1.3.1 Compression, Encryption and Hashing

Question 1

Why is it beneficial to compress files? (2)

Answer 1

To reduce storage space needed for files in physical storage (1) and on the internet to reduce buffering time/increase loading speed (1)

Question 2

What type of compression removes unnecessary information? (1)

Answer 2

Lossy compression (1)

Question 3

What type of compression retains all original information? (1)

Answer 3

Lossless compression (1)

Question 4

Which media types are usually compressed using lossy compression? (3)

Answer 4

Audio (1) video (1) images (1)

Question 5

Which media types are usually compressed using lossless compression? (2)

Answer 5

Text files (1) Program code (1)

Question 6

What is meant by the word compression? (2)

Answer 6

(An algorithm that) makes a file storage size smaller (1) but information is lost in the process (1)

Question 7

Why is asymmetric encryption more suited than symmetric to transmissions over the Internet? (4)

Answer 7

Any four from Symmetric encryption would require both parties to have copy of the key (1) this couldn’t be transmitted over the internet or an eavesdropper monitoring the message may see it (1) Asymmetric gets round thisrequirement as there are two different keys (1) One key encrypts the data (1) which can be publically distributed (1) and a different key to decrypt it (1) which is kept private (1)

Question 8

Describe the pros and cons of encryption (5)

Answer 8

The strength and ease of use of encryption has made it widely used on the Internet. (1) E-Commerce would not be possible without it. (1) Governments are no longer able to easily crack encrypted messages they intercept. (1) This gives individuals unprecedented levels of privacy (1) But also means those communicating for nefarious purposes can do so undetected. (1)

Question 9

Define Hashing and its uses (3)

Answer 9

A result gained by applying an algorithm to a value (1). Used for gererating predictable indexes for data (1). Used as a type of one way encryption (1).

Question 10

Define Rehashing(2)

Answer 10

The process of resolving DATA COLLISIONS (1) by selecting where to put clashing data (1).

Question 11

What are the 3 types of Rehashing? (3)

Answer 11

Linear moves to the next available space (1). Chaining uses a linked list (1). Overflow designates an area for rehashes (1).

Question 12

What is Salt? (1)

Answer 12

It is data added to a hash to ensure each output is unique (1).

Question 13

Why do we use salt? (3)

Answer 13

Most hashing algorithms are well known and hackers can use rainbow tables that store pre hashed values of a whole dictionary of possible passwords to look for a match (1). When a match is found the associated password is revealed (1). We use salt to make all password unique so that the hackers find no matches and can find out the passwords (1).