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IPSec IS 511 8 -1 IPSec IS 511 8 -1

IPSEC v v TLS: transport layer IPSec: network layer Network Security 8 -2 IPSEC v v TLS: transport layer IPSec: network layer Network Security 8 -2

What is network-layer confidentiality ? between two network entities: v sending entity encrypts datagram What is network-layer confidentiality ? between two network entities: v sending entity encrypts datagram payload, payload could be: § TCP or UDP segment, ICMP message, OSPF message …. v all data sent from one entity to other would be hidden: § web pages, e-mail, P 2 P file transfers, TCP SYN packets … v “blanket coverage” Network Security 8 -3

Virtual Private Networks (VPNs) motivation: vinstitutions often want private networks for security. § costly: Virtual Private Networks (VPNs) motivation: vinstitutions often want private networks for security. § costly: separate routers, links, DNS infrastructure. v. VPN: institution’s inter-office traffic is sent over public Internet instead § encrypted before entering public Internet § logically separate from other traffic Network Security 8 -4

Virtual Private Networks (VPNs) IP header Secure payloa d IPsec heade r r router Virtual Private Networks (VPNs) IP header Secure payloa d IPsec heade r r router w/ IPv 4 and IPsec pa IP er ad he ylo a d router w/ IPv 4 and IPsec laptop w/ IPsec salesperson in hotel e cur Se load y pa IP heade IPsec header ec IPs der ea IP r h e ad he Secur e payloa d public Internet ad ylo I he P ad er pa headquarters branch office Network Security 8 -5

IPsec services v data integrity origin authentication replay attack prevention confidentiality v two protocols IPsec services v data integrity origin authentication replay attack prevention confidentiality v two protocols providing different service models: v v v § AH § ESP Network Security 8 -6

IPsec transport mode IPsec v v IPsec datagram emitted and received by end-system protects IPsec transport mode IPsec v v IPsec datagram emitted and received by end-system protects upper level protocols Network Security 8 -7

IPsec – tunneling mode IPsec v IPsec edge routers IPsecaware IPsec v IPsec hosts IPsec – tunneling mode IPsec v IPsec edge routers IPsecaware IPsec v IPsec hosts IPsec-aware Network Security 8 -8

Two IPsec protocols v Authentication Header (AH) protocol § provides source authentication & data Two IPsec protocols v Authentication Header (AH) protocol § provides source authentication & data integrity but not confidentiality v Encapsulation Security Protocol (ESP) § provides source authentication, data integrity, and confidentiality § more widely used than AH Network Security 8 -9

Four combinations are possible! Host mode with AH Host mode with ESP Tunnel mode Four combinations are possible! Host mode with AH Host mode with ESP Tunnel mode with AH Tunnel mode with ESP most common and most important Network Security 8 -10

Security associations (SAs) v before sending data, “security association (SA)” established from sending to Security associations (SAs) v before sending data, “security association (SA)” established from sending to receiving entity § SAs are simplex: for only one direction v ending, receiving entitles maintain state information about SA § recall: TCP endpoints also maintain state info § IP is connectionless; IPsec is connection-oriented! v how many SAs in VPN w/ headquarters, branch office, and n traveling salespeople? Network Security 8 -11

Example SA from R 1 to R 2 Internet headquarters 200. 168. 1. 100 Example SA from R 1 to R 2 Internet headquarters 200. 168. 1. 100 R 1 172. 16. 1/24 branch office 193. 68. 2. 23 security association R 2 172. 16. 2/24 R 1 stores for SA: v v v v 32 -bit SA identifier: Security Parameter Index (SPI) origin SA interface (200. 168. 1. 100) destination SA interface (193. 68. 2. 23) type of encryption used (e. g. , 3 DES with CBC) encryption key type of integrity check used (e. g. , HMAC with MD 5) authentication key Network Security 8 -12

Security Association Database (SAD) endpoint holds SA state in security association database (SAD), where Security Association Database (SAD) endpoint holds SA state in security association database (SAD), where it can locate them during processing. v with n salespersons, 2 + 2 n SAs in R 1’s SAD v when sending IPsec datagram, R 1 accesses SAD to determine how to process datagram. v when IPsec datagram arrives to R 2, R 2 examines SPI in IPsec datagram, indexes SAD with SPI, and processes datagram accordingly. v Network Security 8 -13

