OpenPGP_Crypt_RSA::try_decrypt_session PHP Method

    static function try_decrypt_session($key, $edata)
    {
        $key->setEncryptionMode(CRYPT_RSA_ENCRYPTION_PKCS1);
        $data = $key->decrypt($edata);
        $sk = substr($data, 1, strlen($data) - 3);
        $chk = unpack('n', substr($data, -2));
        $chk = reset($chk);
        $sk_chk = 0;
        for ($i = 0; $i < strlen($sk); $i++) {
            $sk_chk = ($sk_chk + ord($sk[$i])) % 65536;
        }
        if ($sk_chk != $chk) {
            return NULL;
        }
        return array(ord($data[0]), $sk);
    }