Cryptography and network security
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Eyad Alshareef 1 Cryptography and Network Security - PowerPoint PPT Presentation

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Cryptography and Network Security. Introduction. The most critical phase of e-transactions is ensuring the security of e-payments and the privacy of the information Transaction contents can be read, modified, or made up by anyone. . Introduction.

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Introduction l.jpg

  • The most critical phase of e-transactions is ensuring the security of e-payments and the privacy of the information

  • Transaction contents can be read, modified, or made up by anyone.

Eyad Alshareef

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  • Internet security is not about protecting hardware or physical environment

  • It is about protecting information

  • Electronic security

    • Focuses on designing measures that can enforce security policies

    • When a malicious attack occurs

Eyad Alshareef

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  • Information Security requirements have changed in recent times

  • traditionally provided by physical and administrative mechanisms

  • computer use requires automated tools to protect files and other stored information

  • use of networks and communications links requires measures to protect data during transmission

Eyad Alshareef

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  • Computer Security - generic name for the collection of tools designed to protect data and to thwart hackers (in your computer)

  • Network Security - measures to protect data during their transmission

  • Internet Security - measures to protect data during their transmission over a collection of interconnected networks

Eyad Alshareef

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The Internet Is An Insecure Place

  • Many protocols do not provide any security.

  • Viruses, worms, Trojan horses etc.

  • Client/server applications often require transmission of user identity/passwords.

  • “Hackers” may sniff passwords and other sensitive information of the network.

  • Need to restrict control access privileges

  • No system is totally immune to security problems.

Eyad Alshareef

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  • There is nothing more secure then a computer which is not connected to the network – and powered off!

  • But…

  • These restrictions are simply unrealistic and unacceptable.

Eyad Alshareef

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What we want from Security

  • Some characteristics we might like:

    • messages should be transmitted to destination

    • only the recipient should see it

    • only the recipient should get it

    • proof of the sender’s identity

    • message shouldn’t be corrupted in transit

    • message should be sent/received once only

Eyad Alshareef

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Services, Mechanisms, Attacks

  • consider three aspects of information security:

    • security attack

    • security mechanism

    • security service

  • consider in reverse order

Eyad Alshareef

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Security Service

  • is something that enhances the security of the data processing systems and the information transfers of an organization

  • intended to counter security attacks

  • make use of one or more security mechanisms to provide the service

  • replicate functions normally associated with physical documents

    • eg have signatures, dates; need protection from disclosure, tampering, or destruction; be notarized or witnessed; be recorded or licensed

Eyad Alshareef

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Security Mechanism

  • a mechanism that is designed to detect, prevent, or recover from a security attack

  • no single mechanism that will support all functions required

  • however one particular element underlies many of the security mechanisms in use: cryptographic techniques

  • hence our focus on this area

Eyad Alshareef

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Security Attack

  • any action that compromises the security of information owned by an organization

  • information security is about how to prevent attacks, or failing that, to detect attacks on information-based systems

  • have a wide range of attacks

  • can focus of generic types of attacks

  • note: often threat & attack mean same

Eyad Alshareef

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Attacks, Services and Mechanisms

  • Security Attack:Any action that compromises the security of information.

  • Security Mechanism:A mechanism that is designed to detect, prevent, or recover from a security attack.

  • Security Service:A service that enhances the security of data processing systems and information transfers. A security service makes use of one or more security mechanisms.

Eyad Alshareef

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What Functionality Is Needed?

  • Authentication -- who user is

  • Authorization -- who is allowed to do what

  • Enforcement -- make sure people do what they are supposed to do

Eyad Alshareef

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  • Cryptography

    • Converting messages to unreadable forms...

      and then converting it back to the readable form

  • Steganography

    • Hiding the existence of a message

Eyad Alshareef

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Eyad Alshareef

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  • Used for concealing information inside other information

  • Some techniques:

    • Character marking: selected letter of printed or typewritten text are overwritten in pencil

    • Invisible ink

    • Pin punctures: small pin punctures are only shown if paper is hold against a light source

    • Typewriter correction ribbon: used between lines of normal black ribbon. Only visible under strong light.

Eyad Alshareef

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Null Cipher

Fishing freshwater bends and saltwater coasts rewards anyone feeling stressed. Resourceful anglers usually find masterful leapers fun and admit swordfish rank overwhelming anyday.

Send lawyers, guns, and money.

Eyad Alshareef

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Invisible Ink

  • Write with lemon juice and a toothpick/ cotton swab. Let the paper dry.

  • Heat the paper with an iron to reveal the hidden message.

Eyad Alshareef

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Introduction to Security

  • Businesses are increasingly dependent on information and communication technology

  • security is becoming a primary concern with public access systems

  • there are different types of attack:

    • viruses

    • unauthorised access

    • hacking

Eyad Alshareef

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What Can Go Wrong…

  • …when your computer y receive or is waiting for a message m?