IPsec datagram focus for now on tunnel mode with ESP “enchilada” authenticated encrypted new IPsec datagram focus for now on tunnel mode with ESP “enchilada” authenticated encrypted new IP header ESP hdr SPI original IP hdr Seq # Original IP datagram payload padding ESP trl ESP auth pad next length header Network Security 8 -14

What happens? Internet headquarters 200. 168. 1. 100 R 1 branch office 193. 68. What happens? Internet headquarters 200. 168. 1. 100 R 1 branch office 193. 68. 2. 23 security association 172. 16. 1/24 R 2 172. 16. 2/24 “enchilada” authenticated encrypted new IP header ESP hdr SPI original IP hdr Seq # Original IP datagram payload padding ESP trl ESP auth pad next length header Network Security 8 -15

R 1: convert original datagram to IPsec datagram v v v appends to back R 1: convert original datagram to IPsec datagram v v v appends to back of original datagram (which includes original header fields!) an “ESP trailer” field. encrypts result using algorithm & key specified by SA. appends to front of this encrypted quantity the “ESP header, creating “enchilada”. creates authentication MAC over the whole enchilada, using algorithm and key specified in SA; appends MAC to back of enchilada, forming payload; creates brand new IP header, with all the classic IPv 4 header fields, which it appends before payload. Network Security 8 -16

Inside the enchilada: “enchilada” authenticated encrypted new IP header ESP hdr SPI v v Inside the enchilada: “enchilada” authenticated encrypted new IP header ESP hdr SPI v v original IP hdr Seq # Original IP datagram payload padding ESP trl ESP auth pad next length header ESP trailer: Padding for block ciphers ESP header: § SPI, so receiving entity knows what to do § Sequence number, to thwart replay attacks v MAC in ESP auth field is created with shared secret key Network Security 8 -17

IPsec sequence numbers v v for new SA, sender initializes seq. # to 0 IPsec sequence numbers v v for new SA, sender initializes seq. # to 0 each time datagram is sent on SA: § sender increments seq # counter § places value in seq # field v goal: § prevent attacker from sniffing and replaying a packet § receipt of duplicate, authenticated IP packets may disrupt service v method: § destination checks for duplicates § doesn’t keep track of all received packets; instead uses a window Network Security 8 -18

Security Policy Database (SPD) v v policy: For a given datagram, sending entity needs Security Policy Database (SPD) v v policy: For a given datagram, sending entity needs to know if it should use IPsec needs also to know which SA to use § may use: source and destination IP address; protocol number v v info in SPD indicates “what” to do with arriving datagram info in SAD indicates “how” to do it Network Security 8 -19

Summary: IPsec services v suppose Trudy sits somewhere between R 1 and R 2. Summary: IPsec services v suppose Trudy sits somewhere between R 1 and R 2. she doesn’t know the keys. § will Trudy be able to see original contents of datagram? How about source, dest IP address, transport protocol, application port? § flip bits without detection? § masquerade as R 1 using R 1’s IP address? § replay a datagram? Network Security 8 -20

IKE: Internet Key Exchange v previous examples: manual establishment of IPsec SAs in IPsec IKE: Internet Key Exchange v previous examples: manual establishment of IPsec SAs in IPsec endpoints: Example SA SPI: 12345 Source IP: 200. 168. 1. 100 Dest IP: 193. 68. 2. 23 Protocol: ESP Encryption algorithm: 3 DES-cbc HMAC algorithm: MD 5 Encryption key: 0 x 7 aeaca… HMAC key: 0 xc 0291 f… v v manual keying is impractical for VPN with 100 s of endpoints instead use IPsec IKE (Internet Key Exchange) Network Security 8 -21

IKE: PSK and PKI v authentication (prove who you are) with either § pre-shared IKE: PSK and PKI v authentication (prove who you are) with either § pre-shared secret (PSK) or § with PKI (pubic/private keys and certificates). v PSK: both sides start with secret (pre-shared key) § run IKE to authenticate each other and to generate IPsec SAs (one in each direction), including encryption, authentication keys v PKI: both sides start with public/private key pair, certificate § run IKE to authenticate each other, obtain IPsec SAs (one in each direction). § similar with handshake in SSL. Network Security 8 -22

