2
2
22 to 2 2
What is this course about?
This course is to discuss
 security needs
 security services
 security mechanisms and protocols
for data stored in computers and
transmitted across computer networks

3
3
33 to 3 3
What we will/won’t cover?
 We will cover
 security threats
 practical security issues (practice in labs)
 security protocols in use
 security protocols not in use
 securing computer systems
 introductory cryptography
 We will not cover
 advanced cryptography
 computer networks
 operating systems
 computers in general
 how to hack 

4
4
44 to 4 4
What security is about in general?
 Security is about protection of assets
 D. Gollmann, Computer Security, Wiley
 Prevention
 take measures that prevent your assets from being
damaged (or stolen)
 Detection
 take measures so that you can detect when, how,
and by whom an asset has been damaged
 Reaction
 take measures so that you can recover your assets

5
5
55 to 5 5
Real world example
 Prevention
 locks at doors, window bars, secure the walls
around the property, hire a guard
 Detection
 missing items, burglar alarms, closed circuit TV
 Reaction
 attack on burglar (not recommended ), call
the police, replace stolen items, make an
insurance claim

6
6
66 to 6 6
Internet shopping example
 Prevention
 encrypt your order and card number, enforce
merchants to do some extra checks, using PIN
even for Internet transactions, don’t send card
number via Internet
 Detection
 an unauthorized transaction appears on your
credit card statement
 Reaction
 complain, dispute, ask for a new card number,
sue (if you can find of course )
 Or, pay and forget (a glass of cold water) 

7
7
77 to 7 7
Information security in past & present
 Traditional Information Security
 keep the cabinets locked
 put them in a secure room
 human guards
 electronic surveillance systems
 in general: physical and administrative
mechanisms
 Modern World
 Data are in computers
 Computers are interconnected

8
8
88 to 8 8
Terminology
 Computer Security
 2 main focuses: Information and Computer itself
 tools and mechanisms to protect data in a computer (actually
an automated information system), even if the
computers/system are connected to a network
 tools and mechanisms to protect the information system itself
(hardware, software, firmware, *ware )
 Against?
 against hackers (intrusion)
 against viruses
 against denial of service attacks
 etc. (all types of malicious behavior)

9
9
99 to 9 9
Terminology
 Network and Internet Security
 measures to prevent, detect, and correct security
violations that involve the transmission of
information in a network or interconnected
networks

10
10
1010 to 1010
A note on security terminology
 No single and consistent terminology in the
literature!
 Be careful not to confuse while reading
papers and books
 See the next slide for some terminology taken
from Stallings and Brown, Computer Security
who took from RFC4949, Internet Security
Glossary

11
11
1111 to 11
Computer
Security
Terminology
RFC 4949,
Internet Security
Glossary, May
2000

12
12
1212 to 12
Relationships among the security
Concepts
12

13
13
1313 to 1313
Security TrendsSkill and knowledge required to
mount an attack

14
14
1414 to 14
The global average cost of cyber crime/attacks
14
2017 Cost of
Cyber Crime
Study by
Accenture*
* https://www.accenture.com/t20170926T072837Z__w__/us-en/_acnmedia/PDF-61/Accenture-2017-CostCyberCrimeStudy.pdf
Steeper
increasing
trend in the
recent years

15
15
1515 to 15
Average cost of cyber crime for
seven countries
15
2017 Cost of
Cyber Crime
Study by
Accenture*
- Germany
has highest
percentage
increase;
- UK, US are
around the
mean in
percentage
increase
254 institutions
responded

16
16
1616 to 16
A Scattergram of Respondents
16
2017 Cost of
Cyber Crime
Study by
Accenture*
- Mean is
US$11.7 M
- High
variance
- 163
institutions
are below
mean (out of
254)

17
17
1717 to 17
Breakdown by Sector
17
2017 Cost
of Cyber
Crime
Study by
Accenture*
- Financial
Services
Sector has
the Highest
Cost due to
Cyber
Crime

18
18
1818 to 18
Types of cyber attacks experienced
18
2017 Cost
of Cyber
Crime
Study by
Accenture*
- Percentage
of the
respondents
experienced
- Ransomware
doubled

19
19
1919 to 19
Deployment Rate of Security
Technologies
19
2017 Cost
of Cyber
Crime
Study by
Accenture*
- Percentage
of the
respondents
experienced
- Ransomware
doubled

20
20
2020 to 20
Annual Return of Investment (RoI)
20
2017 Cost of Cyber Crime
Study by Accenture*
- More or less in
parallel with
deployment rate
- But AI, Data
Mining based
novel techniques
have higher RoI
- Bad
performance for
encryption and
DLP, but they are
needed

