Information Security Concepts.pdf

Level III - Semester 5
© 2022 e-Learning Centre, UCSC
1 : Information Security Concepts
IT5306 - Principles of Information Security

List of sub topics
2
1.1 Computer Security Concepts: Confidentiality, Integrity, and
Availability
1.2. Threats, Attacks, and Assets
1.3. Security Functional Requirements
1.4. Fundamental Security Design Principles
1.5. Attack Surfaces and Attack Trees
1.6. Computer Security Strategy
1.7. Concepts of Encryption, Decryption, Plain Text and Cipher Text
1.8. Stream and Block Ciphers

What do we mean by “secure”?
3
● At one time Bank robbery was common. Now its very rare. What
has changed or been implemented to provide this security?
− Sophisticated alarms
− Criminal investigation techniques (DNA testing)
− Change in “assets” (cash was/is inherently insecure)
− Improvements in communication and transportation
● Risk becomes so high that it is no longer beneficial.
Introduction

Security is all about protecting valuables
● In our case the “valuables” are computer related assets
instead of money
− Though these days money is so electronic that one can
argue that the protection of money is a subset of
computer asset security
● Information seems to be the currency of the 21st century.
4
Introduction

Money vs. Information
5
● Size and portability
− Banks are large and unportable.
− Storage of information can be very small and extremely
portable. (So small that an entire corporations intellectual
property can be stored on something the size of a postage
stamp.)Ability to avoid physical contact
− Banks: physical interaction with the bank and the loot is
unavoidable or impossible to circumvent
− Computers: require no physical contact to either gain access
to, copy or remove data.
● Value of assets:
− Bank: generally very high (or why would somebody bother
to put it in a bank?)
− Computers: Variable, from very low (useless) to very high.
Introduction

Information security
are methods and technologies
for protection, integrity, availability,
authenticity and extended functionality
of computer programs and data
“Definition” of Information Security
6

Method, Opportunity and Motive
7
● Method: The skills knowledge and tools that enable the attack
● Opportunity: The time, access and circumstances that allow
for the attack
● Motive: The reason why the perpetrator wants to commit the
attack
Threats, Attacks and Assert

Accidental access
to unauthorized resources
and execution of
unauthorized operations
(no harm to regular users)
Amateurs . . .
Crackers
Criminals
Regular users
8
People
8

Active attempts to access
sensitive resources and to
discover system
vulnerabilities
(minor inconveniences
to regular users)
Amateurs
Crackers . . .
Criminals
Regular users
9
People
9

Active attempts to utilize
weaknesses in protection
system in order to steal or
destroy resources
(serious problems to
regular users)
Amateurs
Crackers
Criminals . . .
Regular users
10
People
10

Special requirements:
authentication in open
networks, authorization,
message integrity,
non-repudiation,
special transactions
Amateurs
Crackers
Criminals
Regular users . . .
The People Involved
11
People
11

Vulnerability,Attack,Control, Problems, Threats,
and Risks
12
● Vulnerability: A weakness in the security system.
● Attack: A human exploitation of a vulnerability.
● Control: A protective measure. An action, device or measure
taken that removes, reduces or neutralizes a vulnerability.
● Problems : Consequences of unintentional accidental errors
● Threat: a set of circumstances that has the potential to cause
loss or harm.
● Risks : Probabilities that some threat or problem will occur
due to system vulnerabilities

Threats with a single system
– Illegal access to a system
– Authentication of users
13

14
• Active attacks are attacks in which the attacker
attempts to change or transform the content of
messages or information.
• These attacks are a threat to the integrity and
availability of the system.
• Due to these attacks, systems get damaged, and
information can be altered.
• The prevention of these attacks is difficult due to their
high range of physical and software vulnerabilities.
Attack Types: An Active Attack

15
• Passive attacks are the ones in which the attacker
observes all the messages and copy the content of
messages or information.
• They focus on monitoring all the transmission and gaining
the data.
• The attacker does not try to change any data or
information he gathered.
• Although there is no potential harm to the system due to
these attacks, they can be a significant danger to your
data’s confidentiality.
Attack Types: A Passive Attack

