Method and apparatus for remotely controlling and monitoring the use of computer software

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Patent issued

07/15/1997

Inventor(s):	Hornbuckle, Gary D.
Assignee	SofTel, Inc. (San Francisco, CA)
Application	No. 08/537,030 filed on 09/29/1995
Current US Class	707/10, 709/224, 709/229, 713/100, 713/2, 714/18, 714/E11.195, 717/127, 717/178
Field of search	380/4, 395/200.09, 395/490, 395/491, 395/182.16, 395/600, 395/700, 395/610, 395/652, 395/653, 395/712
International Classes:	G06Q 30/00 (20060101), G06F 11/34 (20060101), G06F 1/00 (20060101), G07F 17/00 (20060101), G07F 17/16 (20060101), G06F 21/00 (20060101), G07F 7/00 (20060101), G06F 013/00 (), G06F 015/177 ()
Examiners
Primary	Thomas G. Black
Secondary	John C. Loomis
Attorney, agent or firm:	LaRiviere, Grubman & Payne
Foreign patents	WO8502310 (05/01/1985, WO), WO8503584 (08/01/1985, WO), WO8802202 (03/01/1988, WO), WO8802960 (04/01/1988, WO)

Remote control of the use of computer data is described in a system for renting computer software which derives use and billing information, prevents unauthorized use, maintains integrity of the software and controls related intercomputer communications. A user at a target computer "downloads" programs or data, via a telephone line and remote control modules, from a host computer. Usage of the programs or data by the target computer or other accounting data are recorded and stored and, at predetermined times, the host computer "uploads" the usage data for processing. Other features include: (1) software and usage security for rental programs; (2) a polynomial generator/checker for generating block check characters for assuring integrity of data transmitted and received; (3) a voice-data switch for switching between data communication and normal telephone communication; and (4) an audio amplifier and speaker for monitoring of activity on the communication line during data transfers.

What is claimed is:

1. A method of renting an application program for use on a customer computer, comprising the steps of:

encrypting a key module of the program, the program being inoperable without the key module;

storing the program in the customer computer;

retrieving the program when it is desired to run the program;

upon retrieval of the program, automatically decrypting the key module to permit use of the program; and

during use of the program on the customer computer, recording accounting data representative of the use to facilitate transactions based on the use.

2. The method of claim 1, further comprising the step of transmitting the accounting data to a central host computer at preprogrammed times.

3. The method of claim 2, further comprising the steps of:

monitoring the state of a time monitoring means connected to the customer computer, the time monitoring means for monitoring the use of the program; and

preventing the use of the program when the time monitoring means is disconnected from the computer.

4. Apparatus for renting computer programs comprising:

a rental control unit coupled to a rental computer and including first transmitting and receiving means for transmitting first type information to a user computer and for receiving second type information from said user computer, said first type information including at least one computer application program, said rental control unit also including encryption means for encrypting at least one preselected portion of said computer program to form an encrypted module before transmission of said first type information by said transmitting and receiving means, said encryption means including a first encryption key for use in forming said encrypted module, said encryption module being only a fraction less than one of said computer program; and

a user control unit coupled to a user computer and including second transmitting and receiving means coupled to said first transmitting and receiving means for transmitting second type information to said rental computer and for receiving said first type information from said rental computer, said second transmitting and receiving means including decryption means for decrypting said encrypted module to form a decrypted module, said user control unit also including storage means coupled to said decryption means for storing said decrypted module and transfer means for causing said decrypted module to be transferred from said storage means to said user computer for execution by said user computer and for removing said decrypted module from said user computer when execution by said user computer is completed.

5. Apparatus as in claim 4 wherein said encryption means includes a second encryption key for use in encrypting said first encryption key to form an encrypted first encryption key, and said decryption means includes a copy of said second encryption key for use in decrypting said encrypted first encryption key.

6. Apparatus as in claim 4 wherein said second type information includes time accounting data for determining rental charges for use of said computer program, said rental charges based at least in part on the length of time said decrypted module is being executed by said user computer.

7. Apparatus for controlling the use by a second computer of information stored in a first computer, said apparatus comprising:

first transmitting and receiving means coupled to said first computer for transmitting information to said second computer;

a second transmitting and receiving means coupled to said first transmitting and receiving means and to said second computer for receiving information transmitted by said first computer;

said first and second transmitting and receiving means each including encryption/decryption means for encrypting and decrypting, respectively, preselected portions of the information, said preselected portions including application program information, and a first encryption key for encrypting and decrypting said preselected portions of the information including, said application program information;

said first and second transmitting and receiving means each including a second encryption key for encrypting and decrypting, respectively, said first encryption key;

error detection means for detecting errors, on a block-by-block basis using a polynomial checker, in data transmitted from said second computer to said first computer and for producing an error signal representative thereof; and

retransmission means coupled to said error detection means and responsive to said error signal for producing a signal representing a request for retransmission of said data, said second transmitting and receiving means responsive to said request for retransmission for retransmitting said data.

