You can export the key file always from boxcryptor
Web site login, why should the key file be different,
if you reinstall anything ? Only problem is, that you may not
forget your password, and if you have forgotten it, all your
files are lost. But you also can backup your exported
keyfile to different places on several device, so you don't
lose anything if one device is damaged.
After you lose your password, your account can only be
reset, and you are losing your files, if you don't have
several backup positions.
A moderator is missing here, but meanwhile I only wanted
to help, so we are waiting for the moderator, maybe he is on a