electronic cash
TRANSCRIPT
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Report
On
Electronic Cash
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Contents
Sr.No. Page No.
1. What is electronic cash 3
2. Defination of cash 3-4
3. How does it work
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What is electronic cash?
'Electronic Cash' is the debit card system of the German Central Credit
Committee, the association which represents the top German financial interest
groups. Usually paired with a checking account, cards with an Electronic Cash
logo are only handed out by proper credit institutions. An electronic card payment
is generally made by the card owner entering their PIN (Personal Identification
Number) at a so-called EFT-POS-terminal (Electronic-Funds-Transfer-Terminal).
The name “EC” originally comes from the unified European checking
systemEurocheque. Comparable debit card systems are Maestro and Visa
Electron. Banks and credit institutions who issue these cards often pair EC debit
cards with Maestro functionality. These combined cards, recognizable by an
additional Maestro logo, are referred to as “EC/Maestro cards”.
Electronic money (also known as e-currency, e-money, electronic cash, electronic
currency, digital money, digital cash, digital currency, cyber currency) refers
to money or scrip which is only exchanged electronically. Typically, this involves
the use of computer networks, the internet and digital stored
value systems. Electronic Funds Transfer (EFT), direct deposit, digital gold
currency and virtual currency are all examples of electronic money.
A number of electronic money systems use contactless payment transfer in order to
facilitate easy payment and give the payee more confidence in not letting go of their
electronic wallet during the transaction.
In technical terms, electronic money is an online representation, or a system of
debits and credits, used to exchange value within another system, or within itself
as a stand alone system.
Definition of ecash
ecash was introduced by David Chaum as an anonymous electronic cash system. He
used blind signatures to achieve unlink ability between with drawal and spend
transactions. Depending on the properties of the payment transactions, one distinguishes
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between on-line and off-line electronic cash. The first off-line e-cash system was
proposed by Chaum and Naor. Like the first on-line method, it is based on RSA blind
signatures.
In the United States, only one bank implemented ecash, the Mark Twain bank, and the
system was dissolved in 1997 after the bank was purchased by Mercantile Bank, a large
issuer of credit cards. Similar to credit cards, the system was free to purchasers, while
merchants paid a transaction fee.
In Australia ecash was implemented by St.George Bank, but the transactions were not
free to purchasers. In June 1998, ecash became available through Credit Suisse in
Switzerland. It was also available from Deutsche Bank in Germany, Bank Austria,
Finland's Merita Bank/Eunet, Sweden's Posten, and Den norske Bank of Norway.
"ecash" was a trademark of DigiCash, which went bankrupt in 1998, and was sold to
eCash Technologies, which was acquired by InfoSpace in 2002.
How does Digital Cash work?
There are a number of electronic cash protocols. To a degree, all digital cash schemes
operate in the following manner: A user installs a "cyber wallet" onto computer. Money
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can be put in the wallet by deciding how much is needed and then sending an encrypted
message to the bank asking for this amount to be deducted from the user's account. The
bank reads the message with private key decryption and verifies if it has been digitally
signed in order to identify the user. The bank then generates "serial numbers", encrypts
the message, signs it with its digital signature and returns it. The user is now entitled to
use the message (coin or token) to spend it at merchant sites. Merchants receive e-cash
during a transaction and see that it has been authorized by a bank. They then contact the
bank to make sure the coins have not been spent somewhere else, and the amount is
credited to the merchant's account.
General Structure of Digital Cash Transactions
There are three different types of transactions during a digital cash procedure:
a) Withdrawal, in which Alice transfers some of her money from her bank account to her
wallet (it could be a smart card or a personal computer).
b) Payment, in which Alice transfers money from her wallet to Bob’s.
c) Deposit, in which Bob transfers the money he has received to his bank account.
In a digital cash system we have three kind of actors:
• A financial network (The bank).
• A payer or consumer (Alice).
• A payee or a shop (Bob).
General models for Digital Cash
There are two types of system for digital cash, namely, the online system and offline
system.
Online Digital Cash
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Result
Bank
User Merchant
Withdraw Coins
Receipt
Payment
Deposit Coins
Deposit Coins
Link with other banks
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The diagram above shows the structure of the online digital cash system, the structure is
indeed very similar to the one which is being used in the existing paper cash system. In
this system, we have got three main components; the bank, customers and merchants, the
user withdraw coins from the back, spend in the shop and the shop deposit the coin back
to the bank.