8. Apparatus as in claim 7 further including monitoring means for monitoring usage by said second computer of the information transmitted to said second computer for developing time accounting data relative to rental charges for said usage, and for preventing usage of the information if said second transmitting and receiving means is disconnected from said second computer.

9. Apparatus as in claim 8 further including memory means coupled to said monitoring means for storing said time accounting data, said second transmitting and receiving means being responsive to a second command from said first computer for transmitting said time accounting data to said first computer.

10. Apparatus as in claim 7 wherein:

said encryption/decryption means in said second transmitting and receiving means decrypts the encrypted portion of the application program information only upon request of a user of said second computer to use the information, said second transmitting and receiving means thereupon transmits the decrypted information to said second computer.

11. Apparatus as in claim 7 further including:

error detection means for detecting the presence of an error in the information transmitted by said first transmitting and receiving means and for producing an error signal; and

retransmission means coupled to said error detection means and responsive to said error signal for producing a signal representing a request for retransmission of the information transmitted by said first computer, said first transmission and receiving means being responsive to said request for retransmission for retransmitting the information.

12. Apparatus as in claim 7 wherein said first and second transmitting and receiving means are coupled to each other via a public communication network.

13. Apparatus as in claim 12 wherein said first and second transmitting and receiving means each include connection means for connecting said first and second transmitting and receiving means, respectively, to said public communications means.

14. Apparatus as in claim 13 further including a telephone coupled to said connection means associated with said second transmitting and receiving means, said connection means including means for connecting said telephone to said public communications network when said second transmitting and receiving means is not receiving the information and said transmitting means is not transmitting said time accounting data.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to remotely controlling and monitoring the use of computer software. More particularly, this invention relates to a system for renting computer software products while 1) deriving customer use and billing information; 2) preventing unauthorized copying and use; 3) maintaining the integrity of the rented software product (hereafter also "package"); and 4) controlling related voice, program and data communications between the host and user's computers.

For purposes of the present invention, rental computer software refers to the service of providing computer software to customers (hereafter also users) on a pay-as-used basis, where the software is executed on the customer's own personal computer. In the past, the only software offered for "rent" was software installed on centrally located computers, accessible via remotely located workstations or terminals. Such systems are well-known as "time-sharing" systems.

In time-share systems, software is executed on the central computer system, and not on the customer's own computer. Time-shared software is typically accessed over telephone networks using a "dumb" terminal or equivalent located at the customer's home or office. In such systems, all customers share the central computer resource, and the quality and delivery of services provided generally degrade, i.e., slow down, as more customers attempt to use the resource simultaneously. In addition to charges for the central computer to execute the users program (i.e. CPU time), charges for time-share usage must also include the cost for continuous use of the public telephone network for the duration of the connection to the central computer (i.e. connect time), whether or not the central computer is actually executing the user's program. Thus, as the number of users increase, both CPU time and connect time increase; as CPU time and connect time increase, charges escalate as service degrades.

In general, and particularly in the circumstances just described, charges for use of software via time-share systems are likely to be much greater and far less predictable than for the rental of software which is executed on the customer's own computer. On the other hand, host-based, time-share systems have successfully provided software that is too expensive or complex to be made available on smaller systems such as personal computers. Thus it is desirable to continue offering expensive and complex software installed on host-based systems, while eliminating the disadvantages of time-share systems.

The software rental system of the present invention has some features which are not unlike pay-for-view television systems enjoyed by television viewers today. In pay-for-view television systems, the customer generally pays to watch a particular program. For that purpose, the customer is provided with a control box supplied by a cable television company. The control box, once activated from the cable company office, decrypts encrypted television signals transmitted to the user by the cable company. If the customer is not authorized to view a particular program, the image remains scrambled, and is unintelligible to the viewer. Conversely, once the customer has selected and paid for the program desired, the control box decrypts the signal and the program is understandable by the viewer.

In the relevant prior art, U.S. Pat. No. 4,361,851 discloses a television usage monitoring system comprising a modified program selector (installed in the home of a subscriber) which is used to select television programs for viewing while, at the same time, providing the selection information to a remote monitoring unit (also installed in the subscriber's home). The remote monitoring unit is connected to the subscriber's telephone line and is programmed to periodically communicate, via telephone lines, with a central computer for the purpose of transmitting the television usage data thereto. The disclosed remote monitoring system can be utilized for "[a]ccess to centralized public database networks" (see column 2, line 4). The system is also described as having the capability of producing a "disable" signal from the central computer to the remote unit if, for example, the subscriber has not timely paid charges due on his account. It should be noted that U.S. Pat. No. 4,361,851 does not disclose a system for 1) secure and remotely controlled downloading and use of computer programs and data; 2) remotely controllable monitoring of use and security of the downloaded programs and data; and 3) accessing and retrieving stored usage data. In addition, neither means for generating block check characters for data transmitted and received, nor voice-data switching capability is described.

U.S. Pat. No. 4,624,578 discloses a rental contract timer system for operating a relay to connect power to the rental equipment such as a television set, only during the time for which rental has been paid. A magnetic card reader determines, from an inserted card, the rental period and identifying information, and the timer contains a real-time clock and a microprocessor to compare the current time with the time in the rental period.