IKE phases v IKE has two phases § phase 1: establish bi-directional IKE SA IKE phases v IKE has two phases § phase 1: establish bi-directional IKE SA • note: IKE SA different from IPsec SA • aka ISAKMP security association § phase 2: ISAKMP is used to securely negotiate IPsec pair of Sas v Phase 1 negotiates § § § Authentication method (for example, pre-shared key or RSA signature) Hash algorithm (for example, MD 5 or SHA 1) Encryption algorithm (for example, DES, 3 DES or AES) Diffie-Hellman group information (for example, group 1, group 2, group 5 or group 14) Life time and life size of the ISAKMP SA Network Security 8 -23

Phase 1 Network Security 8 -24 Phase 1 Network Security 8 -24

Phase 2 v v v Protocol (AH, ESP, or both AH and ESP) Authentication Phase 2 v v v Protocol (AH, ESP, or both AH and ESP) Authentication algorithm (for example, Hmac. Md 5 or Hmac-Sha) Encapsulation mode (tunnel or transport) Encryption algorithm (for example, DES, 3 DES or AES) Diffie-Hellman group information (for example, group 1, group 2, group 5 or group 14) Life time and life size of the IPSec SA Network Security 8 -25

Network Security 8 -26 Network Security 8 -26

IPsec summary v v v IKE message exchange for algorithms, secret keys, SPI numbers IPsec summary v v v IKE message exchange for algorithms, secret keys, SPI numbers either AH or ESP protocol (or both) § AH provides integrity, source authentication § ESP protocol (with AH) additionally provides encryption IPsec peers can be two end systems, two routers/firewalls, or a router/firewall and an end system Network Security 8 -27

Chapter 8 roadmap 8. 1 What is network security? 8. 2 Principles of cryptography Chapter 8 roadmap 8. 1 What is network security? 8. 2 Principles of cryptography 8. 3 Message integrity 8. 4 Securing e-mail 8. 5 Securing TCP connections: SSL 8. 6 Network layer security: IPsec 8. 7 Securing wireless LANs 8. 8 Operational security: firewalls and IDS Network Security 8 -28

WEP design goals v symmetric key crypto § confidentiality § end host authorization § WEP design goals v symmetric key crypto § confidentiality § end host authorization § data integrity v v self-synchronizing: each packet separately encrypted § given encrypted packet and key, can decrypt; can continue to decrypt packets when preceding packet was lost (unlike Cipher Block Chaining (CBC) in block ciphers) Efficient § implementable in hardware or software Network Security 8 -29

Review: symmetric stream ciphers key v v keystream generator keystream combine each byte of Review: symmetric stream ciphers key v v keystream generator keystream combine each byte of keystream with byte of plaintext to get ciphertext: § m(i) = ith unit of message § ks(i) = ith unit of keystream § c(i) = ith unit of ciphertext § c(i) = ks(i) m(i) ( = exclusive or) § m(i) = ks(i) c(i) WEP uses RC 4 Network Security 8 -30

Stream cipher and packet independence v v v recall design goal: each packet separately Stream cipher and packet independence v v v recall design goal: each packet separately encrypted if for frame n+1, use keystream from where we left off for frame n, then each frame is not separately encrypted § need to know where we left off for packet n WEP approach: initialize keystream with key + new IV for each packet: Key+IVpacket keystream generator keystreampacket Network Security 8 -31

WEP encryption (1) v sender calculates Integrity Check Value (ICV) over data § four-byte WEP encryption (1) v sender calculates Integrity Check Value (ICV) over data § four-byte hash/CRC for data integrity v v v each side has 104 -bit shared key sender creates 24 -bit initialization vector (IV), appends to key: gives 128 -bit key sender also appends key. ID (in 8 -bit field) 128 -bit key inputted into pseudo random number generator to get keystream data in frame + ICV is encrypted with RC 4: § Bbytes of keystream are XORed with bytes of data & ICV § IV & key. ID are appended to encrypted data to create payload § payload inserted into 802. 11 frame encrypted IV Key ID data ICV MAC payload Network Security 8 -32

