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BACKGROUND OF THE INVENTION
This invention relates to video games, and more particularly to a method
and system for limiting the number of machines on which a compatible video
game cartridge or other software medium may be played.
One of the problems faced by manufacturers of video game machines, such as
those sold under the trademarks Nintendo and Sega, is that companies which
rent videotapes often rent video game cartridges as well. Instead of the
manufacturer making multiple sales of cartridges to different persons who
desire to play a particular game, fewer sales are made to a "video store"
which then rents the cartridges to different customers. It is the video
store which realizes the profit on multi-user play of a particular game
rather than the machine manufacturer under whose authorization the
cartridges are sold in the first place.
Machine manufacturers have developed techniques for preventing the copying
of cartridges and even the manufacture of original game cartridges.
Nintendo Co., Ltd., for example, provides a microprocessor in each of its
cartridges for communicating with a similar microprocessor in each
machine. The Nintendo security system requires for its effectiveness that
the microprocessor not be duplicated by other manufacturers, and Nintendo
has achieved considerable success with this system. The arrangement is
described in Nakagawa U.S. Pat. No. 4,799,635 and Nakagawa et al. U.S.
Pat. No. 4,865,321. However, while the Nintendo approach prevents the
copying of software cartridges and even the distribution of original
unauthorized software, it in no way limits the rental of cartridges by a
retailer who purchases them in a legitimate way.
SUMMARY OF THE INVENTION
It is a general object of my invention to provide a cost-effective way for
a manufacturer, such as a manufacturer of video game machines, to
effectively prevent the purchase of software packages (cartridges, etc.)
and their rental to owners of the machines.
It is another object of my invention to provide a way to do this which can
be applied to new cartridges and new machines, yet allow them to be
compatible with a family of cartridges and machines already being
marketed, i.e., new machines will play old cartridges and old machines
will play new cartridges.
Briefly, in accordance with the principles of my invention, I employ a
security chip, comparable to those disclosed in the above-identified
Nintendo patents, in both new machines and new cartridges. Each security
chip has added to it a small write-once memory. A first memory location in
any chip used in a machine has stored in it a serial number assigned to
the machine by the manufacturer. The first location of the write-once
memory of any chip used in a cartridge serves no purpose. As will become
apparent below, it is not necessary that every machine which is
manufactured have a unique serial number. It is only necessary that there
be a sufficient number of identification codes such that for any
relatively large group of renters interested in playing the same
cartridge, it is unlikely that together they have a small group of
different identification codes in their machines. It is sufficient, for
example, that there be as few as 250 different identification codes
(serial numbers) for the entire machine population.
When a cartridge is sold, the purchaser is informed that the cartridge may
be played on at most ten different machines. (The number ten is arbitrary,
and some other number may be selected.) The idea is to select a number of
different machines which exceeds the number of different machines on which
any cartridge purchased by an ordinary consumer is likely to be played. If
a child typically allows a half dozen of his/her friends to play with
his/her cartridges, then it is unlikely that that child will be frustrated
by not being able to loan his/her cartridges to more than nine friends. It
is only a rental store which typically provides a cartridge to more than
ten machine owners.
The method of the invention entails storing in the write-once memory of a
cartridge security chip the serial numbers of the first ten machines on
which the cartridge is played. Thereafter, the cartridge will not play in
any machine whose serial number is not contained in the cartridge. Toward
this end, ten storage locations are required in the write-once memory of a
cartridge security chip. These locations are not used in security chips
placed in machines. (While the first memory location is used only in chips
included in machines, and the next ten locations are used only in chips
included in cartridges, in accordance with the Nintendo approach it is
cheaper to provide the same security chip--with the same ROM program--for
both cartridges and machines, with a particular chip operating in a
machine mode or a cartridge mode depending on a pin connection to the
chip.)