21
21
2121 to 21
Security Objectives: CIA Triad and Beyond

22
22
2222 to 22
Computer Security Objectives
• Data confidentiality
• Assures that private or confidential information is not made available or
disclosed to unauthorized individuals
• Privacy
• Assures that individuals control or influence what information related to them
may be collected and stored and by whom and to whom that information
may be disclosed
• Data integrity
• Assures that information changed only in a specified and authorized
manner
• System integrity
• Assures that a system performs its intended function in an unimpaired
manner, free from deliberate or inadvertent unauthorized manipulation
of the system
• Assures that systems work promptly and service is not denied to
authorized users

23
23
2323 to 23
Additional concepts:

24
24
2424 to 2424
Services, Mechanisms, Attacks
 3 aspects of information security:
 security attacks (and threats)
 actions that (may) compromise security
 security services
 services counter to attacks
 security mechanisms
 used by services
 e.g. secrecy is a service, encryption
(a.k.a. encipherment) is a mechanism

25
25
2525 to 2525
Attacks
 Attacks on computer systems
 break-in to destroy information
 break-in to steal information
 blocking to operate properly
 malicious software
 wide spectrum of problems
 Source of attacks
 Insiders
 Outsiders

26
26
2626 to 2626
Attacks
 Network Security
 Active attacks
 Passive attacks
 Passive attacks
 interception of the messages
 What can the attacker do?
 use information internally
 hard to understand
 release the content
 can be understood
 traffic analysis
 hard to avoid
 Hard to detect, try to prevent

27
27
2727 to 27
Attacks
 Active attacks
 Attacker actively manipulates
the communication
 Masquerade
 pretend as someone else
 possibly to get more privileges
 Replay
 passively capture data
and send later
 Denial-of-service
 prevention the normal use of
servers, end users, or network
itself

28
28
2828 to 2828
Attacks
 Active attacks (cont’d)
 deny
 repudiate sending/receiving a message later
 modification
 change the content of a message

29
29
2929 to 2929
Security Services
 to prevent or detect attacks
 to enhance the security
 replicate functions of physical documents
 e.g.
 have signatures, dates
 need protection from disclosure, tampering, or
destruction
 notarize
 record

30
30
3030 to 3030
Basic Security Services
 Authentication
– assurance that the communicating entity is the one it
claims to be
– peer entity authentication
• mutual confidence in the identities of the parties involved
in a connection
– Data-origin authentication
• assurance about the source of the received data
 Access Control
– prevention of the unauthorized use of a resource
– to achieve this, each entity trying to gain access must
first be identified and authenticated, so that access rights
can be tailored to the individual

31
31
3131 to 3131
 Data Confidentiality
 protection of data from unauthorized disclosure
(against eavesdropping)
 traffic flow confidentiality is one step ahead
 this requires that an attacker not be able to observe
the source and destination, frequency, length, or
other characteristics of the traffic on a
communications facility
 Data Integrity
 assurance that data received are exactly as sent
by an authorized sender
 i.e. no modification, insertion, deletion, or
replay

32
32
3232 to 3232
 Non-Repudiation
 protection against denial by one of the
parties in a communication
 Origin non-repudiation
 proof that the message was sent by the
specified party
 Destination non-repudiation
 proof that the message was received by the
specified party

33
33
3333 to 3333
Relationships
 among integrity, data-origin
authentication and non-repudiation
Integrity
Authentication
Non-repudiation

34
34
3434 to 34
Security Mechanisms
 Cryptographic Techniques
 will see next
 Software and hardware for access limitations
 Firewalls
 Intrusion Detection and Prevention Systems
 Traffic Padding
 against traffic analysis
 Hardware for authentication
 Smartcards, security tokens
 Security Policies / Access Control
 define who has access to which resources.
 Physical security
 Keep it in a safe place with limited and authorized physical
access
34

35
35
3535 to 3535
Cryptographic Security Mechanisms
 Encryption (a.k.a. Encipherment)
 use of mathematical algorithms to
transform data into a form that is not
readily intelligible
 keys are involved

36
36
3636 to 3636
Cryptographic Security Mechanisms
 Message Digest
 similar to encryption, but one-way (recovery
not possible)
 generally no keys are used
 Digital Signatures and Message
Authentication Codes
 Data appended to, or a cryptographic
transformation of, a data unit to prove the
source and the integrity of the data
 Authentication Exchange
 ensure the identity of an entity by exchanging
some information

37
37
3737 to 3737
Security Mechanisms
 Notarization
 use of a trusted third party to assure certain
properties of a data exchange
 Timestamping
 inclusion of correct date and time within
messages