The user ID in this online digital cash system is fully anonymous and it is done by using a
protocol called Blind Signature Protocol. This protocol simply eliminates the association
between the user ID and the serial number of the coin. Although it is good to hide user’s
identity totally, but this raises the problem of “double spending” – since the digital cash is
digitally represented, it is very easy to duplicate and let the user spend the coin twice.
To tackle the double spending problem, the merchant has to verify the coin with the bank
at the point of sale in each of the transaction, this verification of the legitimacy of the
coin requires extra bandwidth and is a potential bottleneck of the system especially when
the traffic is high. The real time verification also means there is a need for the
synchronization between bank servers.
2. Offline Digital Cash
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Bank 1
MerchantUsers
Temper-resistant device
T.R.D.
Others
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In the off-line scheme, the withdrawal and disposal of the coins are very similar to the
one in the on-line scheme; the main difference is in the transaction part of the model.
Instead of verifying coins during every transaction, the security of each entity in the
system is guaranteed without a direct involvement with the bank. This is achieved by
adding an additional component in the model called the “Temper – Resistant Device”. In
a real life example, you could think of it as the Smart Card Reader at the Point of Sale.
The device is trusted by the bank and is used to verify the authenticity of the coin but
does not check whether the coin has been double spent. This device makes the whole
transaction offline but let the system suffers from the double spending problem.
Therefore, we need a new method to let the bank to trace back who double spent the
money but at the same time, keeping the system to be anonymous. One may ask that how
could a system be traceable and anonymous? Are they not the opposite of each other in
the first place? A method called “Secret Splitting” is commonly used to allow the user to
be anonymous as long as he/she doesn’t double spend. The technique will be explained
later in this handout.
So now, having tackled the problem of double spending and making it offline, the
merchant can deposit the collective amount of coins before it deposit back to the bank
possibly at the end of the day. Notice that the system could be implemented so that the
coin itself can be reusable. The merchant can spend the coin elsewhere with other parties
through another temper-resistant device before the coin finally deposited back to the bank
for verification.
In additional to the secret splitting method, in order to add extra security to the offline
system, there could be a link between the bank and the temper-resistant device which
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allows the T.R.D. to download a blacklist of double spenders in a set period of time when
the traffic is low. This reduces the chance of people double spending their money in the
first place.
Important Properties of Digital Cash
Digital cash is designed to construct an electronic payment system modelled after our
paper cash system. Therefore Digital Cash should have the same features as paper cash
like: recognizable hence readily acceptable, transferable, untraceable, anonymous and
portable and has the ability to make “change”.Here we present in detail some necessary
properties of digital cash.
Security
With security we mean that digital cash cannot be copied and reused. Then we have to
minimize the risks for forgery and establish a good authenticity system.
Forgery
The most obvious risk with any payment system is forgery or counterfeiting. As with
paper cash we have two kinds of forgery in a digital cash system.
• Token forgery: to create a valid-looking coin without making a corresponding bank
withdrawal.
• Multiple spending: using the same token over again. Multiple spending is also
commonly called re-spending, double-spending, and repeat-spending. To protect against
token forgery, one relies on the usual authenticity functions of user identification and
message integrity. To protect against multiple spending, the bank maintains a database of
spent electronic coins. Coins already in the database are to be rejected for deposit. If the
payments are on-line, this will prevent multiple spending. If off-line, the best one can do
is to detect when multiple spending has occurred. To protect the payee, it is then
necessary to identify the payer. Thus it is necessary to disable the anonymity mechanism
in the case of multiple spending.
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Authenticity
As a consequence of the problems of forgery, it becomes necessary to establish various
levels of authenticity measures.
• user identification: A user must know with whom he is dealing with.
• message integrity: To be sure that the copy of the message is the as same as it was in
the beginning.
• nonrepudiation: To protect against later denial of a transaction.
The authenticity features are attained via key management. Key management is carried
out using a certification authority(CA), a trusted agent who is responsible for confirming
a user’s identity. Without a trusted CA and a secure infrastructure, the security features of
digital cash will be practically impossible over an entrusted transmission medium like
Internet.
