3.4: encryption Flashcards
what is encryption
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
what is required to decrypt a message
the encryption method and the key
how are keys created
from number using binary digits
key length
the number of binary digits used
the longer the key length the more possible combinations
how are keys generated
by computers
brute force attack
when computers try and deteremine what keys have been used by genererating every possible combination in a key length
how many bit keys do modern encryption methods use
128 bit keys
why are 128 bit keys used
because it gives a range of combinations too big for a computer to generate every possible combination
symetric encryption
the same key is used to encrypt and decrypt the message
this means that 2 people with the key can share messages
problem with symetric keys
messages sent over a network can be intercepted
therefore if the key is known by unauthorised users the encryption is useless
asymetric encryption
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
the first key in asymetric encryption
used to encrypt the message
can be sent to anyone from who the user wants to recieve an encrypted message
the second key in asymetric encryption
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
uses of asymetric encryption
used by organisations who need to send confidential data for example:
banks
online shops
how asymetric encryption works
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
advantage of asymetric encryption
the source of the message can be trusted
for example a user connected to an online bank can trust the message they recieve
encryption algorithms
used to keep data secret from interceptors
ciphers are used to encrpyt and decrypt messages
caesar cipher
an alphabetical substitution cipher that replaces letters with other letters
pigpen cipher
substitution cipher by substituting letters in the alphabet by symbols
vigenere cipher
a key made of letters
add value of each letter to the value of its corresponding letter in the key
rail fence cipher
uses numbers to create N different levels
the word is written in zigzag across different levels
caesar cipher example
offset of 3 letters
BSB
would be
EVE
advantages of vigenere cipher
letters in the original message will have different substituted letters in the encrypted message
vigenere cipher example
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
rail fence cipher example
message = BSB IS
N = 3
B——-S
–S—I—
—-B—–
encrypted message = BSSIB
