Your objective is to develop a secure software product to

control an Automated Teller Machine $($ATM$).$ An ATM has a magnetic

stripe reader for reading an ATM card, a keyboard and a display for

interaction with the customer, a slot for depositing envelopes, a

dispenser for cash, a printer for printing customer receipts, and a

key$-$operated switch to allow an operator to start or stop the

machine. The ATM will communicate with the bank's computer over an

appropriate communication link. The ATM services one customer at a

time. A customer is required to insert an ATM card and enter a

personal identification number $($PIN$)-$ both of which will be sent

to the bank for validation as part of each transaction. The

customer will then be able to perform one or more transactions. The

card will be retained in the machine until the customer indicates

that he$/$she desires no further transactions, at which point it will

be returned $-$ except as noted below. The ATM must be able to

provide the following services to the customer:$$ A customer must be able to make a cash withdrawal, In addition

to the money, the user is given a receipt showing the date, time,

machine location, type of transaction, account number, amount

withdrawn, and account balance after the withdrawal. The customer

can have up to three bank accounts, namely: checking account,

saving account, and credit card account.$$ A customer must be able to make a deposit to any account

linked to the card, consisting of cash and$/$or checks in an envelope

and a receipt is printed.$$ A customer must be able to make a transfer of money between

any two accounts linked to the card. The user is given a

receipt.$$ A customer must be able to determine the balance of any

account linked to the card. This is displayed on the screen.$$ A customer must be able to quit at any time. When this is the

case, the card will be rejected.$$The ATM communicates each transaction to the bank and obtains

verification that it was allowed by the bank. If the bank

determines that the customer's PIN is invalid, the customer will be

required to re$-$enter the PIN before a transaction can proceed. If

the customer is unable to successfully enter the PIN after three

tries, the card will be permanently retained by the machine, and

the customer will have to contact the bank to get it back. If a

transaction fails for any reason other than an invalid PIN, the ATM

will display an explanation of the problem, and will then ask the

customer whether he$/$she wants to do another transaction. The ATM

has an operator panel with a key$-$operated switch, located on the

"inside the bank" side that allows an operator to start and stop

the servicing of customers. When the switch is moved to the "off"

position, the machine will shut down, so that the operator may

remove deposit envelopes and reload the machine with cash, blank

receipts, etc. The operator will be required to verify and enter

the total cash on hand before starting the system from this

panel.

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