6 th edition Jim Kurose Keith Ross AddisonWesley March 2012 A note on the use of these ppt slides We re making these slides freely available to all faculty students readers They ID: 656231
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Slide1
Chapter 8Security
Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith RossAddison-WesleyMarch 2012
A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:
If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!)If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.Thanks and enjoy! JFK/KWR All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights ReservedSlide2
Trimmed/Mods For Use in WSU CEG4900/6900Android Internals and Securitywww.cs.wright.edu/~pmateti/Courses/4900Network SecuritySlide3
Network Security
Chapter 8: Network SecurityChapter goals: understand principles of network security: cryptography and its many uses beyond “confidentiality”authenticationmessage integritysecurity in practice:firewalls and intrusion detection systemssecurity in application, transport, network, link layersSlide4
Network Security
Chapter 8 roadmap8.1 What is network security?8.2 Principles of cryptography8.3 Message integrity, authentication8.4 Securing e-mail8.5 Securing TCP connections: SSL8.6 Network layer security: IPsec8.7 Securing wireless LANs8.8 Operational security: firewalls and IDSSlide5
Network Security
What is network security?confidentiality: only sender, intended receiver should “understand” message contentssender encrypts messagereceiver decrypts messageauthentication: sender, receiver want to confirm identity of each other message integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detectionaccess and availability: services must be accessible and available to usersSlide6
Network Security
Friends and enemies: Alice, Bob, Trudywell-known in network security worldBob, Alice (lovers!) want to communicate “securely”Trudy (intruder) may intercept, delete, add messages
securesenderssecurereceiver
channeldata, control messages
data
data
Alice
Bob
TrudySlide7
Network Security
Who might Bob, Alice be?… well, real-life Bobs and Alices!Web browser/server for electronic transactions (e.g., on-line purchases)on-line banking client/serverDNS serversrouters exchanging routing table updatesother examples?Slide8
Network Security
There are bad guys (and girls) out there!Q: What can a “bad guy” do?A: A lot! See section 1.6eavesdrop: intercept messagesactively insert messages into connectionimpersonation:
can fake (spoof) source address in packet (or any field in packet)hijacking: “take over” ongoing connection by removing sender or receiver, inserting himself in placedenial of service: prevent service from being used by others (e.g., by overloading resources)Slide9
Network Security
The language of cryptographym plaintext messageKA(m) ciphertext, encrypted with key KAm = KB(KA(m))
plaintextplaintextciphertext
KAencryptionalgorithm
decryption algorithm
Alice
’
s
encryption
key
Bob
’
s
decryption
key
K
BSlide10
Network Security
Breaking an encryption schemecipher-text only attack: Trudy has ciphertext she can analyzetwo approaches:brute force: search through all keys statistical analysisknown-plaintext attack: Trudy has plaintext corresponding to ciphertexte.g., in monoalphabetic cipher, Trudy determines pairings for a,l,i,c,e,b,o,chosen-plaintext attack: Trudy can get ciphertext for chosen plaintextSlide11
Network Security
Symmetric key cryptographysymmetric key crypto: Bob and Alice share same (symmetric) key: Ke.g., key is knowing substitution pattern in mono alphabetic substitution cipherQ: how do Bob and Alice agree on key value?plaintext
ciphertextKS
encryptionalgorithmdecryption algorithm
S
K
S
plaintext
message, m
K (m)
S
m = K
S
(K
S
(m))Slide12
Network Security
Simple encryption schemesubstitution cipher: substituting one thing for anothermonoalphabetic cipher: substitute one letter for anotherplaintext: abcdefghijklmnopqrstuvwxyzciphertext: mnbvcxzasdfghjklpoiuytrewq
Plaintext: bob. i love you. aliceciphertext: nkn. s gktc wky. mgsbce.g.:
Encryption key: mapping from set of 26 letters to set of 26 lettersSlide13
Network Security
A more sophisticated encryption approachn substitution ciphers, M1,M2,…,Mncycling pattern:e.g., n=4: M1,M3,M4,M3,M2; M1,M3
,M4,M3,M2; ..for each new plaintext symbol, use subsequent subsitution pattern in cyclic patterndog: d from M1, o from M3, g from M4 Encryption key: n substitution ciphers, and cyclic patternkey need not be just n-bit patternSlide14
Network Security
Symmetric key crypto: DESDES: Data Encryption StandardUS encryption standard [NIST 1993]56-bit symmetric key, 64-bit plaintext inputblock cipher with cipher block chaininghow secure is DES?DES Challenge: 56-bit-key-encrypted phrase decrypted (brute force) in less than a dayno known good analytic attackmaking DES more secure:3DES: encrypt 3 times with 3 different keysSlide15
Network Security
AES: Advanced Encryption Standardsymmetric-key NIST standard, replacied DES (Nov 2001)processes data in 128 bit blocks128, 192, or 256 bit keysbrute force decryption (try each key) taking 1 sec on DES, takes 149 trillion years for AESSlide16
Network Security
Public Key Cryptographysymmetric key cryptorequires sender, receiver know shared secret keyQ: how to agree on key in first place (particularly if never “met”)?
