Data Representation - Encryption

What is encryption?

Using an algorithm and a key to scramble data and make it incomprehensible without decrypting it with the same key (plain text into cipher text)

What is decryption?

Using an algorithm and a key to unscramble encrypted data into its original, comprehensible form (cipher text into plain text)

What is plain text?

Data before its encryption (After decryption)

What is cipher text?

Data after its encryption

In encryption, what is a key?

An item of data that defines how the plain text is converted into the cipher text

Why do we encrypt data?

To prevent unwanted readers who may want to use the data in malicious or unintended ways

How does the Caesar cipher work?

It encrypts alphabetic messages by replacing letters with ones further down the alphabet

Why is the Caesar cipher considered very weak as an encryption method?

-It is susceptible to brute force

-It is susceptible to frequency analysis

-The same key is used for every letter and for every transmission therefore, once you figure out the key, you can decrypt all messages encrypted in that way

What is the brute force method?

Where you use every key possible to try and decrypt the cipher text

What is frequency analysis?

Where cipher text (which had alphabetic plain text) is analysed and compared with known patterns in the English language

What is a one-time pad?

A key that is used for encryption or decryption but is discarded after use

How does the Vernam cipher work?

The plain text is paired to a one-time pad then each character in the plain text is encrypted with its corresponding character in the onetime pad

What conditions must a one-time pad fulfil?

-It is randomly generated in a truly random way

-It is as long as the plain text

-It is not reused

-It is kept completely secret

What operation is applied to encrypt or decrypt with the Vernam cipher?

XOR

Why is the Vernam cipher perfectly secure?

The key is completely random and and each character is encrypted differently therefore there's no way of knowing what a character in the cipher text represents - it could represent anything

Why would the Vernam cipher be impractical or difficult?

-Generating truly random numbers is complex

-Informing the receiver of the key is difficult as the key could be intercepted

-The more messages you send and the longer the messages, the more keys you need

What are computationally secure ciphers?

Ciphers which are theoretically breakable,

but not using current technology in a practical amount of time

Why are computationally secure ciphers preferred over the Vernam cipher?

Vernam cipher is difficult to use and unnecessary