3.4: encryption

Question 1

what is encryption

Answer 1

the process of converting data into a form that cannot be understood by anyone other than an authorised user
does not prevent data from being acessed but prevents data from being understood

Question 2

what is required to decrypt a message

Answer 2

the encryption method and the key

Question 3

how are keys created

Answer 3

from number using binary digits

Question 4

key length

Answer 4

the number of binary digits used
the longer the key length the more possible combinations

Question 5

how are keys generated

Answer 5

by computers

Question 6

brute force attack

Answer 6

when computers try and deteremine what keys have been used by genererating every possible combination in a key length

Question 7

how many bit keys do modern encryption methods use

Answer 7

128 bit keys

Question 8

why are 128 bit keys used

Answer 8

because it gives a range of combinations too big for a computer to generate every possible combination

Question 9

symetric encryption

Answer 9

the same key is used to encrypt and decrypt the message
this means that 2 people with the key can share messages

Question 10

problem with symetric keys

Answer 10

messages sent over a network can be intercepted
therefore if the key is known by unauthorised users the encryption is useless

Question 11

asymetric encryption

Answer 11

uses 2 keys that work as a pair
the first key is used to encrypt the message
the second key is used to decrypt the message

Question 12

the first key in asymetric encryption

Answer 12

used to encrypt the message
can be sent to anyone from who the user wants to recieve an encrypted message

Question 13

the second key in asymetric encryption

Answer 13

kept secret by the user so that only they know it
called a private key
as long as the private key is kept secret the encryption is very difficult to break

Question 14

uses of asymetric encryption

Answer 14

used by organisations who need to send confidential data for example:
banks
online shops

Question 15

how asymetric encryption works

Answer 15

when a user logs onto a banks website a copy of the banks public key is downloaded to the users browser
any communications sent from the bank to the user are encrypted with the private key
the users browser decrypts the private key using the public key
same works vice versa

Question 16

advantage of asymetric encryption

Answer 16

the source of the message can be trusted
for example a user connected to an online bank can trust the message they recieve

Question 17

encryption algorithms

Answer 17

used to keep data secret from interceptors
ciphers are used to encrpyt and decrypt messages

Question 18

caesar cipher

Answer 18

an alphabetical substitution cipher that replaces letters with other letters

Question 19

pigpen cipher

Answer 19

substitution cipher by substituting letters in the alphabet by symbols

Question 20

vigenere cipher

Answer 20

a key made of letters
add value of each letter to the value of its corresponding letter in the key

Question 21

rail fence cipher

Answer 21

uses numbers to create N different levels
the word is written in zigzag across different levels

Question 22

caesar cipher example

Answer 22

offset of 3 letters
BSB
would be
EVE

Question 23

advantages of vigenere cipher

Answer 23

letters in the original message will have different substituted letters in the encrypted message

Question 24

vigenere cipher example

Answer 24

message = BSB
key = LOCK
first letter of message = B so value is 1
first letter of key = L so value is 11
11+1=12
so first letter is M as it is the 12 letter in the alphabet

Question 25

rail fence cipher example

Answer 25

message = BSB IS
N = 3
B——-S
–S—I—
—-B—–
encrypted message = BSSIB