![SMU
Dual Signature Operation
• The operation for dual signature is as follows:
– Take the hash (SHA-1) of the payment and order information.
– These two hash values are concatenated [H(PI) || H(OI)] and
then the result is hashed.
– Customer encrypts the final hash with a private key creating
the dual signature.
DS = EKRC [ H(H(PI) || H(OI)) ]](https://image.slidesharecdn.com/set1-240107061330-5384df60/85/SET-1-ppt-15-320.jpg)
![SMU
DS Verification by Merchant
• The merchant has the public key of the customer
obtained from the customer’s certificate.
• Now, the merchant can compute two values:
H(PIMD || H(OI))
DKUC[DS]
• Should be equal!](https://image.slidesharecdn.com/set1-240107061330-5384df60/85/SET-1-ppt-16-320.jpg)
![SMU
DS Verification by Bank
• The bank is in possession of DS, PI, the message digest for
OI (OIMD), and the customer’s public key, then the bank
can compute the following:
H(H(PI) || OIMD)
DKUC [ DS ]](https://image.slidesharecdn.com/set1-240107061330-5384df60/85/SET-1-ppt-17-320.jpg)
SET (1).ppt
- 1. SMU CSE 5349/7349 Secure Electronic Transaction (SET)
- 2. Credit Cards on the Internet • Problem: communicate credit card and purchasing data securely to gain consumer trust – Authentication of buyer and merchant – Confidential transmissions • Systems vary by – Type of public-key encryption – Type of symmetric encryption – Message digest algorithm – Number of parties having private keys – Number of parties having certificates
- 3. Credit Card Protocols • SSL 1 or 2 parties have private keys • TLS (Transport Layer Security) – IETF version of SSL • iKP (IBM) • SEPP (Secure Encryption Payment Protocol) – MasterCard, IBM, Netscape • STT (Secure Transaction Technology) – VISA, Microsoft • SET (Secure Electronic Transactions) – MasterCard, VISA all parties have certificates OBSOLETE VERY SLOW ACCEPTANCE
- 4. Secure Electronic Transaction (SET) • Developed by Visa and MasterCard • Designed to protect credit card transactions • Confidentiality: all messages encrypted • Trust: all parties must have digital certificates • Privacy: information made available only when and where necessary
- 5. SMU Participants in the SET System
- 6. SMU SET Business Requirements • Provide confidentiality of payment and ordering information • Ensure the integrity of all transmitted data • Provide authentication that a cardholder is a legitimate user of a credit card account • Provide authentication that a merchant can accept credit card transactions through its relationship with a financial institution
- 7. SMU CSE 5349/7349 SET Business Requirements (cont’d) • Ensure the use of the best security practices and system design techniques to protect all legitimate parties in an electronic commerce transaction • Create a protocol that neither depends on transport security mechanisms nor prevents their use • Facilitate and encourage interoperability among software and network providers
- 9. SMU SET Transactions • The customer opens an account with a card issuer. – MasterCard, Visa, etc. • The customer receives a X.509 V3 certificate signed by a bank. – X.509 V3 • A merchant who accepts a certain brand of card must possess two X.509 V3 certificates. – One for signing & one for key exchange • The customer places an order for a product or service with a merchant. • The merchant sends a copy of its certificate for verification.
- 10. SMU SET Transactions • The customer sends order and payment information to the merchant. • The merchant requests payment authorization from the payment gateway prior to shipment. • The merchant confirms order to the customer. • The merchant provides the goods or service to the customer. • The merchant requests payment from the payment gateway.
- 11. SMU Key Technologies of SET • Confidentiality of information: DES • Integrity of data: RSA digital signatures with SHA-1 hash codes • Cardholder account authentication: X.509v3 digital certificates with RSA signatures • Merchant authentication: X.509v3 digital certificates with RSA signatures • Privacy: separation of order and payment information using dual signatures
- 12. SMU Dual Signatures • Links two messages securely but allows only one party to read each. MESSAGE 1 DIGEST 1 NEW DIGEST HASH 1 & 2 WITH SHA MESSAGE 2 DIGEST 2 CONCATENATE DIGESTS TOGETHER HASH WITH SHA TO CREATE NEW DIGEST DUAL SIGNATURE PRIVATE KEY ENCRYPT NEW DIGEST WITH SIGNER’S PRIVATE KEY
- 13. SMU Dual Signature for SET • Concept: Link Two Messages Intended for Two Different Receivers: – Order Information (OI): Customer to Merchant – Payment Information (PI): Customer to Bank • Goal: Limit Information to A “Need-to-Know” Basis: – Merchant does not need credit card number. – Bank does not need details of customer order. – Afford the customer extra protection in terms of privacy by keeping these items separate. • This link is needed to prove that payment is intended for this order and not some other one.
