Chapter 1  Introduction 1 Overview  What is a secure computer system?  Concerns of a secure system o Data: Privacy, Integrity, Availability o Users: Authentication, Authorization, Privacy  Security in stand-alone, networked, and internetworked environments

Chapter 1  Introduction 2 Secure Computer System  A security policy specifies exactly what types of actions are and are not permitted on the system  Example security policy o Only authorized users able to use the system o Authorization/Access control o Resources sharing among users  A secure system obeys its security policy

Chapter 1  Introduction 3 Security Breaches  A violation of a system’s security policy is called a security breach  Security breaches can occur o Accidentally – faulty program o Intentionally – virus  Creating a system where security breaches cannot occur can be easy or impossible depending on o What the security policy requires o How the system implements the policy

Chapter 1  Introduction 4 Secure Systems Design  Policy Simplicity Principle o Policy as simple as possible (but no simpler) o Should state what is allowed and forbidden  System Functionality Principle o Include necessary functionality (and no more) o Perform job it was designed to do (and no more)

Chapter 1  Introduction 5 Policy Simplicity  Simpler security policies are easier to get right, reason about and implement  Security breaches caused by policy shortcomings are most often due to o Incomplete or inconsistent policy o Misunderstanding the policy’s requirements o Error in implementation

Chapter 1  Introduction 6 System Functionality  Limiting functionality limits attacks  Security breaches caused by system functionality can be caused by o Software bugs o Unforeseen interactions between components

Chapter 1  Introduction 7 Relative Security  Few useful systems will be absolutely secure  We view security in a relative sense  This does not mean that good security design and implementation is unimportant  Example: safes

Chapter 1  Introduction 8 Cost vs Security  Proper security level depends on value of the items that system is protecting (other concerns?)  Trade-off between cost and security  Select security level appropriate for user needs

Chapter 1  Introduction 9 Cost vs Security (continued)  Example: user authentication o System A - authenticates the user by retinal scan o System B - authenticates users once with password  System A is probably more secure than system B, but more costly and inconvenient  Is added security and expense called for? o Maybe for NSA o Not for an individual

Chapter 1  Introduction 10 Secure System Concerns  Data o Privacy o Integrity o Availability  Users o Authentication o Privacy

Chapter 1  Introduction 11 Data Privacy  Data privacy: access to information is limited to authorized entities  Examples o Certain files only accessible to certain users o Communications between two users cannot be read by some third party  Cryptography for privacy of data

Chapter 1  Introduction 12 Data Integrity  Data has integrity if it can only be modified by authorized principals  Examples o Bank must ensure that only authorized personnel can change account balances o Company must make sure that its freeware program has not been modified  Message-digests used to protect integrity

Chapter 1  Introduction 13 Data Availability  Data availability means that data is accessible in a timely manner as needed  Examples o Non-working laptop brought to open-note test o Student’s laptop notes poorly organized so time wasted finding relevant information  Replication and fault tolerance can be used to ensure the availability of data

Chapter 1  Introduction 14 User Authentication  User authentication means that system accurately determines user’s identity  Examples o Files readable only by their owner o Only certain users should be able to add or delete system accounts  Authenticate by: something you know, something you have, something you are

Chapter 1  Introduction 15 User Privacy  privacy means that users have control over info collected and made available to others  Examples: o User may not want others to know programs they run, who they communicate with, etc. o User may not want to receive spam  Anonymity can protect privacy

Chapter 1  Introduction 16 Network and Internet  Additional challenges o Privacy  Stand-alone system - the operating system is likely to control all communication channels  Networked systems - no host controls the communication medium; eavesdropping usually easy o User authentication  Stand-alone system – user is physically present  Internetworked systems – user may access system over an insecure communication channel

Chapter 1  Introduction 17 Summary  A secure computer system follows security policy  Security concerns involve protecting o Data privacy o Data integrity o Data availability o User authentication o User privacy o Network and internetwork  additional risks