Security

Digital Signatures

Digital Signatures Using MD

Authorization/Access Control• Verifying access rights is called access control• Granting access rights is called authorization• Used interchangeably• Subject – Entity that requests access• Object – Entity that is being accessed

General Issues in Access Control

General model of controlling access to objects.

Access Control Matrix• Subject is represented as a row and object as column• M[s, o] indicates the access rights of s on o• Inefficient if large numbers of subjects & objects• Access control lists

– Object maintains a list of all subjects allowed to access it and operations they can perform

• Capabilities– Each subject maintains a list of “rights” on various

objects– Need for making capabilities tamper proof

Access Control Matrix

Comparison between ACLs and capabilities for protecting objects.

a) Using an ACLb) Using

capabilities.

Protection Domains

The hierarchical organization of protection domains as groups of users.

Firewalls

A common implementation of a firewall.