W.Buchanan (1)

Uni

t 7: W

irele

ss

Advanced Security and Mobile Networks

W.Buchanan (2)

Uni

t 7: W

irele

ss

Unit 7: Mobile Networks.• Wireless.• Security.• Mobile IP.• Mobile Agents.• Spread spectrum.• Military/Emergency Networks

8. Ad-hoc

9. GSM/3G

7. Mobile Networks

Security Elements

W.Buchanan (3)

Uni

t 7: W

irele

ss

• Mobile phone technology. This integrates with the GSM network.

• Wireless (IEEE 802.11). This normally integrated with a fixed network.

• Bluetooth. This normally allows networking between non-computer-type devices, such as mobile phones, hi-fi’s, and so on.

• Infra-red. This technology is too slow and has a limited range for most applications.

• Line-of-sight optics. This allows for easy connections between buildings, and involves a laser directing it beam to a receiver. It is typically used around cities and gives speeds of several Gbps.

Wireless connections … which technology?

W.Buchanan (4)

Uni

t 7: W

irele

ss

• IEEE 802.11a. 802.11a deals with communications available in the 5GHz frequency, and has a maximum data rate of 54 Mbps.

• IEEE 802.11b. 802.11b, or Wi-Fi, is the standard that is most commonly used in wireless LAN communications. It has a maximum bandwidth of 11Mbps, at a frequency of 2.4GHz.

• IEEE 802.11c. 802.11c is a group set up to deal with bridging operations when developing access points.

• IEEE 802.11f. 802.11f is concerned with standardising access point roaming.which is involved in making sure that interoperability between access points is guaranteed.

• IEEE 802.11g (Proposed). 802.11g is a proposed standard that hopes to provide 54Mbps maximum bandwidth over a 2.4GHz connection, the same frequency as the popular 802.11b standard.

IEEE 802.11 - Wireless

W.Buchanan (5)

Uni

t 7: W

irele

ss

Operating Channels:11 for N. America, 14 Japan, 13 Europe (ETSI), 2 Spain, 4 FranceOperating Frequency:2.412-2.462 GHz (North America), 2.412-2.484 GHz (Japan), 2.412-2.472

GHz (Europe ETSI), 2.457-2.462 GHz (Spain), 2.457-2.472 GHz (France)

Data Rate:1, 2, 5.5 or 11MbpsMedia Access Protocol:CSMA/CA, 802.11 CompliantRange:11Mbps: 140m (460 feet)5.5Mbps: 200m (656 feet)2Mbps: 270m (885 feet)1Mbps: 400m (1311 feet)RF Technology:Direct Sequence Spread Spectrum Modulation:CCK (11Mps, 5.5Mbps), DQPSK (2Mbps), DBPSK (1Mbps)

IEEE 802.11b

W.Buchanan (6)

Uni

t 7: W

irele

ss

A wireless access point (AP) allowseveral wireless clients to connectto a single device.

Wireless access point

W.Buchanan (7)

Uni

t 7: W

irele

ss

Wireless (IEEE 802.11b)Connection.

And possibly a Bluetoothconnection

Wireless adaptor

W.Buchanan (8)

Uni

t 7: W

irele

ss

IEEE 802.11b settings

W.Buchanan (9)

Uni

t 7: W

irele

ss

Server

Access point

LAN01

LAN02

Access point

Ethernet backbone

Infrastructure network

W.Buchanan (10)

Uni

t 7: W

irele

ss

SSID = group 1

SSID = group 1

SSID = group 1

SSID = group 1Access point

Ethernet

SSID = group 1

SSID = group 1

SSID = group 1

SSID = group 1Access point

Ethernet

SSID

W.Buchanan (11)

Uni

t 7: W

irele

ss Channel is identical such as channel = 3

Ad-hoc wireless LAN 1 Ad-hoc wireless LAN 2

Channel = 5Channel is identical such as channel = 3

Ad-hoc wireless LAN 1 Ad-hoc wireless LAN 2

Channel = 5

Ad-hoc network

W.Buchanan (12)

