificate should be
* included in the returned Registration object (optional)
* @return Registration
* @throws U2FException
*/
public static function register(RegistrationRequest $request, $response, $attestDir = null, $includeCert = true)
{
// Parameter Checks
// $request is safe because of the php typehint
if( !is_object( $response ) ) {
throw new \InvalidArgumentException('$response of register() method only accepts object.');
}
if( property_exists( $response, 'errorCode') && $response->errorCode !== 0 ) {
throw new U2FException(
'User-agent returned error. Error code: ' . $response->errorCode,
U2FException::BAD_UA_RETURNING
);
}
if( !is_bool( $includeCert ) ) {
throw new \InvalidArgumentException('$include_cert of register() method only accepts boolean.');
}
// Unpack the registration data coming from the client-side token
$rawRegistration = static::base64u_decode($response->registrationData);
$registrationData = array_values(unpack('C*', $rawRegistration));
$clientData = static::base64u_decode($response->clientData);
$clientToken = json_decode($clientData);
// Check Client's challenge matches the original request's challenge
if($clientToken->challenge !== $request->challenge()) {
throw new U2FException(
'Registration challenge does not match',
U2FException::UNMATCHED_CHALLENGE
);
}
// Begin validating and building the registration
$registration = new Registration();
$offset = 1;
$pubKey = substr($rawRegistration, $offset, static::PUBKEY_LEN);
$offset += static::PUBKEY_LEN;
// Validate and set the public key
if(static::publicKeyToPem($pubKey) === null) {
throw new U2FException(
'Decoding of public key failed',
U2FException::PUBKEY_DECODE
);
}
$registration->setPublicKey(base64_encode($pubKey));
// Build and set the key handle.
$keyHandleLength = $registrationData[$offset++];
$keyHandle = substr($rawRegistration, $offset, $keyHandleLength);
$offset += $keyHandleLength;
$registration->setKeyHandle(static::base64u_encode($keyHandle));
// Build certificate
// Set certificate length
// Note: length of certificate is stored in byte 3 and 4 (excluding the first 4 bytes)
$certLength = 4;
$certLength += ($registrationData[$offset + 2] << 8);
$certLength += $registrationData[$offset + 3];
// Write the certificate from the returning registration data
$rawCert = static::fixSignatureUnusedBits(substr($rawRegistration, $offset, $certLength));
$offset += $certLength;
$pemCert = "-----BEGIN CERTIFICATE-----\r\n";
$pemCert .= chunk_split(base64_encode($rawCert), 64);
$pemCert .= "-----END CERTIFICATE-----";
if($includeCert) {
$registration->setCertificate( base64_encode($rawCert) );
}
// If we've set the attestDir, check the given certificate can be used.
if($attestDir) {
if(openssl_x509_checkpurpose($pemCert, -1, static::get_certs($attestDir)) !== true) {
throw new U2FException(
'Attestation certificate can not be validated',
U2FException::ATTESTATION_VERIFICATION
);
}
}
// Attempt to extract public key from the certificate, if we can't something went wrong in making it.
if(!openssl_pkey_get_public($pemCert)) {
throw new U2FException(
'Decoding of public key failed',
U2FException::PUBKEY_DECODE
);
}
// Generate signature from the remaining part of the raw registration data
$signature = substr($rawRegistration, $offset);
// Build a verification string from the components we've made in this function
$dataToVerify = chr(0);
$dataToVerify .= hash('sha256', $request->appId(), true);
$dataToVerify .= hash('sha256', $clientData, true);
$dataToVerify .= $keyHandle;
$dataToVerify .= $pubKey;
// Verify our data against the signature and the certificate, on success return the registration object
if(openssl_verify($dataToVerify, $signature, $pemCert, 'sha256') === 1) {
return $registration;
} else {
throw new U2FException(
'Attestation signature does not match',
U2FException::ATTESTATION_SIGNATURE
);
}
}
/**
* Called to get an authentication request.
*
* @param stdClass[] $registrations An array of the registrations to create authentication requests for.
* @param string $appId Application id for the running application, Basically the app's URL
* @return SignRequest[] An array of SignRequest
* @throws \InvalidArgumentException
*/
public static function makeAuthentication(array $registrations, $appId)
{
$signatures = [];
$challenge = static::createChallenge();
foreach ($registrations as $reg) {
if( !is_object( $reg ) ) {
throw new \InvalidArgumentException('$registrations of makeAuthentication() method only accepts array of object.');
}
$signatures[] = new SignRequest([
'appId' => $appId,
'keyHandle' => $reg->keyHandle,
'challenge' => $challenge,
]);
}
return $signatures;
}
/**
* Called to verify an authentication response
*
* @param SignRequest[] $requests An array of outstanding authentication requests
* @param stdClass[] $registrations An array of current registrations
* @param object $response A response from the authenticator
* @return \stdClass
* @throws U2FException
*
* The Registration object returned on success contains an updated counter
* that should be saved for future authentications.
* If the Error returned is ERR_COUNTER_TOO_LOW this is an indication of
* token cloning or similar and appropriate action should be taken.
