Security Flashcards
• To discuss security threats and attacks. • To understand the fundamentals of encryption
1
Q
The Security Problem
A
- A system is secure if its resources are used and accessed as intended
under all circumstances.- Unfortunately, total security
cannot be achieved. - Security mechanisms can limit
security breaches.
- Unfortunately, total security
- Security violations (or misuse) of the system can be categorized as
intentional (malicious) or accidental. - An attack is an attempt to breach security.
- Threat is a potential security violation, something that may or may not
happen, but has the potential to cause serious damage. Threats can
lead to attacks on computer devices and networks. - A person who attempts to gain unauthorised access to a system is called
an intruder. - An intruder
- attempts to damage a system
or disturb the data on a system. - attempts to violate security.
- attempts to damage a system
2
Q
Types of Security Violation
A
Breach of confidentiality
Breach of integrity
Breach of availability
Theft of service
Denial of service
3
Q
Breach of confidentiality
A
- Involves unauthorised access to data (or theft of information). For example,
credit-card information, identity information, etc.
4
Q
Breach of integrity
A
- Involves unauthorised modification of data. For example, change the
content of a website, change the text of a message, etc
5
Q
Breach of availability
A
- Involves unauthorised destruction of data. For example, website
defacement, etc
6
Q
Theft of service
A
- Involves unauthorised use of resources. For example, an intruder (or
intrusion program) may install a daemon on a system that acts as a file
server.
7
Q
Denial of service
A
- Involves preventing legitimate use of the system. Denial-of-service (DOS) by
overwhelming the service with illegitimate traffic
8
Q
Typical Security Violation
Methods
A
Masquerading
Replay attack
Man-in-the-middle attack
Session hijacking
9
Q
Masquerading
A
- One participant in a communication pretends to be someone else
(another host or another person). - This is breach of authentication, gaining access that would not normally be
allowed or obtaining privileges to which would not normally be entitled
10
Q
Replay attack
A
- Consists of the malicious or fraudulent repeat of a valid data
transmission. - e.g. repeat of a request to transfer money, frequently along with message modification.
11
Q
Man-in-the-middle attack
A
- An attacker sits in the data flow of a communication, masquerading as
the sender to the receiver, and vice versa
12
Q
Session hijacking
A
- Intercept an active communication to bypass authentication
13
Q
Security Measure Levels
A
- Impossible to have absolute security, but make cost to
perpetrator sufficiently high to deter most intruders - Security must occur at four levels to be effective:
- Physical
- Data centres, servers, connected terminals
- Human
- Avoid social engineering, phishing, dumpster diving
- Operating System
- Protection mechanisms, debugging
- Network
- Intercepted communications, interruption, DOS
- Security is as weak as the weakest link in the chain
14
Q
Program Threats
A
- Trojan Horse
- Pretend to be something else,
e.g. login is system - Can block, modify, delete data
- Install backdoor
- Can not self-replicate
- Pretend to be something else,
- Trap Door
- Leave a “hole” for accessing the
system, e.g. hardcoded
credentials
- Leave a “hole” for accessing the
- Logic Bomb
- Activated under certain
circumstances, e.g. at specific
date/time
- Activated under certain
- Stack and Buffer Overflow
* Writes arguments into the
return address on stack - Viruses
- A fragment of code embedded
in a legitimate program - Can self-replicate
- Can spread over a network –
infect other machines
- A fragment of code embedded
15
Q
Viruses
A
- There are thousand of viruses but they fall under several
main categories - File / parasitic
- Boot / memory
- Macro
- Source code
- Polymorphic to avoid having a virus signature
- Encrypted
16
Q
System and Network Threats
A
- Program threats typically use a breakdown in the protection
mechanisms of a system to attack programs. - In contrast, system and network threats involve the abuse of
services and network connections. - System and network threats create a situation in which
operating-system resources and user files are misused. - Sometimes, a system and network attack is used to launch a
program attack, and vice versa
17
Q
Types of threats
A
- Worms
- Can self-replicate
- Spawns copies of itself /
consume resources - Standalone
- Port scanning
- Automated attempt to connect
to a range of ports on one or a
range of IP addresses - Usually zombie systems are
used for port scanning
- Automated attempt to connect
- Denial of service
- Overload the targeted
computer preventing it from
doing any useful
work
- Overload the targeted
- E.g. applet to start pop up window infinitely
18
Q
The Morris Internet Worm
A
- One of the first computer worms distributed via the Internet
(Nov 1988) - Written by UG student (Robert Tappan Morris - Cornell
University) - Made up of two programs
- A grappling hook (bootstrap or vector) program
- The main program
- Exploited UNIX security vulnerabilities
19
Q
What is Cryptography?
A
“The science or study of the techniques of secret writing, especially code
and cipher systems, methods, and the like.”
20
Q
Encryption
A
is the process of encoding a message in a way that the information can not be
accessed by unauthorised parties
21
Q
Decryption
A
is the process of decoding a message using a key
22
Q
Cipher (or cypher)
A
It is an algorithm used to perform encryption/decryption
23
Q
Plaintext
A
is the original message (unencrypted
24
Q
Ciphertext
A
is the coded message (encrypted
25
Cryptosystem (or cipher system)
is a set of algorithms for performing cryptography actions (e.g. encryption,
decryption, key generation)
26
Cryptanalysis
is the study of how to crack encryption algorithm
27
Encryption algorithms
* An encryption algorithm must provide the following
essential property:
* given a ciphertext c
∈ C, a computer can compute a plaintext
m such that Ek (m) = c ONLY IF it possesses the key k
* Then, a computer holding k can decrypt ciphertexts to the
plaintexts used to produce them, but a computer not
holding k cannot decrypt these ciphertexts
* Also, it is very important to be infeasible to derive k from
the ciphertext (c is exposed)
* There are two main types of encryption algorithms:
symmetric and asymmetric
28
Symmetric Encryption
* In a symmetric encryption algorithm, the same key is used to encrypt
and to decrypt a message
* Therefore, key k must be kept secret between the two communicating
entities (shared secret)
* Key exchange can take place directly between the two parties or via a
trusted third party (i.e. a certificate authority)
29
Symmetric encryption algorithms
* Block ciphers
* Data-encryption standard (DES)
cipher adopted by NIST.
* Triple DES
* Advanced encryption standard
(AES)
* Stream ciphers
* RC4
* Rivest Cipher 4 – invented by
Ron Rivest in 1987
* Considered insecure
30
Asymmetric Encryption
* aka public-key encryption
* In an asymmetric encryption algorithm there are different
encryption and decryption keys
* For example,
* One who receives encrypted
messages generates a pair of
private –
public keys
* The public key is made available
* This key can be used by anyone
to encrypt messages
* Only the private key holder can
decrypt these messages
31
RSA Algorithm
* The most widely used public-key algorithm, based on the difficulty of
the factorisation of the product of two large prime numbers
* A user of RSA creates and then publishes a public key based on two
large prime numbers and an auxiliary value
* Anyone can use the public key to encrypt a message
* The prime numbers must be kept secret – if the public key is large
enough, only knowing the prime numbers enables decoding the
message feasibly
* RSA is a relatively slow algorithm and often used for exchanging
encrypted shared keys for symmetric key cryptograph