16
• In active attacks, modification of messages is done, but on
the other hand, in passive attacks, the information remains
unchanged.
• The active attack causes damage to the integrity and
availability of the system, but passive attacks cause
damage to data confidentiality.
• In active attacks, attention is given to detection, while in
the other one, attention is given to prevention.
• The resources can be changed in active attacks, but passive
attacks have no impact on the resources.
Active vs Passive Attacks

17
• The active attack influences the system services, but the
information or data is acquired in passive attacks.
• Inactive attacks, information is gathered through passive
attacks to attack the system, while passive attacks are
achieved by collecting confidential information such as
private chats and passwords.
• Active attacks are challenging to be prohibited, but passive
attacks are easy to prevent.
Active vs Passive Attacks

18
● What makes a “secure” system?
− Financial “Security” requirements
− Home “security”
− Physical “security”
− Information “security”
● All these concepts of security have different requirements. We
are, of course, interested mostly on computer security; which
requires three items:
Security Functional Requirements

● The presence of all three things yields a secure system:
Secure
Integrity
Availability
Confidentiality
19

Thing one:
20
● Confidentiality:
Computer related assets are only available to authorized
parties. Only those that should have access to something
will actually get that access.
● “Access” isn't limited to reading. But also to viewing,
printing or...
● Simply even knowing that the particular asset exists
(steganography)
− Straight forward concept but very hard to implement.

21
● Integrity
Can mean many things: Something has integrity if it is:
● Precise
● Accurate
● Unmodified
● Consistent
● Meaningful and usable

Integrity
22
● Three important aspects towards providing computer related
integrity:
− Authorized actions
− Seperation and protection of resources
− Error detection and correction.
● Again, rather hard to implement; usually done so through
rigorous control of who or what can have access to data and in
what ways.

Thing three:
23
● Availability
− There is a timely response to our requests
− There is a fair allocation of resources (no starvation)
− Reliability (software and hardware failures lead to graceful
cessation of services and not an abrupt crash)
− Service can be used easily and in the manner it was
intended to be used.
− Controlled concurrency, support for simultaneous access
with proper deadlock and access management.

Threats to Data and
Programs:
illegal read, illegal access,
data (files) deletion,
illegal users, criminal acts,
sabotage, etc.
Confidentiality . . .
Integrity
Availability
Functionality
24
Security Design Principles

Threats to software and
data: technical errors,
software errors,
processing errors,
transmission correctness,
etc.
Integrity . . .
Availability
Functionality
Confidentiality
25

Requirements for:
timely response, fair
allocation, fault tolerance,
usability, controlled
concurrency
Integrity
Availability . . .
Functionality
Confidentiality
Principles of Computer Security
26

New functions needed for
electronic data
transactions: authentication,
digital signature,
confidentiality, and others
Integrity
Availability
Functionality . . .
Confidentiality
27

So what does computer security concern
itself with?
28
● The entire system:
− Hardware
− Software
− Storage media
− Data
− Memory
− People
− Organizations
− Communications
Attack Surface

29
An attack surface consists of reachable and exploitable
vulnerabilities in a system and can be classified into three
categories:
Network attack surface refers to vulnerabilities over an
enterprise network or the internet. Examples of this include
network protocol vulnerabilities, such as those used for a DDoS
attack, disruption of communication links and various forms of
intruder attacks.
Software attack surface refers to vulnerabilities in application,
utility, or operating system code. A particular focus in this
category is web server software.
Human attack surface refers to vulnerabilities created by
personnel or outsiders, such as social engineering, human error
and trusted insiders.
Attack Surface

30
• An attack tree is a tree structure that represents attacks
against a system.
• Each subnode defines a subgoal, and each subgoal may, in
turn, have its own set of subgoals, and so on.
• The leaf nodes of the attack tree represent different ways to
initiate an attack.
• Each node other than a leaf is either an AND-node or an OR-
node.
• To achieve the goal represented by an AND-node, all of the
child subgoals must be achieved; and for an OR-node, at least
one of the child subgoals must be achieved.
Attack trees

