IC 3 -1 Network security Part 1 —

IC 3 -1 Network security Part 1 - Introductory network concepts Matthew Joyce Dresdner Kleinwort Wasserstein IC 3 -1

Outline 1. 2. 3. 4. 5. Internet Protocols Protocol hierarchies The OSI reference model Services in the OSI model Example networks IC 3 -1 2

1. Internet Protocols Web Browser Network Web Server IC 3 -1 3

Application Layer > How does web browser retrieve data from web server? > Application Protocol: Hypertext Transfer Protocol (HTTP). > Users invoke applications which “speak” using application protocol. > Applications interact with a transport protocol to send or receive data. > Others: FTP, SMTP, DNS, SMB, … IC 3 -1 4

Application Layer Example > HTTP outline: > GET /directory/dirsearch. html HTTP/1. 1 > Host: www. phoenix. co. uk GET /directory/dirsearch. html HTTP/1. 1 Host: www. phoenix. co. uk HTTP Message IC 3 -1 5

Transport Layer > Provides end-to-end communication between applications. > Transport Protocol: Transport Control Protocol (TCP) > A transport protocol may be reliable, flow may be regulated. > Divides stream of application messages into packets. > Interacts with Internet Layer to send or receive data. > Others: UDP, ICMP IC 3 -1 6

Transport Layer Example > TCP outline: > Source Port: 1081 > Destination Port: 80 > Checksum: 0 xa 858 Src: 1081 Dst: 80 Chksum: 0 xa 858 TCP header GET /directory/dirsearch. html HTTP/1. 1 Host: www. phoenix. co. uk HTTP Message IC 3 -1 7

Internet Layer > Communication between one machine and another. > Accepts requests to send packets to destination address. > Encapsulates packets in IP datagram with IP header and uses routing algorithm to decide if to send directly or indirectly. > Also handles incoming IP datagrams. > If addressed to local machine, remove the IP datagram header and pass up to transport layer. IC 3 -1 8

Internet Layer Example > IP outline: > Time to live: 128 > Header checksum: 0 x 57 d 1 > Source: pelican (192. 168. 0. 40) > Destination: www. phoenix. co. uk (192. 168. 0. 50) IP datagram header Src: 192. 168. 0. 40 Dst: 192. 168. 0. 50 TTL: 128 TCP header Src: 1081 Dst: 80 Chksum: 0 xa 858 IC 3 -1 HTTP Message GET /directory/dirsearch. html HTTP/1. 1 Host: www. phoenix. co. uk 9

Network Interface Layer > Accepts IP datagrams and transmits over specific networks. > Maybe a simple device driver (e. g. an Ethernet driver) or a complex subsystem with further data link protocols. IC 3 -1 10

Network Interface Layer Example > Ethernet outline: > Destination: 00: a 0: cc: 54: 1 d: 4 e > Source: 00: e 0: 81: 10: 19: fc > Type: IP Ethernet Frame Src: 00: e 0: 81: 10: 19: fc Dst: 00: a 0: cc: 54: 1 d: 4 e Type: IP Src: 192. 168. 0. 40 Dst: 192. 168. 0. 50 TTL: 128 Src: 1081 Dst: 80 Chksum: 0 xa 858 IC 3 -1 GET /directory/dirsearch. html HTTP/1. 1 Host: www. phoenix. co. uk 11

Protocol Layering Host A Host B Application Layer Message Transport Layer Packet Internet Layer Datagram Network Layer Frame Physical Network IC 3 -1 12

Protocol Layering Web Browser Web Server Application Layer HTTP Message Transport Layer TCP Packet Internet Layer IP Datagram Network Layer Ethernet Frame Physical Network IC 3 -1 13

Internetworking > No single networking technology can satisfy all requirements. > Universal interconnection is desired. > Protocols allow communication between nodes without understanding underlying mechanisms. IC 3 -1 14

