1.3.1 Compression, Encryption and Hashing

Question 1

Explain lossy compression

Answer 1

Data is removed, which is not essential to the overall file

Question 2

What is the advantage of lossy compression?

Answer 2

Achieves more compression than lossless

Question 3

What are the disadvantages of lossy compression?

Answer 3

It is an irreversible process

Loses quality as it removes data

Question 4

Explain lossless compression

Answer 4

Data is compressed such that none of the original data is lost

Question 5

What are the advantages of lossless compression?

Answer 5

No data is lost

It is a reversible process

Question 6

What is the disadvantage of lossless compression?

Answer 6

Results in less compression than lossy compression

Question 7

Explain dictionary compression

Answer 7

Each repeated pattern is stored as its own unique binary code.

This means a short codeword represents a longer piece of data

Question 8

What are examples of lossless compression?

Answer 8

Dictionary compression

Run Length Encoding

Question 9

What is the advantage and disadvantage of dictionary compression?

Answer 9

Reduces the size without losing the original data

Reduces the size less than lossy compression would

Question 10

Explain run length encoding

Answer 10

Finds sets of repeated binary patterns and replaces them with single instances.

The instance includes the pattern with a number specifying the times it repeats

Question 11

What is the advantage and disadvantage of run length encoding?

Answer 11

Reduces the size without losing the original data

Reduces the size less than lossy compression would

Question 12

Explain symmetric encryption

Answer 12

The same encryption key will be used to encrypt and decrypt the message

Question 13

What are the advantages and disadvantages of symmetric encryption?

Answer 13

• The message cannot be decrypted if a hacker doesn’t have the encryption key
• The key could be intercepted
• Not secure for critical information

Question 14

What are the advantages and disadvantages of asymmetric encryption?

Answer 14

• One key cannot be worked out from the other
• The message can be authenticated
• The receiver must have access to the sender’s public key

Question 15

Define encryption

Answer 15

The process of changing plaintext to ciphertext using a key

Question 16

Define a key pair

Answer 16

An encryption and decryption key used in asymmetric encryption

Question 17

Define a combined key

Answer 17

When the sender’s private key and the receiver’s public key are used to encrypt the message

Question 18

Define a public key

Answer 18

An encryption key that can be seen by anyone

Question 19

Define a private key

Answer 19

An encryption key that cannot be seen by anyone

Question 20

Explain asymmetric encryption

Answer 20

Different keys encrypt and decrypt a message, one a public key, the other a private key.

• The receiver’s public key is used to encrypt the data, then the receiver uses their private key to decrypt it
• The sender’s private key can be used as well to encrypt the key, then the receiver’s private key and the sender’s public key is used to decrypt the message
  
  • No one can read the message
  • The message can be checked if authentic or if modified

Question 21

Explain hashing

Answer 21

A technique to map data of variable lengths to a fixed-length data value

Question 22

Explain the use of hashing

Answer 22

It is needed to reduce the size and increase the security of the data

Question 23

Explain how hashing works

Answer 23

A hashing algorithm is applied to a piece of data to create a hash value

Question 24

What is the difference between hashing and encryption?

Answer 24

Hashing is a one-way process, whereas encryption is two-way

Question 25

How is hashing used in sending files?

Answer 25

If a file is sent with errors or is modified during transfer, then the hash value will turn out differently

Question 26

How is hashing used in searching a database?

Answer 26

If a database needs to be searched, the primary key field can be applied to a hashing algorithm.

Then the primary key of a record can be passed through the algorithm, which will then relate to only one given location in the hash table

Question 27

How is hashing used in keeping passwords?

Answer 27

When a user enters a password, it can be hashed and then stored in a database.

When the user enters their password, it can be hashed and then compared to the stored pre-hashed passwords.

This means the original password isn’t kept

Question 28

Explain a digital signature

Answer 28

The digital signature is an algorithm used to encrypt the data.

It is the equivalent of a hand-written signature as it is a method of authenticating received data.

Question 29

How does a digital signature work?

Answer 29

• The data will be encrypted with the digital signature algorithm and a check-sum will be calculated
• At the receiving end, the check-sum will be recalculated and compared to the sent value
• If they match, the data has been authenticated
• Not all data is sent with a digital signature

Question 30

What is a digital signature used for?

Answer 30

To authenticate installation files

Used to sign digital documents

Question 31

Explain a digital certificate

Answer 31

A method of verifying the trustworthiness of a website

Question 32

How does a digital certificate work?

Answer 32

• It will verify a website is the real edition
• The certificate details will be compared, and the user will be notified if the details match
  
  • This usually is shown next to the UML as a padlock