31
Privacy Attack Tree with Threat Scenarios

32
Computer Security Strategy

Encryption
Policies
Physical controls
SW & HW Controls
33

Effective for:
confidentiality,
users and messages
authentication,
access
control
Encryption . . .
Policies
Physical controls
SW & HW Controls
34

Available methods:
software and hardware
controls (internal SW, OS
controls, development
controls, special HW
devices)
Encryption
Policies
Physical controls
SW & HW Controls
Protection Methods
35

Precise
specifications:
special procedures,
security methods,
security parameters,
organizational issues
Policies . . .
Encryption
Physical controls
SW & HW Controls
Protection Methods
36

Measures for:
isolation of equipment,
access to equipment,
authorization for
personnel,
backup and archiving
SW & HW Controls
Encryption
Policies
Physical controls
Protection Methods
37

Cipher
Algorithm
Encrypted
Data
Cipher
Algorithm
Basic Concept
38
Concept of Cryptography
P clear (plain) text, message-readable (intelligible) information
C ciphertext-encrypted information
E encryption (enciphering)-transforming clear text into
ciphertext
D decryption (deciphering)-transforming ciphertext back into
plaintext

Cryptography Basic
39
● Why Encrypt?
− Protect stored information
− Protect information in transmission
● Cryptography originally used for secrecy
● Encryption - process by which plaintext is converted to
ciphertext using a key
● Decryption - process by which ciphertext is converted to
plaintext (with the appropriate key)
● plaintext (cleartext)- intelligible data

Cryptography History
40
▪ Historic examples...
● Earliest cryptography: an Egyptian scribe using non-standard
hieroglyphics
● Julius Caesar (“Caesar Cipher”)
Each plaintext letter is replaced by a letter some fixed
number of positions further down the alphabet (e.g. Belgica
(3 positions) ehojlfd)
● The Kama Sutra recommends cryptography as 44th and 45th
art
(of 64) men and women should know

Cryptography History
41
− ENIGMA Used by the Germans in WW2 – and the
subsequent
code-breaking activities at Bletchley park
(still a popular subject of books and movies)
− 1976: Public Key Cryptography concept
(Whitfield Diffie & Martin Hellman)
− 1977: first (published) practical PKC cryptosystem
invented
(RSA - Rivest, Shamir, Adleman)
− October 2000 Rijndael is chosen as AES
(Advanced Encryption Standard)

Ci = E(Pi)= Pi+3
Plain Text : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Cipher Text : D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
42
The Caesar Cipher

Kamasutra
43
One of the earliest descriptions of
encryption by substitution appears in
the Kama-sutra, a text written in the 4th
century AD by the Brahmin scholar
Vatsyayana, but based on manuscripts
dating back to the 4th century BC.
How it work
The kamasutra generate list of 26
alphabet with no duplicate. Then divide
by 2 row. Find for each letter of
message text in table and choose the
opposite of the letter
Kamasutra

for example:
Key = G H A J R I O B E S Q C L F V Z T Y K M X W N U D P
divide by 2 rows
G H A J R I O B E S Q C L
F V Z T Y K M X W N U D P
Given String = KAMASUTRA
K is at 2nd row and 5th column. Get the opposite of K that is I.
Do each letter until the end
Cipher : IZOZNQJYZ
44
Kamasutra

Cipher Text : K E Y G H I J K L M N O P Q R S T U V W X Y Z A B C
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Letter Frequency
45
Polyalalphaberic Substitutions

Cipher Text : A D G J N O S V Y B E H K N Q T W Z C F I L O R U X
Table for Odd Positions
Cipher Text : N S X C H M R W B G I Q V A F K P U Z E J O T Y D I
Table for Even Positions
Plain Text : SSIBL
Cipher Text : czysh
46
Polyalalphaberic Substitutions

Columnar Transposition
c1 c2 c3 c4 c5
c6 c7 c8 c9 c10
c11 c12 etc.
c1 c2 c3 c4 c5
c6 c7 c8 c9 c10
c11 c12 etc.
Cipher text formed by c1 c6 c11 c2 c7 c12 c3 c8 ...
Transposition (Permutation) Substitutions
47
Transposition (Permutation) Substitutions