WEP encryption (2) new IV for each frame Network Security 8 -33 WEP encryption (2) new IV for each frame Network Security 8 -33

WEP decryption overview encrypted IV Key ID data ICV MAC payload v v receiver WEP decryption overview encrypted IV Key ID data ICV MAC payload v v receiver extracts IV inputs IV, shared secret key into pseudo random generator, gets keystream XORs keystream with encrypted data to decrypt data + ICV verifies integrity of data with ICV § note: message integrity approach used here is different from MAC (message authentication code) and signatures (using PKI). Network Security 8 -34

End-point authentication w/ nonce Nonce: number (R) used only once –in-a-lifetime How to prove End-point authentication w/ nonce Nonce: number (R) used only once –in-a-lifetime How to prove Alice “live”: Bob sends Alice nonce, R. Alice must return R, encrypted with shared secret key “I am Alice” R KA-B (R) Alice is live, and only Alice knows key to encrypt nonce, so it must be Alice! Network Security 8 -35

WEP authentication request nonce (128 bytes) nonce encrypted shared key success if decrypted value WEP authentication request nonce (128 bytes) nonce encrypted shared key success if decrypted value equals nonce Notes: v v v not all APs do it, even if WEP is being used AP indicates if authentication is necessary in beacon frame done before association Network Security 8 -36

Breaking 802. 11 WEP encryption security hole: v v 24 -bit IV, one IV Breaking 802. 11 WEP encryption security hole: v v 24 -bit IV, one IV per frame, -> IV’s eventually reused IV transmitted in plaintext -> IV reuse detected attack: § Trudy causes Alice to encrypt known plaintext d 1 d 2 d 3 d 4 … § Trudy sees: ci = di XOR ki. IV § Trudy knows ci di, so can compute ki. IV § Trudy knows encrypting key sequence k 1 IV k 2 IV k 3 IV … § Next time IV is used, Trudy can decrypt! Network Security 8 -37

802. 11 i: improved security v v v numerous (stronger) forms of encryption possible 802. 11 i: improved security v v v numerous (stronger) forms of encryption possible provides key distribution uses authentication server separate from access point Network Security 8 -38

802. 11 i: four phases of operation AP: access point STA: client station AS: 802. 11 i: four phases of operation AP: access point STA: client station AS: wired network Authentication server 1 Discovery of security capabilities 2 STA and AS mutually authenticate, together generate Master Key (MK). AP serves as “pass through” 3 STA derives Pairwise Master Key (PMK) 4 STA, AP use PMK to derive Temporal Key (TK) used for message encryption, integrity 3 AS derives same PMK, sends to AP Network Security 8 -39

EAP: extensible authentication protocol v v EAP: end-end client (mobile) to authentication server protocol EAP: extensible authentication protocol v v EAP: end-end client (mobile) to authentication server protocol EAP sent over separate “links” § mobile-to-AP (EAP over LAN) § AP to authentication server (RADIUS over UDP) wired network EAP TLS EAP over LAN (EAPo. L) IEEE 802. 11 RADIUS UDP/IP Network Security 8 -40

SSL/TLS Performance v SSL handshake performance § For each connection, you need to exchange SSL/TLS Performance v SSL handshake performance § For each connection, you need to exchange the key § Matters the most for small objects v Who is the performance bottleneck? § Client generates a random key, encrypts it with public key of the server § Server decrypts the pre_master_secret § Both parties run PRNG twice v Server has to deal with lots of clients § Performance bottleneck § Mitigation: connection resumption, persistent connection § Tcpcrypt[USENX Security’ 10]: client decrypts the key 8 -41 41

Why is RSA decryption slower? Encryption ci = mie (mod n) Decryption mi = Why is RSA decryption slower? Encryption ci = mie (mod n) Decryption mi = cid (mod n) v The encryption power is usually chosen to be a prime of the form 2^n+1 v Can use squaring v D is often larger than e. v With the typical modular exponentiation algorithms used to implement the RSA algorithm, public key operations take O(k^2) steps, private key operations take O(k^3) steps Network Security 8 -42

