Compression, Encryption And Hashing

Question 1

Why is file compression used?

Answer 1

To reduce the storage of files on disk

Question 2

Though disk storage is becoming larger and cheaper, why is reducing file size important?

Answer 2

Its important in the sharing and transmission of data as ISPs impose limits and charges on bandwidth

Question 2

Why do images on a website need to be compressed?

Answer 2

To enable the web pages to load quickly and for streaming to reduce buffering

Question 3

What are the two compression techniques that I need to know?

Answer 3

Lossy and lossless

Question 4

What is the difference between lossy and lossless?

Answer 4

With lossy unnecessary information is removed from the original file while when lossless compresses it retains all information required to replicate the original file exactly

Question 5

What compression technique does MP3 use?

Answer 5

Lossy, removing frequencies that are too high for most of us to hear and remove quieter sounds that are played at the same time as louder sounds

Question 6

How much of an MP3 file is compressed under compression?

Answer 6

Around 10% of the original size, meaning that 1 minute of MP3 audio equates to roughly 1MB in size

Question 7

How is voice compressed over the internet or mobile telephone networks?

Answer 7

Using lossy compression, which shows us the apparent difference between lossy and lossless, that lossy loses data

Question 8

How does lossless compression work in terms of compression?

Answer 8

Records patterns in data rather than the actual data, giving the computer the ability to reverse the procedure and get the file back to its exact accuracy with no data lost

Question 9

What would use lossless compression?

Answer 9

Program files, as a lose of a character would result in an error in the program code

Question 10

What is the disadvantage of lossless compression?

Answer 10

That it results in a larger file than lossy, but one that is significantly smaller than the original

Question 11

What is Run Length Encoding (RLE)?

Answer 11

Rather than recording every pixel in a sequence, it records its value and the number of times it repeats it, so if there is BBBDDAACCCC that would become 3B2D2A4C

Question 12

How does dictionary compression work?

Answer 12

The compression algorithm searches through the text to find suitable entries in its own dictionary and translates the messages accordingly

Question 13

What does dictionary compression also have to be stored with?

Answer 13

With the text dictionary, so that it can compare the symbols and translate them to what they were, making the original message can still be reassembled perfectly

Question 14

What is encryption?

Answer 14

The transformation of data from one from to another to prevent an unauthorised third party from being able to understand it

Question 15

What is the original data or message before encryption called?

Answer 15

Plaintext

Question 16

What is encrypted data known as?

Answer 16

Ciphertext

Question 17

What is the encryption method or algorithm known as?

Answer 17

Cipher

Question 18

What us the secret information to lock or unlock the message known as?

Answer 18

Key

Question 19

What is the difference between the Caesar cipher and the Vernam cipher?

Answer 19

They are polar opposites, the Vernam offers perfect security, while the Caesar cipher is very easy to break with little or no computational power

Question 20

What is the Caesar cipher also known as?

Answer 20

The shift cipher

Question 21

what is the Caesar cipher?

Answer 21

A type of substitution cipher and works by shifting the letters if the alphabet along by a given number of characters

Question 22

How many different possibilities are there for the Caesar cipher?

Answer 22

There are only 26 different possibilities

Question 23

What is the Vernam cipher?

Answer 23

Invented in 1917 by American scientist Gilbert Vernam, is the only cipher proven to be unbreakable, all others are based on computational security and are theocratically discoverable given enough time, cipher text and computational power

Question 24

What are the requirements for the encryption key or one time pad?

Answer 24

It must be equal to or longer in character than the plaintext, truly random and be used only once

Question 25

How are one-time pads used?

Answer 25

They are used in pairs where the sender and recipient are both party to the key

Question 26

How must a truly random sequence be collected?

Answer 26

From a physical and unpredictable phenomenon, such as white noise, the timing of a hard disk read/write head or radioactive decay

Question 27

What is symmetric encryption, also known as private key encryption?

Answer 27

Encryption that uses the same key to encrypt and decrypt data, this means that the key must also be transferred to the same destination as the ciphertext, which causes obvious security problems

Question 28

What is the problem with symmetric encryption?

Answer 28

The key can be intercepted as easily as the ciphertext message to decrypt the data

Question 29

What is Asymmetric encryption?

Answer 29

Encryption that use two separate, but related keys, with one key, known as the public key, is made public so other wishing to send you data can use this to encrypt the data, the public key cannot decrypt data, another private key is known only by you and only this can be used to decrypt the data

Question 30

What is done to authorise the sender, in case of a malicious third party encrypting a message using your own public key?

Answer 30

A message can be digitally ‘signed’ to authenticate the sender

Question 31

What does a hashing function provide?

Answer 31

A mapping between an arbitrary length input and a usually fixed length or smaller output and is one way; you cannot get back to the original,

Question 32

What is a hash total?

Answer 32

Is a mathematical value calculated from unencrypted message date

Question 33

What is a hash total also referred to?

Answer 33

A checksum or digest

Question 34

What is a digital signature, also known as a hash value?

Answer 34

When the sender of the message use their own private key to encrypt the hash total, the encrypted total become the digital signature since only the holder of the private key could have encrypted it, when the receipt decrypts the message using their private key and decrypts the digital signature using the senders public key

Question 35

Who issues a digital certificate issued by?

Answer 35

Issued by the official Certificate Authorities (CAs) such as Symantec or Verisign

Question 36

What does a digital certificate verify?

Answer 36

The trustworthiness of a message sender or website