I must implement a One Time Password. For single petitions and although there are loads of resources of information in internet I still having doubts.
It is possible to make it survive system reboot with no use of databases?
The only way I know to store persistent data without databases is to write into an external file (actually databases are only files in disguise). In your case you have to carefully think about security issues of this solution. You have to make sure that your file is stored in a secure repository.