SSL/TLS Performance v SSL data transfer performance § Matters in large data transfer § SSL/TLS Performance v SSL data transfer performance § Matters in large data transfer § Videos on https? § Symmetric key crypto is the bottleneck • AES-NI enables fast AES encryption/decryption v SSL/TLS performance summary § For small files, public key crypto performance matters § For large files, symmetric key crypto performance matters § See for yourself in doing homework 43 8 -43

Secure Key Size in SSL/TLS v 1024 -bit public key crypto is considered insecure Secure Key Size in SSL/TLS v 1024 -bit public key crypto is considered insecure § 768 -bit RSA is broken in 2010 § 1024 -bit is no longer considered secure § As of 2013, all US government equipments should use 2048 bit or larger public key size for SSL v Performance implication § As RSA key size doubles, the computation needs increases by a factor of 8 (O(n^3)) § In fact, you can see 6 x to 8 x performance degradation § SSLShader[NSDI’ 2011]: use GPU for cheap computation 44 8 -44

Perfect Forward Secrecy (PFS) v Definition: a session key will be not compromised even Perfect Forward Secrecy (PFS) v Definition: a session key will be not compromised even if a private key is revealed in the future § E. g. , revealing a private key does not allow getting the plaintext of the encrypted data in the past v Diffie-Hellman provides perfect forward secrecy § Ephemeral public key/private key § Security-sensitive sites provide PFS § RSA does not provide perfect forward secrecy • Yet, many sites use RSA due to performance concern, etc. 45 8 -45

Network Security 8 -46 Network Security 8 -46

v https: //www. eff. org/deeplinks/2014/04/why-webneeds-perfect-forward-secrecy Network Security 8 -47 v https: //www. eff. org/deeplinks/2014/04/why-webneeds-perfect-forward-secrecy Network Security 8 -47

Security Level of a System l How strong is the weakest point of your Security Level of a System l How strong is the weakest point of your system? 48 8 -48

RC 4 in TLS is Broken v v v v http: //www. isg. rhul. RC 4 in TLS is Broken v v v v http: //www. isg. rhul. ac. uk/tls/ RC 4 was very popular Google: ECDHE-RSA-AES 128 -GCM-SHA 256 ECDHE: the key agreement mechanism. RSA: the authentication mechanism. AES 128 -GCM: the cipher. SHA: the message authentication primitive. Network Security 8 -49

Two Security Analysis Papers v “Analysis of the SSL 3. 0 protocol” § David Two Security Analysis Papers v “Analysis of the SSL 3. 0 protocol” § David Wagner and Bruce Schneier § Security of a new SSL protocol (circa 1996) v “Cryptography in Theory and Practice: The case of Encryption in IPsec” § Kenneth Paterson and Arnold Yau § Vulnerabilities in unauthenticated IPsec • Focuses on the gap between theory and practice of IPsec 50 8 -50

Chapter 8 roadmap 8. 1 What is network security? 8. 2 Principles of cryptography Chapter 8 roadmap 8. 1 What is network security? 8. 2 Principles of cryptography 8. 3 Message integrity 8. 4 Securing e-mail 8. 5 Securing TCP connections: SSL 8. 6 Network layer security: IPsec 8. 7 Securing wireless LANs 8. 8 Operational security: firewalls and IDS Network Security 8 -51

Firewalls firewall isolates organization’s internal net from larger Internet, allowing some packets to pass, Firewalls firewall isolates organization’s internal net from larger Internet, allowing some packets to pass, blocking others public Internet administered network trusted “good guys” firewall untrusted “bad guys” Network Security 8 -52

Firewalls: why prevent denial of service attacks: v SYN flooding: attacker establishes many bogus Firewalls: why prevent denial of service attacks: v SYN flooding: attacker establishes many bogus TCP connections, no resources left for “real” connections prevent illegal modification/access of internal data v e. g. , attacker replaces CIA’s homepage with something else allow only authorized access to inside network v set of authenticated users/hosts three types of firewalls: v stateless packet filters v stateful packet filters v application gateways Network Security 8 -53

