Yes, unfortunately our service has been down yesterday due to an internal connectivity issue between our servers. The issues have been resolved yesterday and everything is running smoothly again. Already signed in users could continue to use Boxcryptor without any problems and we're sorry for the inconveniences this caused for those users who tried to to sign in or use the website.
PS: Did you know that you can export your keys? https://support.boxcryptor.com/display/DOCEN/08.+Key+export