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
Q

Explain lossy compression

A

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

2
Q

What is the advantage of lossy compression?

A

Achieves more compression than lossless

3
Q

What are the disadvantages of lossy compression?

A

It is an irreversible process

Loses quality as it removes data

4
Q

Explain lossless compression

A

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

5
Q

What are the advantages of lossless compression?

A

No data is lost

It is a reversible process

6
Q

What is the disadvantage of lossless compression?

A

Results in less compression than lossy compression

7
Q

Explain dictionary compression

A

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

This means a short codeword represents a longer piece of data

8
Q

What are examples of lossless compression?

A

Dictionary compression

Run Length Encoding

9
Q

What is the advantage and disadvantage of dictionary compression?

A

Reduces the size without losing the original data

Reduces the size less than lossy compression would

10
Q

Explain run length encoding

A

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
Q

What is the advantage and disadvantage of run length encoding?

A

Reduces the size without losing the original data

Reduces the size less than lossy compression would

12
Q

Explain symmetric encryption

A

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

13
Q

What are the advantages and disadvantages of symmetric encryption?

A
  • 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
Q

What are the advantages and disadvantages of asymmetric encryption?

A
  • 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
Q

Define encryption

A

The process of changing plaintext to ciphertext using a key

16
Q

Define a key pair

A

An encryption and decryption key used in asymmetric encryption

17
Q

Define a combined key

A

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

18
Q

Define a public key

A

An encryption key that can be seen by anyone

19
Q

Define a private key

A

An encryption key that cannot be seen by anyone

20
Q

Explain asymmetric encryption

A

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
Q

Explain hashing

A

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

22
Q

Explain the use of hashing

A

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

23
Q

Explain how hashing works

A

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

24
Q

What is the difference between hashing and encryption?

A

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

25
Q

How is hashing used in sending files?

A

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

26
Q

How is hashing used in searching a database?

A

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
Q

How is hashing used in keeping passwords?

A

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
Q

Explain a digital signature

A

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
Q

How does a digital signature work?

A
  • 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
Q

What is a digital signature used for?

A

To authenticate installation files

Used to sign digital documents

31
Q

Explain a digital certificate

A

A method of verifying the trustworthiness of a website

32
Q

How does a digital certificate work?

A
  • 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