- 14. SMU Why Dual Signature? • Suppose that customers send the merchant two messages: • The signed order information (OI). • The signed payment information (PI). • In addition, the merchant passes the payment information (PI) to the bank. • If the merchant can capture another order information (OI) from this customer, the merchant could claim this order goes with the payment information (PI) rather than the original.
- 15. SMU Dual Signature Operation • The operation for dual signature is as follows: – Take the hash (SHA-1) of the payment and order information. – These two hash values are concatenated [H(PI) || H(OI)] and then the result is hashed. – Customer encrypts the final hash with a private key creating the dual signature. DS = EKRC [ H(H(PI) || H(OI)) ]
- 16. SMU DS Verification by Merchant • The merchant has the public key of the customer obtained from the customer’s certificate. • Now, the merchant can compute two values: H(PIMD || H(OI)) DKUC[DS] • Should be equal!
- 17. SMU DS Verification by Bank • The bank is in possession of DS, PI, the message digest for OI (OIMD), and the customer’s public key, then the bank can compute the following: H(H(PI) || OIMD) DKUC [ DS ]
- 18. SMU What did we accomplish? • The merchant has received OI and verified the signature. • The bank has received PI and verified the signature. • The customer has linked the OI and PI and can prove the linkage.
- 19. SMU SET Supported Transactions card holder registration merchant registration purchase request payment authorization payment capture certificate query purchase inquiry purchase notification sale transaction authorization reversal capture reversal credit reversal
- 20. SMU Purchase Request • Browsing, Selecting, and Ordering is Done • Purchasing Involves 4 Messages: – Initiate Request – Initiate Response – Purchase Request – Purchase Response
- 21. SMU Purchase Request: Initiate Request • Basic Requirements: – Cardholder Must Have Copy of Certificates for Merchant and Payment Gateway • Customer Requests the Certificates in the Initiate Request Message to Merchant – Brand of Credit Card – ID Assigned to this Request/response pair by customer – Nonce
- 22. SMU Purchase Request: Initiate Response • Merchant Generates a Response – Signs with Private Signature Key – Include Customer Nonce – Include Merchant Nonce (Returned in Next Message) – Transaction ID for Purchase Transaction • In Addition … – Merchant’s Signature Certificate – Payment Gateway’s Key Exchange Certificate
- 23. SMU Purchase Request: Purchase Request • Cardholder Verifies Two Certificates Using Their CAs and Creates the OI and PI. • Message Includes: – Purchase-related Information – Order-related Information – Cardholder Certificate
- 24. SMU Purchase Request • The cardholder generates a one-time symmetric encryption key, KS,
- 25. SMU Merchant Verifies Purchase Request • When the merchant receives the Purchase Request message, it performs the following actions: – Verify the cardholder certificates by means of its CA signatures. – Verifies the dual signature using the customer’s public key signature.
- 26. SMU Merchant Verification (cont’d) – Processes the order and forwards the payment information to the payment gateway for authorization. – Sends a purchase response to the cardholder.
- 27. SMU Purchase Response Message • Message that Acknowledges the Order and References Corresponding Transaction Number • Block is – Signed by Merchant Using its Private Key – Block and Signature Are Sent to Customer Along with Merchant’s Signature Certificate • Upon Reception – Verifies Merchant Certificate – Verifies Signature on Response Block – Takes the Appropriate Action
- 28. SMU Payment Process • The payment process is broken down into two steps: – Payment authorization – Payment capture
- 29. SMU Payment Authorization • The merchant sends an authorization request message to the payment gateway consisting of the following: – Purchase-related information • PI • Dual signature calculated over the PI & OI and signed with customer’s private key. • The OI message digest (OIMD) • The digital envelop – Authorization-related information – Certificates
- 30. SMU Payment Authorization (cont’d) – Authorization-related information • An authorization block including: – A transaction ID – Signed with merchant’s private key – Encrypted one-time session key – Certificates • Cardholder’s signature key certificate • Merchant’s signature key certificate • Merchant’s key exchange certificate
- 31. SMU Payment: Payment Gateway • Verify All Certificates • Decrypt Authorization Block Digital Envelope to Obtain Symmetric Key and Decrypt Block • Verify Merchant Signature on Authorization Block • Decrypt Payment Block Digital Envelope to Obtain Symmetric Key and Decrypt Block • Verify Dual Signature on Payment Block • Verify Received Transaction ID Received from Merchant Matches PI Received from Customer • Request and Receive Issuer Authorization
- 32. SMU Authorization Response • Authorization Response Message – Authorization-related Information – Capture Token Information – Certificate
- 33. SMU SET Overhead Simple purchase transaction: • Four messages between merchant and customer • Two messages between merchant and payment gateway • 6 digital signatures • 9 RSA encryption/decryption cycles • 4 DES encryption/decryption cycles • 4 certificate verifications Scaling: • Multiple servers need copies of all certificates