1.3.1 Compression, Encryption and Hashing Flashcards Preview

A Level Computer Science > 1.3.1 Compression, Encryption and Hashing > Flashcards

Flashcards in 1.3.1 Compression, Encryption and Hashing Deck (32)
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1

Explain lossy compression

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

2

What is the advantage of lossy compression?

Achieves more compression than lossless

3

What are the disadvantages of lossy compression?

It is an irreversible process

Loses quality as it removes data

4

Explain lossless compression

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

5

What are the advantages of lossless compression?

No data is lost

It is a reversible process

6

What is the disadvantage of lossless compression?

Results in less compression than lossy compression

7

Explain dictionary compression

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

This means a short codeword represents a longer piece of data

8

What are examples of lossless compression?

Dictionary compression

Run Length Encoding

9

What is the advantage and disadvantage of dictionary compression?

Reduces the size without losing the original data

 

Reduces the size less than lossy compression would

10

Explain run length encoding

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

11

What is the advantage and disadvantage of run length encoding?

Reduces the size without losing the original data

 

Reduces the size less than lossy compression would

12

Explain symmetric encryption

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

13

What are the advantages and disadvantages of symmetric encryption?

  • The message cannot be decrypted if a hacker doesn't have the encryption key

 

  • The key could be intercepted
  • Not secure for critical information

14

What are the advantages and disadvantages of asymmetric encryption?

  • 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

15

Define encryption

The process of changing plaintext to ciphertext using a key

16

Define a key pair

An encryption and decryption key used in asymmetric encryption

17

Define a combined key

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

18

Define a public key

An encryption key that can be seen by anyone

19

Define a private key

An encryption key that cannot be seen by anyone

20

Explain asymmetric encryption

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

21

Explain hashing

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

22

Explain the use of hashing

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

23

Explain how hashing works

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

24

What is the difference between hashing and encryption?

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

25

How is hashing used in sending files?

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

26

How is hashing used in searching a database?

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

27

How is hashing used in keeping passwords?

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

28

Explain a digital signature

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.

29

How does a digital signature work?

  • 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

30

What is a digital signature used for?

To authenticate installation files

Used to sign digital documents