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Hoang Nguyen Van
Mail: hoangnvvnua@gmail.com
Department of Computer Science – FITA – HUA
Information Security Course -----...
Information Security ------------- Fall 2013
Hoang Nguyen Van
How I can share with my boyfriend, a secret key.
Information Security ------------- Fall 2013
Hoang Nguyen Van
How to manage mutual keys
Information Security ------------- Fall 2013
Hoang Nguyen Van
I hate my keys
Information Security ------------- Fall 2013
Hoang Nguyen Van
Information Security ------------- Fall 2013
Hoang Nguyen Van
Online Trusted 3rd Party (TTP)
O(n) keys per user
Information Security ------------- Fall 2013
Hoang Nguyen Van
Online Trusted 3rd Party (TTP)
O(1) one key per user
kAB
Information Security ------------- Fall 2013
Hoang Nguyen Van
Online Trusted 3rd Party (TTP)
Generating keys: a toy protoc...
Information Security ------------- Fall 2013
Hoang Nguyen Van
Can we generate shared keys without
an online trusted 3rd pa...
Information Security ------------- Fall 2013
Hoang Nguyen Van
Ralph Merkle (1952)
Information Security ------------- Fall 2013
Hoang Nguyen Van
Merkle Puzzles (1974)
Information Security ------------- Fall 2013
Hoang Nguyen Van
Merkle Puzzles (1974)
“Puzzle # xi” ll ki
Information Security ------------- Fall 2013
Hoang Nguyen Van
Merkle Puzzles (1974)
BobAlice
puzzle1 , … , puzzlen
xj
kj k...
Information Security ------------- Fall 2013
Hoang Nguyen Van
The Diffie-Hellman protocol
Information Security ------------- Fall 2013
Hoang Nguyen Van
2
5
Very easy
Very hard
One-way function
Information Security ------------- Fall 2013
Hoang Nguyen Van
10 10
510 310
10 5
3
10 5
3
310 510
KEY
Alice Bob
The Diffie...
Information Security ------------- Fall 2013
Hoang Nguyen Van
The Diffie-Hellman protocol
Alice Bob
choose random a in {1,...
Information Security ------------- Fall 2013
Hoang Nguyen Van
Information Security ------------- Fall 2013
Hoang Nguyen Van
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Key Exchange

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Key exchange problem

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Key Exchange

  1. 1. Hoang Nguyen Van Mail: hoangnvvnua@gmail.com Department of Computer Science – FITA – HUA Information Security Course --------------------------------------------- Fall 2013 Dept. of Computer Science – FITA – HUA
  2. 2. Information Security ------------- Fall 2013 Hoang Nguyen Van How I can share with my boyfriend, a secret key.
  3. 3. Information Security ------------- Fall 2013 Hoang Nguyen Van How to manage mutual keys
  4. 4. Information Security ------------- Fall 2013 Hoang Nguyen Van I hate my keys
  5. 5. Information Security ------------- Fall 2013 Hoang Nguyen Van
  6. 6. Information Security ------------- Fall 2013 Hoang Nguyen Van Online Trusted 3rd Party (TTP) O(n) keys per user
  7. 7. Information Security ------------- Fall 2013 Hoang Nguyen Van Online Trusted 3rd Party (TTP) O(1) one key per user kAB
  8. 8. Information Security ------------- Fall 2013 Hoang Nguyen Van Online Trusted 3rd Party (TTP) Generating keys: a toy protocol “Alice wants key with Bob” (kA) choose random kABE(kA,”AB”||kAB) ticket = E(kA,”AB”||kAB) (kB) ticket kAB kAB (Eavesdropping security only)
  9. 9. Information Security ------------- Fall 2013 Hoang Nguyen Van Can we generate shared keys without an online trusted 3rd party?
  10. 10. Information Security ------------- Fall 2013 Hoang Nguyen Van Ralph Merkle (1952)
  11. 11. Information Security ------------- Fall 2013 Hoang Nguyen Van Merkle Puzzles (1974)
  12. 12. Information Security ------------- Fall 2013 Hoang Nguyen Van Merkle Puzzles (1974) “Puzzle # xi” ll ki
  13. 13. Information Security ------------- Fall 2013 Hoang Nguyen Van Merkle Puzzles (1974) BobAlice puzzle1 , … , puzzlen xj kj kj O(n) O(n) O( n2 ) But Infeasible
  14. 14. Information Security ------------- Fall 2013 Hoang Nguyen Van The Diffie-Hellman protocol
  15. 15. Information Security ------------- Fall 2013 Hoang Nguyen Van 2 5 Very easy Very hard One-way function
  16. 16. Information Security ------------- Fall 2013 Hoang Nguyen Van 10 10 510 310 10 5 3 10 5 3 310 510 KEY Alice Bob The Diffie-Hellman protocol
  17. 17. Information Security ------------- Fall 2013 Hoang Nguyen Van The Diffie-Hellman protocol Alice Bob choose random a in {1,…,p-1} choose random b in {1,…,p-1} kAB = gab (mod p) = (ga) b = Ab (mod p)Ba (mod p) = (gb) a =
  18. 18. Information Security ------------- Fall 2013 Hoang Nguyen Van
  19. 19. Information Security ------------- Fall 2013 Hoang Nguyen Van

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