public key cryptoradically different approach [Diffie-Hellman76, RSA78]sender, receiver do not share secret key
public encryption key known to allprivate decryption key known only to receiverSlide17
Network Security
Public key cryptographyplaintextmessage, mciphertext
encryptionalgorithmdecryption algorithm
Bob’s public key
plaintextmessageK (m)
B
+
K
B
+
Bob
’
s
private
key
K
B
-
m = K
(
K (m)
)
B
+
B
-Slide18
Network Security
RSA: Creating public/private key pair1. choose two large prime numbers p, q. (e.g., 1024 bits each)2. compute n = pq, z = (p-1)(q-1)
3. choose e (with e<n) that has no common factors with z (e, z are “relatively prime”).
4. choose d such that ed-1 is exactly divisible by z. (in other words: ed mod z = 1 ).5. public key is (n,e). private key is (n,d).
K B
+
K
B
-Slide19
Network Security
RSA: encryption, decryption0. given (n,e) and (n,d) as computed above1. to encrypt message m (<n), compute
c = m mod ne
2. to decrypt received bit pattern, c, computem = c mod ndm = (m
mod n)e
mod n
d
magic
happens!
cSlide20
Network Security
RSA: another important propertyThe following property will be very useful later:K
(K (m)) = m BB
-+K (K (m)) BB
+-
=
use public key first, followed by private key
use private key first, followed by public key
result is the same!
Slide21
Network Security
follows directly from modular arithmetic:(me mod n)d mod n = med mod n = mde mod n = (md mod n)e mod n
K (K (m)) = m B
B-+K (K (m)) B
B
+
-
=
Why
?Slide22
Network Security
Why is RSA secure?suppose you know Bob’s public key (n,e). How hard is it to determine d?essentially need to find factors of n without knowing the two factors p and q fact: factoring a big number is hardSlide23
Network Security
RSA in practice: session keysexponentiation in RSA is computationally intensiveDES is at least 100 times faster than RSAuse public key cryto to establish secure connection, then establish second key – symmetric session key – for encrypting datasession key, KSBob and Alice use RSA to exchange a symmetric key KSonce both have KS, they use symmetric key cryptographySlide24
Network Security
Authentication: ap5.0ap4.0 requires shared symmetric key can we authenticate using public key techniques?ap5.0: use nonce, public key cryptography
“I am Alice”
R
Bob computes
K (R)
A
-
“
send me your public key
”
K
A
+
(K (R)) = R
A
-
K
A
+
and knows only Alice could have the private key, that encrypted R such that
(K (R)) = R
A
-
K
A
+Slide25
Network Security
ap5.0: security holeman (or woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice)
I am Alice
I am Alice
R
T
K (R)
-
Send me your public key
T
K
+
A
K (R)
-
Send me your public key
A
K
+
T
K (m)
+
T
m = K (K (m))
+
T
-
Trudy gets
sends m to Alice encrypted with Alice
’
s public key
A
K (m)
+
A
m = K (K (m))
+
A
-
RSlide26
Network Security
d
ifficult to detect:
Bob receives everything that Alice sends, and vice versa. (e.g., so Bob, Alice can meet one week later and recall conversation!)problem is that Trudy receives all messages as well! ap5.0: security holeman (or woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice)Slide27
Network Security
Digital signatures cryptographic technique analogous to hand-written signatures:sender (Bob) digitally signs document, establishing he is document owner/creator. verifiable, nonforgeable: recipient (Alice) can prove to someone that Bob, and no one else (including Alice), must have signed document Slide28
Network Security
simple digital signature for message m:Bob signs m by encrypting with his private key KB, creating “
signed” message, KB(m)
-
-
Dear Alice
Oh, how I have missed you. I think of you all the time! …(blah blah blah)
Bob
Bob
’
s message, m
Public key
encryption
algorithm
Bob
’
s private
key
K
B
-
Bob
’
s message, m, signed (encrypted) with his private key
m,K
B
-
(m)
Digital signatures Slide29
Network Security
-
Alice thus verifies that:Bob signed mno one else signed mBob signed m and not m‘non-repudiation:
Alice can take m, and signature KB(m) to court and prove that Bob signed m
-Digital signatures
suppose Alice receives msg m, with signature: m, K
B(m)
Alice verifies m signed by Bob by applying Bob
’
s public key K
B
to K
B
(m) then checks K
B
(K
B
(m) ) = m.
