CSCE 715: Network Systems Security

CSCE 715:Network Systems Security

Chin-Tser [email protected]

University of South Carolina

02/18/2009 2

Network Security Designs After discussion of cryptographic tools, we

turn to look at various network security designs at different layers in protocol stack

Link layer – secure address resolution Network layer – IPsec, hop integrity Transport layer – SSL/TLS Application layer – Kerberos, X.509

certificate, firewall design

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Ethernet Most widely used LAN technology Low cost and high flexibility Versions of different speed:

10Mbps, 100Mbps, Gigabit Use globally unique media access

control (MAC) address (hardware address) for every interface card

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Use of Hardware Address Need an address to send a message

to receiver on same Ethernet IP address is not usable because the

data link does not recognize IP address

Use hardware address to identify receiver’s interface

Need to resolve receiver’s hardware address from receiver’s IP address

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Address Resolution Protocol ARP maps each IP address to corresponding

hardware address in subnetwork For computer i to get hardware address of computer

j, i broadcasts a rqst message with IP address of j to the subnetwork

Internet

i

j

r

defaultrouterswitch

rqst(ipa.j)

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Address Resolution If j sees a rqst message from i with its IP

address, j sends a rply message with its IP address and hardware address to i

Internet

i

j

r

defaultrouterswitch

rply(ipa.j,hda.j)

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Functions of ARP Three functions of ARP

Resolving IP addresses Supporting dynamic assignment of

addresses Detecting destination failures

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ARP Spoofing Attack To stop traffic from i to j, an adversary sends

to i a spoofed rply message with IP address of j and a non-existent hardware address

Internet

i

j

A

r

defaultrouterswitch

rply(ipa.j,hda.x)

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Another ARP Spoofing Attack To stop traffic from i to default router r,

an adversary sends to i a spoofed rply message with IP address of r and its own hardware address

Internet

i

j

A

r

defaultrouterswitch

rply(ipa.r,hda.A)

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Countering ARP Spoofing Attacks Proposed solutions include ARPWATCH

and static ARP caches ARPWATCH monitors transmission of rqst

and rply messages over Ethernet and check them against a database of (IP addr, hardware addr) pairings

Static ARP cache stores permanent (IP addr, hardware addr) pairings of trusted hosts to avoid sending rqst and rply messages over Ethernet

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Insufficiencies of Proposed Solutions ARPWATCH does not support

dynamic assignment of IP addresses

Static ARP caches does not support dynamic assignment of IP addresses and detection of destination failures

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Need for Secure Address Resolution When a computer receives a message

m, it needs to determine whether m was indeed sent by claimed source, or was inserted, modified, or replayed by an adversary

Use secure address resolution protocol between each computer and a secure address resolution server

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Architecture of Secure Address Resolution Protocol

Interface

hr[i]

hn[i]

Applications Transport Network

Interface

sr

sn

Applications Transport Network

invite-accept protocol Subnetwork Subnetwork

Ethernet

write arrays ipa, hda, valid

h[i] s

request-reply protocol

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Adversary Adversary can perform three types

of actions to disrupt communication between server s and any computer h[i] on the Ethernet Message loss Message modification Message replay

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Secure Address Resolution Protocol Use three mechanisms to counter

adversarial actions timeouts to counter message loss shared secrets to counter message

modification nonces to counter message replay

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Invite-Accept Protocol Periodically, server s sends out an invt

message to every computer on Ethernet Every up computer is required to send

back an acpt message including its IP address and hardware address

s updates its address database according to received acpt messages

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Invite-Accept Protocols h[0..n-1]: invt(nc, md)

where md=MD(nc;scr[0])||MD(nc;scr[1])||…||MD(nc;scr[n-1])

h[i] s: acpt(nc, ipa[i], hda[i], d)where d=MD(nc;ipa[i];hda[i];scr[i])

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Request-Reply Protocol When a computer needs to resolve a

destination’s hardware address, it sends a rqst message to server s

If destination’s hardware address is still valid, s sends back a rply message with address information

If destination’s hardware address is not valid anymore, s sends back a rply message with no address information

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Request-Reply Protocolh[i] s: rqst(nc, ipa[j], d)

where d=MD(nc;ipa[j];scr[i])

If found,s h[i]: rply(nc, ipa[j], hda[j], d)

where d=MD(nc;ipa[j];hda[j];scr[i])If not found,s h[i]: rply(nc, ipa[j], 0, d)

where d=MD(nc;ipa[j];0;scr[i])

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Extensions Four extensions of secure address

resolution protocol Insecure address resolution Backup server System diagnosis Address resolution across multiple

Ethernets

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Next Class IPsec

Authentication Header (AH) Encapsulation Security Payload (ESP) key management

Read Chapter 16