diff --git a/src/lib/WebAuthn/Attestation/Format/U2f.php b/src/lib/WebAuthn/Attestation/Format/U2f.php
new file mode 100644
index 0000000..2b51ba8
--- /dev/null
+++ b/src/lib/WebAuthn/Attestation/Format/U2f.php
@@ -0,0 +1,93 @@
+<?php
+
+
+namespace lbuchs\WebAuthn\Attestation\Format;
+use lbuchs\WebAuthn\Attestation\AuthenticatorData;
+use lbuchs\WebAuthn\WebAuthnException;
+use lbuchs\WebAuthn\Binary\ByteBuffer;
+
+class U2f extends FormatBase {
+    private $_alg = -7;
+    private $_signature;
+    private $_x5c;
+
+    public function __construct($AttestionObject, AuthenticatorData $authenticatorData) {
+        parent::__construct($AttestionObject, $authenticatorData);
+
+        // check u2f data
+        $attStmt = $this->_attestationObject['attStmt'];
+
+        if (\array_key_exists('alg', $attStmt) && $attStmt['alg'] !== $this->_alg) {
+            throw new WebAuthnException('u2f only accepts algorithm -7 ("ES256"), but got ' . $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);
+        }
+
+        if (!\array_key_exists('x5c', $attStmt) || !\is_array($attStmt['x5c']) || \count($attStmt['x5c']) !== 1) {
+            throw new WebAuthnException('invalid x5c certificate', WebAuthnException::INVALID_DATA);
+        }
+
+        if (!\is_object($attStmt['x5c'][0]) || !($attStmt['x5c'][0] instanceof ByteBuffer)) {
+            throw new WebAuthnException('invalid x5c certificate', WebAuthnException::INVALID_DATA);
+        }
+
+        $this->_signature = $attStmt['sig']->getBinaryString();
+        $this->_x5c = $attStmt['x5c'][0]->getBinaryString();
+    }
+
+
+    /*
+     * returns the key certificate in PEM format
+     * @return string
+     */
+    public function getCertificatePem() {
+        $pem = '-----BEGIN CERTIFICATE-----' . "\n";
+        $pem .= \chunk_split(\base64_encode($this->_x5c), 64, "\n");
+        $pem .= '-----END CERTIFICATE-----' . "\n";
+        return $pem;
+    }
+
+    /**
+     * @param string $clientDataHash
+     */
+    public function validateAttestation($clientDataHash) {
+        $publicKey = \openssl_pkey_get_public($this->getCertificatePem());
+
+        if ($publicKey === false) {
+            throw new WebAuthnException('invalid public key: ' . \openssl_error_string(), WebAuthnException::INVALID_PUBLIC_KEY);
+        }
+
+        // Let verificationData be the concatenation of (0x00 || rpIdHash || clientDataHash || credentialId || publicKeyU2F)
+        $dataToVerify = "\x00";
+        $dataToVerify .= $this->_authenticatorData->getRpIdHash();
+        $dataToVerify .= $clientDataHash;
+        $dataToVerify .= $this->_authenticatorData->getCredentialId();
+        $dataToVerify .= $this->_authenticatorData->getPublicKeyU2F();
+
+        $coseAlgorithm = $this->_getCoseAlgorithm($this->_alg);
+
+        // check certificate
+        return \openssl_verify($dataToVerify, $this->_signature, $publicKey, $coseAlgorithm->openssl) === 1;
+    }
+
+    /**
+     * validates the certificate against root certificates
+     * @param array $rootCas
+     * @return boolean
+     * @throws WebAuthnException
+     */
+    public function validateRootCertificate($rootCas) {
+        $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;
+    }
+}