Privacy
The definition of privacy is not really clear. For some people privacy means protection
against eavesdropping but for others like David Chaum privacy means anonymity for the
payer during payment and untraceability of the payment such that the bank cannot tell
whose money was used in a particular payment. Just as cash is anonymous, digital cash is
anonymous in that it cannot be traced back to a particular individual, it is considered to
be “unconditionally untraceable”. However, the service provider is assured of its
authenticity, all that is missing is the ability to link the transaction with a particular
person. If a user’s coin is linkable, we can identify the user by finding a single payment in
which the user has identified himself. Then a digital cash system will protect user’s
privacy if it is both unlinkable and untraceable. Digital cash systems that don’t pay
attention to privacy are “privacy-invading systems”. Virtually all commercial systems
currently being proposed are privacy-invading. They emphasize the bank’s security, but
pay little attention to the security of the customer. Anonymity increases the danger with
money laundering, illegal purchasing, blackmailing and counterfeiting that are far more
serious than with paper cash. Anonymity would increase the danger of these problems.
More anonymity means less security and vice versa.
Portablility
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The security and use of digital cash is not dependent on any physical location. The cash
can be transferred through computer networks into storage devices and vice versa.
Transferability
Transferability allows a user to spend a coin that he has received in a payment without
having to contact the bank. A payment is transfer if the payee can use the received coin in
a payment. A payment system is transferable if it allows at least one transfer per coin. We
have to notice that the ability to transfer paper cash is very important in our daily life.
• Any transferrable electronic cash system has the property that the coin must grow in
size each time it is spent because of the information it has to contain. This information is
about every person who has spent the coin for the bank to maintain its ability to catch
multiple spenders. This limits the maximum number of transfers allowed in the system by
the allowable size of the coin.
• Money laundering and tax evasion are hard to detect since no records of the transactions
are available.
• Each transfer delays detection of multiple spending or forged coins. Multiple spending
will not be noticed until two copies of the same coin are deposited and it may be too late
by then.
• Users can recognize their coin if they sees it later in another payment.
Divisibility
With divisibility we mean the ability to make change. So digital cash will come in cent or
smaller denominations that can make high-volume, small-value transactions on the
internet practical. A solution for divisible coins is using coins that can be divided to coins
whose total value is equal to the value of the original coin. This allows off-line payments
to be made without the need to store a supply of coins of different denominations. Three
divisible off-line schemes have been proposed at a cost of transaction time and additional
storage, Eng and Okamoto’s scheme, Okamoto’s scheme and Okamoto and Ohta scheme.
Off-line Payment
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Off-line payment means that Bob submits Alice's electronic coin for verification and
deposit sometime after the payment transaction is completed. It means that with an
offline system Alice can freely pass value to Bob at any time of the day without involving
any third party like a bank.Although off-line systems are preferable from a practical
viewpoint, they are however susceptible to the multi-spending problem and therefore
suitable for low value transactions. Over the past years, some off-line cash systems have
been designed that can not only guarantee security for the bank and shops, but also
privacy for the users.
On-line
On-line payment means that Bob calls the bank and verifies the validity of Alice’s token
by a simple question like “have you already seen this coin” before accepting her payment
and delivering his merchandise.On-line payment remains necessary for transactions that
need a high value of security.With an on-line system, the payment and deposit are not
separate steps. On-line systems require communication with the bank during each
payment, which costs more money and time, however the protocols are just simplification
of off-line protocols. Since on-line systems have to be able to check the credibility of
payers for shops, it is almost impossible to protect the anonymity of its users, besides as
on-line systems require communication with a third party during the payment transaction,
then we can not have transferable coin if the system is an on-line one.
The Technology of Electronic Cash
The Bank for International Settlements reports that more than 300 billion consumer
cash transactions take place in the United States each year, 270 billion of which are
for amounts under $2. Soon banks will be offering a coin card with the capability to
displace cash as the payment medium for a large number of these small transactions.
