1.3.1 Compression, Encryption and Hashing

Question 1

What is compression?

Answer 1

• Process used to reduce the storage space required by a file
• More files in same space
• Important to share large files over internet

Question 2

What are the types of compression?

Answer 2

• Lossy
• Lossless

Question 3

What is lossy compression?

Answer 3

• Reduces size of the file by removing some of its information
• Original file cannot be recovered as information is completely disregarded

Question 4

What is lossless compression?

Answer 4

• Reduces the file size
• Original file can be recovered

Question 5

What are the types of lossless compression?

Answer 5

• Run Length Encoding
• Dictionary encoding

Question 6

What is Run Length Encoding?

Answer 6

• Repeated values are removed and replaced with one occurance of the data followed by the number of times it is repeated
• Relies on consecutive pieces of data being the same

Question 7

What is Dictionary Encoding?

Answer 7

• Frequently occuring pieces of data are replaced with an index
• Compressed data is stored alongside a dictionary
• Dictionary matches frequently occuring data to an index
• Original data can then be restored using dictionary
• Compressed data must be transferred alongside its dictionary

Question 8

What is encryption?

Answer 8

• Used to keep data secure whilst its being transmitted
• Disguises data before it is transmitted
• Dta is then deciphered once it arrives at its destination

Question 9

What are the types of encryption?

Answer 9

• Symmetric
• Asymmetric

Question 10

What is symmetric encryption?

Answer 10

• Sender and recipient share the same private key
• Distributed to each other in a process called a key exchnage
• Key is used to encrypt and decrypt data

Question 11

What is the disadvantage of symmetric encryption?

Answer 11

• Privat key must be kept a secret
• If the key is intercepted during the key exchange then any communicatons can be intercepted and decrypted

Question 12

What is asymmetric encryption?

Answer 12

• Two keys used: one public and the second a private key
• Public key can be accessed by anyone
• Private key must be kept secret
• Data encrypted by public key can only be decripted by private key
• If you wish to send data, you encrypt it with the recipients public key and then send it them so they can decrypt it using their private key

Question 13

What is hashing?

Answer 13

• An input (called a key) is turned into a fixed size value (called a hash)
• Output cant be reversed

Question 14

What are the uses of hashing?

Answer 14

• Can store passwords safetly as it cant be reversed
• Can create hash tables which allow for values stored in them to quickly be found