If K
B
(K
B
(m) ) = m, whoever signed m must have used Bob
’
s private key.
-
-
-
+
+
+Slide30
Network Security
Message digestscomputationally expensive to public-key-encrypt long messages goal: fixed-length, easy- to-compute digital “fingerprint”apply hash function H to m, get fixed size message digest, H(m).Hash function properties:many-to-1produces fixed-size msg digest (fingerprint)given message digest x, computationally infeasible to find m such that x = H(m)
large
messagem
H: Hash
Function
H(m)Slide31
Network Security
message
m
H: Hash
function
H(m)
digital
signature
(encrypt)
Bob
’
s
private
key
K
B
-
+
Bob sends digitally signed message:
Alice verifies signature, integrity of digitally signed message:
K
B
(H(m))
-
encrypted
msg digest
K
B
(H(m))
-
encrypted
msg digest
message
m
H: Hash
function
H(m)
digital
signature
(decrypt)
H(m)
Bob
’
s
public
key
K
B
+
equal
?
Digital signature = signed message digestSlide32
Network Security
Hash function algorithmsMD5 hash function widely used (RFC 1321) computes 128-bit message digest in 4-step process. arbitrary 128-bit string x, appears difficult to construct msg m whose MD5 hash is equal to xSHA-1 is also usedUS standard [NIST, FIPS PUB 180-1]160-bit message digestSlide33
Network Security
Recall: ap5.0 security holeman (or woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice)
I am Alice
I am Alice
R
T
K (R)
-
Send me your public key
T
K
+
A
K (R)
-
Send me your public key
A
K
+
T
K (m)
+
T
m = K (K (m))
+
T
-
Trudy gets
sends m to Alice encrypted with Alice
’
s public key
A
K (m)
+
A
m = K (K (m))
+
A
-
RSlide34
Network Security
Public-key certificationmotivation: Trudy plays pizza prank on BobTrudy creates e-mail order: Dear Pizza Store, Please deliver to me four pepperoni pizzas. Thank you, BobTrudy signs order with her private keyTrudy sends order to Pizza StoreTrudy sends to Pizza Store her public key, but says it’s Bob’s public keyPizza Store verifies signature; then delivers four pepperoni pizzas to BobBob doesn’t even like pepperoniSlide35
Network Security
Certification authoritiescertification authority (CA): binds public key to particular entity, E.E (person, router) registers its public key with CA.E provides “proof of identity” to CA. CA creates certificate binding E to its public key.certificate containing E’s public key digitally signed by CA – CA says “this is E’s public key”
Bob’s publickey
K B+Bob’s identifying information
digital
signature
(encrypt)
CA
private
key
K
CA
-
K
B
+
certificate for Bob
’
s public key, signed by CASlide36
Network Security
when Alice wants Bob’s public key:gets Bob’s certificate (Bob or elsewhere).apply CA’s public key to Bob’s certificate, get Bob’s public key
Bob’s publickey K
B+
digital
signature(decrypt)
CA
public
key
K
CA
+
K
B
+
Certification authoritiesSlide37
Network Security
Secure e-mail Alice generates random symmetric private key, KS encrypts message with KS (for efficiency) also encrypts KS with Bob’
s public key sends both KS(m) and KB(KS) to Bob Alice wants to send confidential e-mail, m, to Bob.
K
S
( )
.
K
B
( )
.
+
+
-
K
S
(m )
K
B
(K
S
)
+
m
K
S
K
S
K
B
+
Internet
K
S
( )
.
K
B
( )
.
