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. Merchant forwards coins to e-cash bank which ensures that these have not already been spent and credits the account of the merchant.
E-cash Coins
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. In other words, a coin of one dollar would consist of the following: Coin = Serial#, key version, {Serial #}SK bank’s $1 key Each coin has a unique value, partly minted by the client and partly by the e-cash bank.
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.
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