Uni

t 7: W

irele

ss

L

Ad-hocRadius of coverage =2L

Access point

L L

Infrastructure

Span of network

W.Buchanan (13)

Uni

t 7: W

irele

ss

• Military and rescue operations• Battlefield• Evacuation of a building on fire

• Terrorism & Rescue Operations• Hospitals

• Retrieve patient’s information from hospital’s database while in surgery

• Conference meetings• Share information quickly• Schedule meetings

• Networking while on the road• Inter-vehicle communication

Applications of Ad-hoc networks

W.Buchanan (14)

Uni

t 7: W

irele

ss

• Authentication algorithm. This sets whether the adapter uses an open system (where other nodes can listen to the communications), or uses encryption (using either a WEP key, or a shared key).

• Channel. If an ad-hoc network is used, then the nodes which communicate must use the same channel.

• Fragmentation threshold. This can be used to split large data frames into smaller fragments. The value can range from 64 to 1500 bytes. This is used to improve the efficiency when there is a high amount of traffic on the wireless network, as smaller frames make more efficient usage of the network.

• Network type. This can either be set to an infrastructure network (which use access points, or wireless hubs) or Ad-hoc, which allows nodes to interconnect without the need for an access point.

Network settings

W.Buchanan (15)

Uni

t 7: W

irele

ss

• Preamble mode. This can either be set to Long (which is the default) or short. A long preamble allows for interoperatively with 1Mbps and 2Mbps DSSS specifications. The shorter allows for faster operations (as the preamble is kept to a minimum) and can be used where thetransmission parameters must be maximized, and that there are nointeroperatablity problems.

• RTS/CTS threshold. The RTS Threshold prevents the Hidden Nodeproblem, where two wireless nodes are within range of the same access point, but are not within range of each other. As they do not know that they both exist on the network, they may try to communicate with the access point at the same time. When they do, their dataframes may collide when arriving simultaneously at the Access Point, which causes a loss of data frames from the nodes. The RTS threshold tries to overcome this by enabling the handshaking signals of Ready To Send (RTS) and Clear To Send (CTS). When a node wishes to communicate with the access point it sends a RTS signal to the access point. Once the access point defines that it can then communicate, the access point sends a CTS message. The node can then send its data.

Network settings (cont.)

W.Buchanan (16)

Uni

t 7: W

irele

ss

• Multipath radio wave propagation. Radio wave propagate outwards in all directions, and will thus hit obstacles, which causes multiple paths for the radio wave. These waves thus add/subtract to signal, and can cause distortion on the wave.

• Radio data frames collide. Two or more radio devices can be transmitting a data frame at the same time using the same radio frequency. The data frames may thus collide and cause errors in the data frames.

• Out-of-range threshold. Wireless devices which are at the boundary of the wireless domain can suffer from problems with signal strength as the data frames is being transmitted. This will typically occur when a device is moving around the threshold of the domain, as weak signal strengths are more affected by noise than strong ones.

• Noisy environment. Many types of electrical equipment can generate high-frequency radio waves, which might interfere with the transmitted data frame.

Problems with wireless environments

W.Buchanan (17)

Uni

t 7: W

irele

ss

Multiple paths for the wireless signal

W.Buchanan (18)

Uni

t 7: W

irele

ss

IEEE 802.11 can use two mechanisms for shared access:

• CSMA/CA. CSMA/CA is, like standard Ethernet (IEEE 802.3) a contention-based protocol, but uses collision avoidance rather than collision detection. It would be impossible to use collision detection as a radio wave is always either sending or receiving and can never do both at the same time. The nodes will thus not be able to listen on the channel while they are transmitting.

• Point Coordination Function (PCF). This is an optional priority-based protocol, which provides contention-free frame transfer for transmission of time-critical data, such as real-time video or audio. With this, the point coordinator (PC) operates in the wireless access point andidentifies the devices which are allowed to transmit at any given time. Each PC then, with the contention-free (CF) period, the PC polls each of the enabled PCF to determine if they wish to transmit data frames. No other device is allowed to transmit while a another node is being polled. Thus, PCF will be contention-free and enables devices to transmit data frames synchronously, with defined time delays between data frame transmissions.

