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Anonymous Digital Cash - PowerPoint PPT Presentation

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Anonymous Digital Cash. Ashok Reddy Madhu Tera Laxminarayan Muktinutalapati (Lux) Venkat Nagireddy. Overview. What is digital cash? Need for anonymous digital cash Concepts in anonymous digital cash Protocol: Dining Cryptographers’ protocol Achieving anonymity Illustration

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Anonymous digital cash l.jpg


Ashok Reddy

Madhu Tera

Laxminarayan Muktinutalapati (Lux)

Venkat Nagireddy

Overview l.jpg

  • What is digital cash?

  • Need for anonymous digital cash

  • Concepts in anonymous digital cash

  • Protocol: Dining Cryptographers’ protocol

  • Achieving anonymity

  • Illustration

  • Practical concerns

  • Conclusion

What is digital cash l.jpg
What Is Digital Cash?

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

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Need for Anonymous Digital Cash

  • Increase in electronic surveillance by governments and other institutions

  • Lack of privacy features associated with ordinary electronic transactions

Concepts in anonymous digital cash l.jpg
Concepts in Anonymous Digital Cash

Anonymity is chiefly concerned with

  • Unlinkability

  • Untraceability

Protocol l.jpg

  • Dining cryptographers’ protocol

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Achieving Anonymity

  • Blind digital signatures

  • Blinding factor

Illustration l.jpg

  • 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

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  • 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"

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  • 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"

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Practical Concerns

  • Counterfeiting or Double-spending: Fraudulently spending the same money more than once


  • 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

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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 hasn’t.


  • Similar to those discussed earlier

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Practical Concerns…(3)

Other concerns:

  • Theft

  • Adaptability

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  • 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