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 ACL b)Using capabilities.

Protection Domains The hierarchical organization of protection domains as groups of users.

Firewalls A common implementation of a firewall.