CSMA/CA and PCF

W.Buchanan (19)

Uni

t 7: W

irele

ss

1

Listen for no activity

ACK

2

2

ACK time-out

• Node has gone.• Data frame has collided with another

• Data frame corrupted with noise.

CSMA/CD

W.Buchanan (20)

Uni

t 7: W

irele

ss

Framecontrol

Duration/ID

Address1

Address2

Address3

Sequencecontrol

Address4

Framebody FCS

2 Bytes 2 6 6 6 2 6 0-2312 4

· Frame control. This contains control information.· Duration/ID. This contains information on how long the data frame will last.· Address fields. This contains different types of address, such as an individual address of group addresses. The two main types of group addresses are broadcast and multicast.· Sequence control. This identifies the sequence number of the data frames, and allows the recipient to check for missing or duplicate data frames.· Frame body. This part contains the actual data. The maximum amount is 2312 bytes, but most implementations use up to 1500 bytes.FCS (Frame Check Sequence). This is a strong error detection code.

IEEE 802.11 data frame

W.Buchanan (21)

Uni

t 7: W

irele

ss

• To avoid interference in the band, radio LANs (RLANs) use either Frequency Hopping or Direct Sequence Spread Spectrum techniques (FHSS & DSSS). These two methods avoid or lower the potential for interference within the band as shown in the next slide. Spread spectrum technologies work by spreading the actual signal over a wider bandwidth for transmission. Using these methods provides resilience from narrow band interference and also reduces interference to other sources using the ISM band.

• Frequency Hopping Spread Spectrum technology works by splitting the ISM band into 79 1MHz channels. Data is transmitted in a sequence over the available channels, spreading the signal across the band according to a hopping pattern, which has been determined between the wireless devices. Each channel can only be occupied for a limited period of time before the system has to hop.

Spread Spectrum and Frequency Hopping

W.Buchanan (22)

Uni

t 7: W

irele

ss

Military systems have been using Spread Spectrumand Frequency Hopping for many years. This is to:

• Avoid jamming on a certain channel.• Avoid noise on a certain channel.• Confuse the enemy as the transmitting frequency moves in a way that only the sender and receiver known. Imagine having to move the dial of your radio receiver, each minute to a certain frequency in a give way. Such as Radio 1 is broadcast on 909MHz from 12:00, then 915MHz until 12:01, then 900MHz unit 12:02, and so on.

Spread Spectrum and Frequency Hopping

W.Buchanan (23)

Uni

t 7: W

irele

ss

FHSS

2400MHz 2483.5MHzCH2 -22MHz

Ch74 Ch75Ch03Ch02Ch01

1MHz

CH1 - 22MHz CH7 - 22MHz CH13 - 22MHz

DSSS

Nonoverlappingchannels

W.Buchanan (24)

Uni

t 7: W

irele

ss

IEEE 802.11 Security

Access Control

W.Buchanan (25)

Uni

t 7: W

irele

ss Wireless networkscan be easily jammedby transmitting jammingsignals on frequenciesaround the 2.4GHz.

2.4GHz 2.48GHz

Not recommendedfor battlefieldconditions

Interference and Jamming

W.Buchanan (26)

Uni

t 7: W

irele

ss

F

Wireless Intrusion

PublicFTPserver

De-MilitarizedZone (DMZ)

N

FF

F

Externaldevicegets behindthe firewall

W.Buchanan (27)

Uni

t 7: W

irele

ss

F PublicFTPserver

Wireless Access is Untrusted

De-MilitarizedZone (DMZ)

N

FF

F

All wirelessconnectionsare untrusted

W.Buchanan (28)

Uni

t 7: W

irele

ss

Connect?Download

Deprivation ofservice attack

DoS attack

DoS and Deprivation of Service Attack

W.Buchanan (29)

Uni

t 7: W

irele

ss

Spoofing

The client spoofs its MAC addresses to gain an IP address. MAC addresses cannot be used to authenticate nodes, as MAC addresses can be setup in some network cards

Spoofdevice

Correctdevice

Devices connect to the spoof device.