In addition, U.S. Pat. No. 4,700,296 discloses an electronic access control system for controlling customer access to rental appliances located in the customer's home or other location away from the direct physical control of the renter. The system comprises a control module wired into the appliance with a card reader for programming the module to permit access and usage of the appliance by the customer.

In the software rental system of the present invention, a control module is installed on or in cooperation with the customer's computer (hereafter also target computer), and the customer pays for services, i.e., the use of the software, received. While operation of the system is as convenient to use, substantially different features, advantages and implementation with respect to the corresponding television system are necessary and desirable. Specifically, the customer in a software rental system may rent any program of an entire library of computer programs at any time, rather than waiting for a particular time slot during which a particular program would be available. Moreover, it is not necessary to install a separate transmission system, such as a TV cable system, to access programs, since they are downloaded over conventional telephone lines. Finally, the software available for rent is not broadcast over the entire system, but rather individual programs are down-loaded to the user's system from the host only after selection by the user.

The control module used in the proposed software rental system performs many more functions than its counterpart in the pay-for-view television system. For example, it controls and verifies that use of a program is authorized; it records the actual time that the program is used; and it protects the rental program from theft, copying, vandalism or modification. In addition, facilities for communication via the telephone lines between the control module installed at the user's site and the central or host computer are provided.

A software rental system according to the present invention is also efficient and highly automated, for performing a number of overhead functions. At the same time, in order to maximize customer satisfaction, the overhead activities of the control module are essentially transparent to the user. Thus, for example, accounting and billing activities are automated to avoid the need for manual "meter readers", and other control operations conventionally involving a high degree of overhead expense are reduced or eliminated where possible.

By means of the present invention, an authorized user at the target computer is able to "download" programs or data, via a telephone line and a programmable remote control module (RCM) connected at each end thereof from a central or host computer. Usage and other accounting data are monitored by the RCM and stored in memory resident therein. At predetermined times, the central or host computer accesses the RCM for the purpose of "uploading" the usage and other accounting data to the central or host computer.

The RCM of the present invention also includes: (1) programmable modules for preventing unauthorized use, copying, vandalism and modification of downloadable data and programs during or after transmission to the target computer; (2) a polynomial generator/checker for generating block check characters for assuring the integrity of data and programs transmitted and received; (3) a voice-data switch for switching between data communication (with the central or host computer) and voice usage of the telephone line via the RCM; and (4) an audio amplifier and speaker so as to permit monitoring of activity on the communication line during data transfers by the RCM.

With the features listed above, the proposed system provides for error-free transmission of programs or other data between a host computer and a target computer, and for the secure transmission, reception and usage of programs or other data transferred between the host computer and the target computer. The audio amplifier and speaker can be used by the customer to monitor activity on the communication line during data transfers between the target and host computers. Finally, the RCM can be controlled to function as a conventional modem when conventional telecommunications service is desired. A voice/data selector switch is provided so that the user can select between voice and data communications.

The proposed software rental system has the capability to provide users with access to a wide range of software, including virtually all software that is sold for use on a personal computer. Thus, the system is particularly suited to the dissemination, on a pay-for-use basis, of otherwise expensive and complex software, such as certain engineering or scientific software, as well as certain financial accounting or tax programs.

The system is also well-suited for allowing a customer to use moderately priced software on a rental basis to see if it really meets his needs. If satisfied, the software could be purchased, and marketing programs whereby the customer may apply some or all of the rental fees to the purchase price of the software could be devised. The proposed software rental system, therefore, offers software on a rental basis to new or low-usage customers at lower cost than would be otherwise incurred by purchase of the same software.

Rental software, as contemplated by the present invention, is less expensive than time-share software, and more convenient to use because execution is controlled by the user and unaffected by the number of other users. By eliminating the high initial cost of purchasing software and unpredictable cost and inconvenience of time-sharing, the number of users of a software rental system could be expected to grow indefinitely. Moreover, with more users becoming acquainted with various software products, the software industry as a whole would benefit, since the number of ultimate purchasers of the software would be likely to increase. Thus, with respect to both rental and purchase of software, the revenue of software vendors may be expected to increase.

The above and other objects, features and advantages, as will hereinafter appear, and the nature of the invention will be more fully understood by means of the detailed description set forth below, with reference to the associated drawings and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of the data communication system in which a remote control module of the present invention is employed.

FIG. 2 is a block diagram of the remote control module employed in accordance with the present invention.

FIGS. 3A, 3A1-6, 3B, and 3B1-3 are circuit diagrams of the remote control module shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, software rental system 10 generally comprises host computer 12, target computer 14, remote control module (RCM) 16 associated with the host computer 12, and RCM 18 associated with the target computer 14. Communication between the host computer 12 and the target computer 14 and their respective RCMs 16 and 18 is accomplished via a standard serial RS232 communications link.

