Computer Security
description
Transcript of Computer Security
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Computer Security
Hugo Andrés López
Summary
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Distributed System Security• Distributed systems• – computers connected by a network• • Communications (network) security• – addresses security of the communications links• • Computer security• – addresses security of the end systems• • Application security• – relies on both to provide services securely to end• users• • Security Management• – Not just the system but also the people!
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Computer Security
• OBJECTIVE:– Protect accessible resources in spite of malicious
intent and behaviour that involves information and communication technologies
• CAVEAT:– This course: an overview of techniques but beware
that most computer attacks involve some form of social engineering and user psychology
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Why Computer Security is different?
Are security bugs different from ordinary bugs?“On balance I claim that they are, not for a technical but for a social
reason.Consider a paradigmatic “ordinary” bug, such as library that wrongly
calculates the square root of 2 while apparently doing everything else right. After certain amount of hilarity the community response would be either to use a different library, or, more likely, to avoid taking the square root of 2.
If a security bug is found in a system there is a community of people who make their personal priority to make the wrong behavior happen, typically in other people’s computers.”
Roger Needham
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Dramatis Personae…• Users/agents and all that:
– In Computer Security and in Networks we often have some casting of characters:• Alice and Bob are the good users who wants to communicate or do some
other things • Eve, Charlie wants to disrupt it
– Dramatis personae is a comfortable simplification but it should be clear that it is a simplification
• CAVEAT:– we should not attribute human form to computer processes. The word “user” is
often used for a human being or a process acting on behalf (maybe) of a human being, or a process acting on behalf of a process, acting on behalf on a process…
• Terminology Principal– Some entity on a network or on a system that ask for some security relevant
services
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ISO 7498-2 Standard
• definitions of security terminology,• 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
• security threat– a possible means by which a security policy may be
breached (e.g. loss of integrity or confidentiality).
• security service– a measure which can be put in place to address a
threat (e.g. provision of confidentiality).
• security mechanism– a means to provide a service (e.g. encryption, digital
signature).
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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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Security Policy Types
• identity-based– access to and use of resources determined on the
basis of the identities of users and resources,
• rule-based– resource access controlled by global rules imposed
on all users, e.g. using security labels.
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Security threats
• Threat– person, thing, event or idea which poses some danger to an
asset (in terms of confidentiality, integrity, availability or legitimate use).
• Attack– realisation of a threat.
• Safeguards– measures (e.g. controls, procedures) to protect against threats.
• Vulnerabilities– weaknesses in safeguards.
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Risk
• Risk– measure of the cost of a vulnerability– takes into account probability of a successful attack
• Risk analysis– determines whether expenditure on (new/better)
safeguards is warranted.
• Quality of Protection?– A missing concept in ISO
“Total Security will only be achieved when we are all dead”
Classroom thought
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Fundamental Threats
• 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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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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Security Services classification
• 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.
• Password Authentication, Challenge-Response Protocols, OTPs…
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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• RBAC, White – Blacklisting …
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Data Confidentiality
• Protection against unauthorised disclosure of information.
• Four types:– Connection confidentiality (e-banking),– Connectionless confidentiality (p2p networks),– Selective field confidentiality (e-voting),– Traffic flow confidentiality.
• Ex: 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.
• Think of SQL injection and you’ll get an idea
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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).
• I.e.: Signed letter with a recorded delivery
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Security mechanisms
• They exist with a single purpose: Provide and Support Security services.
• Classes– Specific security mechanisms.– Pervasive security mechanisms (not specific from
a particular service)
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Specific Security Mechanisms
• Cyphering,• digital signature,• access control mechanisms,• data integrity mechanisms,• authentication exchanges,• traffic padding,• routing control,• Notarisation (Trusted 3rd Parties).
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Pervasive Security Mechanisms
• trusted functionality,• security labels,• event detection,• security audit trail,• security recovery.
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Examples on Pervasive Mechanisms
• 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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Focus of Security Services?
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Where to focus security controls?
• The focus may be on data – operations – users • Data– e.g. integrity requirements may refer to rules on Format and
content of data items (internal consistency).– account balance is an integer
• Operations that may be performed on a data item– credit, debit, transfer, …
• Users who are allowed to access a data item– account holder and bank clerk have access to account
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Security Controls: Protection
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• Thanks:– To you, your groups and your performance.
To Fabio Massacci:For making wonderful slides I can reuse now.