Access Control

Who and what has access to which resource has to be controled on every IT System.

Introduction

Controlled are issues like

• access to files
• access to memory
• execution of programs
• sharing data with other principals

Access is controlled at different levels:

• application
• middleware
• operating system
• hardware

The complexity of administering Access Control is growing complexity.

Hardware Protection

Protection Problem: preventing one process from interfering with another

Confinement Problem: preventing programs communicating outwards through other than authorized channels (e.g. memory overwriting)

Intel 80x86 (Pentium) Processors

8088/8086:	any running program controlled the whole machine
80286:	protected segment addressing and rings, operating systems could run proper
80386:	built-in virtual memory and large memory segments, treated as a 32-bit flat-address machine

Rings

• process in ring 0 (kernel) manages privilege level of other processes
• ring 1, 2 usually system processes (e.g. win32 subsys, virtual DOS)
• ring 3 user programs
• gates between rings for executing code at an other level

Other Procssors

Acorn Risc Machine (ARM)

• most commonly licensed to third-party vendors of embedded systems
• 32-bit processor
• separate banks of registers for user and system processes
• hardware protection can be customized

Security Processors

• hardware security support for cryptography and access control
• authorized state
• password covered memory access

s.o.

Operating Systems

• access control for files and processes, ring management, IO-management, memory, processors s.o. as deep as the hardware permits it
• matrix is often used to manage this
• not usable for large organizations, because the administration becomes to difficult for humans

Do it by groups and/or roles !

Groups and Roles

• every user fits into one or some categories
• rights have to be defined for these categories
• user gets role and fits in group

What is the difference ?

There‘s no final definition.

Access Control Lists

• just one column of the access control matrix stored for every resource
• not very performant
• difficult to administrate

Unix

• simple list: owner, group, world for user – not for programs
• indirect method for programs: SUID and SGID
• or by user dummy

Win NT

• more attributes (take ownership, change permission, delete)
• arrangement in domains with trust between them

Capabilities

• just one row of the access control matrix stored for every resource
• some experimental implementatios in the 70s
• today a comeback in the form of public key certificates

Win 2k/XP

• used combined with ACL
• group policies
• active directory

Understands

Granularity	control access at the right level file access ↔ database file different systems, different access controls
Sandboxing	access to a restricted environment
Proof-Carrying-Code	tests the behaviour of a program
Object Request Brokers	controlling calls for several objects/resources

Problems

• problem if any level doesn’t controll access
• "Every system has at least one bug – Windows much more."
• "The most serious bug is sitting in front of the monitor."
• smashing the stack
• bypassing denied permissions
• trojans
• structural defects in operating systems (Windows user has to be admin for installation)

Background

Decisions were made one time, consequences work eternally, but environment changes very rapidly.

Sometimes, also a developer uses the easier way to reach a goal.

Sometimes it‘s just user friendly.