Communication system having a transmitter and a receiver that engage in reduced size encrypted data communication

The present invention relates to communication systems that utilize encrypted data communication, and is particularly directed to size reduction for encrypted data communication signals of a remote convenience system.

Communication systems that engage in transmission of encrypted data (e.g., information) are known in the art. One example of a communication system that utilizes data encryption is a remote convenience system, which permits remote control of certain functions. Within the remote convenience system, data that conveys security code(s), command(s), and the like is encrypted for transmission via signal. Only an authorized receiver decrypts and responds to the signal. Also, the encryption prevents unauthorized remote control of the certain remote convenience functions.

One example type of a remote convenience system is for remotely controlling vehicle functions. Other example types of remote convenience systems include garage door opener systems and entry light activation systems. Focusing on the remote convenience vehicle systems, remotely controlled vehicle functions include locking and unlocking of one or more vehicle doors. A remote convenience system that permits remote locking and unlocking is commonly referred to as a remote keyless entry system.

Known remote convenience vehicle systems include a receiver/controller unit mounted in an associated vehicle and a portable hand-held transmitter unit located remote from the receiver/controller unit. The transmitter unit is provided with one or more manually actuatable switches. Each switch is associated with a vehicle function to be performed. The transmitter unit includes circuitry that responds to the actuation of one of the switches to provide a message package. The message package includes a remote function command, a security code, and a sequence counter. The message package is transmitted to the receiver in the form of a digital signal.

In order to ensure that the contents of the message package cannot be understood by any receiver other than the intended authorized receiver, the digital bits of the signal are partially or completely encrypted by the transmitter. In order for the receiver to act upon the requested function, the signal is decrypted, a security code compared, and the like. As an extra level of security, the encryption methodology for the communication is changed routinely. Specifically, the transmitter and the receiver utilize a sequence counter arrangement. With each transmission from the transmitter, the sequence counter is adjusted. Upon receipt at the receiver, adjustment is made to the sequence counter value, accordingly. Thus, the receiver utilizes the sequence counter value to recognize a transmitted signal from the authorized transmitter.

As the sophistication of the remote convenience vehicle systems has increased, so has the number of bits that are typically transmitted via the signal. It is to be appreciated that increases in the number of transmitted data bits results in an increase in the possibility of corruption of the data.

In accordance with one aspect, the present invention provides a transmitter. The transmitter includes means for providing a message package. Means encrypts a first fraction of the message package using a second fraction of the message package as an encryption key. Means outputs a signal that conveys the encrypted first fraction of the message package.

In accordance with another aspect, the present invention provides a receiver that includes means for receiving an encrypted signal. Means decrypts the signal using a decryption key. Means assembles a message package using the decryption key as part of the message package.

In accordance with another aspect, the present invention provides a communication system that includes means for providing a message package. Means encrypts a first fraction of the message package using a second fraction of the message package as an encryption key. Means outputs a signal that conveys the encrypted first fraction of the message package. Means receives the signal. Means decrypts the signal using a decryption key. Means reassembles the message package using the decryption key as the second fraction of the message package.

In accordance with yet another aspect, the present invention provides a remote convenience system for remotely controlling a convenience function. The system includes portable transmitter means for outputting a signal containing remote control message information. Receiver/controller means receives the signal and controls performance of a function in accordance with the remote control message. The remote control message includes first and second fractions. The transmitter means includes encryption means for encrypting the first fraction of the remote control message using a second fraction of the remote control message as an encryption key.

In accordance with still another aspect, the present invention provides a remote convenience system for remotely controlling a convenience function. The system includes portable transmitter means for outputting a signal containing remote control message information. Receiver/controller means receives the signal and controls performance of a function in accordance with the remote control message. The remote control message includes first and second information portions. The signal contains the first portion and a first part of the second portion that are encrypted. The receiver/controller means includes decryption means for decrypting the first portion and the first part of the second portion using a decryption key. The receiver/controller means includes means for assembling a decrypted message using the decryption key as the second part of the second portion.

The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an example of a communication system in accordance with the present invention and associated with a vehicle;

FIG. 2 is a diagram showing an encryption process in accordance with the present invention;

FIG. 3 is a diagram showing a decryption process in accordance with the present invention;

FIG. 4 is a diagram of a known encryption process;

FIG. 5 is a diagram illustrating relative size of a message transmitted via a system that utilizes the known encryption process of FIG. 4; and

FIG. 6 is a diagram showing the relative size of a message transmitted utilizing the present invention.

A communication system 10 in accordance with the present invention is schematically shown in FIG. 1 . Preferably, the communication system 10 is a remote convenience system for remotely controlling a convenience function. Thus, hereinafter the communication system 10 is referred to as the remote convenience system 10 . In the illustrated example of FIG. 1, the remote convenience system 10 is for remote control of convenience functions at an associated vehicle 12 .

