Security Problems in Computer Systems

• "As society becomes more dependent on computers, computer crime is becoming not only more disastrous in its potential impact, but also more attractive to the criminal"
• by K Shankar

Threats to Computer Systems

• Privacy and security are problems associated with computer systems and applications that were not foreseen until well into the second half of the present computer age."
• by R. Turn and W. Ware

General Issues Relating to Security

• Threats
• Vulnerabilities
• Attacks
• Controls
• Effectiveness of Controls
• Impediments to Security

Threats

• Potential occurrences, malicious or otherwise, that can have undesirable effects on assets or resources associated with computer systems
• Goals of computer security with respect to mitigating threats is to provide
• insights
• techniques
• methodologies

Vulnerabilities

• Characteristics of computer systems that make it possible for a threat to potentially occur
• threats can be mitigated by identifying and eliminating vulnerabilities

Attacks

• Actions taken by an entity that exploit certain vulnerabilities in order to cause an existing threat to occur
• often heuristic (trial and error)

Controls

• Goals of security controls are to provide:
• confidentiality
• integrity
• availability
• authentication
• Controls can be procedures or mechanisms

Effectiveness of Controls

• Must be used
• users must be convinced of the necessity for controls
• Must be effective
• timeliness
• reviewed periodically
• Necessary and sufficient

Impediments to Security

• Existing systems must be retrofitted
• Assurance is difficult
• Effective procedures
• Security requirements are difficult to identify
• Attitude of computer community

Confidentiality

• Assets of a computer system are accessible only by authorized parties or entities
• The property of confidentiality protects a system from the threat of disclosure
• A Disclosure Threat is the possibility that data will be accessed by unauthorized entities
• Eavesdropping and resource stealing are disclosure attacks

Confidentiality Controls

• Encryption
• Data is transformed (encoded) so that it is unintelligible to an entity that does not have a key to decode the data
• encryption is at the heart of all computer security
• Laws
• eavesdropping and wiretapping are illegal

Integrity

• Unauthorized changes in data can not occur
• Unauthorized changes in data can be detected
• The property of integrity protects against threats of modification and fabrication

Integrity Controls

• Encryption
• Message integrity check (MIC)
• One-way functions

Availability

• Capacity to meet service needs
• includes timeliness and usability
• The property of availability protects against threats of denial of service
• Denial of service occurs when when access to computer system assets are blocked
• unauthorized access to computer system assets frequently results in denial of service to an authorized user

Availability Controls

• Passwords
• Still mainly unexplored
• Overlap with concerns of the real-time community

Assurance

• Convincing evidence that control mechanisms really do mitigate threats
• Examples of assurance evidence
• test results
• field results
• formal methods
• Providing adequate assurance is a difficult task

Privacy

• Concerns data about humans
• Privacy assures that this data is not made public or accessible by unauthorized individuals
• Threats on the privacy property include snooping on information about users
• Accounting logs made for security purposes are a vulnerability to a snooping attack

Threats, Vulnerabilities, Attacks, and Controls Reviewed

• Threat -- possibility of an attack
• Vulnerability -- a weakness or characteristic that makes it possible for an attack to occur
• Attack -- an action that exploits a vulnerability causing an existing threat to occur
• Control -- a mechanism or procedure that mitigates a threat

System Security Engineering

• Spiral Approach
• Iterative process
• Specify system architecture
• Identify threats, vulnerabilities, attacks
• Estimate component risk -- exit spiral if acceptably low
• Prioritize vulnerabilities
• Identify and install safeguards -- go back to first step

Threat Tree Approach

• Threats are the highest concern of the science of computer security
• Threat tress can be used to insure that security requirements are:
• complete (and organized)
• justifiable
• well-documented