These coin, or payment, cards are designed to be used in an open system composed of
multiple card issuers, acquirers, and merchants.Issuing banks provide cards to
consumers, who load value onto these cards at specially adapted ATMs (automatic
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teller machine).Consumers then use their cards at various designated merchants. At
the point of sale, an electronic data-capture terminal records both the value of the
purchase and the routing number of the issuing bank. At the end of the day, the
merchant submits the entire batch of electronic cash transactions to his or her
bank(Acquiring Bank), which forwards the electronic receipts to the system operator
The system operator transmits these claims to the issuing banks, which then fulfill the
interbank financial obligations resulting from the electronic-value transactions. When
these interbank transactions are settled, the merchants are reimbursed by their
banks.The coin card will be equipped with a microchip through which funds can be
electronically credited and debite. Just as people now withdraw cash by inserting a
card into an automatic teller machine, cardholders will transfer money from their
bank accounts to their coin cards in the same way.This electronic purse will carry a
running cash balance in its memory. Each time the card is used, the purchase amount
will automatically be deducted from the card and credited to the merchant by an
electronic reader. Payments will take just seconds. As with cash, no signatures will
have to be validated and no personal identification numbers (PINs) will be needed to
confirm identities.
Hardware and Software
A card terminal, also called EFT-POS terminal, consists
of hardware and software components. The main hardware components are the security
module, the PIN pad, the printer, the display, the magnetic card reader, the chip-card
reader, the communication module and the power supply.
The software mainly consists of the operating system, the communication software, the
software of the security module and various software modules for OPT (Online-
Personalization of Terminals), EMV as well as additional applications such as
prepayment, customer loyalty systems and remote administration. The most important
element is the so-called security module, without which the terminal can only be used for
electronic direct debit (EDD) transactions.
Chip card vs magnetic stripe card
Every ec-card is equipped with a magnetic stripe. This magnetic stripe is read-only and
thus only contains static information. In addition, since the year 2000, more and more
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banks have started to add the EMV chip to newly issued cards. By 2008, 70% of the
cards issued had that chip. The new chip is capable of processing data like a small
computer and can respond to requests without the entire contents being read. In contrast
to magnetic stripes, the chips cannot be copied easily. To maintain downward
compatibility, especially with the Maestro card, which is most often integrated, the cards
are still equipped with magnetic stripes
Payment Authorization
Electronic cash with a magnetic stripe card
Paying at a POS-Terminal (Point Of Sales) works as follows: Online authorization is a
key feature of this payment method. Online authorization validates the card against the
list of blocked account numbers and checks the given PIN. Finally, it verifies whether the
amount due is covered by the account balance (balance plus overdraft facility minus
pending debits). Payment is rejected if any of the criteria listed above are not met. The
authorization as well as the validation regarding sufficient funds and the daily limit is
carried out by the headquarters of the institute from which the card is issued. General
procedure for electronic cash payment using the magnetic stripe:
Amount is entered.
Card is asked for in order to be read by a card reader
Security module is activated and requires the input of the PIN
The communication module connects to the provider and logs in for the exchange
of data
The exchange of data operates the plausibility check
The online connection to the bank verifies:
a) if the card is blocked
b) if the PIN is correct
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c) if the amount is covered
The payment is rejected if any of the criteria listed above is not fulfilled.
The communication module logs out of the system and terminates the connection.
The printer issues a record of the payment or the rejection, which can be viewed
on the screen. The result "Successful payment" guarantees the retailer payment (if
submitted on time).
Electronic cash with chip, chip offline.
The general procedure for electronic cash-payment using a chip:
The amount is entered.
The card is demanded, and is read with the help of the chip reader.
The security module is activated, and demands the PIN.
The accuracy of the PIN is checked in the chip. If the pin is entered correctly, the
wrong entry counter is set to zero. If the PIN given is incorrect, the wrong entry count
increases to one, and if it is entered incorrectly three times, the bank can block the
card. The bank can unlock the card with the help of special bank terminals (BSFT).
The demand for payment is sent to the card chip. If there is enough money and/or
credit on the card, the amount will be deducted and the credit limit updated on the
chip. Go to step 11.
The communications module establishes the connection to the provider and logs
the data exchange.
Data exchanges are carried out via the communications link and plausibility
checks.
Via the online connection the bank verifies whether the card is on the blacklist,
and whether payment lies withiin the available financial means.
If one of these criteria is not met, payment will be rejected.
A payment approval (authorization) is transmitted to the chip and stored there.
The communication module logs off at the provider and terminates the
connection.
The printer creates a record of payment or rejection, which is shown on the
screen. The resulting “payment success” guarantees the retailer payment (if submitted
on time).
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Steps three to six are not applicable if the credit limit has not been reached, thus resulting
in no transaction costs.
Future progression
The main focuses of electronic money development are:
1. being able to use it through a wider range of hardware such as secured credit
cards
2. linked bank accounts that would generally be used over an internet means, for
exchange with a secure micropayment system such as in large corporations
(PayPal, KlickEx).
