1.3.1 - Compression, Encryption, Hashing

Question 1

Compression advantages

Answer 1

• Reduces download time
• Uses less bandwidth
• Takes up less storage

Question 2

Compression disadvantages

Answer 2

• Takes time to compress

- Uses processor time

Question 3

Lossy compression

Answer 3

Where compression removes non-essential data. Compresses to a smaller size

Question 4

JPG

Answer 4

Compresses pixels in an image by removing colours the human eye cannot distinguish between

Question 5

MP3

Answer 5

Removes audio frequencies the human ear can’t detect

Question 6

MP4

Answer 6

Only records changes in differences between picture frames of video rather than each entire frame

Question 7

Lossless compression

Answer 7

Patterns of data are summarised and recorded in a shorter format without removing any data
The original file can be recovered

Question 8

Run Length Encoding

Answer 8

Summarises data by saying the data and how many times repeated data is repeated

Question 9

Dictionary compression

Answer 9

Spots patterns of data that are repeated and stores them in a dictionary, stores in the main file
Any occurence of the repeated data will be replaced by its index

Question 10

ZIP

Answer 10

Identifies repeated file content and replaces every occurence with a repeated code

Question 11

End-to end encryption

Answer 11

The ciphertext is only decoded when it reaches the device of the recipient

Question 12

Encryption

Answer 12

A way of making sure data cannot be understood if you don’t possess the means to decrypt it.
The message is encrypted using a cipher algorithm and key and decrypted when received

Question 13

Ciphertext

Answer 13

The text produced by the cipher algorithm and key

Question 14

Plaintext

Answer 14

The text produced when the ciphertext is decoded

Question 15

Caesar cipher

Answer 15

A cipher in which each letter of the alphabet is shifted by the same amount

Question 16

Vernam cipher

Answer 16

A random sequence equal than or greater in length than the plaintext is used once.
Works by using a XOR between the ASCII codes of the encrypted characters and the characters of the one-time pad.

Question 17

Vernam cipher one-time pad

Answer 17

The encryption key (one-time pad) is shared with the recipient by hand and is destroyed immediately.
The one-time pad is generated from physical and unpredictable phenomena.

Question 18

Symmetric encryption

Answer 18

Also known as private key encryption

The same key is used to encrypt and decrypt data so it must be shared with the recipient

Question 19

Asymmetric encryption

Answer 19

The recipient’s public key is used to send data securely

Only the recipient’s private key can be used to decrypt the ciphertext

Question 20

Hashing

Answer 20

Uses a hashing algorithm to map an input to a shorter length of hex characters
You cannot convert the encrypted message back to the original

Question 21

Hashing uses

Answer 21

Storing PINS/passwords securely

Question 22

Hashing salt

Answer 22

Adding random data to the input to change the hashing output

Question 23

Compression

Answer 23

The process to reduce the storage space required by a file