Stateless packet filtering Should arriving packet be allowed in? Departing packet let out? v Stateless packet filtering Should arriving packet be allowed in? Departing packet let out? v v 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 Network Security 8 -54

Stateless packet filtering: example v v example 1: block incoming and outgoing datagrams with Stateless packet filtering: example v v example 1: block incoming and outgoing datagrams with IP protocol field = 17 and with either source or dest port = 23 § result: all incoming, outgoing UDP flows and telnet connections are blocked example 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. Network Security 8 -55

Stateless packet filtering: more examples Policy Firewall Setting No outside Web access. Drop all Stateless packet filtering: more examples Policy Firewall Setting No outside Web access. Drop all outgoing packets to any IP address, port 80 No 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 Do. S attack. Drop all ICMP packets going to a “broadcast” address (e. g. 130. 207. 255). Prevent your network from being tracerouted Drop all outgoing ICMP TTL expired traffic Network Security 8 -56

Access Control Lists v ACL: table of rules, applied top to bottom to incoming Access Control Lists v ACL: table of rules, applied top to bottom to incoming packets: (action, condition) pairs action source address dest address allow 222. 22/16 outside of 222. 22/16 allow outside of 222. 22/16 deny all protocol source port dest port flag bit TCP > 1023 80 TCP 80 > 1023 ACK UDP > 1023 53 --- UDP 53 > 1023 ---- all all any Network Security 8 -57

Stateful packet filtering v stateless packet filter: heavy handed tool § admits packets that Stateful packet filtering v stateless packet filter: heavy handed tool § admits packets that “make no sense, ” e. g. , dest port = 80, ACK bit set, even though no TCP connection established: action allow v source address dest address outside of 222. 22/16 protocol source port dest port flag bit 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 packets Network Security 8 -58

Stateful packet filtering v ACL augmented to indicate need to check connection state table Stateful packet filtering v ACL augmented to indicate need to check connection state table before admitting packet action source address dest address proto source port dest port allow 222. 22/16 outside of 222. 22/16 TCP > 1023 80 allow outside of 222. 22/16 TCP 80 > 1023 ACK allow 222. 22/16 UDP > 1023 53 --- allow outside of 222. 22/16 UDP 53 > 1023 ---- deny all all all 222. 22/16 outside of 222. 22/16 flag bit check conxion any x x Network Security 8 -59

Application gateways host-to-gateway telnet session v v filters packets on application data as well Application gateways host-to-gateway telnet session v v filters packets on application data as well as on IP/TCP/UDP fields. example: allow select internal users to telnet outside. application gateway-to-remote host telnet session 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. Network Security 8 -60

Application gateways v v filter packets on application data as well as on IP/TCP/UDP Application gateways v v filter 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 application gateway router and filter gateway-to-remote host telnet session 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. Network Security 8 -61

Limitations of firewalls, gateways v v v IP spoofing: router can’t know if data Limitations of firewalls, gateways v v v IP spoofing: router can’t know if data “really” comes from claimed source if multiple app’s. need special treatment, each has own app. gateway client software must know how to contact gateway. § e. g. , must set IP address of proxy in Web browser v v v filters often use all or nothing policy for UDP tradeoff: degree of communication with outside world, level of security many highly protected sites still suffer from attacks Network Security 8 -62

Intrusion detection systems v packet filtering: § operates on TCP/IP headers only § no Intrusion detection systems v packet filtering: § operates on TCP/IP headers only § no correlation check among sessions v IDS: intrusion detection system § deep packet inspection: look at packet contents (e. g. , check character strings in packet against database of known virus, attack strings) § examine correlation among multiple packets • port scanning • network mapping • Do. S attack Network Security 8 -63

Intrusion detection systems v multiple IDSs: different types of checking at different locations firewall Intrusion detection systems v multiple IDSs: different types of checking at different locations firewall internal network IDS sensors Internet Web DNS server FTP server demilitarized zone Network Security 8 -64

Network Security (summary) basic techniques…. . . § cryptography (symmetric and public) § message Network Security (summary) basic techniques…. . . § cryptography (symmetric and public) § message integrity § end-point authentication …. used in many different security scenarios § § secure email secure transport (SSL) IP sec 802. 11 operational security: firewalls and IDS Network Security 8 -65