Eyad Alshareef

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Message Loss

  • Adversary A can discard m in its transit





Eyad Alshareef

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Message Interception

  • Adversary A can get a copy of m when m passes by







Eyad Alshareef

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Message Modification

  • Adversary A can arbitrarily modify the content of m to become m’






Eyad Alshareef

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Message Insertion

  • Adversary A can arbitrarily fabricate a message m, pretending that m was sent by x

src: x

dst: y





Eyad Alshareef

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Message Replay

  • Adversary A can replay a message m that has been sent earlier by x and received by y






Eyad Alshareef

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Denial-of-Service Attack

  • Adversary A can send huge amount of messages to y to block m from arriving at y






Eyad Alshareef

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Network Security Is Great…

  • Protect messages from interception in their transit

  • Detect and discard messages that are modified, inserted, or replayed

  • Disallow unauthorized access to local system resource and sensitive data

Eyad Alshareef

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Types of Security Threats

  • Normal flow

  • Interruption

  • Interception

  • Modification

  • Fabrication

Eyad Alshareef

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Security Attacks

Eyad Alshareef

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What is network security?

Confidentiality: only sender, intended receiver should “understand” message contents

  • sender encrypts message

  • receiver decrypts message

    Authentication: sender, receiver want to confirm identity of each other

    Message Integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection

    Access and Availability: services must be accessible and available to users

Eyad Alshareef

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Security Attacks

  • Interruption: This is an attack on availability

  • Interception: This is an attack on confidentiality

  • Modfication: This is an attack on integtrity

  • Fabrication: This is an attack on authenticity

Eyad Alshareef

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Security Criteria

Eyad Alshareef

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Friends and enemies: Alice, Bob, Trudy

  • well-known in network security world

  • Bob, Alice (lovers!) want to communicate “securely”

  • Trudy (intruder) may intercept, delete, add messages



data, control messages









Eyad Alshareef

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A Model for Network Security

  • Security techniques commonly have three components:

    • security related transformation of message

    • secret keys shared by the participants

    • need for third party notary support for some transactions

Eyad Alshareef

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  • can be an effective means of protecting a system or network from network-based security threats

  • while providing access to the outside world

  • positioned between the system(s) and the outside world

  • all external traffic must pass through it

  • a single choke point where security measures can be concentrated

Eyad Alshareef

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Types of Firewall

  • there are hardware and software firewalls

  • can be implemented on a designated gateway or dedicated machine

  • there are three types:

    • packet filtering routers

    • application-level gateway

    • circuit-level gateway

Eyad Alshareef

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Packet Filtering Routers

  • A router that applies a set of rules to incoming and outgoing packets:

    • based on fields in the IP and transport header

    • e.g. source, destination IP, port and IP protocol

    • where no rule exists to discard of forward

Eyad Alshareef

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Application-Level Gateway

  • An application-level gateway acts as a relay of application-level traffic

  • also known as a proxy server

  • users contact the proxy using TCP/IP based applications

  • the gateway checks and forwards for supported/allowed applications or safe sub-sets/features thereof

  • these tend to be more secure than packet filters

  • disadvantage: processing overhead

Eyad Alshareef

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Circuit-level Gateway

  • Can be stand-alone system or hosted

  • does not permit end-to-end TCP connection

  • sets up two TCP connection one on either side

  • TCP segments are relayed without examining content

  • based on the principle of allowing connections only to select/trusted hosts

  • usually used for outgoing connections

  • can therefore complement application-layer gateways for incoming traffic

Eyad Alshareef

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Security Services (X.800)

  • Authentication - assurance that the communicating entity is the one claimed

  • Access Control - prevention of the unauthorized use of a resource

  • Data Confidentiality –protection of data from unauthorized disclosure

  • Data Integrity - assurance that data received is as sent by an authorized entity

  • Non-Repudiation - protection against denial by one of the parties in a communication

Eyad Alshareef

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Classify Security Attacks as

  • passive attacks - eavesdropping on, or monitoring of, transmissions to:

    • obtain message contents, or

    • monitor traffic flows

  • active attacks – modification of data stream to:

    • masquerade of one entity as some other

    • replay previous messages

    • modify messages in transit

    • denial of service

Eyad Alshareef

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Model for Network Security

  • using this model requires us to:

    • design a suitable algorithm for the security transformation

    • generate the secret information (keys) used by the algorithm

    • develop methods to distribute and share the secret information

    • specify a protocol enabling the principals to use the transformation and secret information for a security service

Eyad Alshareef

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Model for Network Access Security

  • using this model requires us to:

    • select appropriate gatekeeper functions to identify users

    • implement security controls to ensure only authorised users access designated information or resources

  • trusted computer systems can be used to implement this model

Eyad Alshareef

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More Information

  • Spyware

    • Software the user unknowingly installs through an email attachment or downloading an effected file that could be used for illicit reasons

    • Usually used to collect information from infected computer

Eyad Alshareef

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More Information

  • Adware

    • Software that sneaks into user hard disk

    • Installed by internet advertising companies tp promote pop-up ads and release information for advertisers on the outside

Eyad Alshareef