W.Buchanan (30)

Uni

t 7: W

irele

ss

Wireless Security

Wireless Security StandardsIPSec standardsfor VPN’s

- Limited to IP- Required for public access systems.

Encryption Authentication

EAPS - Extensible Authentication Protocol

LEAP - Lightweight EAP

EAP-TLS - EAP -Transport Layer Security

EAP-TTLS - Tunnelled TLS

PEAP - Protected EAP

WEP - Wireless Encryption Protocol

WPA - Wireless Protected Access

IEEE 802.11i

Disaster area for wireless access

Wireless Security

W.Buchanan (31)

Uni

t 7: W

irele

ss

WEP Wired Equivalent PrivacyAka Weak Encryption Protocol

Access Control

W.Buchanan (32)

Uni

t 7: W

irele

ss

Generating the WEP key

WEP encryption key reduces eavesdropping

It stops unauthorized access to a Wireless Access Point (alongwith the SSID, of course)

40-bitKeys(24 bitsfor IV)

104-bitKeys(24 bitsfor IV)

napier01

Generate key

No standard exists todefine how the WEPkey is created

W.Buchanan (33)

Uni

t 7: W

irele

ss

Same key is used for all nodes. Thus an eavesdropper can eventually gain the key

Initialization Vector Encryption Key

24 bits 40 bits

This key is used for encryptionof all the data in the domain

W.Buchanan (34)

Uni

t 7: W

irele

ss

WEP uses a stream cipher based on the RC4 algorithm.

- Expands a short key into an infinite pseudo-random key.

ReceiverSender Same shared key is used

Short-keyShort-key

Infinite pseudo-random keyInfinite pseudo-random key

10100101000101010101. . .

01111010100101000101. . .

1101111110000001000. . .

X-OR

Short-keyShort-key

1101111110000001000. . .

01111010100101000101. . .

Infinite pseudo-random keyInfinite pseudo-random key

X-OR

10100101000101010101. . .

Data stream:

W.Buchanan (35)

Uni

t 7: W

irele

ss

EavesdropperEavesdropper

Short-keyShort-key

Infinite pseudo-random keyInfinite pseudo-random key

10100101000101010101. . .

‘A’ ‘B’

100000010000101010. . .

X-OR10100101000101010101. . .

‘C’ ‘D’

1101111110000001000. . .

X-OR

Eavesdroppercan detect the keyif it can read to streamsencoded with the samekey

WEP - Possible Problem? Statistical Analysis

W.Buchanan (36)

Uni

t 7: W

irele

ss

Short-keyShort-key

Infinite pseudo-random keyInfinite pseudo-random key

10100101000101010101. . .

‘A’ ‘B’

1101111110000001000. . .

X-OR

Short-keyShort-key

1101111111000001000. .

01111010100101000101. . .

Infinite pseudo-random keyInfinite pseudo-random key

X-OR

‘A’ ‘C’

Man-in-the-middleMan-in-

the-middle1101111111000001000. . .

Man-in-the-middle can flip a few bits and change the text. Letters can thus bechanged.

WEP - Possible Problem? Man-in-the-Middle

W.Buchanan (37)

Uni

t 7: W

irele

ss

WEP guards against these attacks with:

An Initialization Vector (IV). This is a secret key which varies the key for every data packet.An Integrity Checker (IC). This is a 32-bit CRC (Cyclic Redundancy Check). If bits are flipped, it will not give the same CRC value. Thus an error is caused.

Unfortunately both methods have not been implemented properly!!! Which leads to lots of problems.

