CS134a: Security

1. CS134a: Security • Overall outline • Basic Issues • Types of protection and security • Penetration of a computing facility • Access and information-flow control mechanisms • Protection Problems Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

2. User authentication methods • Based on one or more of the following: • Knowledge of some “secret” information (e.g. password) • Possession of some artifact (e.g, key) • Physical characteristic (e.g. fingerprint, brainwave) • Secret information may be • password • an interactive dialog (what’s your SS#, mother’s maiden name, etc.) • a combination to the lock on a room Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

3. Physical artifacts • A card with machine-readable information • Bank machines (ATMs) require card+PIN • Badges • Keys Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

4. Physical characteristics • Kinds • Fingerprints: hard to implement • Hand geometry: lengths of fingers, etc. • Voice patterns • Signatures: speed and force of writing • Uncertain recognition may reject an authorized user • or accept an impostor Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

5. Penetration • A user may bypass authentication mechanisms • A user may obtain information that will permit legal entry • Wire tapping • Watching the network for cleartext passwords • Never send a cleartext password over Internet! Use encryption (like ssh) to protect your passwords • Trial-and-error • Guess a password: seems hard with 8-character passwords (64^8 combinations) • In practice, people tend to use a small subsets Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

6. Penetration • Browsing: When storage is deallocated, the system rarely erases it (free disk blocks or memory pages). Defense systems often require garbage to be copied onto deallocated areas. • Waste searching. Looking through garbage cans, etc., is highly successful. • Trap doors: applications may contain secret entries. A Trojan Horse is a program offered for public use that performs unadvertised actions. Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

7. Access and Information Flow Control • Process information locations • Registers • Associative memories (cache, TLB) • Primary memory • Secondary memory • Protection • OS saves and restores registers on each context switch; registers are private • Cache and TLB are inaccessible to user-mode programs Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

8. Access and information flow control • An execution environment includes • programs, files, processes residing in primary and secondary memory • hardware components like IO devices or special processors • Execution environment may be • static: constant for the life of a process • dynamic: varies with time • Dynamic environments are needed to provide the smallest possible execution environment Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

9. Main memory protection • Control process access to it’s own instructions, and to another process • A process should only be allowed to access in areas that are assigned by OS • Memory access rights: • Read(R): may read the contents, even copy it into executable areas • Write(R): may modify the contents; Append(R) only allows writing onto the end • Execute(R): may execute the contents as a program Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

10. Access control • Boolean logic • Ø(R Ú W Ú X): no access • R Ù Ø(W Ú X): read-only Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

11. Access control without virtual memory • Bounds registers Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

12. Access control without virtual memory • Identification keys • Memory is divided into blocks (like pages) • Each memory block has an n-bit pattern called a lock • Each process contains an n-bit key • Hardware compares the key with the lock on every access Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

13. Access control with virtual memory • Relocation register Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

14. Relocation register • Same problem: access control is inflexible • Could use locks and keys • Better to associate access control with each process and extend the Mmap function to handle extra info Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

15. Paged segmentation • Access rights are associated with each segment • Segment table entry: • pt_base: pointer to page table • int pt_len: length of page table • bool pt_resident: whether page table is in memory • access_rights access: access control info • Page table entry • pg_base: pointer to page • pg_resident: whether page is in memory Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014

16. Paged segmentation address translation Computing Systems http://www.cs.caltech.edu/cs134/cs134a November 13, 2014