Anonymity Application Example: E-Cash

54 Pages·2016·8.63 MB·English

CS 134
Winter 2016
Anonymity Application Example:
Electronic Cash (E-Cash) and Bitcoin
1
Motivation For E-Cash
Conventional Cash is:
• Counterfeitable
• Slow
• Costly
• Vulnerable
• Bad for Remote Transactions
2
Credit Cards, Bank Cards, Checks,
and Phone/Subway cards:
Easy Fraud
Little Privacy
3
Off-line Electronic Cash is for
2-Party (PayeràPayee) Payment
Withdrawal
Payment
Deposit
• Low Communication Requirements
4
In Contrast, On-line Payments:
“ ”
OK
5
E-Cash in 1970s
• Stephen Wiesner‘s (graduate student at Columbia) paper “Conjugate Coding
and Quantum Money” sent in 1970 to IEEE Transactions on Information
Theory
• Paper immediately rejected
• Published in 1983 as is in ACM SIGACT
• Proposed design of unforgaeble bank notes based on quantum properties
• Influenced Quantum (Cryptographic) Key Distribution (QKD)
E-Cash in 1980s and 1990s
• Chaum’s “Blind Signatures for Untraceable Payments” paper is the
first to propose (realizable) E-Cash using blind digital signatures
• Based on RSA (Rivest Shamir and Adelman) signatures
1990s
1970s
2000s
• RSA breaks if one can factor large composite numbers (100s of
decimal digits, 1000s of bits)
• DigiCash (anonymous ecash) launched by Chaum in 1990.
DigiCash declared bankruptcy in 1998.
Requirements for Anonymous Payments
(afterwards known as E-Cash)
From Chaum’s “Blind Signatures for Untraceable Payments” paper:
Unlinkability: third parties can not determine payee (amount
•
and time of payment)
Provability: individuals can provide (unforgaeble) proof of
•
payment, or determine identity of payee under exceptional
circumstance (e.g., by courts)
Revocation: revoke stolen coins or payment media
•
Anonymous Payments
user 1
user 2
Anonymous Payments
user 1
user 2