Computer Network 2 - Khoa Khoa học và Kỹ thuật Máy tính - hcmut ...

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Nov 20, 2013 (4 years and 7 months ago)

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Cryptography &

Network Security

Principles of modern ciphers

Implement crypto library

Network Security Applications

System Security

MSc. NGUYEN CAO DAT

Dr. TRAN VAN HOAI

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TP.HCM

Course details


Number of credits: 3



Study time allocation per week:



2 lecture hours for theory



2 lecture hours for lab, exercises



6 hours for self
-
study



Website: http://www.cse.hcmut.edu.vn/~dat

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Course outline (1/2)



Basics of Cryptography


Symmetric key


Public key


Hash function



Network Security Applications


Authentication applications


E
-
mail security


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Course outline (2/2)


Network Security Applications (
con’t
)


Web security


IP security



System Security


IDS/IPS


Firewalls






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References


[1]


Cryptography and Network Security
Principles and Practices
”, W. Stallings, 4
th

ed.,
Prentice Hall, 2005


[2]

Slides “Cryptography and Network Security”,
Bộ

môn

Hệ

thống



Mạng
,
Khoa

Khoa

học



Kỹ

thuật

máy

tính
,
ĐHBK

Tp.HCM.


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Assessment Scheme


Attending lectures: >80% lecture times


Reading textbooks and references


Self
-
study and working in group


Lab: 20%


Assignments: 20%


Midterm Exam: 20%, multiple question choice
test


45’


Final Exam: 40%, multiple question choice test


60’


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Chapter 1

Introduction

MSc. NGUYEN CAO DAT

Dr. TRAN VAN HOAI

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Background


Information Security requirements have
changed in recent times.


traditionally provided by physical and
administrative mechanisms.


computer use requires
automated tools to
protect files and other stored information.


use of networks and communications links
requires measures to protect data during
transmission.





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Definitions


Computer Security

-

generic name for the
collection of tools designed to protect data and
to thwart hackers.


Network Security

-

measures to protect data
during their transmission.


Internet Security

-

measures to protect data
during their transmission over a collection of
interconnected networks.



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Aim of Course


our focus is on
Internet Security


which consists of measures to deter, prevent,
detect, and correct security violations that
involve the transmission & storage of
information


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Security Trends

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OSI Security Architecture


ITU
-
T X.800 “Security Architecture for OSI”


defines a systematic way of defining and
providing security requirements


for us it provides a useful, if abstract, overview
of concepts we will study

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Aspects of Security


consider 3 aspects of information security:


security attack


security mechanism


security service


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Security Attack


any action that compromises the security of
information owned by an organization


information security is about how to prevent
attacks, or failing that, to detect attacks on
information
-
based systems


often
threat

&
attack

used to mean same thing


have a wide range of attacks


can focus of generic types of attacks


passive


active

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Classify Security Attacks


passive attacks

-

eavesdropping on, or
monitoring of, transmissions to:


obtain message contents, or


monitor traffic flows



active
attacks



modification of data stream to:


masquerade of one entity as some other


replay previous messages


modify messages in transit


denial of service



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Types of Attacks

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Passive Attacks

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Active Attacks

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Security Service


enhance security of data processing systems
and information transfers of an organization


intended to counter security attacks


using one or more security mechanisms


often replicates functions normally associated
with physical
documents

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Security Services


X.800

“a service provided by a protocol layer of
communicating open systems, which ensures
adequate security of the systems or of data
transfers”



RFC
2828

“a processing or communication service provided
by a system to give a specific kind of protection
to system resources”

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Security Services (X.800)


Authentication

-

assurance that the
communicating entity is the one claimed


Access Control

-

prevention of the
unauthorized use of a resource


Data Confidentiality


protection of data from
unauthorized disclosure


Data Integrity

-

assurance that data received is
as sent by an authorized entity


Non
-
Repudiation

-

protection against denial by
one of the parties in a communication





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Security Mechanism


feature designed to detect, prevent, or recover
from a security attack


no single mechanism that will support all
services required


however
one particular element underlies many
of the security mechanisms in use:


cryptographic techniques


hence our focus on this topic


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Security Mechanisms (X.800)


specific security
mechanisms


encipherment
, digital signatures, access
controls, data integrity, authentication exchange,
traffic padding, routing control, notarization


pervasive security
mechanisms


trusted functionality, security labels, event
detection, security audit trails, security recovery


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Model for Network Security

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Model for Network Security


using this model requires us to:

1.
design a suitable algorithm for the security
transformation

2.
generate the secret information (keys) used by
the algorithm

3.
develop methods to distribute and share the
secret information

4.
specify a protocol enabling the principals to use
the transformation and secret information for a
security service

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Model for Network Access Security

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Model for Network Access Security


using this model requires us to:

1.
select appropriate gatekeeper functions to
identify users

2.
implement security controls to ensure only
authorised users access designated information
or resources


trusted computer systems may be useful to
help implement this model


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Cryptography

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Cryptography


characterize
cryptographic system by:


type of encryption operations used


substitution / transposition / product


number of keys used


single
-
key or private / two
-
key or public


way in which plaintext is processed


block / stream

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Cryptanalysis


objective to recover key not just
message


general approaches:


cryptanalytic attack


brute
-
force attack

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Cryptanalytic Attacks


ciphertext

only



only know algorithm &
ciphertext
, is statistical,
know or can identify plaintext


known plaintext



know/suspect plaintext &
ciphertext


chosen plaintext



select plaintext and obtain
ciphertext


chosen
ciphertext



select
ciphertext

and obtain plaintext


chosen text



select plaintext or
ciphertext

to en/decrypt

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More Definitions


unconditional security



no matter how much computer power or time 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 (
eg

time
needed for calculations is greater than age of
universe), the cipher cannot be broken

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Brute Force Search


always possible to simply try every key


most basic attack, proportional to key size


assume either know / recognise plaintext





Key Size (bits)

Number of Alternative
Keys

Time required at 1
decryption/µs

Time required at 10
6

decryptions/µs

32

2
32

= 4.3


10
9

2
31

µs

= 35.8 minutes

2.15 milliseconds

56

2
56

= 7.2


10
16

2
55

µs

= 1142 years

10.01 hours

128

2
128

= 3.4


10
38

2
127

µs

= 5.4


10
24

years

5.4


10
18

years

168

2
168

= 3.7


10
50

2
167

µs

= 5.9


10
36

years

5.9


10
30

years

26 characters
(permutation)

26! = 4


10
26

2


10
26

µs

= 6.4


10
12

years

6.4


10
6

years

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Summary


have considered:


definitions for:


computer, network, internet security


X.800 standard


security attacks, services, mechanisms


models for network (access)
securityto


Cryptography
, cryptanalysis

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Self study


Symmetric Cipher Model


Classical Substitution Ciphers


Caesar Cipher


Monoalphabetic

Cipher


Playfair

Cipher


Polyalphabetic

Ciphers


Vigenère

Cipher


C
ryptanalysis

using letter frequencies






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