Principles of System Security - University Of Maryland

Principles of System Security - University Of Maryland

Privacy Enhancing Te chnologies Lecture 4 Principles of System Security Elaine Shi slides partially borrowed from Jonathan Katz 1 Roadmap

Privacy and System Security Principle of least privilege Principle of Privilege Separation 2 Why System Security? System security is necessary for privacy. e.g. If OS is cpmpromised, data can be bre ached.

3 System security Several meanings of system security here: Security of the entirety of what is being pro tected Operating-system security Host security

4 Principle of least privilege A subject should be given only the privileges it needs to accomplish its task E.g., only allow access to information it needs E.g., only allow necessary communication The function of a subject (not its identity) should dete rmine this

I.e., if a subject needs some privileges to complete a specifi c task, it should relinquish those privileges upon completion If reduced privileges are sufficient for a given task, the subje ct should request only those privileges 5 Principle of least privilege Every program and every privileged user of the system should operate using the least amount

of privilege necessary to complete the job.[Jero me Saltzer 74] 6 Example User account management: normal user does not have administrator's privilege. A CEO share his office key only with his assis tant, but not anyone else.

7 More example A web server should not run with root pr ivilege if root privilege is not needed. 8 Privilege Separation

Divided system into parts which are limited to the spe cific privileges they require in order to perform a spec ific task. E.g., OS ensures isolation between apps Hypervisor ensures isolation between OS 9 OS ensures isolation between apps

App App App App OS

If one of the application is buggy and thus is compromised or crashed, it will not affect the behavior of other applications 10 Hypervisor ensures isolation between OS OS OS

OS Hypervisor Hardware 11 Homework Can you give some more examples in real life that indicat

e principle of least privilege and privilege separation? 12 Reading list [Saltzer and Schroeder 1975] The Protection of Information in Computer Systems 13

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