In operation, programs to be provided to authorized users on a rental basis are stored in the host computer 12. Typically, the host computer 12 is owned by a software rental service or company and is located at their offices. As shown in FIG. 1, the host computer 12 is connected to the public switched telephone network 26 via serial data line 20 RCM 16.

The target computer 14 is the computer of any user, and may be a workstation, minicomputer, or even a mainframe. However, for purposes of software rental, the most likely target computer is expected to be a personal computer, owned and operated by a user in a home or office setting.

The target computer 14 is connected to telephone network 26 via serial data line 22 and RCM 18. RCM 18 is also connected to a conventional source of AC power via power line 28, which also can be provided to the target computer 14 by RCM 18 via power line 24.

In operation, the host computer 12 can "dial up" the target computer 14 and, conversely, the target computer 14 can "dial up" the host computer 12. Functions of the host computer 12 include transmission of software to the target computer 14, request for and reception of customer usage data associated with the target computer 14 from RCM 18, and performance of various accounting and software rental business functions.

RCMs 16 and 18 and the methods for using them which are disclosed herein are intended to work with any type of host computer 12 and target computer 14. The software installed in the host computer 12 and the target computer 14 will, of course, be different for different types of computers, but the methods remain the same.

In accordance with the present invention, at any given time, the host computer 12 can communicate simultaneously with any number of target computers depending on the number of RCM's attached to, and the communications capacity of the host computer 12. Thus, by adding host computer RCMs and, if necessary, host computers, a virtually unlimited number of target computers 14 associated with RCMs 18 can simultaneously access rental software packages from the host computer(s).

Communication with the host computer 12 is an integral part of the software rental concept of the present invention, but the timing of communication of usage data to the host is not critical, since it is primarily for accounting and other administrative functions. Of course, the target computer(s) 14 can run rental software whenever and as often as the user desires.

Host computer 12 employs RCM 16 rather than merely a conventional modem to provide also for data integrity and program security. RCM 16 includes error detection circuits and data encryption modules for use in conjunction with communication from host computer 12.

Finally, as seen in FIG. 1, telephone 30 may be connected to RCM 18 via telephone line 32, using standard RJ11 modular plugs. In addition, a switch (not shown) may be provided on the front panel (not shown) of RCM 18 for use by the customer to select voice or data modes of communication. In the voice mode, telephone 30 can be used to conduct voice communication over telephone network 26.

Referring now also to FIGS. 2, 3A and 3B, RCM 18 comprises microprocessor 50, program memory 52, read/write memory 54, real-time clock (RTC) 56, power supply 58, priority interrupt control circuit 60, light-emitting diode (LED) displays 62, modem 64, dial access arrangement (DAA) 66, RS232 serial data interface 68, data encryption/decryption module 70, and polynomial generator and checker (PGC) 72.

Microprocessor 50 is any conventional microprocessor, but may be a multi-port integrated circuit device, such as an 8031 microprocessor, the ROM-less version of the 8051 microprocessor 50 (FIG. 2) and the speed of the communications link between the host computer 12 and the target computer 14 (FIG. 1) are not critical to systems constructed according to the principles of the present invention. Thus, while higher speed communication is typically superior to lower speed communication, the only requirement is that microprocessor 50 be fast enough to implement the various tasks that it is called upon to perform in its operating environment.

Program memory 52 is any conventional read-only memory (ROM) and is used to store the program executed by microprocessor 50 in performing the functions of RCM 18. An erasable/programmable read-only memory (EPROM), e.g., a 27128, may be used for program memory 52 when the modification of functions performed by RCM 18 may be desirable. However, an equivalent conventional ROM is acceptable and, typically, is a lower cost device.

Read/write memory 54 is, preferably, implemented by a Toshiba TC5565 static random access memory (RAM) having a capacity of at least 8 kilobytes. Back-up battery power is provided by power supply 58 to ensure that the contents of memory 54 are not lost if power to the RCM 18 is interrupted.

RTC 56 is, preferably, an ICM 7170 device manufactured by Intersil. The latter circuit maintains the date and time to the nearest 0.01 second. The occurrence of a leap year is automatically accommodated. RTC 56 is connected to the power supply 58 and receives battery backup therefrom in case of power failure. RTC 56 functions in a conventional manner to provide control and time information, upon request, to microprocessor 50. This enables the RCM 18 to perform its function of developing time, accounting and billing data relative to customer access to and use of programs initially stored in the host computer 12. Such time and billing data are provided to the host computer 12 by RCM 18 on command from the host computer 12.

Power supply 58 provides direct current power to the various other circuit elements of the RCM 18. In the event of a power failure or turning off of the AC power to the RCM 18, a "battery backup" feature of the present invention detects such condition, and the internal battery of RCM 18 provides battery backup power to the read/write memory 54 to protect data stored therein, and to RTC 56 to maintain operation thereof. In this manner, the contents of the memory 54 and the operation of the RTC 56 are not disturbed by a loss of AC power. Preferably, the internal battery of power supply 58 is a conventional rechargeable battery such as to preserve the contents of memory 54 and maintain operation of RTC 56 for several years, if necessary. Once AC power is restored to the system, the internal battery returns to its "wait" state, and power is not expended by the internal battery.