The system 10 includes a portable, hand-held transmitter unit 14 , and an associated receiver/controller unit 16 that is mounted in the vehicle 12 . The transmitter unit 14 is operable to communicate, via a signal 18 , with the receiver/controller unit 16 to achieve remote control performance of at least one convenience function (e.g., unlock doors) at a vehicle system 20 (e.g., vehicle door lock actuators) of the vehicle 12 . The transmitter unit 14 is operable by an operator (not shown) when the operator desires performance of the requested remote convenience function at the vehicle 12 .

The transmitter unit 14 includes at least one manually actuatable pushbutton switch (e.g., 22 ). In the example shown in FIG. 1, there are three pushbutton switches 22 - 24 . A first pushbutton switch 22 and a second pushbutton switch 23 are associated with door lock and unlock functions, respectively. A third pushbutton switch 24 is associated with a vehicle alarm or “panic” function. It is to be appreciated that the system could be configured to control different remote convenience functions, and that the transmitter unit structure (e.g., the number, type, and location of the pushbutton switches on the transmitter unit) would be accordingly different.

Each actuation or predefined series of actuations of one of the pushbutton switches (e.g., 22 ) of the transmitter unit 14 is a request to perform a corresponding predefined remote convenience function. For example, actuating the first pushbutton switch 22 is a request to lock the doors of the vehicle 12 . The pushbutton switches 22 - 24 are operatively connected to a controller 26 . In response to pushbutton actuation, a process portion 28 of the controller 26 generates/assembles a message package containing information that is to be transmitted. Preferably, data strings that represent the information are retrieved from a memory 30 of the controller 26 .

The controller 26 is operatively connected to RF transmit circuitry 32 . In turn, the RF transmit circuitry 32 is operatively connected to a broadcast transmission antenna 34 . Upon provision of message information from the controller 26 to the RF transmit circuitry 32 , the antenna 34 is energized to emit the signal 18 . Preferably, the transmitted signal 18 is a pulse-width-modulated (PWM) signal that has a radio frequency (RF) carrier frequency. It is to be appreciated that other signal types (e.g., frequency modulation, frequency shift key or the like) can be used without deviating from the present invention.

The message package information that is generated/assembled within the controller 26 includes a start/wakeup instruction, a security code, and at least one command that represents the remote function request. At least some of the information that is to be transmitted to the receiver/controller unit 16 is encrypted by an encryption portion 36 of the controller 26 in order to prevent unauthorized interception and use. The portions of the message information that are encrypted preferably include the security code and the command(s).

To further increase security, a sequence counter is also part of the message information. The sequence counter is changed (e.g., advanced) for each communication interaction between the transmitter unit 14 and the receiver/controller unit 16 . Encryption is also used to secure the sequence counter during transmission.

The sum of all the information that is to be conveyed from the transmitter unit 14 to the receiver/controller unit 16 results in a relatively large volume of data bits. Thus, in accordance with the present invention, an encrypted portion of the transmitted signal 18 is provided with a reduced number of data bits compared to the overall number of bits of the information.

FIG. 2 illustrates an example of an encryption process 40 performed by the encryption portion 36 (FIG. 1) of the controller 26 , in accordance with the present invention. In the preferred embodiment, the encryption process 40 (FIG. 2) has two encryption stages 42 and 44 (i.e., level 1 and level 2). Moreover, a part 46 of the sequence counter is used as an encryption key for one of the encryption stages (e.g., 42 ).

M bits of data 48 (e.g., the security code, command(s)) and K least significant bits 50 of the sequence counter are encrypted via a linear encryption algorithm of the first encryption stage 42 . The sequence counter has N total bits, and K (i.e., the least significant bits) is less than N. Preferably, the most significant bits 46 (i.e., N−K) of the sequence counter are used as the encryption key within the first stage 42 of the encryption process 40 . Thus, a first fraction of the message package (i.e., the M bits of data and the K least significant bits of the sequence counter) is encrypted using a second fraction of the message package (i.e., the N-K most significant bits of the sequence counter). The output of the first stage 42 of the encryption process 40 is a bit string that contains M+K bits.

As an example for the first stage 42 of the encryption process 40 , consider data string sizes where M=32 bits, N=16 bits, and K=8 bits. Further, assume that the 32-bit data 48 that is to be encrypted is equal to the value 87654321 and that the sequence counter at this instance is equal to the value 1234. The most significant bits 46 (i.e., N−K) of the sequence counter represent the value 12 and the least significant bits 50 (i.e., K) of the sequence counter represent the value 34.

An example of a simple linear encryption algorithm that occurs at the first stage 42 adds the 32 data bits (i.e., data 48 ) to the eight (8) most significant bits of the sequence counter (i.e., the encryption key 46 for the first stage 42 ), and then concatenates the eight (8) least significant bits 50 of the sequence counter to the addition sum value. Thus, the algorithm first provides 87654321+12=87654333. The addition sum value (i.e., 87654333) is concatenated with the value 34 to provide a value of 8765433334. The result of the concatenation (i.e., 8765433334) is a forty (40) bit number (i.e., 32 bits+8 bits) and is the output of the first stage 42 of the encryption process 40 . It is to be noted that the number of bits (i.e., 40 bits) output from the first stage 42 is less than the total bits for the data (i.e., 32 bits) and the sequence counter (i.e., 16 bits).

