1 / 24

CS244B Final Review Session

CS244B Final Review Session. Anthony Ho. Administration. Distributed File Systems project: -Working on grading -Majority of students fail at least one test. Final exam. Tuesday 3:30 – 6:30 pm Gates B01 Cumulative Closed book Multiple choice and short answer. Agenda.

jeff
Download Presentation

CS244B Final Review Session

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. CS244B Final Review Session Anthony Ho

  2. Administration • Distributed File Systems project:-Working on grading-Majority of students fail at least one test.

  3. Final exam • Tuesday 3:30 – 6:30 pm Gates B01 • Cumulative • Closed book • Multiple choice and short answer

  4. Agenda • Directories and Naming • Accounts and Authentication • Transactions, Agreement, and Reconciliation

  5. Common, Proper Names, Description • Common names can refer to a set of objects • Proper names refer to a specific object • Common names have synonymy, ambiguity, substitutability with description

  6. Pure and Impure names • Pure names – No encoding or description of the entity being referred to • Impure names – Contains some information about the entity

  7. Advantages/Disadvantages of Impure Names • Can encode structure used for mappingEx: • Can include some information about the object. Ex: dev/cdrom • Can use structure to facilitate distributed allocation – Some controller assigned responsibility for some subset of names • Can lose flexibility – Entities cannot as easily change without changing their name • Longer names

  8. External/Internal names • External names are necessary for: -error reporting-referring to objects from user-visible interfaces-address-space and machine-independent identification of objects

  9. Internal Names • More efficient and simpler for software to implement • “External names are a necessity; internal names are an optimization” • Sometimes a necessary optimization • Internal names cannot capture intent • Examples: IP addresses

  10. UUID • Identifiers that can be unique for every object in the universe. An internal name • 256 bits? • May introduce impurities for structuring to facilitate mapping due to size of identifier • All problems of internal names. • Legacy issues. • Semantics of UUID naming unclear

  11. When to use internal names • Internal names are much shorter than external names • Only must be unique in the context that uses them. Transient • How large should they be, 32 usually. Up to 64. Or variable length

  12. Cheriton’s view of names • Usually, a server maps names to objects. • Cheriton argues that each object maps external names for objects that it implements • Fate-sharing violated if a name server used

  13. Decentralized/Centralized naming • Centralized. All naming lookups go to one place • Decentralized: Multiple name authorities • Security issue of decentralized: How to know a server is responsible for naming of a certain object

  14. Examples: • Lampson Directory Naming: Database changes updated in “sweeps” • Epidemic approach: Names spread like an epidemic • V-system: Uses internal naming

  15. URLs • Initially impurity limits the flexibility of this name. Cannot move object without renaming it • Benefit: Associated brand • Benefit: Subtree redirection • Benefit: Logical or virtual name

  16. Shared vs Public Key Encryption • Shared key – Symmetric key. Same key used for encryption and decryption • Public key – Asymmetric key. Different keys used for encryption and decryption. • Public key encryption much slower than Shared keys

  17. Encryption Terms • Confidentiality – Communication cannot be read by others • Integrity – Communication cannot be modified without detection • Authentication – Can determine who the message is from

  18. Three issues with key management • Lifetime – How long before regenerating key. • Selection – How to generate a key • Distribution – How to distribute keys among parties: Outside channel, chained key distribution, two-level key distribution, trusted third party

  19. How to Authenticate • Supply key or password • Encrypt a value, if decrypts to the right value, then the principal must have the key • Third party vouches for principal. Certificates

  20. Problems with Certificates • Revocation difficult • Difficult to determine liability • Verifying entities is expensive and might not be worth it

  21. Open Security vs Secrecy • Secrecy has a single point of failure, the key • Cannot tell when key is no longer secret • Open security goes for safety and availability • Open security puts everything in the open and clear to everyone • Unexpected actions will be contested and detected quickly

  22. Non-blocking commit • Disseminate result of prepare to commit and before to commit. • Two phase commit is blocking. Servers block while waiting for result of prepare to commit • Surviving server that knows state of prepare to commit can complete the protocol by committing

  23. Consistency vs Availability • The more servers you have the more possibility for inconsistency • Consistency is safer, but typically availability is more useful

  24. Any questions? • Good luck on the final!

More Related