Quiz 1 Flashcards
Cryptanalysis
trying to break encryption
Cryptanalysis Types
Differential and Linear
What is Differential Cryptanalysis?
Used to analyze block ciphers
compares 2 related pairs of encryptions
What is Linear Cryptanalysis?
Use a large number of trial encryptions
Types of attacks on Cryptography?
- Ciphertext only
- Chosen Plaintext/ciphertext/text
What is a substitution cipher?
units of plaintext are replaced with ciphertext
Types of substitution cipher?
monoalphabetic and polyalphabetic
monoalphabetic cipher
uses fixed substitution over the entire message
polyalphabetic cipher
uses a number of substitutions at different positions in the message
Ex of monoalphabetic Cipher
Ceasar Cipher
Ex of polyalphabetic Cipher
Vignere Table
transposition cipher
plaintext are rearranged in a different and usually quite complex order
Columnar
characters rearranged into columns
Ex) transposition cipher
Perfect Substitution Cipher
uses a one time pad for encryption ex) Vernam Cipher
Unbreakable Cipher
uses vignere table with 1 time key and 2 decryption types with 2 keys
Block vs Stream Ciphers
Stream-convert a symbol into plain text (mono/polyalphabetic) Block-groups of plaintext (Colmnar and fractioned morse)
S-Permutation
uses s and p boxes
Feistel Cipher
block of 2 halves that process multiple rounds, perform substitution, then swap halves
Design principles of feistel cipher
Block size, Key size, # rounds, Subkey generation, Round function, Fast soft encrypt/decryption
What is DES?
Type of block cipher that uses a 56 bit key to encrypt 64 bits of data (concern with key size)
Outline:
- split data in half
- scramble each half indep
- combine key with one half
- swap the two halves
- repeat the process 16 times
Avalanche Effect
change to 1 input or key results in ½ output bits
DES variants
- Multiple DES
- Triple DES
- DES with Indep subkeys
- DESX CRYPT3
- Generalized DES
- DES with Alternative S-Box
- DES with key dependent S-Box
