This error may be caused by the non-compliance of your computer's system time and the real time. Please check the time and date set on your computer, and correct it if necessary.
Also this error may be caused by antivirus/firewall or some software replacing SSL certificate. In such a case, switch off SSL validation of your antivirus. Please make sure that your firewalls, antiviruses do not block the game. Add "War Thunder" to your antivirus exceptions list. Please follow this link for instructions on how to configure Windows Firewall.
If it's not caused by antivirus/firewall - please contact your ISP, some of them are replacing SSL certificates by default.