There still are some encryption schemes that can be run with nothing more than a pencil and paper. See SMSPP for example: https://gist.github.com/plugnburn/6b50

There still are some encryption schemes that can be run with nothing more than a pencil and paper. See SMSPP for example: https://gist.github.com/plugnburn/6b50ceee3a89893a9e48 https://gist.github.com/plugnburn/6b50ceee3a89893a9e48 You can also use straddling checkerboards if you can do some very simple math.