Encryption

Spies and prisoners have found may ways to get secret messages from one person to another, without begin detected. There are many recipes that have been used over the years, including porridge, lemon juice and other household materials. Now, with technology and miniaturization, other methods to transfer secret messages are being developed.

[|Encryption] - a method which allows information (for example, a secret message) to be hidden so that it cannot be read without special knowledge (such as a password). Once this is done the information is encrypted. Decryption is a way to change an encrypted piece of information back into unencrypted or decrypted form.
 * one-time pad - the secret key must only be used once. To send more than one message, a different key must be used for each one. Spies had to carry little books ("pads") filled with random letters or random numbers. Each page from the pad could only be used once. If this process is used correctly, it is impossible to reveal the secret message without knowing the secret key.

On the Internet, several encryption protocols are used, such as Transport Layer Security (TLS), IPsec, and SSH. They use the RSA encryption system and others. The protocol for protected web browsing is called HTTPS.


 * What's the problem?**

[|The Enigma machine] was a cipher machine used to encrypt and decrypt secret messages with electro-mechanical rotor mechanisms. The Enigma was used commercially from the early 1920s on, and was also adopted by the military and governmental services of a number of nations—most famously by Nazi Germany before and during World War II.
 * **Ask** - During World War II, there needed to be lots secret communications among armies and governments. Designing and building special machines to encrypt messages was an important improvement over the tedious work previous done by huge numbers of workers. How could the machines understand what had been encrypted another machine? How could the sender be sure that only the intended receiver would be able to decrypt the message?
 * **Imagine** - How could computers be used to do the work of encrypting and decrypting?
 * **Design, Build** - At this time, electronics were new and still controlled by wires and mechanical switches. Building the Engima machines was itself very manual.
 * **Improve** - As computers and electronics improved, technologies for keeping information secret and secure have improved, and are in general use for all internet and telephone communications.


 * That's engineering**
 * [|Transport Layer Security (TLS)] Protocol - cryptographic protocol that provides security and data integrity for communications over networks such as the Internet.
 * [|RSA encryption system] - an algorithm for public-key encryption

> electro-mechanical rotor, miniturization, complex, protocol, password, key, security, data integrity, communications, network
 * Engineering ideas**

Challenges for you to work on...
 * Do It**
 * [|Recipe for Invisible Ink] - follow the recipe and create your invisible ink. Write a message on paper, wait until it drys, then make the message visible.


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