diff --git a/src/lib/WebAuthn/Attestation/Format/Packed.php b/src/lib/WebAuthn/Attestation/Format/Packed.php
new file mode 100644
index 0000000..c2ced07
--- /dev/null
+++ b/src/lib/WebAuthn/Attestation/Format/Packed.php
@@ -0,0 +1,139 @@
+<?php
+
+
+namespace lbuchs\WebAuthn\Attestation\Format;
+use lbuchs\WebAuthn\Attestation\AuthenticatorData;
+use lbuchs\WebAuthn\WebAuthnException;
+use lbuchs\WebAuthn\Binary\ByteBuffer;
+
+class Packed extends FormatBase {
+    private $_alg;
+    private $_signature;
+    private $_x5c;
+
+    public function __construct($AttestionObject, AuthenticatorData $authenticatorData) {
+        parent::__construct($AttestionObject, $authenticatorData);
+
+        // check packed data
+        $attStmt = $this->_attestationObject['attStmt'];
+
+        if (!\array_key_exists('alg', $attStmt) || $this->_getCoseAlgorithm($attStmt['alg']) === null) {
+            throw new WebAuthnException('unsupported alg: ' . $attStmt['alg'], WebAuthnException::INVALID_DATA);
+        }
+
+        if (!\array_key_exists('sig', $attStmt) || !\is_object($attStmt['sig']) || !($attStmt['sig'] instanceof ByteBuffer)) {
+            throw new WebAuthnException('no signature found', WebAuthnException::INVALID_DATA);
+        }
+
+        $this->_alg = $attStmt['alg'];
+        $this->_signature = $attStmt['sig']->getBinaryString();
+
+        // certificate for validation
+        if (\array_key_exists('x5c', $attStmt) && \is_array($attStmt['x5c']) && \count($attStmt['x5c']) > 0) {
+
+            // The attestation certificate attestnCert MUST be the first element in the array
+            $attestnCert = array_shift($attStmt['x5c']);
+
+            if (!($attestnCert instanceof ByteBuffer)) {
+                throw new WebAuthnException('invalid x5c certificate', WebAuthnException::INVALID_DATA);
+            }
+
+            $this->_x5c = $attestnCert->getBinaryString();
+
+            // certificate chain
+            foreach ($attStmt['x5c'] as $chain) {
+                if ($chain instanceof ByteBuffer) {
+                    $this->_x5c_chain[] = $chain->getBinaryString();
+                }
+            }
+        }
+    }
+
+
+    /*
+     * returns the key certificate in PEM format
+     * @return string|null
+     */
+    public function getCertificatePem() {
+        if (!$this->_x5c) {
+            return null;
+        }
+        return $this->_createCertificatePem($this->_x5c);
+    }
+
+    /**
+     * @param string $clientDataHash
+     */
+    public function validateAttestation($clientDataHash) {
+        if ($this->_x5c) {
+            return $this->_validateOverX5c($clientDataHash);
+        } else {
+            return $this->_validateSelfAttestation($clientDataHash);
+        }
+    }
+
+    /**
+     * validates the certificate against root certificates
+     * @param array $rootCas
+     * @return boolean
+     * @throws WebAuthnException
+     */
+    public function validateRootCertificate($rootCas) {
+        if (!$this->_x5c) {
+            return false;
+        }
+
+        $chainC = $this->_createX5cChainFile();
+        if ($chainC) {
+            $rootCas[] = $chainC;
+        }
+
+        $v = \openssl_x509_checkpurpose($this->getCertificatePem(), -1, $rootCas);
+        if ($v === -1) {
+            throw new WebAuthnException('error on validating root certificate: ' . \openssl_error_string(), WebAuthnException::CERTIFICATE_NOT_TRUSTED);
+        }
+        return $v;
+    }
+
+    /**
+     * validate if x5c is present
+     * @param string $clientDataHash
+     * @return bool
+     * @throws WebAuthnException
+     */
+    protected function _validateOverX5c($clientDataHash) {
+        $publicKey = \openssl_pkey_get_public($this->getCertificatePem());
+
+        if ($publicKey === false) {
+            throw new WebAuthnException('invalid public key: ' . \openssl_error_string(), WebAuthnException::INVALID_PUBLIC_KEY);
+        }
+
+        // Verify that sig is a valid signature over the concatenation of authenticatorData and clientDataHash
+        // using the attestation public key in attestnCert with the algorithm specified in alg.
+        $dataToVerify = $this->_authenticatorData->getBinary();
+        $dataToVerify .= $clientDataHash;
+
+        $coseAlgorithm = $this->_getCoseAlgorithm($this->_alg);
+
+        // check certificate
+        return \openssl_verify($dataToVerify, $this->_signature, $publicKey, $coseAlgorithm->openssl) === 1;
+    }
+
+    /**
+     * validate if self attestation is in use
+     * @param string $clientDataHash
+     * @return bool
+     */
+    protected function _validateSelfAttestation($clientDataHash) {
+        // Verify that sig is a valid signature over the concatenation of authenticatorData and clientDataHash
+        // using the credential public key with alg.
+        $dataToVerify = $this->_authenticatorData->getBinary();
+        $dataToVerify .= $clientDataHash;
+
+        $publicKey = $this->_authenticatorData->getPublicKeyPem();
+
+        // check certificate
+        return \openssl_verify($dataToVerify, $this->_signature, $publicKey, OPENSSL_ALGO_SHA256) === 1;
+    }
+}
+