Introduction to Computer Security

Introduction to Computer SecurityCourse Introduction

Pavel LaskovWilhelm Schickard Institute for Computer Science

Computer security in headlines

Motivation for security abuse

Intelligence and military use (5th century BC – 1980’s)“security by obscurity”, crypto-wars

Hacker spirit, fun and fame (1980’s – 2000’s)Pwnie, CCC, CTF

Cybercrime, monetary gain (2000’s – currently)Phishing, botnets, spam

Political goals, cyberconflict (2007 – currently)Attack on Estonia, Russian-Georgian conflict, Stuxnet

“Hacktivism” (2011 – currently)

Computer security in numbers

New malicious code samples observed (Symantec)

Technische Universität Berlin

Gefährliches Internet

» Internet als Risikofaktor?

» Omnipräsenz von Angriffen, Würmern und Viren» Massive Schäden bei Unternehmen und Bürgern» Zunehmende Kriminalisierung von Schadsoftware

750.000

1.500.000

2.250.000

3.000.000

2002 2003 2004 2005 2006 2007 2008 2009

Neuer Schadcode pro Jahr (Symantec)

Why are computer systems insecure?

Growing complexity of computer systemslarge number of components, complex interaction

High competitionshort “time-to-market”, high ROI

Leveraging of risks through high connectivityworm outbreaks, botnets

Slow incident response“incident hiding”, manual handling

Human error

What can go wrong will go wrong!

Human error

Human error: a case study

Human error: lessons learned

Users make errorselaborate social engineering designtime pressure

Significant monetary motivationBusiness efficiency via Internet

Security instruments

Prevention

Detection

Reaction

Prevention instruments

Goal: enforce certain operational policies.Examples:

Encrypt messages during transmission over public networks.Require user authentication for certain services.Control access to different resources.

Limitations:Not always applicable, e.g. in open systems such as webservices.Strong assumptions, can be circumvented.

Detection instruments

Goal: detect violations of security policies.Examples:

Antivirus scanners: detection of malicious code or behavior.Intrusion detection systems: detection of attacks in networktraffic.Detection of malicious websites.

Limitations:Significant latency in decisions.Significant workload: a detection system without an operator isuseless.

Reaction instruments

Goals:Understand the root causes of successful attacks.Update prevention mechanisms.Real-time response, autonomous decisions.

Examples:Computer forensics: investigation of infected systems.Malware collection and analysis.Intelligent firewalls.

Limitations:Even larger latency, “post-mortem” operation.Significant risk of real-time response.

What will you learn?

Findamental concepts of computer securitydry, but important!

Basic security goals and mechanismsauthentication, access control, encryption, etc.

Practical security instrumentsWindows and Linux security

Further selected topicsnetwork securitysoftware securityweb application and browser security

Coarse administration

Lectures:Wed, 14:00 (ct) – 16:00, A301

Formalities:Credit hours (diploma): 2 SWS (lectures) + 1 SWS (exercises)Credit points (B.Sc.): 3 LP (lectures) + 1 LP (exercises)

Exams and grading:diploma: oral exam by appointment, graded certificate forexercisesB.Sc: written exam at the end of semester, 30% of the finalgrade from exercises

Office hours: by appointmentCourse web page:http://www.cogsys.cs.uni-tuebingen.de/lehre/ws12/it sicherheit.html

Homework assignments

Meetings:Thu, 14:00 (ct) – 16:00, F122, on selected datesFirst meeting: 08.11

3 written homework assignments2 lab meetings and practical assignmentsTeaching assistant: Nedim SrndicEvaluation and grade:

diploma: a grade reflects the percentage of points acquired.B.Sc.: a grade contributes 30% to the final grade.

Bibliography

Dieter Gollmann.Computer Security. 3rd edition.Wiley & Sons, 2010.

Ross Anderson.Security Engineering.Wiley & Sons, 2001.

Bruce Schneier.Secrets and Lies: Digital Security in a Networked World.Wiley & Sons, 2004. (fun to read)

A typical web application

Legitimate user

BrowserWebserver

Internet

Attack: interception of communication

Legitimate user

BrowserWebserver

Internet

Attacker

Credit card number

Security goal: confidentiality

Prevention of unauthorized reading of dataPrevention of unauthorized learning of informationPotential abuse scenarios:

Discovery of confidential information (e.g. details of a businesscontract)Discovery of authentication credentials (e.g. password sniffing)

Enforcement intruments:Symmetric or asymmetric cryptographyAnonymization techniques

Legitimate user

BrowserWebserver

Internet

Attack: identity spoofing

Legitimate user

BrowserWebserver

Internet

Fake webserver

Attacker

Security goal: authentication

Verification of an identity of a person or a computerPrerequisite for access controlAuthentication methods:

Shared secrets (e.g. password or PIN)Ticket systems (identity cards, digital certificates)Challenge-response techniquesBiometric techniquesHuman authentication: CAPTCHA’s, Turing test, etc.

Authentication risks: identity theft

Legitimate user

BrowserWebserver

Internet

Attack: injection of malicious code

Legitimate user

BrowserWebserver

Internet

Attacker

Malware

XSS attack

Security goal: integrity

Prevention of malicious tampering of dataPotential abuse scenarios:

Fraudulent modification of data (e.g. 100,000¤ instead of100¤ in an online transaction request)Injection of malicious code in downloaded softwareEvading detection by modification of a compromized operatingsystem

Enforcement instruments:Integrity checking using cryptographic hash functions

Legitimate user

BrowserWebserver

Internet

Attack: server overload

Legitimate user

Browser

Internet

Server overloaded

Security goal: availability

A joint objective of security and dependabilityMay be caused by attacks as well as natural phenomena,such as design errors or flash crouds.Enforcement instruments:

Detection of DoS-attacksRouter and firewall reconfigurationService redundancyVirtualization

Legitimate user

BrowserWebserver

Internet

Attack: transaction denial by a user

Legitimate user

BrowserWebserver

Internet

Credit card charded

Transaction cancelled

Security goal: accountability

An audit trail of security-related eventsA key instrument of detection/responseA stronger form of accountability is non-repudiation:unforgeable evidence that a certain action occurred.Similar attacks as integrityEnforcement instruments:

Integrity checksRead-only auditDigital certificates and trusted third parties

Summary

Security is not a solution but an ongoing process.Security can only be achieved by a combination of technicaland organizational measures.One of the biggest security risks is a user.Security is a big challenge but lots of fun as well: a greatfield of study and research.

Next lecture

The economics of computer securitySecurity threatsSecurity design principles

Introduction to Computer Security - Course Introduction to Computer Security Course Introduction ......

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