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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
Showing 665 out of 1137
Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 665
634
SECURITY
CHAP. 9
contains the user’s password (e.g., PIN code) so the terminal can perform an identi-
ty check even if the link to the main computer is down. Typically the password is
encrypted by a key known only to the bank.
These cards cost about $0.10 to $0.50,
depending on whether there is a hologram sticker on the front and the production
volume. As a way to identify users in general, magnetic stripe cards are risky be-
cause the equipment to read and write them is cheap and widespread.
Chip cards contain a tiny integrated circuit (chip) on them. These cards can be
subdivided into two categories: stored value cards and smart cards.
Stored value
cards
contain a small amount of memory (usually less than 1 KB) using ROM
technology to allow the value to be remembered when the card is removed from
the reader and thus the power turned off. There is no CPU on the card, so the value
stored must be changed by an external CPU (in the reader).
These cards are mass
produced by the millions for well under $1 and are used, for example, as prepaid
telephone cards. When a call is made, the telephone just decrements the value in
the card, but no money actually changes hands. For this reason, these cards are
generally issued by one company for use on only its machines (e.g., telephones or
vending machines).
They could be used for login authentication by storing a 1-KB
password in them that the reader would send to the central computer, but this is
rarely done.
However, nowadays, much security work is being focused on the
smart cards
which currently have something like a 4-MHz 8-bit CPU, 16 KB of ROM, 4 KB of
ROM, 512 bytes of scratch RAM, and a 9600-bps communication channel to the
reader.
The cards are getting smarter in time, but are constrained in a variety of
ways, including the depth of the chip (because it is embedded in the card), the
width of the chip (so it does not break when the user flexes the card) and the cost
(typically $1 to $20, depending on the CPU power, memory size, and presence or
absence of a cryptographic coprocessor).
Smart cards can be used to hold money, as do stored value cards, but with
much better security and universality. The cards can be loaded with money at an
ATM machine or at home over the telephone using a special reader supplied by the
bank. When inserted into a merchant’s reader, the user can authorize the card to
deduct a certain amount of money from the card (by typing YES), causing the card
to send a little encrypted message to the merchant. The merchant can later turn the
message over to a bank to be credited for the amount paid.
The big advantage of smart cards over, say, credit or debit cards, is that they do
not need an online connection to a bank.
If you do not believe this is an advantage,
try the following experiment. Try to buy a single candy bar at a store and insist on
paying with a credit card.
If the merchant objects, say you have no cash with you
and besides, you need the frequent flyer miles. You will discover that the merchant
is not enthusiastic about the idea (because the associated costs dwarf the profit on
the item).
This makes smart cards useful for small store purchases, parking meters,
vending machines, and many other devices that normally require coins. They are in
widespread use in Europe and spreading elsewhere.
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