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   1  <?php
   2  
   3  
   4  namespace lbuchs\WebAuthn\Attestation\Format;
   5  use lbuchs\WebAuthn\Attestation\AuthenticatorData;
   6  use lbuchs\WebAuthn\WebAuthnException;
   7  use lbuchs\WebAuthn\Binary\ByteBuffer;
   8  
   9  class Apple extends FormatBase {
  10      private $_x5c;
  11  
  12      public function __construct($AttestionObject, AuthenticatorData $authenticatorData) {
  13          parent::__construct($AttestionObject, $authenticatorData);
  14  
  15          // check packed data
  16          $attStmt = $this->_attestationObject['attStmt'];
  17  
  18  
  19          // certificate for validation
  20          if (\array_key_exists('x5c', $attStmt) && \is_array($attStmt['x5c']) && \count($attStmt['x5c']) > 0) {
  21  
  22              // The attestation certificate attestnCert MUST be the first element in the array
  23              $attestnCert = array_shift($attStmt['x5c']);
  24  
  25              if (!($attestnCert instanceof ByteBuffer)) {
  26                  throw new WebAuthnException('invalid x5c certificate', WebAuthnException::INVALID_DATA);
  27              }
  28  
  29              $this->_x5c = $attestnCert->getBinaryString();
  30  
  31              // certificate chain
  32              foreach ($attStmt['x5c'] as $chain) {
  33                  if ($chain instanceof ByteBuffer) {
  34                      $this->_x5c_chain[] = $chain->getBinaryString();
  35                  }
  36              }
  37          } else {
  38              throw new WebAuthnException('invalid Apple attestation statement: missing x5c', WebAuthnException::INVALID_DATA);
  39          }
  40      }
  41  
  42  
  43      /*
  44       * returns the key certificate in PEM format
  45       * @return string|null
  46       */
  47      public function getCertificatePem() {
  48          return $this->_createCertificatePem($this->_x5c);
  49      }
  50  
  51      /**
  52       * @param string $clientDataHash
  53       */
  54      public function validateAttestation($clientDataHash) {
  55          return $this->_validateOverX5c($clientDataHash);
  56      }
  57  
  58      /**
  59       * validates the certificate against root certificates
  60       * @param array $rootCas
  61       * @return boolean
  62       * @throws WebAuthnException
  63       */
  64      public function validateRootCertificate($rootCas) {
  65          $chainC = $this->_createX5cChainFile();
  66          if ($chainC) {
  67              $rootCas[] = $chainC;
  68          }
  69  
  70          $v = \openssl_x509_checkpurpose($this->getCertificatePem(), -1, $rootCas);
  71          if ($v === -1) {
  72              throw new WebAuthnException('error on validating root certificate: ' . \openssl_error_string(), WebAuthnException::CERTIFICATE_NOT_TRUSTED);
  73          }
  74          return $v;
  75      }
  76  
  77      /**
  78       * validate if x5c is present
  79       * @param string $clientDataHash
  80       * @return bool
  81       * @throws WebAuthnException
  82       */
  83      protected function _validateOverX5c($clientDataHash) {
  84          $publicKey = \openssl_pkey_get_public($this->getCertificatePem());
  85  
  86          if ($publicKey === false) {
  87              throw new WebAuthnException('invalid public key: ' . \openssl_error_string(), WebAuthnException::INVALID_PUBLIC_KEY);
  88          }
  89  
  90          // Concatenate authenticatorData and clientDataHash to form nonceToHash.
  91          $nonceToHash = $this->_authenticatorData->getBinary();
  92          $nonceToHash .= $clientDataHash;
  93  
  94          // Perform SHA-256 hash of nonceToHash to produce nonce
  95          $nonce = hash('SHA256', $nonceToHash, true);
  96  
  97          $credCert = openssl_x509_read($this->getCertificatePem());
  98          if ($credCert === false) {
  99              throw new WebAuthnException('invalid x5c certificate: ' . \openssl_error_string(), WebAuthnException::INVALID_DATA);
 100          }
 101  
 102          $keyData = openssl_pkey_get_details(openssl_pkey_get_public($credCert));
 103          $key = is_array($keyData) && array_key_exists('key', $keyData) ? $keyData['key'] : null;
 104  
 105  
 106          // Verify that nonce equals the value of the extension with OID ( 1.2.840.113635.100.8.2 ) in credCert.
 107          $parsedCredCert = openssl_x509_parse($credCert);
 108          $nonceExtension = $parsedCredCert['extensions']['1.2.840.113635.100.8.2'] ?? '';
 109  
 110          // nonce padded by ASN.1 string: 30 24 A1 22 04 20
 111          // 30     — type tag indicating sequence
 112          // 24     — 36 byte following
 113          //   A1   — Enumerated [1]
 114          //   22   — 34 byte following
 115          //     04 — type tag indicating octet string
 116          //     20 — 32 byte following
 117  
 118          $asn1Padding = "\x30\x24\xA1\x22\x04\x20";
 119          if (substr($nonceExtension, 0, strlen($asn1Padding)) === $asn1Padding) {
 120              $nonceExtension = substr($nonceExtension, strlen($asn1Padding));
 121          }
 122  
 123          if ($nonceExtension !== $nonce) {
 124              throw new WebAuthnException('nonce doesn\'t equal the value of the extension with OID 1.2.840.113635.100.8.2', WebAuthnException::INVALID_DATA);
 125          }
 126  
 127          // Verify that the credential public key equals the Subject Public Key of credCert.
 128          $authKeyData = openssl_pkey_get_details(openssl_pkey_get_public($this->_authenticatorData->getPublicKeyPem()));
 129          $authKey = is_array($authKeyData) && array_key_exists('key', $authKeyData) ? $authKeyData['key'] : null;
 130  
 131          if ($key === null || $key !== $authKey) {
 132              throw new WebAuthnException('credential public key doesn\'t equal the Subject Public Key of credCert', WebAuthnException::INVALID_DATA);
 133          }
 134  
 135          return true;
 136      }
 137  
 138  }
 139