Semester 1 Test Flashcards
What is the easiest form of attack against a Caesar Cipher?
Brute force
Decode the following message encoded using a Caesar Cipher: JSTZLMJCFRX
x = -5. “enough exams”
Decode the following Rail Fence encoded message: TSASHITTISE
TSAS
HITT
ISE
“This is a test”
Why are Mono-alphabetic Substitution Ciphers not as strong as they may initially appear?
Mono-alphabetic substitution ciphers appear strong as brute force attacks can take long (2^88.4). However the language used can be exploited to find letter frequencies.
Using a Playfair Cipher with ‘EDUCATION’ as the Keyword encode the word FIRSTCLASS
playfair a 5 * 5 matrix and keyword.
“GT SM NE SB QZ QZ”
What is meant by a letter frequency graph and why is it important to try and get it as flat as possible?
Because accurate average letter frequencies can be easily gleaned by analyzing a large amount of representative text, one must try to make it so their ciphertext has even frequency counts to prevent bruteforce with knowledge of the plaintext langauge.
What type of encryption is a Vigenere Cipher an example of?
It is a simple form of polyalphabetic substitution.
Using a Vigenere Cipher with ‘EDUCATION’ as the Keyword encode the word FIRSTCLASS
“JLLUTVTOFW”
What is the primary concern associated with the use of any symmetric encryption mechanism?
Secure communication of the key
Explain what is meant by the terms ‘confusion’ and ‘diffusion’ in terms of symmetric encryption
Diffusion seeks to make the statistical relationship between plaintext and ciphertext as complex as possible in order to thwart attempts to deduce the key.
Confusion seeks to make the relationship between the statistics of the cipher text and the value of the encryption key as complex as possible ( achieved by use of complex substitution cipher)
List the main variables/parameters associated with any implementation of a Fiestel Cipher
Block size
Key size
Number of rounds
Describe what is meant when an encryption algorithm is said to exhibit a ‘strong avalanche effect’
A change in a single bit results in the change of at least half of the bits in the cipher text
Name the four separate functions performed within each round of AES
Subbytes
Mix Columns
Shift Rows
Add Round key
Explain why the security of RSA depends upon the difficulty of factoring large numbers
Instead of using substitution and permutation, Asymmetric cryptography instead treats input as numbers and performs calculations.
Describe what a digital signature is and briefly explain how one is constructed
A digital signature is an unique identifier for the sender created by putting a message through a hash algorithm, encrypted with using their private keys.
List the five separate functions provided by PGP when using it to secure emails
Authentication Compression Segmentation Email compatibility Confidentiality
List the two main protocols that make up the SSL/TLS architecture
handshake protocol
Record protocol
What is the main difference between Transport Mode and Tunnel Mode when using IP Sec?
Transport Mode - Encrypts the data
Tunnel Mode - Also encrypts sender and receiver identifiers
Briefly describe why WEP is not considered a secure protocol for use with WLANs
Wired Equivalent Privacy uses a stream cipher, the same traffic key must never be used twice. The purpose of an IV, which is transmitted as plain text, is to prevent any repetition, but a 24-bit IV is not long enough to ensure this on a busy network. The way the IV was used also opened WEP to a related key attack. For a 24-bit IV, there is a 50% probability the same IV will repeat after 5000 packets.
Why was TKIP considered as a replacement for WEP even though AES-CCMP was available?
Unlike AES - CCMP, TKIP is compatible with hardware currently in use.
