1. Ralph C. Merkle Department of Electrical Engineering and Computer Science University of California, Berkeley SECURE COMMUNICATIONS OVER INSECURE CHANNELS Reporter: Ông Đắc Thiên Thọ 51003243 Võ Xuân Thịnh 51003243

2. AGENDA 1. Review 2. The New Approach • The paradigm • The method • Implementation 3. Implications 4. Addenda 5. Evaluations

3. REVIEW KeyE • Overview • Click here… • How about Key? => TRUSTED THIRD PARTY • All attempts by Malice to modify or alter messages can be detected • Malice is unable to determine the content of any message over the key channel Plaintext Ciphertext Crypto-system Hello, This content is confidential …................... ……………….. …. Encryption À¿¾«§¶  ………………… ………………… ….. Decryption KeyD

4. NEW APPROACH • Dropping the second restriction on the key channel Malice has perfect knowledge of everything that is sent over this channel • A solution: The big-O of work, selecting the key to transmit by Alice or Bob, is much lower than the work put in Malice to determine the key.

5. NEW APPROACH • “Puzzle” • Selecting a strong encryption function (Lucifer encryption function) • Creating N puzzles by encrypting by that function  the puzzle is not unsolvable • Constant is known by all Alice, Bob or Malice as evidence that we have selected right key • Including: • Constant – evidence • Id – Id match for each puzzle • Key – Key that have been encryption from Id

6. Detailed Algorithm • Everyone know: • F and FInverse: Strong encryption function and its reverse, respectively. • N: very “Big” number • C: Constant • X generates: • “Constant” - evidence if anyone using right key • N puzzle with key space in (C*N) with “Constant” in it.

7. Detailed Algorithm • X generates: • K1, K2: secret key for encryption. “Constant” - evidence if anyone using right key. • N puzzle with each puzzle have: • Id = F(I, K1); • Key = F(Id, K2) • “Constant” • Random key in key spaces (C*N). • X public constant and N puzzle.

8. Detailed Algorithm • Y: • Choose 1 in N puzzle. • Try to solve problem with method “Try and error” on key spaces (C*N) • Transfer back Id to X. • Using Key to communication.

9. Detailed Algorithm • Z: • Eavesdropping: • N puzzle and constant X public. • Id that Y response. • Finding key: • Search what puzzle Y used • Search what random key X used. • Solve N puzzles until find match: • Constant from X. • Id from Y.

10. NEW APPROACH • Implementation • To manufacture the N puzzles: Alice takes O(N) • To break the one puzzle: Bob takes O(N) • To determine the key: Malice takes O(N2)

11. IIMPLICATIONS • Malice knows the first transmission. We don’t care about it. • Z can not alter or falsify the message. • Key distribution system problem: • Man in the middle attack • Using a cook book: Each name on book have (C*N) puzzles.

12. EVALUATIONS • New approach • Using strong encryption function. • NOT base on Hard problems. • Parallel processing technology • Strong encryption function • Computational Secure

13. Questions & Answers

14. Thank for your attentions