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Silvio Micali MIT

Key Management and Fair Electronic Exchange. Silvio Micali MIT. Thesis. Key Management can and will be an enabler of Other Crypto Technologies: Fair Electronic Exchange. (= string ). (= string ). A has a. B has b. A gets b. B gets a. A. A. A. A. B. B. B. B.

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Silvio Micali MIT

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  1. Key Management and Fair Electronic Exchange Silvio Micali MIT

  2. Thesis Key Management can and will be an enabler of Other Crypto Technologies: Fair Electronic Exchange

  3. (= string) (= string) A has a B has b A gets b B gets a A A A A B B B B YES endings (Complete transaction) ? b b ? ? a a ? (if both want) (if ≤ 1 wants) NO endings (Incomplete transaction) What? FAIR ELECTRONIC EXCHANGE IF and only IF

  4. m m S R … is Wishful not Fair : R S R S Bye! SIGR(m) Running Example: Certified E-Mail Recipient R gets message IF and only IF Sender S gets R’s receipt for it Crucial to Electronic Commerce but Not Easy (even with digital signatures): More rounds Q: Trusted Parties ? A: No Thanks ! Still Unfair! (Whoever gets first what he wants may stop)

  5. Trusted party = Post Office m m R PO S SIGR(m) SIGR(m) Why Not? Bad: 0. 4 mssgs When PO goes down all receipts are lost. Massive Law Suit! 1. Congestion (at PO) 2. Cost ($1/messg) 3. Liabilities ($10/mssg) Then What?

  6. Virtual Trusted Parties! What does it mean?? • TP is off-line • TP is unaware that S and R are transacting • TP is unaware of S’s message and R’s signing key Yet: IFS and R do not fairly complete their transaction THENthe TP will (ex post) complete it EXACTLY as S and B would have done if honest!

  7. More Specifically… (for Certified Electronic Mail) PO S R receipt message receiptS receipt message receipt message either what you have ?R HOW? If S & R honest Else: Else: Else: receiptS ?S what you have either or messageR messageR

  8.  details EPK(M,S,R) = σ R S SIGR(σ) = y M PO Basic CEM w/ Invisible PO M receipt message PO’s public and secret encryption keys pk (sk)

  9. EPO(M,S,R) = σ R S SIGR(σ) = y M message σ & y y M PO M,S,R Basic CEM w/ Invisible PO  details M receipt pk (sk)

  10. In Sum S & R Honest: no PO! Else: cheating useless Thus: little or no cheating (1 ‰) Great Efficiency (in all senses) • Very Simple: Typical transaction has 3 messages rather than 4 • No congestions: Typical transactions are peer-to-peer • Very Economical: Infrastructure / Liability costs are 1,000 less: • TP handles just 1‰ of the transactions. • (A single laptop can handle the whole country)

  11. what do I gain? Go to Market IF you pay PO $10/month, can send unlimited certified e-mails for free, and if help is requested PO will fairly complete the transaction for $11. ELSE: good luck!” Win-Win User: Better paying $11 after the fact when I know I am dealing with a dishonest user, than paying $11 all the time just in case the other user is dishonest PO: I get $10/month for doing nothing, and get paid extra when I have to work!

  12. $1M per claim traditional trustee $1M / claim Turing test invisible trustee Small TPs = Big TPs ($1B reserves to prove it) 1 claim (1 of the few) $ 1M (reserves=$2M) (1 of the thousands)

  13. Same CEM Solution immediately implies • Software Distribution • Content Downloading • (Sarbanes-Oxley) From Certified E-Mail to Everything Slight Variation implies Fair Contract Signing General Solution implies All Fair Electronic Exchange!

  14. … Blum ’81 Even Goldreich Lempel ’81 Luby Micali Rackoff ’83 Rabin ’81 Ben-OrGoldreich Micali & Rivest ’85 Micali ’95 (U.S. No. 5,666,420) Asokan Schunter Waidener ’97 (’96) Asokan Shoup Waidener ’00 … History Visible TPs [Chandra Mitchell Scedrov Shmaticov]’s impossibility

  15. To reveal sk To decrypt Epk(m) Key Management Mathematical Success = all on a single key + Concrete Wisdom = 1 key  3 keys (2-out-of-3) = key management ! Practical because: PO rarely used! Recommended because: People are People!

  16. Othe Enablements Secure, Distributed, Compact Storage Other talk, Other Patents, Other Day In Sum: Crypto Keys are great friends And (proper) key management an even better one!

  17. Thank You!

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