RCM 18 is provided with one standard 110 VAC output receptacle for receiving the standard electrical power plug for the target computer 14. The receptacle is relay-controlled so that switched AC power output is provided to the target computer 14 via power line 24. In this manner, target computer 14 can be turned on or off by RCM 18 for certain functions as described elsewhere in this specification.

Device interrupts generated within RCM 18 of FIG. 2 are merged in priority interrupt control circuit 60, which comprises a 74LS348 integrated circuit chip. Microprocessor 50 supports only two priority interrupts, namely, INT0 and INT1. INT0 is unassigned and is available as a test point for use with various test equipment. All other interrupts are assigned to INT1. Since all of the devices of RCM 18 have separate interrupt enabling control, any or none of the device interrupts may be used.

The nature and source of a particular interrupt is determined by reading terminals P10-P12 (as shown in FIG. 3A) of interrupt control circuit 60. Once an interrupt has occurred, its cause must be resolved by microprocessor 50, or the same interrupt will continue to recur. A summary of typical interrupts and their priorities is given in Table 1 below.

TABLE I ______________________________________ Interrupt Value of P10-P12 Priority ______________________________________ Power low 0 Highest Incoming Ring 1 Next Highest Modem Interrupt 2 Next Highest UART 3 Next Highest RTC 4 Next Highest PGC 5 Lowest ______________________________________

LED displays 62 comprise a number of single light emitting diode displays to indicate the status of certain conditions and the occurrence of certain events. Such conditions or events include power-on, power-off, and the status of communications activity. During diagnostic and test functions, the LED displays take on different meanings related to these functions.

Modem 64 includes modulation and demodulation circuitry for sending and receiving data over the public switched telephone network 26 (FIG. 1). Preferably, modem 64 is implemented by a 73K222 modem circuit (for 300, 600 and 1200 baud) or a 73K224 modem circuit (for 2400 baud) manufactured by Silicon Systems, Inc. However, other conventional modem circuits, including modem circuits supporting higher baud rates, can be used to implement the functions of modem 64. Moreover, since modem 64 can serve as a standard personal computer type modem when the target computer 14 is not engaged in accessing rental software, it is not necessary to include an additional modem for communication with other computer services or data base services.

Dial access arrangement (DAA) 66 provides for connection of RCM 18 to the public switched telephone network 26. DAA 66 connects private circuits to the public switched telephone network in compliance with FCC regulations, Part 68. Thus, DAA 66 includes transformer isolation, impedance matching circuits, ring detection circuits, voice/data switching circuits, hook relays and other well-known circuitry required for connecting to the public switched telephone network 26.

The serial data interface 68 is a conventional serial interface for communication in accordance with standard RS232 criteria. More specifically, interface 68 is, preferably, a universal asynchronous receiver/transmitter (UART), model SCC2691, for carrying on serial data communication between RCM 18 and the target computer 14. Thus, the interface 68 is coupled to a standard RS232 serial port of the target computer 14 via serial data cable 22. Data is transmitted serially between the target computer 14 and interface 68, whereas data is transmitted in parallel on bus 74 between interface 68 and microprocessor 50.

Further considering the serial link between interface 68 and the target computer 14, the clock for the serial port of the target computer 14 has a frequency equal to one-fourth the frequency of the internal clock of microprocessor 50 of RCM 18. Preferably, the frequency of the serial port clock of the target computer 14 is set to 2.7648 Mhz.

The baud rate between the RCM 18 and the target computer 14 may be any value, provided that the RCM 18 can buffer the data. The baud rate of the modem 64 is set to 300, 600 or 1200 baud, depending on the transmission method chosen.

Data encryption/decryption module 70 performs a decrypting function with respect to data received by RCM 18, from the host computer 12. Data decrypted by module 70 of RCM 18 was encrypted by a corresponding data encryption/decryption module in RCM 16 associated with the host computer 12 prior to transmission to the RCM 18. The encryption and decryption functions will be discussed in more detail herein below in connection with a more complete discussion of the software security technique employed by the present invention.

Polynomial generator/checker (PGC) 72 is, preferably, an SCN2653 device manufactured by Signetics, Inc. Preferably, RCM 18 generates block check characters (BCC) for each block of data to be transmitted by RCM 18 to the host computer 12. Correspondingly, each block of data received from the host computer 12 by RCM 18 is checked in accordance with the BCC. By way of a further preference, PGC 72 employs a CRC-16 polynomial code with an X.sup.16 +X.sup.15 +X.sup.2 +1 divisor. In this manner, all single-bit errors and most multiple-bit errors are detected. The CRC-16 polynomial is employed because the error codes generated are much more reliable than the normal "check sums" typically used. This is especially true for data transmitted over the public switched telephone network 26.