38
38
3838 to 3838
And the Oscar goes to …
 On top of everything, the most
fundamental problem in security is
SECURE KEY EXCHANGE
 mostly over an insecure channel

39
39
3939 to 3939
A General Model for Network Security

40
40
4040 to 4040
Model for Network Security
 using this model requires us to:
 design a suitable algorithm for the security
transformation
 generate the secret information (keys) used by
the algorithm
 develop methods to distribute and share the
secret information
 specify a protocol enabling the principals to use
the transformation and secret information for a
security service

41
41
4141 to 4141
Model for Network Access
Security

42
42
4242 to 4242
Model for Network Access Security
 using this model requires us to:
 select appropriate gatekeeper functions to
identify users and processes and ensure
only authorized users and processes access
designated information or resources
 Internal control to monitor the activity and
analyze information to detect unwanted
intruders

43
43
4343 to 4343
More on Computer System Security
 Based on “Security Policies”
 Set of rules that specify
 How resources are managed to satisfy the security
requirements
 Which actions are permitted, which are not
 Ultimate aim
 Prevent security violations such as unauthorized access, data
loss, service interruptions, etc.
 Scope
 Organizational or Individual
 Implementation
 Partially automated, but mostly humans are involved
 Assurance and Evaluation
 Assurance: degree of confidence to a system
 Security products and systems must be evaluated using
certain criteria in order to decide whether they assure
security or not

44
44
4444 to 4444
Aspects of Computer Security
 Mostly related to Operating Systems
 Similar to those discussed for Network
Security
 Confidentiality
 Integrity
 Availability
 Authenticity
 Accountability
 Dependability

45
45
4545 to 4545
 Confidentiality
 Prevent unauthorised disclosure of information
 Synonyms: Privacy and Secrecy
 any differences? Let’s discuss
 Integrity
 two types: data integrity and system integrity
 In general, “make sure that everything is as it
is supposed to be”
 More specifically, “no unauthorized
modification, deletion” on data (data integrity)
 System performs as intended without any
unauthorized manipulations (system integrity)

46
46
4646 to 4646
 Availability
 services should be accessible when needed and without
extra delay
 Accountability
 audit information must be selectively kept and protected
so that actions affecting security can be traced to the
responsible party
 How can we do that?
 Users have to be identified and authenticated to have a
basis for access control decisions and to find out responsible
party in case of a violation.
 The security system keeps an audit log (audit trail) of
security relevant events to detect and investigate intrusions.
 Dependability
 Can we trust the system as a whole?

47
47
4747 to 47
Attack Surfaces
 An attack surface consists of the reachable and
exploitable vulnerabilities in a system
 Examples:
– Open ports on outward facing Web and other servers,
and code listening on those ports
– Services available in a firewall
– Code that processes incoming data, email, XML, office
documents, etc.
– Interfaces and Web forms
– An employee with access to sensitive information
vulnerable to a social engineering attack

48
48
4848 to 48
Attack Surface Categories
 Network attack surface
– Refers to vulnerabilities over an enterprise network,
wide-area network, or the Internet
• E.g. DoS, intruders exploiting network protocol vulnerabilities
 Software attack surface
– Refers to vulnerabilities in application, utility, or
operating system code
 Human attack surface
– Refers to vulnerabilities created by personnel or
outsiders
– E.g. social engineering, insider traitors

49
49
4949 to 4949
Fundamental Dilemma of Security
 “Security unaware users have specific security
requirements but no security expertise.”
 from D. Gollmann
 Solution: level of security is given in predefined
classes specified in some common criteria
 Orange book (Trusted Computer System Evaluation
Criteria) is such a criteria

50
50
5050 to 5050
Fundamental Tradeoff
 Between security and ease-of-use
 Security may require clumsy and
inconvenient restrictions on users and
processes
“If security is an add-on that people have to do
something special to get, then most of the time
they will not get it”
Martin Hellman,
co-inventor of Public Key Cryptography

51
51
5151 to 5151
Good Enough Security
“Everything should be as secure as
necessary, but not securer”
Ravi Sandhu, “Good Enough Security”, IEEE
Internet Computing, January/February 2003, pp.
66- 68.
 Read the full article at
http://dx.doi.org/10.1109/MIC.2003.1167341

52
52
5252 to 5252
Some Other Security Facts
 Not as simple as it might first appear to the novice
 Must consider all potential attacks when designing a system
 Generally yields complex and counterintuitive systems
 Battle of intelligent strategies between attacker and admin
 Requires regular monitoring
 Not considered as a beneficial investment until a security failure
occurs
 Actually security investments must be considered as insurance
against attacks
 too often an afterthought
 Not only from investment point of view, but also from design point
of view

Meeting 15. network security

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