Routing Router Network B Web Browser Network A Web Server IC 3 -1 15

Protocol Layering Host A Host B Application Layer HTTP Message Transport Layer Router Internet Layer IP Datagram Network Layer Transport Layer TCP Packet Ethernet Frame Internet Layer IP Datagram Network Layer Physical Network Ethernet Frame Network Layer Physical Network IC 3 -1 16

2 Protocol hierarchies > Protocols are stacked vertically as series of ‘layers’. > Each layer offers Services to layer above, shielding implementation details. > Layer n on one machine communicates with layer n on another machine (they are peer processes/entities) using Layer n Protocol. IC 3 -1 17

Layers, protocols & interfaces Layer n/n+1 interface Layer n protocol Layer n-1/n interface Layer 2/3 interface Layer 2 Layer 1/2 interface Layer 1 Layer n/n+1 interface Layer n-1/n interface Layer 2 protocol Layer 1 protocol Layer 2/3 interface Layer 2 Layer 1/2 interface Layer 1 Physical communications medium IC 3 -1 18

Layer/interface design > Important objective is ‘clean’ interfaces, having minimal set of well-defined services. > Clean-cut interfaces enable: > minimisation of inter-layer communications > easy replacement of individual layers > Set of layers and protocols is the Network Architecture. IC 3 -1 19

Virtual & actual comms. > Vital to understand difference between: > virtual and actual communications, > protocols and interfaces. > Peer processes ‘think’ of communications as being ‘horizontal’ using protocol. > Actual communications is via interfaces. > Peer process idea is key to network design. IC 3 -1 20

Design issues > Some issues affect many layers, e. g: > need to address data (say who it’s for), > possible need for setting up connections, > data transfer rules (simplex, half-duplex, . . . ), > error management, > deal with message component re-ordering, > flow control, > routing. IC 3 -1 21

3 The OSI Reference model > OSI Reference Model - internationally standardised network architecture. > An abstract representation of an ideal network protocol stack > OSI = Open Systems Interconnection > Specified in ISO 7498 -1. > Model has 7 layers. IC 3 -1 22

Internet Protocols vs OSI Application Presentation Application 6 Session 5 7 5 4 3 TCP Transport 4 IP Network 3 2 Network Interface Data Link 2 1 Hardware Physical 1 IC 3 -1 23

The OSI model Layer 7 Application Layer 6 Presentation Layer 5 Session Layer 4 Transport Layer 3 Network Layer 2 Data Link Layer 1 Physical Layer IC 3 -1 Communications subnet boundary 24

Lower/Upper Layers > Layers 1 -4 often referred to as ‘lower layers’ > Layers 5 -7 are the upper layers. > Lower layers relate more closely to the communications technology. > Upper layers relate to application. IC 3 -1 25

Layer 7: Application Layer > Home to wide variety of protocols for specific user needs, e. g. : > virtual terminal service, > file transfer, > electronic mail, > directory services. IC 3 -1 26

Layer 6: Presentation Layer > Concerned with representation of transmitted data. > Deals with different data representations, e. g. of numbers, characters. > Also deals with data compression and encryption. > Layer for source coding. IC 3 -1 27

Layer 5: Session Layer > Allows establishment of sessions between machines, e. g. to > allow remote logins > provide file transfer service. > Responsible for dialogue control. > Also performs token management and synchronisation. IC 3 -1 28

Layer 4: Transport Layer > Basic function is to take data from Session Layer, split it up into smaller units, and ensure that the units arrive correctly. > Concerned with efficient provision of service. > The Transport Layer also determines the ‘type of service’ to provide to the Session Layer. IC 3 -1 29

Layer 3: Network Layer > Controls the subnet. > Key issue is routing in the subnet; can be based on: > static tables, > determined at start of session, > highly dynamic (varying for each packet). > Also responsible for congestion control. IC 3 -1 30

Layer 2: Data Link Layer > Provides reliable, error-free service on top of raw Level 1 service. > Breaks data into frames. Requires creation of frame boundaries. > Frames used to manage errors via acknowledgements and selective frame retransmission. IC 3 -1 31