The forty (40) bit value output from the first stage 42 is then provided to the second stage 44 for non-linear encryption. An encryption key 52 is used for the non-linear encryption of the second stage 44 . The non-linear encryption algorithm is not part of the present invention and is not described in detail herein. Any of several known non-linear encryption techniques may be used. The output 54 of the second stage 44 is a forty (40) bit number (i.e., same size data string as output from the first stage 42 ). Thus, it is to be noted that the number of bits (i.e., 40 bits) in the output 54 of the encryption process 40 is less than the total bits for the data (i.e., 32 bits) and the sequence counter (i.e., 16 bits).

The encrypted data 54 (e.g., the first fraction of the message package) and any non-encrypted data are provided to the RF transmit circuitry 32 (FIG. 1 ). The RF transmit circuitry 32 then provides an appropriate electrical signal that conveys the data to the antenna 34 . In response to the stimulus, the antenna 34 broadcasts the signal 18 , which is intended to be received by the receiver/controller unit 16 at the vehicle 12 . It is to be noted that the signal 18 does not convey bits representing the most significant bits 46 of the sequence counter. Thus, the number of bits that is conveyed via the signal 18 is less than the number of bits that would be conveyed if all of the bits of the sequence counter are conveyed.

At the receiver/controller unit 16 , an antenna 56 is operatively connected to RF receive circuitry 58 . In turn, the RF receive circuitry 58 is operatively connected to a decryption portion 60 of the receiver/controller unit 16 . The contents of the signal 18 are conveyed to the decryption portion 60 , and the decrypt portion performs a two-stage decryption process 62 (FIG. 3) upon the encrypted data. Specifically, the M+K bits of encrypted data 54 (i.e., the first fraction of the message package) are provided to a first decryption stage 64 of the decryption process 62 .

The first stage 64 performs a non-linear decryption algorithm that uses a decryption key 66 . A reversal of the encryption provided in the second stage 44 (FIG. 2) of the encryption process 40 is accomplished at the first stage 64 (FIG. 3) of the decryption process 62 . Here also, the non-linear decryption algorithm is not part of the present invention and is thus not described in detail. However, it is to be understood that M+K bits of data, which are now merely linear encrypted, are output from the first stage 64 and are input to a second decryption stage 68 of the decryption process 62 .

At the second stage 68 , the most significant bits 46 of the sequence counter are provided from a memory 72 (FIG. 1) and are used as a decryption key. It is to be understood that since the transmitter unit 14 and the receiver/controller unit 16 are both progressing through the sequence counter during normal operation, the receiver/controller unit will already have in its possession the most significant bits of the sequence counter. In other words, the values of the sequence counter at the transmitter unit 14 and the receiver/controller unit 16 are normally the same or very close. Moreover, the value of the least significant bits of the sequence counter at the transmitter unit 14 can vary from the value of the least significant bits at the receiver/controller unit 16 without effect to the most significant bits 46 (FIG. 3) that are used as the decryption key for the second stage 68 of the decryption process 62 .

It is contemplated that if the sequence counter value at the transmitter unit 14 (FIG. 1) and the sequence counter value at the receiver/controller unit 16 differ significantly enough to effect the most significant bits of the sequence counter, an algorithm or technique may be utilized to resolve such an out-of-sync condition. Such algorithms and techniques are not part of the present invention and are not described herein.

Turning again to the decryption process 62 (FIG. 3 ), the operation of the algorithm of the second stage 68 (i.e., the linear decryption portion) provides the M bits of data 48 and the K least significant bits 50 of the sequence counter in non-encrypted form. In order to complete the process of providing the entire message package, the most significant bits 46 of the sequence counter are appended with the least significant bits 50 of the sequence counter to provide the entire sequence counter value. In other words, the first and second fractions of the message package are reunited. A process portion 74 (FIG. 1) of the receiver/controller unit 16 can then perform appropriate process steps utilizing the data (e.g., the commands) and the sequence counter.

In order to appreciate the advantage of the present invention, attention is directed to FIG. 4, which shows a conventional process 80 of encrypting M bits of data and N bits of a sequence counter (N being the total bits of the sequence counter). The output 82 of the encryption process 80 has M+N encrypted bits. The relative size of the data string for the conventional process 80 is represented in FIG. 5 . In distinction, the relative size of the data string that is produced in accordance with the present invention is shown in FIG. 6 . Again, it is to be noted that the number of bits corresponding to the K least significant bits of the sequence counter is less than the total bits M of the sequence counter (i.e., K<M).

From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.