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← Pairwise Distribution - Applied Cryptography

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Showing Revision 2 created 05/24/2016 by Udacity Robot.

  1. The first approach I'll talk about--I'll call it Solution #0
  2. because it's really not even approaching a solution--
  3. is to have pairwise shared keys.
  4. And the idea here is for everyone who ever might want to communicate
  5. to get together and form keys between them,
  6. so let's say this is Alice, Bob, Colleen, Diana,
  7. someone whose name starts with E, and someone whose name starts with F.
  8. And Alice would set up a pairwise shared key, secretly communicating
  9. with each of the other people.
  10. Bob has a shared key with Alice.
  11. Bob would find a shared key with all of the other people
  12. that he might want to communicate with, and Colleen needs to find
  13. a shared key with the remaining people, and so forth.
  14. And you would have a key between every pair of people,
  15. and so whoever wants to communicate, well,
  16. if it's between Colleen and Edgar, they would have a shared key
  17. that they've previously established to communicate.
  18. This might work for a small number of people.
  19. If we have a large number of people, this gets to be ridiculously expensive,
  20. so we'll have a short warmup quiz to see how expensive.
  21. The question is how many keys would we need
  22. if there was a group of 100 people, and any of pair of them
  23. should be able to communicate secretly with each other?