Silvio Micali

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Key Management and Fair Electronic Exchange

• Silvio Micali
• MIT

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Thesis
Key Management can and will be an enabler of
Other Crypto Technologies Fair Electronic
Exchange
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What?
FAIR
EXCHANGE
ELECTRONIC
IF and only IF
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Running Example Certified E-Mail
Recipient R gets message IF and only IF Sender
S gets Rs receipt for it
Crucial to Electronic Commerce but
Not Easy (even with digital signatures)
Q Trusted Parties ?
A No Thanks !
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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?
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Virtual Trusted Parties!
What does it mean??

• TP is off-line
• TP is unaware that S and R are transacting
• TP is unaware of Ss message and Rs signing key

• Yet
• IF S and R do not fairly complete their
  transaction
• THEN the TP will (ex post) complete it
• EXACTLY as S and B would have done if honest!

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HOW?
More Specifically (for Certified Electronic
Mail)
If S R honest
Else
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Basic CEM w/ Invisible PO
M
receipt
message
POs public and secret encryption keys
pk (sk)
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Basic CEM w/ Invisible PO
? details
M
receipt
pk (sk)
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In Sum
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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!
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Small TPs Big TPs
(1B reserves to prove it)
1 claim
(1 of the few)
1M
(reserves2M)
(1 of the thousands)
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From Certified E-Mail to Everything
Slight Variation implies Fair Contract
Signing General Solution implies All Fair
Electronic Exchange!
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History
Visible TPs
Chandra Mitchell Scedrov Shmaticovs
impossibility
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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!
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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!
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Thank You!