ELEC5616 Computer and Network Security
5. Alice and Bob
Edmund Tse 2010
Computes
Alice computes ( )
Bob computes
Alice and bob now share secret
Strength of Diffie-Hellman
o Based on two issues:
Discrete logarithm problem:
given , , , it is difficult to
Liars and Outliers
Chapter 5 - Societal Dilemmas
Bruce Schneier is a recognized expert in Cryptography and computer security. Recently
he has started to examine the basis of security itself - the nature of trust. One could
argue that this is the same thin
Assignment 1
ELEC5616: Computer and Network Security
Luke Anderson
[email protected]
University of Sydney
May 16, 2016
Date Due:
27th May 15:00 - Deadline for feedback.
Assignments submitted before this time will be marked with feedback
before the
Project 3 : Common Vulnerabilities
Computer & Network Security (Sydney University)
Luke Anderson [email protected]
May 2, 2015
Due: Part 3 is to be marked in labs on the 19th of May
Marking
You are to work on this assignment in groups of 1 or 2. T
Project : Defeating SkyNet
Part 2: Commanding the Legion
ELEC5616: Computer & Network Security
Luke Anderson [email protected]
April 19, 2016
Due at 14:00 on Tuesday the 3rd of May (week 9)
Introduction
In the first part, you created the base found
Project 1 : Defeating SkyNet
(Security Essentials)
Computer & Network Security (Sydney University)
Luke Anderson [email protected]
March 21, 2016
Due: SkyNet is to be marked in labs on the 12th of April (wk6)
This assignment is provided as an early
ELEC5616 Computer and Network Security
Edmund Tse 2010
]
o Now if
is large, then we can guess [
o Optimally for a break,
, i.e. ( = 0 or 1)
o A perfect cipher would have = 0.5
An algorithm to recover key bits
o Given R plaintext, ciphertext pairs where R
ELEC5616 Computer and Network Security
Edmund Tse 2010
Hash Functions
Functions
A function
is defined by:
o Two sets (domain) and (codomain)
o A rule
If
then
o The image of is the element in which rule associates with
o The image of is denoted by
If
then
ELEC5616 Computer and Network Security
Edmund Tse 2010
Ciphers
Symmetric ciphers
o Private key (symmetric) encryption the key used to encrypt and decrypt is the same
o Defined by the rule:
(
)
o
o
o
o
o
o
o
Communicating with symmetric ciphers
Alice and
ELEC5616 Computer and Network Security
2DES
o
Edmund Tse 2010
So for a CPA,
If
nor
Search space is halved.
and
, then
:
nor
Double encryption with DES is bad:
(
o
2DES is vulnerable to meet in the middle attack, i.e. for a fixed message m, create a table:
ELEC5616 Computer and Network Security
Edmund Tse 2010
Iterated hash construction
o Merkle-Damgard method (MD-strengthening)
f is a compression function
Divide message into
-bit blocks
cfw_
cfw_
cfw_
o Why use an MD iterated construction?
Lemma: sup
ELEC5616 Computer and Network Security
Edmund Tse 2010
Introduction
Security in digital world is different since it is easy to copy bits perfectly
o Bits include information, identity, privileges and money.
o Much of information security revolves around m
ELEC5616 Computer and Network Security
Edmund Tse 2010
Key Exchange
Definitions
Key establishment any process whereby a shard secret becomes available to two or more parties for
subsequent cryptographic use
Key management the set of processes and mechanis
ELEC5616 Computer and Network Security
Edmund Tse 2010
Secret Key Encryption
Feistel networks
Ladder structure
o
o
o
Input is split into two blocks left and right halves
Functions
are arbitrary mappings:
cfw_
In each round of the Feistel network:
cfw_
F
ELEC5616 Computer and Network Security
Edmund Tse 2010
o
o
Encryption is XOR for bits or mod-26 addition
OTP is perfectly secure provided:
The secret key is truly random
The plaintext does not repeat
The pad is never used again
o Otherwise, it results
ELEC5616 Computer and Network Security
Edmund Tse 2010
ECB is not recommended for messages longer than 1 block, or reused over >1 message.
o Identical plaintext blocks result in identical ciphertext blocks, so it is vulnerable to dictionary attacks
o Err
Please answer three (3) of the following five questions. I am looking for evidence of your
understanding about the basic issues presented during the course. I do not expect quotes
or references as I would in a research paper. However, if you do use refere