*/
public static function authenticate(array $requests, array $registrations, $response)
{
// Parameter checks
if( !is_object( $response ) ) {
throw new \InvalidArgumentException('$response of authenticate() method only accepts object.');
}
if( property_exists( $response, 'errorCode') && $response->errorCode !== 0 ) {
throw new U2FException(
'User-agent returned error. Error code: ' . $response->errorCode,
U2FException::BAD_UA_RETURNING
);
}
// Set default values to null, so we get fails by default
/** @var object|null $req */
$req = null;
/** @var object|null $reg */
$reg = null;
// Extract client response data
$clientData = static::base64u_decode($response->clientData);
$decodedClient = json_decode($clientData);
// Check we have a match among the requests and the response
foreach ($requests as $req) {
if( !is_object( $req ) ) {
throw new \InvalidArgumentException('$requests of authenticate() method only accepts an array of objects.');
}
if($req->keyHandle() === $response->keyHandle && $req->challenge() === $decodedClient->challenge) {
break;
}
$req = null;
}
if($req === null) {
throw new U2FException(
'No matching request found',
U2FException::NO_MATCHING_REQUEST
);
}
// Check for a match for the response among a list of registrations
foreach ($registrations as $reg) {
if( !is_object( $reg ) ) {
throw new \InvalidArgumentException('$registrations of authenticate() method only accepts an array of objects.');
}
if($reg->keyHandle === $response->keyHandle) {
break;
}
$reg = null;
}
if($reg === null) {
throw new U2FException(
'No matching registration found',
U2FException::NO_MATCHING_REGISTRATION
);
}
// On Success, check we have a valid public key
$pemKey = static::publicKeyToPem(static::base64u_decode($reg->publicKey));
if($pemKey === null) {
throw new U2FException(
'Decoding of public key failed',
U2FException::PUBKEY_DECODE
);
}
// Build signature and data from response
$signData = static::base64u_decode($response->signatureData);
$dataToVerify = hash('sha256', $req->appId(), true);
$dataToVerify .= substr($signData, 0, 5);
$dataToVerify .= hash('sha256', $clientData, true);
$signature = substr($signData, 5);
// Verify the response data against the public key
if(openssl_verify($dataToVerify, $signature, $pemKey, 'sha256') === 1) {
$ctr = unpack("Nctr", substr($signData, 1, 4));
$counter = $ctr['ctr'];
/* TODO: wrap-around should be handled somehow.. */
if($counter > $reg->counter) {
$reg->counter = $counter;
return $reg;
} else {
throw new U2FException(
'Counter too low.',
U2FException::COUNTER_TOO_LOW
);
}
} else {
throw new U2FException(
'Authentication failed',
U2FException::AUTHENTICATION_FAILURE
);
}
}
/**
* Get all files from a directory
*
* @param string $attestDir The folder to find files into
* @return string[]
*/
private static function get_certs($attestDir)
{
$files = [];
$dir = $attestDir;
if($dir && $handle = opendir($dir)) {
while(false !== ($entry = readdir($handle))) {
if(is_file("$dir/$entry")) {
$files[] = "$dir/$entry";
}
}
closedir($handle);
}
return $files;
}
/**
* @param string $data
* @return string
*/
private static function base64u_encode($data)
{
return trim(strtr(base64_encode($data), '+/', '-_'), '=');
}
/**
* @param string $data
* @return string
*/
private static function base64u_decode($data)
{
return base64_decode(strtr($data, '-_', '+/'));
}
/**
* @param string $key
* @return null|string
*/
private static function publicKeyToPem($key)
{
if(strlen($key) !== static::PUBKEY_LEN || $key[0] !== "\x04") {
return null;
}
/*
* Convert the public key to binary DER format first
* Using the ECC SubjectPublicKeyInfo OIDs from RFC 5480
*
* SEQUENCE(2 elem) 30 59
* SEQUENCE(2 elem) 30 13
* OID1.2.840.10045.2.1 (id-ecPublicKey) 06 07 2a 86 48 ce 3d 02 01
* OID1.2.840.10045.3.1.7 (secp256r1) 06 08 2a 86 48 ce 3d 03 01 07
* BIT STRING(520 bit) 03 42 ..key..
*/
$der = "\x30\x59\x30\x13\x06\x07\x2a\x86\x48\xce\x3d\x02\x01";
$der .= "\x06\x08\x2a\x86\x48\xce\x3d\x03\x01\x07\x03\x42";
$der .= "\0".$key;
$pem = "-----BEGIN PUBLIC KEY-----\r\n";
$pem .= chunk_split(base64_encode($der), 64);
$pem .= "-----END PUBLIC KEY-----";
return $pem;
}
/**
* @return string
* @throws U2FException
*/
private static function createChallenge()
{
$challenge = openssl_random_pseudo_bytes(32, $crypto_strong );
if( $crypto_strong !== true ) {
throw new U2FException(
'Unable to obtain a good source of randomness',
U2FException::BAD_RANDOM
);
}
$challenge = static::base64u_encode( $challenge );
return $challenge;
}
/**
* Fixes a certificate where the signature contains unused bits.
*
* @param string $cert
* @return string
*/
private static function fixSignatureUnusedBits($cert)
{
if(in_array(hash('sha256', $cert), static::$FIXCERTS)) {
$cert[strlen($cert) - 257] = "\0"; // Fix the "unused bits" field (should always be 0).
}
return $cert;
}
}
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