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E-cash Payment System

E-cash Payment System. A company, DigiCash , has pioneered the use of electronic cash or e-cash. Anonymity of the buyer is the key feature of this system. There are three participants in it, namely, buyer, merchant and bank.

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E-cash Payment System

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  1. E-cash Payment System A company, DigiCash, has pioneered the use of electronic cash or e-cash. Anonymity of the buyer is the key feature of this system. There are three participants in it, namely, buyer, merchant and bank. Both, symmetric and asymmetric type of cryptography is used in this system. Buyers and merchants, both, have accounts in the E-cash bank. Buyers withdraw coins against their account and store them in e-cash wallet software (Cyber wallet) on their computer. Cyber wallet stores and manages coins and records every transaction.

  2. E-CASH The currency used in this payment system is called an e-cash coin or simply coin. A coin consists of three elements or parts – --serial # -- key version and -- serial no. signed by the secret or private key of a certain denomination of the e-cash bank. Each coin has a unique value, partly minted by the client and partly by the e-cash bank.

  3. Minting of the coin A long serial no. is randomly generated by the client’s Cyber wallet in order to mint a coin. This serial no. is blinded, which means that it is multiplied with a blinding factor “r” and sent to the e-cash bank for signatures. Thus, the e-cash bank cannot see the serial no. it is signing. Key version (corresponding public key of the bank) is also part of the coin, and is sent usually at the time of account opening. An e-cash bank may have 1 dollar signature, 5 dollar signature or 10 dollar signature etc. If the client wants to mint a coin of 2 dollars then e-cash bank would use its private or secret key of 2 dollars to sign the serial no.

  4. How bank signs blindly? Cyberwallet generates a serial # and a blinding factor ‘r’. This blinding factor “r” is only known to the client. Public key of the bank consists of modulus ‘m’ and a no. ‘e’. Bank signs with its secret key of 5 dollars (d5) such that: Bank cannot see serial # it is signing since it does not know ‘r’.

  5. E-cash bank signs the serial nos. and debits the account of the client. A client must maintain his account with the bank. The coins are encrypted with the public key of the bank and are forwarded to the merchant for onwards deposit to the bank. The merchant cannot, therefore, view these coins. E-cash bank decrypts the coins using its corresponding private key and compares the serial nos. , thus revealed, with its database of spent coins to check the validity of the coins.

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