2 - Cypto Key Concepts Flashcards
What is a cipher?
A method to encrypt text.
Usually translates text into symbols, or a function of the alphabet.
What is the problem with sending an unprotected message?
It can be read by anyone who can intercept it
How can you protect a message?
Encypt its contents
What two types of cyptography are used today?
Symmetric and Asymmetric
What is symmetric cryptography?
Using a pair of keys to encrypt and then decrypt a message
plaintext -> encypt(plaintext, key) -> cipher text -> decypt(ciphertext, key) -> plaintext
w -> * -> w
What are some examples of symmetric cryptography?
Substitution and transposition ciphers
What are some substitution ciphers?
Monoalphabetic e.g. Caesar cipher
Polyalphabetic e.g. Vingere cipher
What is a transposition cipher?
Rail fence cipher
What is a Caesar cipher?
Letters are shifted along in the alphabet to encrypt
Shifted back the same amount to decrypt
Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher: DEFGHIJKLMNOPQRSTUVWXYZABC
What is a Vigenere cipher?
Encypts text by using a series of different Caesar ciphers based on the letters of a keyword.
In a grid, same letter won’t be used for same subsitution
What is a rail fence cipher?
Places plaintext in a zigzag along imaginary rails.
What is a column cipher?
Message is written out in rows of a fixed length
Then read out again column by column, and the columns are chosen in some scrambled order (cipher text)
Both the width of the rows and the permutation of the columns are usually defined by a keyword.
What is a stream?
Caesar and Vigenere are streams
What is a block?
Used for DES, AES
0110111001010011
0110 1110 0101 0011
Block ciphers
Translate between plain and cipher text using a key and applying a logic gate to key and block, e.g. XOR