Layer 1: Physical Layer > Concerned with bit transmission over physical channel. > Issues include: > definition of 0/1, > whether channel simplex/duplex, > connector design. > Mechanical, electrical, procedural matters. IC 3 -1 32

4 Services in the OSI model > In OSI model, each layer provide services to layer above, and ‘consumes’ services provided by layer below. > Active elements in a layer called entities. > Entities in same layer in different machines called peer entities. IC 3 -1 33

Layering Principles N+1 PDU (N+1) Entity Service User SDU (N) Entity Service Provider Layer N+1 protocol Layer N Service Access Point (SAP) Layer N protocol N PDU (N+1) Entity Service User (N) Entity Service Provider N PDU - Protocol Data Unit SDU - Service Data Unit IC 3 -1 34

Connections > Layers can offer connection-oriented or connectionless services. > Connection-oriented like telephone system. > Connectionless like postal system. > Each service has an associated Quality-ofservice (e. g. reliable or unreliable). IC 3 -1 35

Reliability issues > Reliable services never lose/corrupt data. > Reliable service costs more. > Typical application for reliable service is file transfer. > Typical application not needing reliable service is voice traffic. > Not all applications need connections. IC 3 -1 36

Services and protocols > Service = set of primitives provided by one layer to layer above. > Service defines what layer can do (but not how it does it). > Protocol = set of rules governing data communication between peer entities, i. e. format and meaning of frames/packets. > Service/protocol decoupling very important. IC 3 -1 37

5 Example networks > Local area networks (IEEE 802) > Internet (TCP/IP) > ISDN > GSM, 3 G IC 3 -1 38

Local Area Networks > The IEEE 802 standards have come to dominate LANs. They specify protocols for use at Layers 1 and 2. > LANs (Local Area Networks) used within limited areas (e. g. buildings/campuses) as opposed to WANs (Wide Area Networks). > ISO/IEC 8802 -n = IEEE 802. n IC 3 -1 39

IEEE 802 > IEEE 802. 2 = Layer 2 (most of). > IEEE 802. 3, 802. 4 and 802. 5 are three options for Layer 1 (and a bit of Layer 2). > IEEE 802. 3 = Ethernet. IC 3 -1 40

ISDN > ISDN=Integrated Services Digital Network. > ISDN enables public-switched telephone network to carry data as well as voice. > Current (N-ISDN) offers 64 kbit/sec channels - via modern telephone exchanges. > Can be used to support variety of applications - e. g. video-conference. IC 3 -1 41

GSM & 3 G > Global System for Mobile Communications > Digital technology and time division multiple access transmission methods. > Voice is digitally encoded, allowing very efficient data rate/information content ratio. > Open, non-proprietary standard > 3 G is 3 rd generation GSM > High end services including substantially enhanced capacity, quality and data rates than currently available. > Makes video on demand, high speed multimedia and internet access possible. IC 3 -1 42

The Internet > Internet - evolved out of a US Government funded network (ARPANET). > Developed in parallel with OSI so it does not conform. > Has its own protocols at layers 3/4 called TCP (layer 4) and IP (layer 3). > Has pushed OSI out (de facto beats de jure) > Now 5 million web sites, 200 million users. IC 3 -1 43

IC 3 -1 Network security Part 2 - Introductory security concepts IC 3 -1

Outline 1. 2. 3. 4. 5. Introduction Security domains and policies Security threats Security services Security mechanisms IC 3 -1 45

1 Introduction > ISO 7498 -2: > provides standard definitions of security terminology, > provides standard descriptions for security services and mechanisms, > defines where in OSI reference model security services may be provided, > introduces security management concepts. IC 3 -1 46

Security life-cycle > Model is as follows: > define security policy, > analyse security threats (according to policy), > define security services to meet threats, > define security mechanisms to provide services, > provide on-going management of security. IC 3 -1 47

