This one is not for paper and pencil, but is based on the same ideas as a bunch of paper and pencil ciphers in this blog. FilePad uses a file as key to encrypt another with extreme security. Here is FilePad, as JavaScript code running on a web page. Now, what’s the use of this, you may ask. Consider this: a 4 TB drive (about $100 in mid-2016) can contain enough bits to encrypt a high-definition video feed (about 1000 kbits/s), continuously, for longer than a year! The trick is that those bits must be truly random, or at least appear to be random so that no cryptanalysis is possible, per Shannon’s criterion. Here’s where FilePad comes in. It takes any file in your computer and scrambles it so its bits are essentially random. Then you can use the scrambled file to encrypt securely another file. (more…)