The term "new machine" refers to a machine whose security chip includes
provision for storing a serial number, as well as the new software (in
addition to the present security program) to be described. The term "new
cartridge" refers to a cartridge whose security chip includes a number of
locations for storing serial numbers of new machines as the cartridge is
played on new machines. Consider first the case in which a new cartridge
is played on a new machine. At the start of the overall security routine,
the machine reads all of the serial numbers already stored in the
cartridge. For example, of the ten initially blank locations used to store
machine serial numbers, three may already be filled. If the machine does
not recognize its own serial number as one of those three, it instructs
the security chip in the cartridge to write the machine's serial number in
the fourth memory location in the cartridge used to store serial numbers
of machines on which the cartridge has already been played. Thereafter,
the machine and the cartridge will continue to execute the usual security
routine provided by Nintendo to insure that the cartridge is authentic.
Similarly, if the machine discovers its own serial number already stored
in the cartridge, it simply moves on to the usual security checks without
causing the security chip in the cartridge to write the machine's serial
number once again. In this latter case, there will still be only three
serial numbers stored in the cartridge.
After the cartridge has been played on ten different machines, there will
be ten different serial numbers stored in the cartridge. If the cartridge
is now played on a machine with an eleventh serial number, when the
machine reads ten serial numbers from the cartridge and realizes that its
own is not included and that there is no room left to store an eleventh
serial number, it will abort or otherwise curtail play of the cartridge.
Ten memory locations are believed to be sufficient because it is unlikely
that a particular cartridge will be "shared" by more than ten users.
However, it is possible to provide more memory locations if desired. The
point is that a video store will certainly rent a cartridge to more than
ten different customers. Even if some of the customers have machines with
the same serial numbers, a point will soon be reached at which most
customers will not be able to play the cartridge on their machines. It
will not pay for a video store to purchase cartridges if they can only be
rented out to a limited number of customers. (Even if only an 8-bit
write-once memory is used, that still allows 256 different serial numbers
to be assigned to machines. While there is a good possibility of a few
more than ten machine owners having ten or fewer different serial numbers,
a video store cannot stay in the cartridge rental business when the
majority of its customers will be returning cartridges which cannot play
on their machines.)
It should also be noted that it is even possible to sell cartridges at
different prices depending upon the number of different machines on which
they can be played. For example, an additional memory location might be
provided for storing the number of different machines on which a cartridge
may be played. One price might be charged for a cartridge which may be
played on two machines, and a slightly higher price may be charged for a
cartridge which may be played on fifteen machines. The additional memory
location in the security chip used in any cartridge would have stored in
it at the time of manufacture the number two or fifteen. While every chip
used in a cartridge might contain fifteen memory locations for the storage
of the maximum number of machine serial numbers, the software in the
machine on which the cartridge is played will first read the number which
represents the maximum number of authorized machines on which the
cartridge may be played and, if it is only two, will allow the writing of
only two serial numbers in the write-once memory of the cartridge security
chip.
The next case to consider is the play of an old cartridge on a new machine.
The old cartridge security chip does not have a write-once memory, and
thus it has no facility for storing the serial numbers of machines on
which it is played. The software in the new machine first attempts to read
all serial numbers stored in a newly inserted cartridge. No such serial
numbers can be read from an old cartridge, and the cartridge does not even
attempt to respond. In such a case, the machine just ignores this part of
the overall security routine--old cartridges can be played on all new
machines (as well as all old machines). That is as it should be since old
cartridges were sold to the consuming public with no restrictions on the
number of machines on which they could be played.
The last case to consider is the play of a new cartridge on an old machine.
An old machine does not even attempt to read serial numbers which have
been stored in an inserted cartridge. Consequently, the fact that a new
cartridge has such serial numbers recorded in it is of no moment. The new
security routine check does not even enter the picture.
It is thus apparent that the method of the invention can be implemented on
new cartridges and new machines without in any way interfering with the
compatibility of old/new cartridges/machines. It should be appreciated,
however, that when it is said that new cartridges can be played on only
ten different machines, for example, what it means is that a new cartridge
can be played only on ten different new machines. That is because if a new
cartridge is played on an old machine, the old machine does not even
interrogate the new cartridge for recorded serial numbers. Thus a new
cartridge will be playable on a total number of machines which is greater
than the number promised to the customer. But it is still not economically
feasible for a rental store to rent out new cartridges when customer after
customer will report that the cartridges do not "work" in his/her machine.