Plain Text : V E R N A M C I P H E R
Numeric Equivalent : 21 4 17 13 0 12 2 8 15 7 4 17
+Random Number : 76 48 16 82 44 3 58 11 60 5 48 88
= Sum : 97 52 33 95 44 15 60 19 75 12 52 105
=Mod 26 : 19 0 7 17 18 15 8 19 23 12 0 1
Cipher text : t a h r s p I t x m a b
Binary Vernam Cipher
Plain Text : 1 0 1 0 0 0 1 1 1 0 0 1 1 0 1
+ Random Stream : 0 1 0 1 1 0 1 0 1 1 1 0 1 0 1
Cipher text : 1 1 1 1 1 0 0 1 0 1 1 1 0 0 0
48
The Vernam Cipher

The One-Time Pad
49
• If a truly random key as long as the message is
used, the cipher will be secure
• Called a One-Time pad
• Has unconditional security:
• ciphertext bears no statistical relationship to the
plaintext since for any plaintext & any ciphertext
there exists a key mapping one to other
• Can only use the key once
• Have problem of safe distribution of key
The One-Time Pad

Encipherment Modes
● Stream Ciphers - Message broken into characters or bits
and enciphered with a “key stream”
• key stream - should be random and generated
independently of the message stream
● Block ciphers process messages in blocks, each of which is
then en/decrypted
50
Stream and Block Ciphers

Y
ISSOPMI WEHTUA..
Plain text Cipher text
Key (Optional)
Advantage
• Speed of transformation
• Low error propagation
Disadvantage
• Low diffusion
• Susceptibility to malicious insertion and modifications
Cipher
Cipher
text(F) Plain text (A)
Stream Cipher
51

Y
XN
OI
TP
YR
CN
BA
QC
KD
EM
MC
Plain text Cipher text
Key (Optional)
Disadvantage
• Slowness of encryption
• Error propagation
Advantage
• Diffusion
• Immunity to insertion
Cipher
Cipher
text(FRWSU)
Plain text
(AKEDF)
Block Cipher
52

Shannon Characteristics - 1949
• The amount of secrecy needed should determine the amount of
labor appropriate for encryption and decryption
• The set of keys and the encryption algorithm should be free from
complexity
• The implementation of the process should be as simple as
possible
• Errors in the ciphering should not propagate and cause
corruption of further information in the message
• The size of enciphered text should be no larger than the text of
the original message
53
Characteristic of “GOOD” Cipher

Kerckhoff’s Principle
54
The security of the encryption scheme must depend only on the
secrecy of the key and not on the secrecy of the algorithms.
Reasons:
•Algorithms are difficult to change
•Cannot design an algorithm for every pair of users
•Expert review
•No security through obscurity!
Kerckhoff’s Principle

2.15 milliseconds
232 = 4.3 x 109
32
5.9 x 1030 years
2168 = 3.7 x 1050
168
5.4 x 1018 years
2128 = 3.4 x 1038
128
10 hours
256 = 7.2 x 1016
56
Time required at
106 Decryption/µs
Number of
Alternative Keys
Key Size
(bits)
Brute Force Search
55
•Always possible to simply try every key
•Most basic attack, proportional to key size
•Assume either know/recognize plaintext
Brute Force Search

Unconditional/Computational Security
56
Unconditional security
no matter how much computer power is available, the
cipher cannot be broken since the ciphertext provides
insufficient information to uniquely determine the
corresponding plaintext
Computational security
given limited computing resources (e.g. time needed
for calculations is greater than age of universe), the
cipher cannot be broken
Unconditional/Computational Security

Sec_rity is not Complete without U
57
You, as a Computer User, have to make your
contribution to computer security: You are
responsible for the security and protection of your
computers, the operating systems you run, the
application you install, the software you program, the
data you own - and the services and systems you
manage.
Sec_rity is not Complete without U

58
Thank You

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