Threats, services and mechanisms > A security threat is a possible means by which a security policy may be breached (e. g. loss of integrity or confidentiality). > A security service is a measure which can be put in place to address a threat (e. g. provision of confidentiality). > A security mechanism is a means to provide a service (e. g. encryption, digital signature). IC 3 -1 48

2 Security domains and policies > In a secure system, the rules governing security behaviour should be made explicit in the form of a Security policy. > Security policy: ‘the set of criteria for the provision of security services’. > Security domain: the scope of a single security policy. IC 3 -1 49

Generic security policy > ISO 7498 -2 generic authorisation policy: > ‘Information may not be given to, accessed by, nor permitted to be inferred by, nor may any resource be used by, those not appropriately authorised. ’ > Possible basis for more detailed policy. > N. b. does not cover availability (e. g. denial of service) issues. IC 3 -1 50

Policy Types > ISO 7498 -2 distinguishes between 2 types of security policy: > identity-based: where access to and use of resources are determined on the basis of the identities of users and resources, > rule-based: where resource access is controlled by global rules imposed on all users, e. g. using security labels. IC 3 -1 51

3 Security threats > A threat is: > a person, thing, event or idea which poses some danger to an asset (in terms of confidentiality, integrity, availability or legitimate use). > An attack is a realisation of a threat. > Safeguards = measures (e. g. controls, procedures) to protect against threats. > Vulnerabilities = weaknesses in safeguards. IC 3 -1 52

Risk > Risk is a measure of the cost of a vulnerability (taking into account probability of a successful attack). > Risk analysis determines whether expenditure on (new/better) safeguards is warranted. IC 3 -1 53

Fundamental threats > Four fundamental threats (matching CIA+ legitimate use): > Information leakage, > Integrity violation, > Denial of service, > Illegitimate use. IC 3 -1 54

Fundamental Threat Examples > Integrity violation > USA Today, falsified reports of missile attacks on Israel, 7/2002 > Denial of service > Yahoo, 2/2000, 1 Gbps > Information Leakage > Prince Charles mobile phone calls, 1993 > Illegitimate use > Vladimir Levin, Citibank, $3. 7 M, 1995 IC 3 -1 55

Primary enabling threats > Realisation of any of these threats can lead directly to a realisation of a fundamental threat: > Masquerade, > Bypassing controls, > Authorisation violation, > Trojan horse, > Trapdoor. IC 3 -1 56

Primary Enabling Threat Examples > Masquerade > Royal Opera House web site, 8/2002 – Information Leakage > Bypassing controls > ADSL modem passwords – Illegitimate Use > Authorisation violation > Cross site scripting – Information Leakage > Trojan horse > PWSteal. Trojan, 1999 – Information Leakage > Trapdoor > Ken Thompson, Unix login – Reflections on Trusting Trust, 1975 - Illegitimate Use IC 3 -1 57

4 Security services > Security services in ISO 7498 -2 are a special class of safeguard applying to a communications environment. > Hence they are the prime focus of IC 3. > Computer security safeguards are covered in IC 4. IC 3 -1 58

Security service classification > ISO 7498 -2 defines 5 main categories of security service: > Authentication (including entity authentication and origin authentication), > Access control, > Data confidentiality, > Data integrity, > Non-repudiation. IC 3 -1 59

Authentication > Entity authentication provides checking of a claimed identity at a point in time. > Typically used at start of a connection. > Addresses masquerade and replay threats. > Origin authentication provides verification of source of data. > Does not protect against replay or delay. > GSM, webservers IC 3 -1 60

Access control > Provides protection against unauthorised use of resource, including: > use of a communications resource, > reading, writing or deletion of an information resource, > execution of a processing resource. > Remote users IC 3 -1 61

Data confidentiality > Protection against unauthorised disclosure of information. > Four types: > Connection confidentiality, > Connectionless confidentiality, > Selective field confidentiality, > Traffic flow confidentiality. > Internet banking session > Encrypting routers as part of Swift funds transfer network IC 3 -1 62