-
K
B
-
K
S
m
K
S
(m )
K
B
(K
S
)
+Slide38
Network Security
Secure e-mail Bob: uses his private key to decrypt and recover KS uses KS to decrypt KS(m) to recover mBob
wants to read confidential e-mail, m, from Alice.
K
S( ).
K
B
( )
.
+
+
-
K
S
(m )
K
B
(K
S
)
+
m
K
S
K
S
K
B
+
Internet
K
S
( )
.
K
B
( )
.
-
K
B
-
K
S
m
K
S
(m )
K
B
(K
S
)
+Slide39
Network Security
Secure e-mail (continued) Alice wants to provide sender authentication message integrity Alice digitally signs message sends both message (in the clear) and digital signature
H( )
.
K
A
( )
.
-
+
-
H(m )
K
A
(H(m))
-
m
K
A
-
Internet
m
K
A
( )
.
+
K
A
+
K
A
(H(m))
-
m
H( )
.
H(m )
compareSlide40
Network Security
Secure e-mail (continued) Alice wants to provide secrecy, sender authentication, message integrity.Alice uses three keys: her private key, Bob’s public key, newly created symmetric key
H( )
.KA( ).-
+
K
A(H(m))
-
m
K
A
-
m
K
S
( )
.
K
B
( )
.
+
+
K
B
(K
S
)
+
K
S
K
B
+
Internet
K
SSlide41
Network Security
SSL: Secure Sockets Layersupported by almost all web browsers/ servershttpsbillions $/year over SSLvariation -TLS: transport layer security, RFC 2246providesconfidentialityintegrityAuthentication
OpenSSL open sourceWeb e-commerce transactions encryption (especially credit-card numbers)Web-server authenticationoptional client authenticationminimum hassle in doing business with new merchantsecure socket interfaceSlide42
Network Security
SSL and TCP/IPApplicationTCP
IPnormal application
ApplicationSSLTCPIP
application with SSL SSL provides application programming interface (API) to applications
SSL libraries/classes readily
available for PLsSlide43
OpenSSL in June 2014“The OpenSSL Project is a collaborative effort to develop a robust, commercial-grade, full-featured, and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) protocols as well as a full-strength general purpose cryptography library. The project is managed by a worldwide community of volunteers that use the Internet to communicate, plan, and develop the OpenSSL toolkit and its related documentation.” http://www.openssl.org/ “Heartbleed” bug June 9More bugs discovered June 17
OpenSSL is maintained by a tiny team (5?)Coding bugs. Not design of SSL.Network Security/MatetiSlide44
Network Security
What is network-layer confidentiality ?between two network entities:sending entity encrypts datagram payload, payload could be:TCP or UDP segment, ICMP message, OSPF message ….all data sent from one entity to other would be hidden:web pages, e-mail, P2P file transfers, TCP SYN packets …“blanket coverage”Slide45
Network Security
Virtual Private Networks (VPNs)motivation:institutions often want private networks for security. costly: separate routers, links, DNS infrastructure.VPN: institution’s inter-office traffic is sent over public Internet instead encrypted before entering public Internetlogically separate from other trafficSlide46
Network Security
IP
headerIPsecheader
SecurepayloadIPheaderIPsecheaderSecurepayload
IPheaderIPsecheader
Secure
payload
IP
header
payload
IP
header
payload
headquarters
branch office
salesperson
in hotel
laptop
w/ IPsec
router w/
IPv4 and IPsec
router w/
IPv4 and IPsec
public
Internet
Virtual Private Networks (VPNs)Slide47
Network Security
IPsec summaryIKE message exchange for algorithms, secret keys, SPI numberseither AH or ESP protocol (or both)AH provides integrity, source authenticationESP protocol (with AH) additionally provides encryptionIPsec peers can be two end systems, two routers/firewalls, or a router/firewall and an end systemSlide48
Network Security
WEP (Wireless Equiv Privacy)symmetric key cryptoconfidentialityend host authorizationdata integrityself-synchronizing: each packet separately encryptedgiven encrypted packet and key, can decrypt; can continue to decrypt packets when preceding packet was lostEfficientimplementable in hardware or softwareSlide49
Network Security
Stream cipher and packet independencerecall design goal: each packet separately encryptedif for frame n+1, use keystream from where we left off for frame n, then each frame is not separately encryptedneed to know where we left off for packet nWEP approach: initialize keystream with key + new IV for each packet:keystream
generatorKey+IVpacketkeystreampacketSlide50
Network Security
