Kids,
By now, you've learned that what you write can be important. For thousands of years people have kept diaries and wanted them to be private. You can still buy blank notebooks
with locks on them.
But those mechanical locks can be picked, or broken.
And you like to use computers to write. (Learn to type, BTW!) Can you control who reads your writing on a computer?
Sure you can. Controlling who reads your stuff is "confidentiality". Here's how we'll do it: You'll give a secret password "key" to a machine called a "cipher" which eats the key, your stuff, and produces a new file. That new file contains your stuff, but you can only read it if you know the key. Enciphering is also called encryption, which means "hiding".
The reverse process is simple: give the cipher the encrypted file and the key, you get your original stuff back.
If you deleted your original stuff, after making the encrypted one, then only someone with the key for that encrypted file can read it.
BTW, Your "stuff" is just a file. That file can mean music (eg mp3) or pictures (eg jpg) or fancy documents (eg doc) or plain text (eg txt) or anything.
BTW, the "cipher machine" is just a computer program.
Search for AxCrypt. Its a little Windows File Explorer plug-in that encrypts and decrypts files. http://www.axantum.com/AxCrypt/
If you share the "key" in person at the play ground you can control who reads
the file. That can be one person, or more, or just you. The "key" is just like a metal key to a door, they're all identical and anyone who has one can
Of course, someone could find the encrypted file and force you to reveal the password. In our next installment we learn about hiding the very fact that you've hidden a file!
(Steganography)
Other topics related to encryption:
authentication (knowing that a message came from your friend)
integrity (no one can change the message without getting caught)
non-repudiation (you can't back out of a signature!)
The "what I know, have, am" triad for identification --tying meatspace to information space. Governments love that stuff.
Anonymity
Traffic analysis
All stuff for the modern 10 year old!
Maybe we'll even dabble in RSA (publishable public keys, web certificates) and DHA (SSL).