Further objects, features and advantages of the invention will become
apparent upon consideration of the following detailed description in
conjunction with the drawing, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is the same as FIG. 2 in the above-identified prior art U.S. Pat.
No. 4,799,635;
FIG. 2 is the same as FIG. 3 in the same patent;
FIG. 3 depicts modifications required to the chip of FIG. 2 in order to
implement the present invention;
FIG. 4 is a flow chart depicting the methodology of the present invention,
which is implemented in software stored in ROM 30b or 34b in the security
chip used in any machine or cartridge; and
FIG. 5 depicts optional additional steps which may be performed to make it
more difficult to foil the system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The prior art Nintendo security, or authorization, scheme is described not
only in U.S. Pat. No. 4,799,635 but also in U.S. Pat. No. 4,865,321, both
of which are hereby incorporated by reference. Only a brief summary of the
operation of the scheme will be presented herein.
Referring to FIG. 1, an authorized cartridge includes an integrated circuit
or chip 34 known as a "key device." Each machine includes a similar chip
30 referred to as a "lock device." The two chips must work together in a
synchronized manner, communicating with each other, in order that the
machine not be reset or play of the cartridge game otherwise stopped.
Protection is afforded as long as unauthorized cartridge manufacturers are
unable to manufacture chip 34 or a chip with equivalent timing and
functions.
The security chip itself, shown in FIG. 2, includes a microprocessor with
on-board RAM and ROM. It includes a bus 30g (34g) and an I/O port
30h(34h). In accordance with the principles of my invention and as
depicted in FIG. 3, the chip must be modified by adding to it a small
write-once memory 30i(34i) which, in the illustrative embodiment of the
invention, has 17 memory locations. Each location need comprise only eight
bits. The write-once memory communicates with the system bus 30g(34g) in a
conventional manner and is addressed as is the other memory (registers,
ROM and RAM). Furthermore, ROM 30b(34b) in FIG. 2 must include code for
executing the program steps illustrated in FIG. 4 and, if desired, the
additional steps depicted in FIG. 5.
It is possible to provide longer words in the write-once memory. With a
sufficient number of bits in each word, every machine could have its own
serial number with no duplications. However, it is not necessary in
accordance with the principles of the present invention to do this. All
that is required is that there be some group of identifying numbers which
is substantially larger than the number of different machines with which
any cartridge is likely to be used. In such a case, the cartridge will not
be playable on most machines. For example, consider the case of 8-bit
words. The first location of the write-once memory, used to store the
machine "serial number," is required only for chips used in machines; the
location is left blank (00000000) in chips used in cartridges. With 8-bit
serial numbers, and if 00000000 is never assigned as a serial number,
there are 255 possibilities. If the maximum number of new machines with
which any cartridge can ever be played is only 15, the first 15 new
machines with different serial numbers on which any cartridge is played
will have their serial numbers written into memory locations 3 through 17
in the write-once memory of the cartridge. Thereafter, if an attempt is
made to play the cartridge on a new machine which has one of the other 240
serial numbers, the cartridge will not play. The important point to note
is that the serial numbers referred to herein are really simply a group of
identification codes, which can be relatively small in number (e.g.,
measured in the hundreds), as long as they provide a way to distinguish
one relatively small subset of machines from a substantially larger
subset.
Before proceeding with a description of the steps depicted in FIGS. 4 and
5, it should be appreciated that the write-once memories of the chips used
in the cartridges and the machines need not be the same. The cartridges
require only memory locations 3 through 17--each cartridge must have
storage for representing the serial numbers of the first group of
"authorized" machines on which the cartridge is played. Since a cartridge
is not assigned a serial number as that term is used herein, the first
location in a write-once memory of a cartridge is not used. On the other
hand, the only data which must be stored in the write-once memory of a
machine security chip is its serial number in the first location.
