Data Compression and Encryption

why do we compress data ?

send data faster
reduces amount of bandwidth used
buffering on audio and video streams is less likely to occur
less storage required

what is lossy compression ?

Non-essential data is permanently removed

what is lossless compression ?

no loss of information as patterns in data is spotted and summarised

what is run length encoding ?

reduces file size by removing repeated information and grouping it together
only works when data is repeated regularly

what is a dictionary ?

a collection of key-value pairs in which a value is accessed by its associated key.

what is encryption ?

scrambling data so it cant be understood if intercepted

what is a shift cipher ?

all letters in the alphabet are shifted by the same value

what is a substitution cipher ?

letters are randomly replaced

what is a vernam cipher ?

one time key pad cipher - each key is used only once

what does the key need to be in a vernam cipher ?

hand delivered
random
long as the plain text

how does a vernam cipher work ?

by using the logical operation XOR on the binary values of the key and plaintext