IC3-1 Network security

Part 1 - Introductory network concepts

Matthew JoyceDresdner Kleinwort Wasserstein

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Outline

1. Internet Protocols 2. Protocol hierarchies3. The OSI reference model4. Services in the OSI model5. Example networks

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1. Internet Protocols

Network

Web Browser

Web Server

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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, …

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Application Layer Example

>HTTP outline: >GET /directory/dirsearch.html HTTP/1.1>Host: www.phoenix.co.uk

GET /directory/dirsearch.html HTTP/1.1Host: www.phoenix.co.uk

HTTP Message

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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

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Transport Layer Example

> TCP outline:>Source Port: 1081>Destination Port: 80>Checksum: 0xa858

GET /directory/dirsearch.html HTTP/1.1Host: www.phoenix.co.uk

Src: 1081 Dst: 80Chksum: 0xa858

HTTP MessageTCP header

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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.

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Internet Layer Example

>IP outline:>Time to live: 128>Header checksum: 0x57d1>Source: pelican (192.168.0.40)>Destination: www.phoenix.co.uk (192.168.0.50)

GET /directory/dirsearch.html HTTP/1.1Host: www.phoenix.co.uk

Src: 1081 Dst: 80Chksum: 0xa858

Src: 192.168.0.40Dst: 192.168.0.50 TTL: 128

HTTP MessageTCP headerIP datagram header

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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.

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Src: 00:e0:81:10:19:fc Dst: 00:a0:cc:54:1d:4e Type: IP

Network Interface Layer Example

>Ethernet outline:>Destination: 00:a0:cc:54:1d:4e>Source: 00:e0:81:10:19:fc>Type: IP

GET /directory/dirsearch.html HTTP/1.1Host: www.phoenix.co.uk

Src: 1081 Dst: 80Chksum: 0xa858

Src: 192.168.0.40Dst: 192.168.0.50 TTL: 128

Ethernet Frame

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Protocol Layering

Application Layer

Transport Layer

Internet Layer

Network Layer

Physical Network

Application Layer

Transport Layer

Internet Layer

Network Layer

Message

Packet

Datagram

Frame

Host A Host B

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Protocol Layering

Application Layer

Transport Layer

Internet Layer

Network Layer

Physical Network

Application Layer

Transport Layer

Internet Layer

Network Layer

HTTP Message

TCP Packet

IP Datagram

Ethernet Frame

Web Browser Web Server

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Internetworking

>No single networking technology can satisfy all requirements.

>Universal interconnection is desired.>Protocols allow communication between

nodes without understanding underlying mechanisms.

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Routing

Web Browser

Web Server

Router

NetworkA

NetworkB

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Protocol Layering

Application Layer

Transport Layer

Internet Layer

Network Layer

Physical Network

Application Layer

Transport Layer

Internet Layer

Network Layer

HTTP Message

TCP Packet

EthernetFrame

EthernetFrame

IP Datagram IP Datagram

Internet Layer

Network Layer

Physical Network

Host BHost A

Router

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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.

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Layers, protocols & interfaces

Physical communications medium

Layer 1 Layer 1Layer 1 protocol

Layer 2 Layer 2Layer 1/2interface

Layer 1/2interface

Layer 2 protocol

Layer n protocolLayer n Layer n

Layer 2/3interface

Layer n-1/ninterface

Layer 2/3interface

Layer n-1/ninterface

Layer n/n+1interface

Layer n/n+1interface

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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.

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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.

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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.

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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.

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Internet Protocols vs OSI

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

TCP

IP

Network Interface

Hardware1

2

3

4

5

1

2

3

4

6

5

7

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The OSI model

Layer 7

Layer 6

Layer 5

Layer 4

Layer 3

Layer 2

Layer 1

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Communications subnet boundary

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Layering Principles

(N+1) EntityService User

(N) EntityService Provider

(N+1) EntityService User

(N) EntityService Provider

Layer N ServiceAccess Point (SAP)

Layer N protocol

N+1PDU

Layer N+1 protocol

SDU

PDU - Protocol Data UnitSDU - Service Data Unit

NPDU

NPDU

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Connections

>Layers can offer connection-oriented or connectionless services.

>Connection-oriented like telephone system.>Connectionless like postal system.>Each service has an associated Quality-of-

service (e.g. reliable or unreliable).

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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.

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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.

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5 Example networks

>Local area networks (IEEE 802)>Internet (TCP/IP)>ISDN>GSM, 3G

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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

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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.

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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.

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GSM & 3G

> 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

> 3G is 3rd 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.

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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.

IC3-1 Network security

Part 2 - Introductory security concepts

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Outline

1. Introduction2. Security domains and policies3. Security threats4. Security services5. Security mechanisms

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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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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Fundamental threats

>Four fundamental threats (matching CIA+ legitimate use):>Information leakage, >Integrity violation,>Denial of service,>Illegitimate use.

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Fundamental Threat Examples

>Integrity violation>USA Today, falsified reports of missile attacks on

Israel, 7/2002

>Denial of service>Yahoo, 2/2000, 1Gbps

>Information Leakage>Prince Charles mobile phone calls, 1993

>Illegitimate use>Vladimir Levin, Citibank, $3.7M, 1995

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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.

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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

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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 IC3.>Computer security safeguards are covered

in IC4.

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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.

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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

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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

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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

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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.

> MD5 hashes http://www.apache.org/dist/httpd/binaries/linux/

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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

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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.

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Specific security mechanisms

>Eight types:>encipherment,>digital signature,>access control mechanisms,>data integrity mechanisms,>authentication exchanges,>traffic padding,>routing control,>notarisation.

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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 IC2, IC3

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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 IC4

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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 3rd party trusted notary.> Notary typically applies a cryptographic transformation to

the data.

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Pervasive security mechanisms

>Five types identified:>trusted functionality,>security labels,>event detection,>security audit trail,>security recovery.

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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.

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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.

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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 non-repudiation service (as part of notarisation).

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Service/mechanism table I

Mechanism Service

Enciph- erment

Digital sign.

Access Control

Data integrity

Entity authentication Y Y

Origin authentication Y Y

Access control Y

Connection confidentiality Y

Connectionless confidentiality Y

Selective field confidentiality Y

Traffic flow confidentiality Y

Connection integrity with recovery Y Y

Connection integrity without recovery Y Y

Selective field connection integrity Y Y

Connectionless integrity Y Y Y

Selective field connectionless integrity Y Y Y

Non-repudiation of origin Y Y

Non-repudiation of delivery Y Y

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Service/mechanism table II

Mechanism Service

Auth. exchange

Traffic padding

Routing Control

Notaris- ation

Entity authentication Y

Origin authentication

Access control

Connection confidentiality Y

Connectionless confidentiality Y

Selective field confidentiality

Traffic flow confidentiality Y Y

Connection integrity with recovery

Connection integrity without recovery

Selective field connection integrity

Connectionless integrity

Selective field connectionless integrity

Non-repudiation of origin Y

Non-repudiation of delivery Y

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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.

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Service/layer tableService/layer table

Layer Service

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5/6

Layer 7

Entity authentication Y Y Y

Origin authentication Y Y Y

Access control Y Y Y

Connection confidentiality Y Y Y Y Y

Connectionless confidentiality Y Y Y Y

Selective field confidentiality Y

Traffic flow confidentiality Y Y Y

Connection integrity with recovery Y Y

Connection integrity without recovery Y Y Y

Selective field connection integrity Y

Connectionless integrity Y Y Y

Selective field connectionless integrity Y

Non-repudiation of origin Y

Non-repudiation of delivery Y