IV and IC

W.Buchanan (38)

Uni

t 7: W

irele

ss

01010101 10101010 01010101 0101010111010101 10101010 01010101 0101011101010101 10111010 01010101 01110111

01010101 10101110 01010101 0101010111010101 10101110 01010101 0101011101010101 10111010 01010101 01110111

Bits are flippedover consecutivebit positions, so thatthe overall CRCstays the same.

Weakness of the Integrity Checker

W.Buchanan (39)

Uni

t 7: W

irele

ss

The IV is a 24-bit value, which is sent as cleartext.

There can only be 224 vectors (16,777,216)

If we use 1500 byte packets, the time to send each packet is 1500×8/11e6 = 1.1ms

Thus, if the device is continually sending thesame vector will repeat after:

1.1ms × 16,777,216 = 18,302.4 seconds

which is 5 hours The attacker thentakes the two cipertextswhich have been encryptedwith the same key, and performsa statistical analysis on it.

W.Buchanan (40)

Uni

t 7: W

irele

ss

IV=“Dah&*43+=f” Cipertext1

Passive Attack to Decrypt Traffic

Eavesdropper listensfor at least five hoursand waits for a recurrenceof the IV

IV=“Dah&*43+=f” Cipertext2

IV=“Dah&*43+=g” Cipertext

Cipertext1X-OR

16,777,214 IV’s Cipertext2

Some network cards actually initial at zero, and thenincrement by 1 each time (in fact the standard does noteven specify that the IV should change, at all.

W.Buchanan (41)

Uni

t 7: W

irele

ss

Plaintext

Corresponding cipertext

If eavesdropper knows part of the plaintext for a corresponding cipertextit is possible to build a correctly encryptedcipertext

Encrypted text CRC-32

By performing bit flips it is possibleto change the characters in the plain-textso that the CRC-32 stays the same.

Modified Plaintext

Active Attack to Inject Traffic

W.Buchanan (42)

Uni

t 7: W

irele

ss

Known IP/TCP headers

Corresponding cipertext

Active Attack from Both Ends

The eavesdropper can expand the methodso that they can examine for know IP and TCPheaders.

By performing bit flips it is possibleto change the characters in the plain-textso that the CRC-32 stays the same.

Modified IP/TCP header

Message

Cipertext

Modified IP/TCP header CRC-32Message

By flipping bits on the IP address, the eavesdropper can send all data packets to their machine.

W.Buchanan (43)

Uni

t 7: W

irele

ss

Plaintext Cipertext

IV=0IV=1IV=2

Hello How %4£$”9h-=+

Table-based

IV= 16,777,214

IV=16,777,215

76504fgh==5%6$”79h-

The eavesdropper can now decrypt all the datapackets with the IV ofzero. Over time others can be learnt.

Avbdc=+34d%£$”9h-4=+

Eavesdropper stores a table of known keys foreach IV (15GB)

W.Buchanan (44)

Uni

t 7: W

irele

ss

Only with this WEPalso allows for authentication using a secret key (sharedkey) or an opensystem.

W.Buchanan (45)

Uni

t 7: W

irele

ss

Private-key

Request forauthentication

Challenge textsent to client

Opensystem

Any node canjoin and there isno encryption or authentication

Encryptedtext

If correctlyencryptedthe device can connect

W.Buchanan (46)

Uni

t 7: W

irele

ss

EAPEfficient Application Protocols

Access Control

W.Buchanan (47)

Uni

t 7: W

irele

ss

EAP provides centralized authentication and dynamic key distribution.

It has been developed by the IEEE 802.11i Task Group as an end-to-end framework and uses 802.1X and EAP.

This is:

- Authentication. This is of both the client and the authentication server (suchas a RADIUS server).- Encryption keys. These are dynamically created after authentication. They are not common to the whole network.- Centralized policy control. A session time-out generates a reauthenticationand the generation of new encryption keys.

A wireless client cannot gain access to the network, unless it has been authenticated by the access point or a RADIUS server, and has encryption keys.

