1.3.1 Compression and Encryption

Question 1

Compression

Answer 1

Compression : Process of reducing number of bits in a file.

Advantages:
- Quicker file transmission
- More files can be stored in same amount of space
- Reduces transmission bandwidth used over internet
- Reduces chance of data collisions
- Files more quickly downloaded

Question 2

Lossy Compression

Answer 2

Lossy : Permanently reduces file size more significantly while removing some information.
- Attempts to remove unnoticeable data
- Cannot be used on executable files
- Best for use on images and sound - reduce sample rate/depth, resolution

Question 3

Lossless Compression

Answer 3

Lossless : Reduces file size without removing any information (by less than lossy)
- Original file recovered using algorithm
- Great for text files (where removing information makes file obsolete)

Question 4

Types of Lossless Compression

Answer 4

Run Length Encoding : Consecutive repeated values replaced number of repeats followed by one occurrence of data.
- Relies on consecutive repetitions
- Works well in images and sound

Dictionary Encoding : Frequently occurring pieces of data replaced with token/index
- Information on tokens stored in dictionary
- File must be sent with dictionary to restore data
- Works well on large text - lots of repeated words and phrases

Question 5

Encryption

Answer 5

Encryption : Scrambles data so that it is unreadable
- Modern encryption can be used without specialist software so widely use don internet
- 2 way - encrypted data can be deciphered with key
- Keeps data safe during transmission - if intercepted it is unreadable

Question 6

Symmetric encryption

Answer 6

Symmetric encryption : Single key used for encryption and decryption
- Faster than asymmetric (less processing)
- Keys distributed in Key exchange - vulnerability as key can be intercepted
- best where same person encrypting and decrypting

Question 7

Asymmetric encryption

Answer 7

Asymmetric : One Key publicly distributed while other kept private
- Often used when exchanging data e.g. E-commerce

• Slower than symmetric as more processing in algorithm
• Can be used to secure keys in key exchange
• Can be used to validate sender (double encryption)
• Keys mathematically related

Question 8

Hashing

Answer 8

Hashing : Process of turning input into hash by mathematical algorithm
- One way (cannot be reversed)
- Same input always produces same hash

Useful for storing passwords as cannot be reversed even if hacker gets data
- Input passwords can be validated by checking hash against stored hash

Question 9

Hashing and encryption uses in security

Answer 9

Hashing :
- Useful for storing passwords as cannot be reversed even if hacker gets data
- Input passwords can be validated by checking hash against stored hash
- Not useful for data that needs to be returned to user

Encryption :
- Useful for most data storage as hackers wont be able to understand data
- Useful in data transmission as intercepted data cannot be read but can be deciphered (especially over open networks)