1.3.1 Compression and hashing

Question 1

What is compression?

Answer 1

-Process used to reduce the storage space required by a file so you can store more files with the same amount of storage space
-Particularly important for sharing files over the internet

Question 2

Lossy compression

Answer 2

Reduces the size of a file while also removing some of its information
(Could result in a more pixelated image or less clear audio recording)

Question 3

Lossless compression

Answer 3

-Reduces the size of a file without losing any information
-Original file can be recovered from the compressed version

Question 4

Run length encoding

Answer 4

-Method of lossless compression in which repeated values are removed and replaced with one occurrence of the data followed by the number of times it should be repeated
i.e. AAABBBBCC = 3A4B2C
-Relies on consecutive pieces of data being the same

Question 5

Dictionary encoding

Answer 5

-Method of lossless compression where frequently occurring pieces of data are replaced with an index and compressed data is stored alongside a dictionary which matches the data to an index
-Original data can then be restored using the dictionary

Question 6

Symmetric encryption

Answer 6

-Both the sender and receiver share the same private key used for both encrypting and decrypting data

Question 7

Asymmetric encryption

Answer 7

-Two keys used; private and public
-Public key can be published anywhere while private key is kept secret
-Messages encrypted with the sender’s public key can only be decrypted with the recipient’s private key

Question 8

What is hashing?

Answer 8

-An input is turned into a fixed size value (a hash)
-Output of a hash cannot be reversed to form the key
-Useful for storing passwords

Question 9

What is a hash table?

Answer 9

-Data structure which holds key-value pairs
-Can be used to lookup data in an array in constant time