diff --git a/src/lib/WebAuthn/Attestation/Format/FormatBase.php b/src/lib/WebAuthn/Attestation/Format/FormatBase.php
new file mode 100644
index 0000000..eed916b
--- /dev/null
+++ b/src/lib/WebAuthn/Attestation/Format/FormatBase.php
@@ -0,0 +1,193 @@
+<?php
+
+
+namespace lbuchs\WebAuthn\Attestation\Format;
+use lbuchs\WebAuthn\WebAuthnException;
+use lbuchs\WebAuthn\Attestation\AuthenticatorData;
+
+
+abstract class FormatBase {
+    protected $_attestationObject = null;
+    protected $_authenticatorData = null;
+    protected $_x5c_chain = array();
+    protected $_x5c_tempFile = null;
+
+    /**
+     *
+     * @param Array $AttestionObject
+     * @param AuthenticatorData $authenticatorData
+     */
+    public function __construct($AttestionObject, AuthenticatorData $authenticatorData) {
+        $this->_attestationObject = $AttestionObject;
+        $this->_authenticatorData = $authenticatorData;
+    }
+
+    /**
+     *
+     */
+    public function __destruct() {
+        // delete X.509 chain certificate file after use
+        if ($this->_x5c_tempFile && \is_file($this->_x5c_tempFile)) {
+            \unlink($this->_x5c_tempFile);
+        }
+    }
+
+    /**
+     * returns the certificate chain in PEM format
+     * @return string|null
+     */
+    public function getCertificateChain() {
+        if ($this->_x5c_tempFile && \is_file($this->_x5c_tempFile)) {
+            return \file_get_contents($this->_x5c_tempFile);
+        }
+        return null;
+    }
+
+    /**
+     * returns the key X.509 certificate in PEM format
+     * @return string
+     */
+    public function getCertificatePem() {
+        // need to be overwritten
+        return null;
+    }
+
+    /**
+     * checks validity of the signature
+     * @param string $clientDataHash
+     * @return bool
+     * @throws WebAuthnException
+     */
+    public function validateAttestation($clientDataHash) {
+        // need to be overwritten
+        return false;
+    }
+
+    /**
+     * validates the certificate against root certificates
+     * @param array $rootCas
+     * @return boolean
+     * @throws WebAuthnException
+     */
+    public function validateRootCertificate($rootCas) {
+        // need to be overwritten
+        return false;
+    }
+
+
+    /**
+     * create a PEM encoded certificate with X.509 binary data
+     * @param string $x5c
+     * @return string
+     */
+    protected function _createCertificatePem($x5c) {
+        $pem = '-----BEGIN CERTIFICATE-----' . "\n";
+        $pem .= \chunk_split(\base64_encode($x5c), 64, "\n");
+        $pem .= '-----END CERTIFICATE-----' . "\n";
+        return $pem;
+    }
+
+    /**
+     * creates a PEM encoded chain file
+     * @return type
+     */
+    protected function _createX5cChainFile() {
+        $content = '';
+        if (\is_array($this->_x5c_chain) && \count($this->_x5c_chain) > 0) {
+            foreach ($this->_x5c_chain as $x5c) {
+                $certInfo = \openssl_x509_parse($this->_createCertificatePem($x5c));
+
+                // check if certificate is self signed
+                if (\is_array($certInfo) && \is_array($certInfo['issuer']) && \is_array($certInfo['subject'])) {
+                    $selfSigned = false;
+
+                    $subjectKeyIdentifier = $certInfo['extensions']['subjectKeyIdentifier'] ?? null;
+                    $authorityKeyIdentifier = $certInfo['extensions']['authorityKeyIdentifier'] ?? null;
+
+                    if ($authorityKeyIdentifier && substr($authorityKeyIdentifier, 0, 6) === 'keyid:') {
+                        $authorityKeyIdentifier = substr($authorityKeyIdentifier, 6);
+                    }
+                    if ($subjectKeyIdentifier && substr($subjectKeyIdentifier, 0, 6) === 'keyid:') {
+                        $subjectKeyIdentifier = substr($subjectKeyIdentifier, 6);
+                    }
+
+                    if (($subjectKeyIdentifier && !$authorityKeyIdentifier) || ($authorityKeyIdentifier && $authorityKeyIdentifier === $subjectKeyIdentifier)) {
+                        $selfSigned = true;
+                    }
+
+                    if (!$selfSigned) {
+                        $content .= "\n" . $this->_createCertificatePem($x5c) . "\n";
+                    }
+                }
+            }
+        }
+
+        if ($content) {
+            $this->_x5c_tempFile = \sys_get_temp_dir() . '/x5c_chain_' . \base_convert(\rand(), 10, 36) . '.pem';
+            if (\file_put_contents($this->_x5c_tempFile, $content) !== false) {
+                return $this->_x5c_tempFile;
+            }
+        }
+
+        return null;
+    }
+
+
+    /**
+     * returns the name and openssl key for provided cose number.
+     * @param int $coseNumber
+     * @return \stdClass|null
+     */
+    protected function _getCoseAlgorithm($coseNumber) {
+        // https://www.iana.org/assignments/cose/cose.xhtml#algorithms
+        $coseAlgorithms = array(
+            array(
+                'hash' => 'SHA1',
+                'openssl' => OPENSSL_ALGO_SHA1,
+                'cose' => array(
+                    -65535  // RS1
+                )),
+
+            array(
+                'hash' => 'SHA256',
+                'openssl' => OPENSSL_ALGO_SHA256,
+                'cose' => array(
+                    -257, // RS256
+                    -37,  // PS256
+                    -7,   // ES256
+                    5     // HMAC256
+                )),
+
+            array(
+                'hash' => 'SHA384',
+                'openssl' => OPENSSL_ALGO_SHA384,
+                'cose' => array(
+                    -258, // RS384
+                    -38,  // PS384
+                    -35,  // ES384
+                    6     // HMAC384
+                )),
+
+            array(
+                'hash' => 'SHA512',
+                'openssl' => OPENSSL_ALGO_SHA512,
+                'cose' => array(
+                    -259, // RS512
+                    -39,  // PS512
+                    -36,  // ES512
+                    7     // HMAC512
+                ))
+        );
+
+        foreach ($coseAlgorithms as $coseAlgorithm) {
+            if (\in_array($coseNumber, $coseAlgorithm['cose'], true)) {
+                $return = new \stdClass();
+                $return->hash = $coseAlgorithm['hash'];
+                $return->openssl = $coseAlgorithm['openssl'];
+                return $return;
+            }
+        }
+
+        return null;
+    }
+}