EAP - Efficient Application Protocols

W.Buchanan (48)

Uni

t 7: W

irele

ss

There are many versions of EAP, including:

• LEAP - Lightweight EAP• EAP-TLS - EAP-Transport Layer Security • PEAP - Protected EAP (PEAP)• EAP-TTLS - EAP-Tunnelled TLS • EAP-SIM - EAP-Subscriber Identity Module

W.Buchanan (49)

Uni

t 7: W

irele

ss

CorporatenetworkCorporatenetwork

Device cannotaccess networkuntil it has beenauthenticated andhas encryption keys

RADIUSserver

Userdatabase

EAPs can either be in the access point or from a RADIUS server

EAPs

W.Buchanan (50)

Uni

t 7: W

irele

ss

1. Client associates with the access point.2. Client provides authentication details.3. RADIUS server authenticates the user.4. User authenticates the RADIUS server.5. Client and RADIUS server derive unicast WEP key.6. RADIUS server gives broadcast WEP key to access point.7. Access point sends broadcast WEP key to client using unicast WEP key.

CorporatenetworkCorporatenetwork

RADIUSserver

Userdatabase

EAPs

W.Buchanan (51)

Uni

t 7: W

irele

ss

CorporatenetworkCorporatenetwork

Client details:

User ID and password.

Or

User ID and digital certificate

Or

On-time passwords

RADIUSserver

Userdatabase

EAPs

W.Buchanan (52)

Uni

t 7: W

irele

ss

CorporatenetworkCorporatenetwork

User Authentication: User ID and digital certificateKey size: 128 bitsEncryption: RC4Device Authentication: CertificateOpen Standard: YesUser differentiation: GroupCertificate: RADIUS server/WLAN client

RADIUSserver/certificateserverUser

database

EAP-TLS

W.Buchanan (53)

Uni

t 7: W

irele

ss

LEAPs

CorporatenetworkCorporatenetwork

User Authentication: User ID and passwordKey size: 128 bitsEncryption: RC4Device Authentication: Not SupportedOpen Standard: No (Cisco-derived)User differentiation: GroupCertificate: None

LEAPs is open toattack from a dictionary attack.Use strong passwords!!!

RADIUSserver

Userdatabase

W.Buchanan (54)

Uni

t 7: W

irele

ss

CorporatenetworkCorporatenetwork

User Authentication: User ID and password or OTP (one-time password)Key size: 128 bitsEncryption: RC4Device Authentication: Not supportedOpen Standard: YesUser differentiation: GroupCertificate: Yes

RADIUSserver

Userdatabase

EAP - PEAPs

W.Buchanan (55)

Uni

t 7: W

irele

ss

User 801.11x to focusauthentication of the connectingdevice.

PEAPs

W.Buchanan (56)

Uni

t 7: W

irele

ss

Along with EAPs, the new enhancements for WLAN are:

TKIP (Temporal Key Integrity Protocol) which are enhancements to RC4-based WEP. The IV has been increased to 48 bits (rather that 24 bits), and the Integrety Checker has been improved.AES, which is a stronger alternative to RC4.

WPA (Wi-fi

ProtectedAccess)

WPA (Wi-fi

ProtectedAccess)

IEEE 802.11i

IEEE 802.11x(Authentication of both client and access point)

W.Buchanan (57)

Uni

t 7: W

irele

ss

Good Design Principles

Access Control

W.Buchanan (58)

Uni

t 7: W

irele

ss

Some Design Tips

10. Layer 2/3 switch 5. RADIUS or TACACS+

Server for centralizedauthentication

F

2. Client supportsEAPs.

4. DCHP forall IP addresses

SNMP

3. Encryptionenabled

9. Management trafficisolated

6. PKI server which providesdigital certificatesfor users andservers.

8. No physicalaccess to access point

7. SNMP community stronghave strong names

1. No ad-hocnetworks 8. Secure protocols, such as SSH using instead

of Telnet (as plaintext passwords can be viewed withTelnet)

W.Buchanan (59)

Uni

t 7: W

irele

ss