1 / 43

VarietyCash: A Multi-purpose Electronic Payment System

VarietyCash: A Multi-purpose Electronic Payment System. By M. Bellare, J. Garay, C. Jutla, M. Yung --- 1998. By Liang Li Chris March 29th. Introduction. What is Electronic Payment System? Essential Component of Electronic Commerce Widely Used in the World Then … Secure???.

chelsey
Download Presentation

VarietyCash: A Multi-purpose Electronic Payment System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. VarietyCash: A Multi-purpose Electronic Payment System By M. Bellare, J. Garay, C. Jutla, M. Yung --- 1998 By Liang Li Chris March 29th

  2. Introduction • What is Electronic Payment System? • Essential Component of Electronic Commerce • Widely Used in the World • Then … Secure???

  3. Issues Concerned • Anonymity • Payment Untraceable to a third party • Account-based or Account-less • Account-based is more expensive in order to maintain the accounts • Network versus card-based • Transactions across the network • Atomicity • Fair and Robust in the sense of network failure

  4. System Proposed • Trust-Based Anonymity • Account-less • Network-Based & Card-Based • Atomicity

  5. System Proposed - More • What is new here? • Coins and Tokens authenticated under an issuer master key • Spent coins can be erased (Improve the scalability) • Combine symmetric-key cryptography for performance with public-key systems

  6. Cryptographic Primitives Used

  7. Model & System Architecture

  8. Security & Design Goals • Protocol Security • Safety guarantees, no adversaries can compromise or spoil the system • Internal Security • Withstand insider attacks, no cheaters • Network Security • Prevent attacks through “break-ins”. Need careful design of interface to the external network • User Security • Protect its own database (E-coin)

  9. Parties & Roles • Participant • A generic name for a party involved in the system • Issuer • Party who issues the coins • Coin Holder * • A party who holds the money • Payee • A party who is willing to accept coins as payment • Bank • A number of banks will be involved in moving funds due to conversions between electronic and real money • Certification Authority • The Party who can certify the public keys of the participants

  10. Coin-Holder • Coin Purchaser • Purchase coins from the issuer • Redeemer • Turn coins into real money • Payer • The party who pays for the good/service • Refresher • Get new coins for old • Changer • Make changes

  11. Others • Register • Register a public key at the issuer • Enroller • Enroll for a particular role such as coin purchaser or merchant

  12. E-coin • The most basic component in the whole system • An object consisting of a unique identifier (coin ID), amount, expiry date and an authenticating cryptographic tag

  13. E-coin • Unique Identifier • Value (Amount) • Expiry Date • Authenticating Cryptographic Tag Fig 1. Structure of an un-encrypted coin

  14. E-coin - More • Unique Identifier • Value (Amount) • Expiry Date • Authenticating Cryptographic Tag • Search Tag • Coin Status Fig 2. Encrypted coin in the Issuer’s database

  15. Protection from Forgery Coin • Tag is computed in protected, tamper-proof hardware • Tag computing algorithm is strong • Coin Database is protected

  16. Coin Purchase Request • Take form of a list of denominations • For example, (2, $2.50), (1, $1.25), (3, $2) means 2 coins of value $2.50, 1 coin of value $1.25, 3 coins of value $2. The total sum is 12.25

  17. Process & Protocols

  18. Operations Involved • Registration – Register ID and Get own PK • Enrollment – A Participant enrolls for a role • Coin Purchase * - Buy E-coin from Issuer • Payment * - Deal Transaction • Change – Make Changes from Issuer • Redeem – Get Real Money • Refresh – Keep freshness of E-coins • Refund – Ask for E-coins if network failure

  19. Coin Purchase ProtocolMore Detail • Design Requirement • Valid Transaction go through • Cannot get coins free • No false debit

  20. Coin Purchase ProtocolMore Detail • Overview • Terminology

  21. Coin Purchase Protocol • How Does ACH Work? • 1.A company/individual (Receiver) authorizes a company/individual (Originator) to initiate a transaction to their financial institution account. • 2.The Originator prepares information about the transactions that are to be automated for its customers or employees and passes it along to an Originating Depository Financial Institution (ODFI).  • 3.The ODFI collects ACH transactions from participating companies, consolidates  the information and presents it to the ACH Operator. (The ODFI may retain entries for its own account holders)  • 4.ACH Operator processes transaction files from submitting ODFIs and distributes it to Receiving Depository Financial Institutions (RDFls). • 5.The RDFI receives entries for its customer accounts and posts entries on the settlement date. Transactions are also reported on account statements

  22. Coin Purchase ProtocolMore Detail • Coin Request

  23. Coin Purchase ProtocolMore Detail • Execution • Issuance

  24. Coin Purchase Protocol • Message Integrity • Plaintext Awareness Encryption Scheme • Correct Decryption convinces the decryptor that the transmitter knows the plaintext encrypted • Prevent from tampering with a ciphertext but no authentication guaranteed

  25. Payment Protocol - More Detail • Design Requirement • Valid Payment go through • Accepted payments are valid • Payment is paid to the correct party • No double spending

  26. Payment Protocol - More Detail • Overview

  27. Payment Protocol - More Detail • Terminology

  28. Payment Protocol - More Detail • Invoice • Send Coins

  29. Payment Protocol - More Detail • Validation Request • Issuance

  30. Payment Protocol - More Detail • Receipt

  31. More Applications Used • Integrate with Card Cash • Card-Based System • Pseudo-anonymous • Offline • Non-circulating

  32. Integrate with Card Based System • Load Protocol • On-line Account-based load • Terminology

  33. Integrate with Card Based System • Protocol Flows

  34. Blind Signature • A signature scheme that the signer signs it with no idea of what the content is • Properties • Cannot prove that he signed it in that particular protocol • The signature is valid • Use cut-and-choose technical

  35. Blind Signature • General Process • Takes a document and multiplies it by a random value which is called a blinding factor. • Send the blinded document • Sign the blinded document • Divide out the blinding factor, leaving the original document signed

  36. Implementation • Scenario • There is a group of counterintelligence agents. They want to the counterintelligence agency sign a document for them for diplomatic immunity. Even the counterintelligence agency have no idea of who they are. The document should insert agent’s cover name that each agent has a list of them. • ?What will he do then?

  37. Protocol • Assumption • The signature function and multiplication are commutative • Parties • ALICE – Agency’s Large Intelligent Computing Engine • BOB – Bogota Operations Branch

  38. Protocol - More • BOB prepares n documents each using a different cover name giving himself diplomatic immunity • BOB blinds each of these documents with a different blinding factor • BOB sends n documents to ALICE • ALICE chooses n-1 documents at random and ask ZBOB for the blinding factor for each of them

  39. Protocol - More • BOB sends ALICE the appropriate blinding factor • ALICE opens n-1 documents, makes sure they are correct --- and not pension authorizations • ALICE signs the remaining document and sends it to BOB • The agent removes the blinding factor and reads the new cover name in the document. It is “James Bond”

  40. Attack on Blind Signature • Probability Guess • Choose n/2 documents rather than n-1 one • Tricky Twin Document • Choose 2 different blinder factor so that transform 2 different document into the same blinded document.

  41. ?Questions? Thank you

  42. Acknowledgement • Prof. C. Lynch • http://www.achnetwork.com/introtoach.html • Applied Cryptography – Bruce Shneier • Blind Signature for Untraceable Payments • --- 2005 Mar 29th

  43. Text Text Text Text Text Text Text Text

More Related