Identity Elisa Bertino CERIAS and CS ECE Departments Purdue University Elisa Bertino Pag 1 Purdue University Topics Chapter 13 of Textbook What is identity Identity for objects referred to as naming mechanisms Identity for users Multiple names for one thing Different contexts environments Pseudonymity and anonymity Elisa Bertino Pag 2 Purdue University Overview A simple definition of identity Object naming Users principals and subjects Certificates and names Hosts and domains State and cookies Anonymity Elisa Bertino Pag 3 Purdue University A Definition of Identity Identity is simply a computer s representation of an entity Identity depends on the context where the object or user are referenced Elisa Bertino Pag 4 Purdue University Object Naming Identity depends on the system containing the object Different names for one object Human use eg file name Process use eg file descriptor or handle Kernel use eg file allocation table entry inode In databases content information example primary keys is used to identify single records Elisa Bertino Pag 5 Purdue University Object Naming Different names for one context Human aliases relative vs absolute path names Kernel deleting a file identified by name can mean two things Delete the object that the name identifies Delete the name given and do not delete actual object until all names have been deleted Semantics of names may differ Elisa Bertino Pag 6 Purdue University Example Names and Descriptors Interpretation of UNIX file name Kernel maps name into an inode using iterative procedure Interpretation of UNIX file descriptor Refers to a specific inode Refers to same inode from creation to deallocation Elisa Bertino Pag 7 Purdue University Example Different Systems Object name must encode location or pointer to location rsh ssh style host object URLs protocol host object Example ftp abccorp com pub README specifies that the object pub README from the host abccorp com can be accessed by using the FTP protocol Need not name actual object rsh ssh style may name pointer link to actual object URL may forward to another host Elisa Bertino Pag 8 Purdue University Users Exact representation depends from the specific system Example UNIX systems Login name used to log in to system Logging usually uses this name User identification number UID unique integer assigned to user Kernel uses UID to identify users One UID per login name but multiple login names may have a common UID Elisa Bertino Pag 9 Purdue University Multiple Identities UNIX systems again Real UID user identity at login but changeable Effective UID user identity used for access control Setuid changes effective UID to the UID of the owner of the program Saved UID UID before last change of UID Used to implement least privilege Work with privileges drop them reclaim them later Audit Login UID user identity used to track original UID Cannot be altered used to tie actions to login identity Elisa Bertino Pag 10 Purdue University Users Principals and Subjects A principal is an entity that can be granted access to objects or can make statements affecting access control decisions Subjects operate on behalf of principals and access is based on the principal s name bound to a user in some unforgeable manner at authentication time Because access control structures identify principals it is important that principal names be globally unique human readable and memorable easily and reliably associated with known people Elisa Bertino Pag 11 Purdue University Users and Principals The system authenticates the user in the context of a particular principal Elisa Bertino User Principals Real World Users Unit of Access Control Pag 12 Purdue University Users and Principals Example smith at purdue edu Bob Smith smith at unimi it User Elisa Bertino Principals Pag 13 Purdue University Users and Principals There should be a one to many mapping from users to principals a user may have many principals but each principal is associated with a unique user This ensures accountability of a user s actions In other words shared accounts principals are bad for accountability Elisa Bertino Pag 14 Purdue University Principals and Subjects Principal and subject are both used to denote the active entity in an access operation The word principal has many different meanings and is the source of much confusion Principals are public keys SDSI 1996 The term principal represents a name associated with a subject Since subjects may have multiple names a subject essentially consists of a collection of principals Li Gong 1999 Elisa Bertino Pag 15 Purdue University Principals and Subjects A subject is a program application executing on behalf of a principal A principal may at any time be idle or have one or more subjects executing on its behalf Elisa Bertino Pag 16 Purdue University Principals and Subjects A recommendation Policy A principal is an entity that can be granted access to objects or can make statements affecting access control decisions Example a user ID System Subjects operate on behalf of principals access is based on the principal s name bound to the subject Example a process running under a user ID Elisa Bertino Pag 17 Purdue University Naming and Certificates Certificates were introduced to provide assurance about the entity associated with a public key Webester s Dictionary defines a certificate as a document containing a certified statement especially as to the truth of something Certificates are issued by certification authorities CA A CA handles the certificates on behalf of his constituency and takes some sort of liability for having performed the necessary trust and security checks Elisa Bertino Pag 18 Purdue University Naming and Certificates Certificates are issued to a principal Principals need to be uniquely identified to avoid ambiguities Problem names may be ambiguous Does the name Matt Bishop refer to The author of the texybook A programmer in Australia A stock car driver in Muncie Indiana Someone else who was named Matt Bishop Elisa Bertino Pag 19 Purdue University Disambiguating Identity Include ancillary information in names Enough to identify each principal uniquely X 509v3 Distinguished Names provide an approach to the unique identification of each principal A distinguished name DN consists of a series of fields each with a key and a value Example X 509v3 DN O University of California OU Davis campus OU Department of Computer Science CN Matt Bishop refers to the Matt Bishop CN is common name in the