The second memory location, "max. no. machines," represents the maximum
number of new machines on which any cartridge can be played. It is not
necessary that this memory location be used. For example, if the maximum
number of machines on which any cartridge can be played is eight, then
that number can be represented in the ROM program which is executed by the
machine, as will be described below. In such a case, seven of the "played
machine no. .sub.---- " locations could also be omitted. Each "played
machine No. .sub.---- " location is initially blank, but can have written
into it the machine number of a machine on which the cartridge was
played.) For maximum flexibility, however, the additional memory locations
are shown in FIG. 3. This allows the machine manufacturer to provide
cartridges which can be played on different numbers of machines. For
example, perhaps the standard cartridge could be played on only two
different machines, but for a premium price a cartridge might be played on
the maximum number of fifteen machines. By providing a variable number in
the second location of the write-once memory, to be written by the
manufacturer during production, the additional flexibility is possible. Of
course, the "max no. machines" location is not required in the chip used
in a machine. The only reason for providing all memory locations on all
security chips is that the additional cost is negligible and it allows the
use of a single part rather than two of them.
It must be borne in mind that prior to the use of any security chip in a
cartridge, a number must be stored in the second memory location of the
write-once memory if this location is used at all. Similarly, a serial
number must be stored in the first location of the write-once memory of
any chip used in a machine. Obviously, it is preferable that the 255
possible serial numbers for machines be used with the same frequency so
that no group of numbers is favored over another. The system would be
self-defeating were most machines to use the same serial number since in
such a case any cartridge would be playable on most machines.
Referring to FIG. 4, at the start of the machine sequencing, a reset signal
is sent to the cartridge, as described in the two above-identified
Nintendo patents. This places the two chips in synchronism. Before the
"old" Nintendo security routine is executed (this is the routine described
in the two patents), the new program steps controlled by the ROM memory
cause the machine to send a data word, represented by "code-1" in the flow
chart of FIG. 4, to the cartridge (step 71). Communication between machine
and cartridge throughout the drawing is shown by the horizontal dashed
lines, with the steps on the left being executed by the machine and those
on the right being executed by the cartridge. When the cartridge receives
the code1 data word, it interprets it as a command to send its stored "max
no. machines" value to the machine. Typically, as described above, the
number 2 or 15 would be returned to the machine (step 74). However, this
will take place only if the cartridge is a "new" one with the additional
software depicted in FIG. 4 as well as the write-once memory. An "old"
cartridge will not return a "max no. machines" value. In fact, it will no
longer be operating in synchronism with the machine program. However, that
is of no moment because the machine immediately performs a test to see
whether a reply has been received, i.e., has the number 2 or 15, or some
other permissible value, been returned from the cartridge. If such a
number has not been returned, then the machine knows that the cartridge is
an old one.
Old cartridges will have been sold with no restrictions on the number of
machines on which they can be played, and consequently they must be played
even on new machines. So after determining that an old cartridge is in the
machine (step 73), the machine restarts play of the cartridge with a reset
command(step 75). Thereafter, the "old" Nintendo security routine, which
is still implemented in the ROM program stored in every "new" security
chip, is executed. (The cartridge security chip is restarted only if
necessary to place it in synchronism with the machine security chip.
Synchronization is required because that is essential to the operation of
the Nintendo security routine.)
On the test in step 73 determines that the other hand, if the reply
received from the cartridge is a number which represents one of the
allowed numbers of machines on which a cartridge may be played, then in
step 77 the machine sends another message to the cartridge, this one
represented by the term "code 2." In response to the receipt of this
message, in step 79 the cartridge, whose security chip is a "new" one
since this has already been determined, sends to the machine all of the
stored played machine nos. in its write-once memory. Instead of sending
all 15 numbers, many of which may still be 00000000, it is possible to
transmit only the non-zero numbers, with only one 00000000 code at the end
to represent that there are no other stored machine numbers. There are
numerous communication schemes for informing the machine of all machine
numbers stored in the cartridge.
