Anonymous%20Digital%20Cash

1
Anonymous Digital Cash

• Ashok Reddy
• Madhu Tera
• Laxminarayan Muktinutalapati (Lux)
• Venkat Nagireddy

2
Overview

• What is digital cash?
• Need for anonymous digital cash
• Concepts in anonymous digital cash
• Protocol Dining Cryptographers protocol
• Achieving anonymity
• Illustration
• Practical concerns
• Conclusion

3
What Is Digital Cash?

• Digital cash is a digitally signed payment
  message that serves as a medium of exchange

4
Need for Anonymous Digital Cash

• Increase in electronic surveillance by
  governments and other institutions
• Lack of privacy features associated with ordinary
  electronic transactions

5
Concepts in Anonymous Digital Cash

• Anonymity is chiefly concerned with
• Unlinkability
• Untraceability

6
Protocol

• Dining cryptographers protocol

7
Dining Cryptographers(2)

• Model

8
Achieving Anonymity

• Blind digital signatures
• Blinding factor

9
Illustration

• The Digital Bank would offer electronic bank
  notes messages signed using a particular private
  key
• The electronic bank notes could be authenticated
  using a corresponding public key
• The bank would also make public, a key to
  authenticate electronic documents sent from the
  bank to its customers

10
Illustration(2)

• To withdraw a dollar from the bank, Alice
  generates a note number (each note bears a
  different number, akin to the serial number on a
  bill) she chooses a 100-digit number at random
• Before sending the note number to the bank for
  signing, Alice multiplies it by a random
  (blinding) factor
• Now she signs the number with the private key
  corresponding to her "digital pseudonym"

11
Illustration(3)

• After receiving the blinded note signed by the
  bank, Alice divides out the blinding factor and
  uses the note as before
• The blinded note numbers are, therefore,
  "unconditionally untraceable"

12
Practical Concerns

• Counterfeiting or Double-spending Fraudulently
  spending the same money more than once
• Remedy
• Checking each note against an on-line central
  list when it is spent
• Using tamper-resistant hardware (called an
  "observer")
• Generating blinded notes that require the payer
  to answer a random numeric query about each note
  when making a payment

13
Practical Concerns(2)

• Framing An attempt by a bank to fraudulently
  claim that a customer has double-spent the same
  piece of cash when the customer hasnt.
• Remedy
• Similar to those discussed earlier

14
Practical Concerns(3)

• Other concerns
• Theft
• Adaptability

15
Conclusion

• Anonymous cash is "unconditionally untraceable"
  which provides enough privacy to the user
• A system (implementing anonymous digital cash)
  closely resembling our current payment system
  will be easier for consumers to understand and
  adapt to

16
Questions?