Issues
Although electronic money can provide many benefits—such as convenience and
privacy, increased efficiency of transactions, lower transaction fees, and new business
opportunities with the expansion of economic activities on the Internet—there are many
potential issues with the use of e-money. The transfer of digital currencies raises local
issues such as how to levy taxes or the possible ease of money laundering. There are also
potential macro-economic effects such as exchange rate instabilities and shortage of
money supplies (total amount of electronic money versus the total amount of real money
available, basically the possibility that digital cash could exceed the real cash available).
Advantages of e-money
Electronic money has made monetary transactions a piece of cake. Be it an amount in
millions, or money transfer to a tiny town in another continent. E-cash transactions are
fast, accurate and easy.
Online Electronic Money
1. Anonymity and untraceability can be maintained: User Id's are kept highly
confidential.
2. No issues regarding "Double spending": Real-time checking of all
transactions makes the possibility of multiple expenditures negligible.
3. No requirement of additional secure hardware: Existing POS (point of
sale) hardwares can be updated and used.
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Offline Electronic Money
1. Portable: This system is fully offline and portable.
2. Anonymity unless double spending: The user is anonymous unless he
commits a double expenditure.
3. Detection of Double Spender: The bank can effectively detect a double
spender.
4. Frequent synchronizations are not required: The bank doesn't need to
synchronize its servers very often. This is mostly done via batch updates.
Disadvantages
Online Electronic Money
1. Communication Overheads: Security and anonymity cost become a
bottleneck of the system. This can happen at times during real-time
verifications.
2. Massive Databases: The bank will have to maintain a detailed and
confidential database.
3. Synchronization: The bank needs to synchronize its server every time
transaction is made. It would be insanely impractical to maintain.
Offline Electronic Money
1. Prevention may not be Immediate: Double spending may not be prevented
effectively and immediately.
2. Implementation Expenditure: the required additional hardware is quite
costly to install.
Conclusion
The elimination of physical cash from our economy is already feasible from a purely
technological perspective. The economic barriers are also disappearing, though a
substantial additional investment in equipment and cards would be needed to permit even
purchases such soft drinks to be made.
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But transactional privacy will be at the heart of the government's attack on digital cash.
Because it’s untraceable, the government concerns about money laundering, offshore
banking and tax havens, and has been closely monitoring developments of digital cash.
The government would probably only license the company’s patents in a way that
preserved the ability to trace for law enforcement purposes. Without the government
support, the investors don’t have confident in the development of digital cash. DigiCash,
a pioneering firm in the area, attracted only $160k US dollar in two years, declared
bankruptcy in 1998 and bought by eCash Technologies. Now eCash is having its own
troubles and bought by another company call InfoSpace.
Advantages of digital cash
E-cash is basically software; it can be programmed to do things that paper money could
never do. This ability opens up a whole range of exciting functionality that money may
offer. Besides this, there are many other advantages on offer.
1. For the Users:
Convenience. One of the most apparent benefits of digital cash is convenience.
Users may access funds, pay for items or be paid from the comfort of their home.
With smart card implementation, users will also be able to initiate financial
transactions wherever they may be. Cell phones are being developed to process
electronic cash transactions; this will ensure convenience reaches unimaginable
heights. Not only is such ease of use desirable, but it saves time and effort and
inevitably money. Such capability will also empower the disabled, making them
more competitive in the financial world.
Security. The user is also protected against the bank's refusal to honor a
legitimate note, since nobody is able to counterfeit the bank's digital signature on
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the note. Another important benefit for the user is improved security. Passwords
for the electronic wallet could safeguard itself from abuse by thieves by making
encrypted backup copies of its contents. A replacement card could then recover
these contents if the original electronic wallet were lost. At the same time, abuse
of a lost or stolen card computer by another individual would be very difficult
without the owner's secret authorizing number. The card would require the
authorizing number, which might typically be about six digits long, before
allowing any transactions. A reasonably tamper-resistant device within the card
computer could for example include biometric information of the user. Current
security standards are already competitive, it is claimed that consumers are 11
times more likely to have their credit card number stolen by a waiter than they are
from an unsecured internet transaction.
Intractability. The primary advantage digital cash promises over other
electronic payments are anonymity. True anonymous digital cash would also
provide unconditional intractability. The “blinding” carried out by the user's own
device makes it impossible for anyone to link payment to payer. But users can
prove unequivocally that they did or did not make a particular payment, without
revealing anything more, if they need to.