Since data communications using the public switched or dial-up telephone network 26 are notoriously error prone, special precautions are often taken to at least detect errors, if not correct them. More elaborate schemes can be used to correct the errors, and such error-correction coding schemes are not precluded by the present design of the RCM 18. However, for reasons of economy and speed in data communications, the preferred embodiment described herein performs error detection only. In the present system, a data block is simply retransmitted in the event of an error detection.

As generally discussed above, the error detection method employed herein involves the transmission of a specially generated 16-bit code at the end of each data block. The check code is generated by PGC 72 using the aforementioned CRC-16 polynomial with the aforementioned divisor. At the receiving end, the check code is, in effect, regenerated and compared to the actual check code received. If identity is not present, a transmission error has occurred and an error signal is generated by PGC 72. Once an error is detected, a request for retransmission is initiated and the data block will be retransmitted by the host computer 12 to RCM 18, or from RCM 18 to the host computer 12, as the case may be.

The check code employed herein can be mathematically shown to be very effective in detecting the types of errors that normally occur over public switched or dial up telephone networks such as network 26 (FIG. 1). Simpler schemes could be implemented, and would not require the use of PGC 72, but such schemes are not as effective for this application.

Accordingly, all communication between the host computer 12 and target computer 14 or RCM 18 employ the above-described error detection method with retransmission of data blocks upon detection of errors. In the latter regard, RCM 18 employs PGC 72 for checking data received from host computer 12, and a corresponding PGC in RCM 16 (FIG. 1) checks data received from the target computer 14 or RCM 18.

Certain applications of the system 10 (as shown in FIG. 1), in particular for the business of software rental, typically will be configured so that the host computer 12 sends and receives data/messages to and from the target computer 14 over the public switched telephone network 26. As also indicated above, RCMs 16 and 18 serve as interface devices to connect the host computer 12 and the target computer 14, respectively, to the telephone network 26. Obviously, while designed to work with the public switched telephone network the present invention can be configured to work with any communications link between the host and target computers.

The circuit configurations of RCMs 16 and 18 are identical. The operation of the RCM 18 associated with target computer 14 and the operation of RCM 16 associated with host computer 12 is determined by program instructions executed by microprocessor 50.

RCMs 16 and 18 provide serial communication, via RS232 serial data interface 68, to the host computer 12 and target computer 14, respectively, each of which is preferably located within a short-distance (i.e., a few feet) of its respective RCM. Whereas a single RCM 18 is required for each target computer 14, a plurality of RCMs 16 may be used with host computer 12. In fact, the number of RCMs 16 must be equal to the number of simultaneous data-transmission links between the host computer 12 and target computers 14 (to download software) or RCMs 18 (to upload usage and accounting data). In this manner, the host computer 12 can carry on data conversations with several target computers 14 simultaneously.

When a customer contracts to participate in the rental software system, the software rental company will provide the customer, either through sale or rental, with RCM 18 for connection to and association with the customer's target computer 14. Installation of the RCM 18 is easily performed by the customer. Referring again to FIG. 1, RCM 18 is connected to the public telephone network 26 by means of a standard RJ11 type modular telephone cord extending between RCM 18 and the telephone system jack. In addition, RCM 18 is connected to the target computer 14 via a serial data cable 22 and power cable 24, RCM 18 deriving its power from a conventional AC power source via cable 28. As an option, telephone (or telephone handset) 30 may also be connected to RCM 18 via telephone cable 32 utilizing standard RJ11 modular plugs. Thus, when RCM 18 is not being used for data communications, the telephone 30 can be used for normal voice communications. When data communications involving RCM 18 are to take place, RCM 18 performs automatic switching so as to break the connection between telephone 30 and telephone network 26, and to establish connection between DAA 66 (FIG. 2) and the network 26.

During preprogrammed times, as established by the software of the host computer 12 and transmitted to RCM 18 and stored in memory 52 of RCM 18, RCM 18 will initiate an "automatic answer" mode of operation so that it may respond to messages received from the host computer 12. Such communications between the host computer 12 and the target computer 14 normally occur at night so as to take advantage of low telephone rates in effect at that time, and also to avoid conflicts with other data transmission functions of target computer 14.

The RCM 18 can also be used as a standard modem for the target computer 14, and can be set up to communicate with remote computer or other database services. RCM 18 distinguishes between its usage as a standard modem and its usage as a special remote control module for controlling access to rental software.

During the time that RCM 18 is not performing data communications and is not set up in its "automatic answer" mode, telephone 30 (if one is attached) is available for normal use,, and will ring in the usual way when called.

One feature of the proposed software rental system is the ability to download software from the host computer 12 to target computer 14 during off-peak hours, such as late at night. Preferably, the customer will not be compelled to participate in or supervise the downloading of software during such late-night hours. Thus RCM 18 is able to control the AC power provided to the target computer 14 in response to control signals from the host computer 12. In order to enable this feature of the present invention, the on/off switch of target computer 14 is left in the "on" position, and the power cable 24 (FIG. 1) of target computer 14 is plugged into a receptacle 102 at the rear of RCM 18, RCM 18 being connected via its own power cord 28 to an AC power source, as previously described. Preferably, the front control panel of RCM 18 is provided with an on/off switch so that the customer can turn on or turn off the target computer 14 manually. However, this switch is preempted when RCM 18 receives a command from the host computer 12 to turn on the target computer 14 for late-night operation.