Data integrity > Provides protection against active threats to the validity of data. > Five types: > Connection integrity with recovery, > Connection integrity without recovery, > Selective field connection integrity, > Connectionless integrity, > Selective field connectionless integrity. > MD 5 hashes http: //www. apache. org/dist/httpd/binaries/linux/ IC 3 -1 63

Non-repudiation > Protects against a sender of data denying that data was sent (non-repudiation of origin). > Protects against a receiver of data denying that data was received (non-repudiation of delivery). > Analagous to signing a letter and sending recorded delivery IC 3 -1 64

5 Security mechanisms > Exist to provide and support security services. > Can be divided into two classes: > Specific security mechanisms, used to provide specific security services, and > Pervasive security mechanisms, not specific to particular services. IC 3 -1 65

Specific security mechanisms > Eight types: > encipherment, > digital signature, > access control mechanisms, > data integrity mechanisms, > authentication exchanges, > traffic padding, > routing control, > notarisation. IC 3 -1 66

Specific Mechanisms 1 > Encipherment mechanisms = encryption or cipher algorithms. > Can provide data and traffic flow confidentiality. > Digital signature mechanisms > signing procedure (private), > verification procedure (public). > Can provide non-repudiation, origin authentication and data integrity services. > Both can be basis of some authentication exchange mechanisms. > More in IC 2, IC 3 -1 67

Specific Mechanisms 2 > Access Control mechanisms > A server using client information to decide whether to grant access to resources > E. g. access control lists, capabilities, security labels. > Data integrity mechanisms > Protection against modification of data. > Provide data integrity and origin authentication services. Also basis of some authentication exchange mechanisms. > Authentication exchange mechanisms > Provide entity authentication service. > More later in IC 4 IC 3 -1 68

Specific Mechanisms 3 > Traffic padding mechanisms > The addition of ‘pretend’ data to conceal real volumes of data traffic. > Provides traffic flow confidentiality. > Routing control mechanisms > Used to prevent sensitive data using insecure channels. > E. g. route might be chosen to use only physically secure network components. > Notarisation mechanisms > Integrity, origin and/or destination of data can be guaranteed by using a 3 rd party trusted notary. > Notary typically applies a cryptographic transformation to the data. IC 3 -1 69

Pervasive security mechanisms > Five types identified: > trusted functionality, > security labels, > event detection, > security audit trail, > security recovery. IC 3 -1 70

Pervasive Mechanisms 1 > Trusted functionality > Any functionality providing or accessing security mechanisms should be trustworthy. > May involve combination of software and hardware. > Security labels > Any resource (e. g. stored data, processing power, communications bandwidth) may have security label associated with it to indicate security sensitivity. > Similarly labels may be associated with users. Labels may need to be securely bound to transferred data. IC 3 -1 71

Pervasive Mechanisms 2 > Event detection > Includes detection of > attempted security violations, > legitimate security-related activity. > Can be used to trigger event reporting (alarms), event logging, automated recovery. > Security audit trail > Log of past security-related events. > Permits detection and investigation of past security breaches. > Security recovery > Includes mechanisms to handle requests to recover from security failures. > May include immediate abort of operations, temporary invalidation of an entity, addition of entity to a blacklist. IC 3 -1 72

Services versus mechanisms > ISO 7498 -2 indicates which mechanisms can be used to provide which services. > Illustrative NOT definitive. > Omissions include: > use of integrity mechanisms to help provide authentication services, > use of encipherment to help provide nonrepudiation service (as part of notarisation). IC 3 -1 73

Service/mechanism table I IC 3 -1 74

Service/mechanism table II IC 3 -1 75

Services versus layers > ISO 7498 -2 lays down which security services can be provided in which of the 7 layers. > Layers 1 and 2 may only provide confidentiality services. > Layers 3/4 may provide many services. > Layer 7 may provide all services. IC 3 -1 76

Service/layer table IC 3 -1 77