2. For the Bank:
Less Processing. Single transactions need not be authorized on line, debited
from the customer's account or printed for the customer. This greatly reduces
processing effort, meaning time is saved and less staff is required
Security. With the security measures built into the electronic wallet, fraud costs
and costs for clarifying disputed transactions could be reduced. Nowadays, card
fraud is a very important problem. The same applies to card counterfeiting and
forged bank notes.
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Handling. Handling costs for paper cash are exorbitant. This includes
guarding, transporting, counting, storing and the like. With weightless cash bereft
of any volume, these massive savings will be made.
3. For the Retailer:
Time saving. The instantaneous quality of electronic transactions, means
retailers accounts will be credited for immediate use if necessary.
Transaction Costs. Retailers must pay a fee of 2 to 7 percent of the
purchased amount to the credit card company. The fees for digital cash
transactions are likely to be smaller than for today's cards because of smaller
operating costs for the issuer. Costs for counting, storing and transporting cash
would also decrease.
Global Disadvantages:
1. Safety. The safety of any system is only as strong as its weakest link. German
national television recently showed how a hacker could create a Web page, with an
embedded ActiveX control, that is able to snatch money from one bank account and
deposit it into another, bypassing the customary personal identification number that is
meant to protect theft.
2. Algorithm. Most algorithms used in these monetary systems have been around for
many years already. Numerous cryptology experts have attempted breaking them without
success. However, one can never rule out the possibility of a security break in the future.
3. Physical Securities. Another weak spot is the user’s personal hardware (e.g. the
smart card) and his copy of the software. Only complete physical security can guarantee
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the safety of the stored money. There are some skeptical of the physical safety of the
smart card chips.
4. Economic Disruption. Another disadvantage is a possible uncontrolled growth of
E-cash systems. Such a monetary explosion could undermine bank- and government-
controlled money systems, giving rise to a confusing and inefficient system. Economists
also predict that speed and ease of e-cash will increase monetary velocity which in turn
will cause unnecessary inflation.
5. Users. First of all, fewer people can understand the technology behind digital money,
and thus it does not inspire confidence. Conventional money on the other hand does not
require any profound knowledge in order to use it. This is an often underestimated topic
as user confidence is the key to the success of digital cash. The rising of e-cash could also
foster a have and have-not society: Those with PCs would have ready access to the new
technology, while those without, many of them low-income consumers, would not.
6. Legal problems. Digital cash's untraceable nature will loosen government's control
over financial information. Money laundering and tax evasion could proliferate in
stateless e-money systems. A major fear is that criminals will take advantage of such
systems to aid illegal activities.
References
1. David Chaum Amos Fiat and Moni Naor, "Untraceable Electronic Cash", in
Advances in Cryptology - CRYPTO '88 Proceedings
2. David Chaum, “Blind Signature System” US Patent #4759063
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3. Pater Wayner, "Digital Cash Commerce on the Net", Academic Press Inc 1996
4. Hitesh Tewari, Donal O'mahony & Michael Peirce (1998). “Reusable Off-Line
Electronic Cash Using Secret Splitting”, Technical Report TCD-CS-1998-27,
Trinity College Dublin Computer Science Department, Dublin.
5. Paul Sprague, “Blind Signatures and Fair Blind Signatures”
http://www.csh.rit.edu/~spraguep/crypto/
6. Digital Cash Mini-FAQ
http://ntrg.cs.tcd.ie/mepeirce/Project/Mlists/minifaq.html
7. Cashless Society or Digital Cash?
http://www.sfasu.edu/finance/FINCASH.HTM
8. Digital Cash and Net Commerce
http://www2.pro-ns.net/~crypto/toc12.html
9. Digital Cash
http://www.simovits.com/archive/dcash.pdf
10. Anonymity & Privacy: The InternetCash TM Example by Yiannis Tsiounis, Ph.D.
http://www.internetcash.com/fgo/0,1383,white02,00.html
11. Digital Cash and Blind Signatures by Zhihao Chen
12. ELECTRONIC MONEY & DIGITAL CASH by Michele Pelossi
http://vrm.vrway.com/issue13/ELECTRONIC_MONEY_DIGITAL_CASH.html
13. InfoSpace
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