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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 Tpm extends FormatBase {
  10      private $_TPM_GENERATED_VALUE = "\xFF\x54\x43\x47";
  11      private $_TPM_ST_ATTEST_CERTIFY = "\x80\x17";
  12      private $_alg;
  13      private $_signature;
  14      private $_pubArea;
  15      private $_x5c;
  16  
  17      /**
  18       * @var ByteBuffer
  19       */
  20      private $_certInfo;
  21  
  22  
  23      public function __construct($AttestionObject, AuthenticatorData $authenticatorData) {
  24          parent::__construct($AttestionObject, $authenticatorData);
  25  
  26          // check packed data
  27          $attStmt = $this->_attestationObject['attStmt'];
  28  
  29          if (!\array_key_exists('ver', $attStmt) || $attStmt['ver'] !== '2.0') {
  30              throw new WebAuthnException('invalid tpm version: ' . $attStmt['ver'], WebAuthnException::INVALID_DATA);
  31          }
  32  
  33          if (!\array_key_exists('alg', $attStmt) || $this->_getCoseAlgorithm($attStmt['alg']) === null) {
  34              throw new WebAuthnException('unsupported alg: ' . $attStmt['alg'], WebAuthnException::INVALID_DATA);
  35          }
  36  
  37          if (!\array_key_exists('sig', $attStmt) || !\is_object($attStmt['sig']) || !($attStmt['sig'] instanceof ByteBuffer)) {
  38              throw new WebAuthnException('signature not found', WebAuthnException::INVALID_DATA);
  39          }
  40  
  41          if (!\array_key_exists('certInfo', $attStmt) || !\is_object($attStmt['certInfo']) || !($attStmt['certInfo'] instanceof ByteBuffer)) {
  42              throw new WebAuthnException('certInfo not found', WebAuthnException::INVALID_DATA);
  43          }
  44  
  45          if (!\array_key_exists('pubArea', $attStmt) || !\is_object($attStmt['pubArea']) || !($attStmt['pubArea'] instanceof ByteBuffer)) {
  46              throw new WebAuthnException('pubArea not found', WebAuthnException::INVALID_DATA);
  47          }
  48  
  49          $this->_alg = $attStmt['alg'];
  50          $this->_signature = $attStmt['sig']->getBinaryString();
  51          $this->_certInfo = $attStmt['certInfo'];
  52          $this->_pubArea = $attStmt['pubArea'];
  53  
  54          // certificate for validation
  55          if (\array_key_exists('x5c', $attStmt) && \is_array($attStmt['x5c']) && \count($attStmt['x5c']) > 0) {
  56  
  57              // The attestation certificate attestnCert MUST be the first element in the array
  58              $attestnCert = array_shift($attStmt['x5c']);
  59  
  60              if (!($attestnCert instanceof ByteBuffer)) {
  61                  throw new WebAuthnException('invalid x5c certificate', WebAuthnException::INVALID_DATA);
  62              }
  63  
  64              $this->_x5c = $attestnCert->getBinaryString();
  65  
  66              // certificate chain
  67              foreach ($attStmt['x5c'] as $chain) {
  68                  if ($chain instanceof ByteBuffer) {
  69                      $this->_x5c_chain[] = $chain->getBinaryString();
  70                  }
  71              }
  72  
  73          } else {
  74              throw new WebAuthnException('no x5c certificate found', WebAuthnException::INVALID_DATA);
  75          }
  76      }
  77  
  78  
  79      /*
  80       * returns the key certificate in PEM format
  81       * @return string|null
  82       */
  83      public function getCertificatePem() {
  84          if (!$this->_x5c) {
  85              return null;
  86          }
  87          return $this->_createCertificatePem($this->_x5c);
  88      }
  89  
  90      /**
  91       * @param string $clientDataHash
  92       */
  93      public function validateAttestation($clientDataHash) {
