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