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Bachelor Degree of Telecommunication Engineering

School of Electrical Engineering

Telkom University

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Nur Andini

Raditiana Patmasari

Cryptography and Network Security 1

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Cryptography and Network Security 2

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⇰ Knowing and understanding application of

cryptography on computer network security

⇰ Knowing and understanding application of

cryptography on WLAN security

⇰ Knowing and understanding application of

cryptography on GSM

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Cryptography and Network Security 3

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1. Introduction

2. WEP

3. WPA

4. WPA2

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Cryptography and Network Security 4

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IEEE 802.11

WirelessLocal Area

Network(WLAN)

IEEE 802.11i

WLAN

Security

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IBSS

IndependentBasic

Service Set

BSS

BasicService Set

ESS

ExtendedService Set

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Cryptography and Network Security 7

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Cryptography and Network Security 8

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Cryptography and Network Security9

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Encryption

AAASegmentation

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• Ron’s Code or Rivest’s Cipher 

• Stream cipher• Protecting internet trafficRC4• Advanced Encryption standard

• Block cipher

• Protecting WLAN dataAES

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Authentication

AuthorizationAccounting

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AuthenticationIt is the first stepof connecting user

to the network.It is to verify theidentity of user.

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AuthorizationIt is the next step

afterauthentication.

It is to grant user

the access ofnetwork resources

and services.

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AccountingIt is the next

step afterauthorization.

It is to track theuse of network

resource.

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It is to segment users into groups.

After authorization, user is

restricted in case of resource andcoverage.

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Cryptography and Network Security 17

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Encryption

process onLayer 2

RC4 isused

64-bitWEP

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Confidentiality

Access

controlIntegrity

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Confidentiality

Providing data privacy

Encrypting the data usingRC4

Cryptography and Network Security 20

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Authentication

Open System

Shared-Key

Access control

Authorization

Granting user theaccess of network

resources and services

Cryptography and Network Security 21

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Cryptography and Network Security 22

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Authentication

Open System

Verifiying useridentitywithout user

verification.

Pre-Shared

Verifiying user identitywithuser verification using

static key.

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Integrity

Providing Integrity CheckValue (ICV)

Preventing the datamodification

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Plaintext

Message

Cyclic Redundancy Check (CRC)

Integrity Check Value

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Key

InitializationVector (IV)

Static keyKeystream

RC4

Statickey

IV

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64-bit WEPkey

24-bitInitializationVector (IV)

40-bit statickey

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Ciphertext

Keystream

XOR

Plaintext

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IV Ciphertext Ciphertext

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IV collisionattack

Weakkey

attack

Re-injectionattack

Bit-flippingattack

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It is easy to get the secret key when IVcollision occurs

IV collision attack

224 IV combination IV is generated on everyframe

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Cryptography and Network Security 31

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It is easy to get secret key byrecovering IV

Weak key attack

RC4 Weak keys aregenerated

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Cryptography and Network Security 32

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Injecting many IVs toaccelerate IV flow

Re-injection attack

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Cryptography and Network Security 33

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ICV is weak

Bit-flipping attack

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Cryptography and Network Security 35

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Improvingencryptionmethod on

WEP

Improvingdata

protection

Improvingaccesscontrol

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Cryptography and Network Security 36

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Confidentiality

Access

controlIntegrity

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Cryptography and Network Security 37

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Encrypting the data usingTemporal Key Integrity

Protocol (TKIP)RC4

Confidentiality

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Cryptography and Network Security 38

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TKIP128-bit static key

Providing key hierarchyand key management

• Removing predictability ofstatic key

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Cryptography and Network Security 39

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Access controlGranting user the access of network resources and

services

Authentication

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Cryptography and Network Security 40

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Authentication

Personal

Pre-Shared key(PSK)

Enterprise

802.1XExtensible

AuthenticationProtocol (EAP)

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Cryptography and Network Security 41

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Preventing data modificationMessage Integrity Check

(MIC)Michael

Integrity

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Cryptography and Network Security 42

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Cryptography and Network Security 43

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WPAAdvancedEncryption

Standard (AES)

WPA2

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Cryptography and Network Security 44

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Encrypting the data usingCounter mode with Cipher BlockChaining-Message Authentication

Code (CCMP)AES

Confidentiality

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Cryptography and Network Security 45

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AES128-bit key

128-bit

plaintext block

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Cryptography and Network Security 46

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Access controlGranting user the access of network resources and

services

Authentication

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Cryptography and Network Security 47

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Authentication

Personal

Pre-Shared key(PSK)

Enterprise

802.1XExtensible

AuthenticationProtocol (EAP)

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Cryptography and Network Security 48

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Preventing data modification8-byte Message

Integrity Check (MIC)Michael

Integrity

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Cryptography and Network Security 49

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*“CWNA Certified Wireless Network

Administrator” by David D. Coleman and David

A. Westcott*“Wi-Fi Protected Access” by Wi-Fi Alliance

*“Cryptography and Network Security” by

William Stallings

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Cryptography and Network Security 50