3.5.6.8 - Encryption Flashcards
What is the definition of encryption?
The process of converting a plain text message into cipher text so that it may not be understood if intercepted by unauthorised users
What is plain text and cipher text?
Plain text - the message in the original form that can be understood easily
Cipher text - the encrypted message
What is a cipher and key
A cipher is an algorithm, a set of instructions, used to encrypt plain text.
A key is additional information that is used by the algorithm to encyrypt the text.
what is symmetric and asymmetric encyrption scheme?
in symmetric encryption scheme, the same key is used to encrypt that is used to decrypt; so the key must be shared between sender and receiver
in asymmetric encryption scheme, two different keys that are mathematically linked to encrypt and decrypt: so they keys don’t need to be shared
What 3 factors determine the security strength of an encryption scheme?
The cipher( the algorithm)
the size of the key
the process of key exchange(does it need to be shared or not/ how)
What is computationally secure?
it means it can’t be cracked in reasonable time by a computer
Explain the caesar cipher
The caesar cypher is a substitution cipher
the key shifts each letter a certain amount of places to the right
why is the caesar cipher insecure
there are 25 keys only (as 26 letters minus original position) which a computer can do in milliseconds
How does the vernam cipher work - conditions needed
it a substitution cipher where a one time pad is used
XOR is applied to ASCII bit code of each letter and it’s corresponding character in key
A totally random key with at least the same amount of characters as the plain text
the key can be used once and only once
it must be destroyed after use
only two copies can exist between the sender and recipient and be kept secret
why is the vernam cipher considered perfect? what is its drawback ?
It is perfectly secure because frequency analysis does not work on when there is a different key for each character
all possible words will be produced if a computer goes through every possibility, si there is no way of knowing which message is the correct one
the key has to be shared between sender and recipient and this can be insecure