WEP encryption (1)sender calculates Integrity Check Value (ICV) over datafour-byte hash/CRC for data integrityeach side has 104-bit shared keysender creates 24-bit initialization vector (IV), appends to key: gives 128-bit keysender also appends keyID (in 8-bit field)128-bit key inputted into pseudo random number generator to get keystreamdata in frame + ICV is encrypted with RC4:B\bytes of keystream are XORed with bytes of data & ICVIV & keyID are appended to encrypted data to create payloadpayload inserted into 802.11 frame
encrypteddataICV
IVMAC payloadKeyIDSlide51
Network Security
WEP encryption (2)new IV for each frame Slide52
Network Security
WEP decryption overview receiver extracts IVinputs IV, shared secret key into pseudo random generator, gets keystreamXORs keystream with encrypted data to decrypt data + ICVverifies integrity of data with ICVnote: message integrity approach used here is different from MAC (message authentication code) and signatures (using PKI).encrypted
dataICVIV
MAC payloadKeyIDSlide53
Network Security
End-point authentication w/ nonceNonce: number (R) used only once –in-a-lifetimeHow to prove Alice “live
”: Bob sends Alice nonce, R. Alicemust return R, encrypted with shared secret key
“I am Alice”RK (R)A-BAlice is live, and only Alice knows key to encrypt nonce, so it must be Alice!Slide54
Network Security
WEP authenticationauthentication request
nonce (128 bytes)nonce encrypted shared keysuccess if decrypted value equals nonce
Notes:not all APs do it, even if WEP is being usedAP indicates if authentication is necessary in beacon framedone before associationSlide55
Network Security
Breaking 802.11 WEP encryptionsecurity hole: 24-bit IV, one IV per frame, -> IV’s eventually reusedIV transmitted in plaintext -> IV reuse detectedattack:Trudy causes Alice to encrypt known plaintext d1 d2 d3 d4 … Trudy sees: ci = d
i XOR kiIVTrudy knows ci di, so can compute kiIVTrudy knows encrypting key sequence k1IV k2IV k3IV …Next time IV is used, Trudy can decrypt!Slide56
Network Security
802.11i: improved securitynumerous (stronger) forms of encryption possibleprovides key distributionuses authentication server separate from access pointSlide57
Network Security
AP:
access point
AS:
Authentication serverwirednetwork
STA:
client station
1 Discovery of
security capabilities
STA and AS mutually authenticate, together
generate Master Key (MK)
. AP serves as
“
pass through
”
2
3
3
STA derives
Pairwise Master
Key (PMK)
AS derives
same PMK,
sends to AP
4
STA, AP use PMK to derive
Temporal Key (TK) used for message
encryption, integrity
802.11i: four phases of operationSlide58
Network Security
EAP TLS
EAP EAP over LAN (EAPoL)
IEEE 802.11 RADIUSUDP/IPEAP: extensible authentication protocolEAP: end-end client (mobile) to authentication server protocolEAP sent over separate “links”mobile-to-AP (EAP over LAN)AP to authentication server (RADIUS over UDP)
wired
networkSlide59
Network Security
Firewallsisolates organization’s internal net from larger Internet, allowing some packets to pass, blocking others
firewall
administered
network
public
Inter
net
firewall
trusted
“
good guys
”
untrusted
“
bad guys
”
Slide60
Network Security
Firewalls: whyprevent denial of service attacks:SYN flooding: attacker establishes many bogus TCP connections, no resources left for “real” connectionsprevent illegal modification/access of internal data
e.g., attacker replaces CIA’s homepage with something elseallow only authorized access to inside network set of authenticated users/hoststhree types of firewalls:stateless packet filtersstateful packet filters
application gatewaysSlide61
Network Security
Stateless packet filtering
internal network connected to Internet via
router firewall
router
filters packet-by-packet,
decision to forward/drop packet based on:
source IP address, destination IP address
TCP/UDP source and destination port numbers
ICMP message type
TCP SYN and ACK bits
Should arriving packet be allowed in? Departing packet let out?Slide62
Stateless packet filtering: example
Network Securityexample 1: block incoming and outgoing datagrams with IP protocol field = 17 and with either source or dest port = 23result: all incoming, outgoing UDP flows and telnet connections are blockedexample 2: block inbound TCP segments with ACK=0.result: prevents external clients from making TCP connections with internal clients, but allows internal clients to connect to outside.Slide63
Network Security
Policy
Firewall SettingNo outside Web access.