In step 81, the machine software then reads its own machine serial number
from the write-once memory in the machine security chip, and a check is
made to see whether this number matches one of the played machine nos.
received from the cartridge. If it does, it is an indication that the
cartridge has already been played on the machine and that repeat play is
authorized. This case is really comparable to that in which an old
cartridge is played-- the old Nintendo security scheme can be continued.
Consequently, in step 83 the cartridge is restarted with a reset as
indicated in the flow chart of FIG. 4.
On the other hand, if the serial number of the machine does not match any
of those stored in the cartridge, it is an indication that the cartridge
has not yet been played on this particular machine. The question now is
whether the cartridge has already been played on the maximum number of
allowable machines. As indicated in the flow chart, in step 85 a test is
performed to see whether there is yet an available played machine no.
location in the write-once memory of the cartridge in which a machine
serial number has not been written. Since the cartridge has transmitted to
the machine the serial numbers of all machines on which the cartridge has
already been played, and the machine knows the maximum number of allowed
machines, a simple subtraction operation yields an answer to the question
whether the cartridge can be played on the particular machine in question.
If the maximum number of serial numbers have already been stored in the
write-once memory of the cartridge, in step 87 play of the cartridge is
aborted as indicated in FIG. 4.
On the other hand, if there is still "room" on the cartridge for another
played machine serial number to be written, in step 89 the machine sends
its own serial number to the cartridge. As indicated in FIG. 4, in step 92
the cartridge software then records the received machine serial number in
the next available "played machine number" location in the write-once
memory. One more cartridge memory location is now used, and the machine on
which the cartridge is now being played will thereafter be authorized to
play the cartridge.
The machine may then execute the optional routine of FIG. 5 if it is
provided, as shown in step 91. Thereafter, as shown in step 93, normal
play of the cartridge ensues. To insure that the two security chips
operate in synchronism, the machine controls restart of the cartridge
security chip software with a reset command, after which the old Nintendo
security routine is executed.
The optional routine of FIG. 5 is simply a safety check. In the event an
attempt is made to foil the security system of the invention, an
additional security check is provided in FIG. 5. In step 95, the machine
sends the "code-2" message to the cartridge, in response to which--as
previously depicted in FIG. 4--the cartridge sends to the machine all
stored played machine numbers, shown in step 97 in FIG. 5. This time the
newly recorded serial number of the machine should be included in the
group. The machine checks in step 98 to see whether its own serial number
is included in those sent by the cartridge. If it is, then the cartridge
is restarted with a reset, the old security routine is executed and the
game is played. But if the serial number of the machine is not received
back from the cartridge, play is aborted in step 99. This additional
sequencing provides an added measure of security because while a
video/cartridge store owner may attempt to foil the system, it is very
difficult to "fix" the cartridge so that it sends back to the machine the
serial number of the machine. It is for this same reason of making it
difficult to foil the system that the major processing, e.g., comparing
the machine serial number with those stored in the cartridge, is performed
in the machine rather than the cartridge--there is less opportunity to
foil the protection mechanism.
Although the invention has been described with reference to a particular
embodiment, it is to be understood that this embodiment is merely
illustrative of the application of the principles of the invention. For
example, although disclosed in the context of the Nintendo security
system, the subject invention can be used on its own without employing the
Nintendo or other equivalent security scheme at all. Or it could be
incorporated in tape players and compatible tape cartridges, with machine
identification codes being written on a reserved portion of the tape in
any cartridge. Similar remarks apply to disc players and discs. Instead of
using a write-once memory in the cartridge, a non-volatile memory, whose
data can be overwritten, might be used. However, in such a case, to
prevent clearing of the stored identification codes by a business
establishment in the cartridge rental business, all writing (including
clearing) should be under control of a pair of security chips so that, as
long as the security chip is not duplicated by an unauthorized source,
identification code overwriting will not be possible. Thus it is to be
understood that numerous modifications may be made in the illustrative
embodiment of the invention and other arrangements may be devised without
departing from the spirit and scope of the invention.
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