We have explored how our data is collected and sometimes misused. In the next two lessons, we are going to dig into protecting our data.

Many of the ideas we use to keep secrets in the digital age are far older than the Internet. The process of encoding a plain text message in some secret way is called Encryption

For example in Roman times Julius Caesar is reported to have encrypted messages to his soldiers and generals by using a simple alphabetic shift - every character was encrypted by substituting it with a character that was some fixed number of letters away in the alphabet.

As a result an alphabetic shift is often referred to as the Caesar Cipher.

With this simple encryption technique it only took a few minutes to decode a small message. What if the message were longer, BUT you had a computational tool to help you?

With the tool, cracking an alphabetic shift is easy. Once you've done one, it only takes a matter of seconds to do others.

Let's review some terminology here.

Terms:

• Encryption: a process of encoding messages to keep them secret, so only "authorized" parties can read it.
• Decryption: a process that reverses encryption, taking a secret message and reproducing the original plain text
• Cipher: the generic term for a technique (or algorithm) that performs encryption
• Caesar's Cipher: a technique for encryption that shifts the alphabet by some number of characters.
• Cracking encryption: When you attempt to decode a secret message without knowing all the specifics of the cipher, you are trying to crack the encryption.

What if instead of shifting the whole alphabet, we matched every letter of the alphabet to a random different letter of th alphabet? This is called a random substitution cipher.

Let's take a look at a new decryption challenge using a random substitution cipher.

A random substitution cipher is very crackable by hand, though it might take some time. However, when aided by computational tools, a random substitution cipher can be cracked by a novice in a matter of minutes. Simple substitution ciphers give insight into encryption algorithms, but as we've seen fall way short when a potential adversary is aided with computational tools... our understanding must become more sophisticated.

If we are to create a secure Internet, we will need to develop tool and protocols which can resist the enormous computational power of modern computers.