Drop all outgoing packets to any IP address, port 80No incoming TCP connections, except those for institution
’s public Web server only.
Drop all incoming TCP SYN packets to any IP except 130.207.244.203, port 80
Prevent Web-radios from eating up the available bandwidth.
Drop all incoming UDP packets - except DNS and router broadcasts.
Prevent your network from being used for a smurf DoS attack.
Drop all ICMP packets going to a
“
broadcast
”
address (e.g. 130.207.255.255).
Prevent your network from being tracerouted
Drop all outgoing ICMP TTL expired traffic
Stateless packet filtering
: more examplesSlide64
Network Security
action
sourceaddressdest
addressprotocolsource
port
dest
port
flag
bit
allow
222.22/16
outside of
222.22/16
TCP
> 1023
80
any
allow
outside of
222.22/16
222.22/16
TCP
80
> 1023
ACK
allow
222.22/16
outside of
222.22/16
UDP
> 1023
53
---
allow
outside of
222.22/16
222.22/16
UDP
53
> 1023
----
deny
all
all
all
all
all
all
Access Control Lists
ACL:
table of rules, applied top to bottom to incoming packets: (action, condition) pairsSlide65
Network Security
Stateful packet filteringstateless packet filter: heavy handed tooladmits packets that “make no sense,” e.g., dest port = 80, ACK bit set, even though no TCP connection established:
actionsourceaddress
destaddressprotocol
source
port
dest
port
flag
bit
allow
outside of
222.22/16
222.22/16
TCP
80
> 1023
ACK
stateful packet filter:
track status of every TCP connection
track connection setup (SYN), teardown (FIN): determine whether incoming, outgoing packets
“
makes sense
”
timeout inactive connections at firewall: no longer admit packetsSlide66
Network Security
action
sourceaddress
destaddressproto
sourceport
dest
port
flag
bit
check conxion
allow
222.22/16
outside of
222.22/16
TCP
> 1023
80
any
allow
outside of
222.22/16
222.22/16
TCP
80
> 1023
ACK
x
allow
222.22/16
outside of
222.22/16
UDP
> 1023
53
---
allow
outside of
222.22/16
222.22/16
UDP
53
> 1023
----
x
deny
all
all
all
all
all
all
Stateful packet filtering
ACL augmented to indicate need to check connection state table before admitting packetSlide67
Network Security
Application gatewaysfilters packets on application data as well as on IP/TCP/UDP fields.example: allow select internal users to telnet outside.
host-to-gateway
telnet session
gateway-to-remote
host telnet session
application
gateway
router and filter
1.
require all telnet users to telnet through gateway.
2.
for authorized users, gateway sets up telnet connection to dest host. Gateway relays data between 2 connections
3.
router filter blocks all telnet connections not originating from gateway.Slide68
Network Security
Application gatewaysfilter packets on application data as well as on IP/TCP/UDP fields.example: allow select internal users to telnet outside1. require all telnet users to telnet through gateway.2. for authorized users, gateway sets up telnet connection to dest host. Gateway relays data between 2 connections
3. router filter blocks all telnet connections not originating from gateway.applicationgateway
host-to-gateway
telnet session
router and filter
gateway-to-remote
host telnet sessionSlide69
Network Security
Limitations of firewalls, gatewaysIP spoofing: router can’t know if data “really” comes from claimed sourceif multiple app’s. need special treatment, each has own app. gatewayclient software must know how to contact gateway.e.g., must set IP address of proxy in Web browserfilters often use all or nothing policy for UDP
tradeoff: degree of communication with outside world, level of securitymany highly protected sites still suffer from attacksSlide70
Network Security
Intrusion detection systemspacket filtering:operates on TCP/IP headers onlyno correlation check among sessions IDS: intrusion detection systemdeep packet inspection: look at packet contents (e.g., check character strings in packet against database of known virus, attack strings)examine correlation among multiple packetsport scanningnetwork mappingDoS attackSlide71
Network Security
Web
server
FTP
server
DNS
server
Internet
demilitarized
zone
firewall
IDS
sensors
Intrusion detection systems
multiple IDSs: different types of checking at different locations
internal
networkSlide72
WSU CEG 4900/6900 coverageARP PoisoningDNS cache poisoningTCP session terminationTCP session hijackingWPA2 Wi-fi Protected Access v2http://www.cs.wright.edu/~pmateti/Courses/4900 Network Security