Security

Butler Lampson

TECS Week 2005

January 2005

Note: These slides were prepared in Word, and some of the formatting is lost in this HTML version. Here are the Word and Acrobat versions.

Outline

Introduction: what is security?

Principals, the “speaks for” relation, and chains of responsibility

Secure channels and encryption

Names and groups

Authenticating systems

Authorization

Implementation

REAL-WORLD SECURITY

It’s about value, locks, and punishment.

-Locks good enough that bad guys don’t break in very often.

-Police and courts good enough that bad guys that do break in get caught and punished often enough.

-Less interference with daily life than value of loss.

Security is expensive—buy only what you need.

-People do behave this way

-We don’t tell them this—a big mistake

-Perfect security is the worst enemy of real security

Elements of Security

Policy: Specifying security
What is it supposed to do?

Mechanism: Implementing security
How does it do it?

Assurance: Correctness of security
Does it really work?

Abstract Goals for Security

Secrecy controlling who gets to read information

Integrity controlling how information changes or resources are used

Availability providing prompt access to information and resources

Accountability knowing who has had access to information or resources

Dangers

Dangers

Vandalism or sabotage that

– damages information integrity

– disrupts service availability

Theft of money integrity

Theft of information secrecy

Loss of privacy secrecy

Vulnerabilities

Vulnerabilities

– Bad (buggy or hostile) programs

– Bad (careless or hostile) people
giving instructions to good programs

– Bad guys corrupting or eavesdropping on communications

Threats

– Adversaries that can and want to exploit vulnerabilities

Defensive strategies

Coarse: Isolate—Keep everybody out

– Disconnect

Medium: Exclude—Keep the bad guys out

– Code signing, firewalls

Fine: Restrict—Let the bad guys in, but keep them from doing damage

– Hardest to implement

– Sandboxing, access control

Recover—Undo the damage. Helps with integrity.