Accordingly, when downloading of software is desired, the host computer 12 calls the target computer 14, and once the call is acknowledged by RCM 18, the host computer 12 turns on the target computer 14 by actuating the AC power switch in power supply 58 (FIG. 2). When the target computer 14 is turned on by RCM 18 at the command of the host computer 12, the host computer 12 can download software to a storage device (not shown) associated with the target computer 14. In addition, for reasons described below, a special patch for the target computer 14 operating system, which is required to run the rental software, is also downloaded (if not previously downloaded) from the host computer 12 to the target computer 14. Once the software downloading process is complete, the host computer 12 commands RCM 18 to turn off power to the target computer 14.

Power to non-essential external peripheral devices associated with target computer 14, such as a printer, a display device and the like, need not be controlled through RCM 18 since the downloading process does not require the use of such external peripherals. However, if desired, such external peripheral devices may be controlled through the RCM 18 by making appropriate power connections to the RCM 18.

Referring again to FIG. 2, RCM 18 contains a program memory 52 and a read/write memory 54. The program memory 52 holds the program instructions which microprocessor 50 implements in order to accomplish the functions of RCM 18. Read/write memory 54 holds the accounting data relating to software rental by the user of the target computer 14, and also provides buffer storage for communications messages passing between the host computer 12 and the target computer 14. Read/write memory 54 may also store other ancillary data.

RTC 56 is included in RCM 18 in order to provide a real-time-base, including exact year, month, day and time. Preferably, accuracy is to the nearest 0.01 second. The setting of RTC 56 with the year, month, day and time is strictly controlled by the host computer 12 using security techniques available to it through data encryption/decryption module 70.

Overall, RCM 18 is a real-time controller that can be called into action independently by host computer 12, target computer 14, a change of state of the power switches of RCM 18, and other internal conditions. Accordingly, an interrupt system is designed into the operation of RCM 18, and is used to enable microprocessor 50 to manage these independently occurring real-time events. The management of interrupts by microprocessor 50 is assisted by priority interrupt control circuits 60.

An important aspect of the present invention concerns security for rental software executed by the target computer 14 (FIG. 1). This software security function is provided by the cooperation of data encryption/decryption module 70 in RCM 18 with a corresponding data encryption/decryption module in RCM 16 associated with the host computer 12. Closely coupled with the function of providing software security is the function of keeping track of and accounting for the time periods during which the target computer 14 is using the rental software on which the rental charges are based.

In at least some instances, the rental software provided by the host computer 12 may have a very large amount of code and many data files. Of course, it is not necessary to provide security or protection for each and every component or module of most rental programs. In accordance with the present invention, a particularly critical module--hereinafter referred to as the "key module"--in each rental program is identified. The key module, according to the present invention is essential to program execution and without which the overall rental program will not run.

In addition to identification of the key module, the security of rental software according to the present invention also requires a special version of the operating system to be utilized in the target computer 14. The special version of the target computer operating system is created by a patch module, hereinafter "operating system patch module" or "OSP" module (the OSP is identical for all rental software executed on target computers of the same or similar type), which is downloaded to the target computer 14 along with the rental software. The OSP module initiates decryption of the encrypted key module of the rental software package by module 70 of RCM 18, then loads the decrypted key module into the internal memory (not shown) of the target computer 14 for execution. In addition, periodically while the rental software package is running, the OSP module communicates with the RCM 18 to provide verification that it is still connected to the target computer 14 for security and accounting purposes.

The key module is encrypted using the Federal Information Processing Data Encryption Standard No. 46, well-known to those of skill in the art, by the data encryption/decryption module 70 of RCM 16. When the rental software is transmitted by the host computer 12 over the telephone network 26, the encrypted key module and the associated OSP module are transmitted as well. Alternatively, the encrypted module, the OSP module and the unencrypted remainder of the rental software may be sent to the customer on floppy disks or magnetic tape by mail or other delivery service. When downloaded from the host computer 12 or loaded from media otherwise provided by a software rental service, the entire rental software package (including the encrypted key module and OSP module) is stored in a peripheral storage device (e.g., hard disk or floppy disk) associated with the target computer 14.

Further referring to the encryption process of the present invention, data encryption/decryption module 70 of RCM 16 uses an encryption key unique to the individual target computer in which the rental software is to be used. Methods of encrypting and decrypting using an encryption key, such as described in U.S. Pat. No. 4,649,233, are well-known. However, since the encryption key is an important element which the software security scheme of the present invention depends, the encryption key itself is always transmitted in encrypted form to RCM 18 (utilizing an encryption key identical to the encryption key provided in RCM 18) to assure proper systems operation and integrity. When transmitted from RCM 16, the encryption key is then automatically decrypted as it is received by RCM 18 using a second, special key built into RCM 18 which is unique to each individual RCM 18. The decrypted encryption key is then stored in the RCM memory 52 until decryption of a key module is required. Since the encryption key is retained in memory 52, the encryption key need only be transmitted to RCM 18 one time. If the RCM 18 is tampered with in any manner, the encryption key is destroyed. Without the encryption key, decryption of the key module of the rental software at the target computer 14 is essentially impossible, and use, copying, vandalizing or modification of the rental software is prevented. The security technique employed by the present invention also provides a high degree of protection during downloading of the package via the public telephone network 26 owing to encryption of the key module and of the encryption key.