  94          return $this->_validateOverX5c($clientDataHash);
  95      }
  96  
  97      /**
  98       * validates the certificate against root certificates
  99       * @param array $rootCas
 100       * @return boolean
 101       * @throws WebAuthnException
 102       */
 103      public function validateRootCertificate($rootCas) {
 104          if (!$this->_x5c) {
 105              return false;
 106          }
 107  
 108          $chainC = $this->_createX5cChainFile();
 109          if ($chainC) {
 110              $rootCas[] = $chainC;
 111          }
 112  
 113          $v = \openssl_x509_checkpurpose($this->getCertificatePem(), -1, $rootCas);
 114          if ($v === -1) {
 115              throw new WebAuthnException('error on validating root certificate: ' . \openssl_error_string(), WebAuthnException::CERTIFICATE_NOT_TRUSTED);
 116          }
 117          return $v;
 118      }
 119  
 120      /**
 121       * validate if x5c is present
 122       * @param string $clientDataHash
 123       * @return bool
 124       * @throws WebAuthnException
 125       */
 126      protected function _validateOverX5c($clientDataHash) {
 127          $publicKey = \openssl_pkey_get_public($this->getCertificatePem());
 128  
 129          if ($publicKey === false) {
 130              throw new WebAuthnException('invalid public key: ' . \openssl_error_string(), WebAuthnException::INVALID_PUBLIC_KEY);
 131          }
 132  
 133          // Concatenate authenticatorData and clientDataHash to form attToBeSigned.
 134          $attToBeSigned = $this->_authenticatorData->getBinary();
 135          $attToBeSigned .= $clientDataHash;
 136  
 137          // Validate that certInfo is valid:
 138  
 139          // Verify that magic is set to TPM_GENERATED_VALUE.
 140          if ($this->_certInfo->getBytes(0, 4) !== $this->_TPM_GENERATED_VALUE) {
 141              throw new WebAuthnException('tpm magic not TPM_GENERATED_VALUE', WebAuthnException::INVALID_DATA);
 142          }
 143  
 144          // Verify that type is set to TPM_ST_ATTEST_CERTIFY.
 145          if ($this->_certInfo->getBytes(4, 2) !== $this->_TPM_ST_ATTEST_CERTIFY) {
 146              throw new WebAuthnException('tpm type not TPM_ST_ATTEST_CERTIFY', WebAuthnException::INVALID_DATA);
 147          }
 148  
 149          $offset = 6;
 150          $qualifiedSigner = $this->_tpmReadLengthPrefixed($this->_certInfo, $offset);
 151          $extraData = $this->_tpmReadLengthPrefixed($this->_certInfo, $offset);
 152          $coseAlg = $this->_getCoseAlgorithm($this->_alg);
 153  
 154          // Verify that extraData is set to the hash of attToBeSigned using the hash algorithm employed in "alg".
 155          if ($extraData->getBinaryString() !== \hash($coseAlg->hash, $attToBeSigned, true)) {
 156              throw new WebAuthnException('certInfo:extraData not hash of attToBeSigned', WebAuthnException::INVALID_DATA);
 157          }
 158  
 159          // Verify the sig is a valid signature over certInfo using the attestation
 160          // public key in aikCert with the algorithm specified in alg.
 161          return \openssl_verify($this->_certInfo->getBinaryString(), $this->_signature, $publicKey, $coseAlg->openssl) === 1;
 162      }
 163  
 164  
 165      /**
 166       * returns next part of ByteBuffer
 167       * @param ByteBuffer $buffer
 168       * @param int $offset
 169       * @return ByteBuffer
 170       */
 171      protected function _tpmReadLengthPrefixed(ByteBuffer $buffer, &$offset) {
 172          $len = $buffer->getUint16Val($offset);
 173          $data = $buffer->getBytes($offset + 2, $len);
 174          $offset += (2 + $len);
 175  
 176          return new ByteBuffer($data);
 177      }
 178  
 179  }
 180