As described above, decryption of the key module is performed in the data encryption/decryption module 70 of RCM 18. The encryption key used in the decryption process is inaccessible to the user. Thus, in accordance with the present invention, a downloaded rental software package will only run on the particular target computer 14 having an encryption key corresponding to the encryption key employed by the host computer 12 when the key module of the rental software package was encrypted. Since the rental software will operate only on a target computer 14 serviced by an RCM 18 utilizing an encryption key unique to the target computer 14 (to decrypt the key module), no other physical or licensing restrictions on the user's ability to make copies of the rental software package are required.

Prior to a customer executing a rental software package on a target computer, the software package will have been transmitted electronically or by other suitable means and be resident in a peripheral storage device associated with the customer's target computer. The rental software package will have the corresponding OSP module appended and the original key module will be replaced with an identical encrypted key module.

Assuming that a customer wishes to run a rental software package protected in accordance with the present invention, the user follows exactly the same procedures for loading the software package from the associated peripheral storage device to the internal memory of target computer 14 as if an unrented version of the same package were being run. However, in a manner transparent to the user, when the key module of the software package is retrieved from the peripheral storage device of target computer 14, the OSP software module is activated. The OSP module fetches the encrypted version of the key module from the peripheral storage device (not shown) and sends it to the RCM 18 for decryption by the encryption/decryption module 70. After decryption, the key module is sent back to the target computer 14 and loaded into its internal memory (RAM) for execution. At the latter step the OSP module also initiates a timer controlled by the RTC 56 to begin recording the actual use time of the rental program for computation of rental time charges.

The rental program with the decrypted key module now stored in the internal memory of target computer 14 will operate in exactly the same manner as it would if it were not a rental package (i.e., the same way as if it were a purchased program). However, when execution of the rental program is complete, control reverts back to the OSP module. The OSP module then automatically erases the rental program including the key module from the RAM of target computer 14 and notifies RCM 18 that the period of use or rental period has stopped. The elapsed time between the starting and stopping of the rental program, as well as the time and date information, are recorded in memory 54 of RCM 18 for subsequent, off-line processing.

It is essential that the RCM 18 be connected to the target computer 14 at the time that the rental period ends. Connection of RCM 18 to the target computer 14 insures that the exact time of termination of the rental period is recorded. Furthermore, to maintain proper security of the rental software in accordance with the present invention, while the rental software package is running, periodically control is passed to the OSP module upon the occurrence of certain periodic events, disk access by the target computer 14 operating system for example. The OSP module then executes routines to prevent circumvention of the rental accounting for use of the rental software package, and to protect the rental software package from theft, vandalism or other unauthorized modification. In particular, the OSP module then queries RCM 18 and verifies, through its response, that RCM 18 is, in fact, connected to the target computer 14. If it is, execution of the rented software continues; if it is not, the execution is terminated by the OSP module and the entire rental software program is erased from the target computer 14 RAM.

It should be noted that the rental software package itself may be modified by adding code to ascertain that the RCM 18 is connected to the target computer 14 rather than modifying the operating system by adding the OSP module for receiving control from the rental software package. However, since modifying the rental package is difficult without assistance from the developers of the package, adding the OSP module is preferable. Therefore, an operating system, so patched, must be used when executing rental software according to the present invention. As described above, the OSP module is downloaded with the rental software package, if it has not already been downloaded earlier with another software package.

The software security scheme of the present invention involves encryption of only the key module of the rental software in a predetermined algorithmic manner using an encryption key. Further, the encryption key itself is encrypted and transmitted by the host computer 12 separately. No changes to the functions of the rental software are made during the encryption process. Thus, any software package may be rented without technical involvement of the software vendor, and all of the security procedures are transparent to the user.

In accordance with the present invention, microprocessor 50 in RCM 18 is programmed to destroy an encryption key if: (1) the RCM 18 is physically tampered with; (2) the telephone number of the target computer 14 is changed without notice or the telephone is disconnected for longer than a preselected period of time (in this case, destruction of the protection key takes place only after power is restored). If the encryption key is destroyed by the RCM 18, RCM 18 will attempt to notify the user by using a special alarm, such as a beeping sound or LED display. The host computer 12 also will be automatically notified by RCM 18, if possible. Restoration of the encryption key is then possible at the option of the rental software company.

While preferred forms and arrangements have been described in illustrating the present invention, it is to be understood that various changes in detail and arrangement may be made without departing from the spirit of the present invention or from the scope of the appended claims.

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