Communications: electrical – Land vehicle alarms or indicators – Of burglary or unauthorized use
Reexamination Certificate
1996-12-24
2001-05-01
Hayes, Gail (Department: 2131)
Communications: electrical
Land vehicle alarms or indicators
Of burglary or unauthorized use
C340S425500, C340S870030, C341S176000, C341S174000
Reexamination Certificate
active
06225889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to a method of producing rolling codes and a keyless entry apparatus using the same, and more particularly to a rolling code producing method of producing a sequence of different codes for ensuring high entry security and a keyless entry apparatus using the same.
2. Background of Related Art
Keyless entry systems are well known in the art for securing anti-theft characteristics in automotive vehicles. In a typical keyless entry system, a transmitter installed in a key transmits an identification code to a receiver mounted in the vehicle to determine whether the transmitted identification code is correct or not. If it is correct, doors and an alarm system are released. This offers a higher degree of security than that of mechanical key entry systems.
Since such keyless entry systems usually use a single identification code, the entry security is, as described above, improved greatly but it is not enough to ensure complete entry security.
In order to alleviate such problems, the following steps are provided:
(1) A rolling code wherein an identification code is changed every communication between a transmitter and a receiver;
(2) The rolling code is further scrambled or encrypted as a random code; and
(3) The algorithm for producing the rolling code is changed every communication of the code between the transmitter and the receiver.
These steps however still do not produce totally satisfactory results. For example, simple usage of the rolling code as in (1) may allow a subsequent rolling code to be estimated based on a known code. When the number of figures of the random code as in (2) is small, it can be easily decoded by using all possible combinations of numbers of the same figures as those of the random code. Additionally, if the same operation is performed whenever the rolling code is scrambled, the algorithm for producing the rolling code may be easily decoded based on a change in output of the code.
Changing the algorithm as in (3) requires a storage memory having a large enough capacity to store different programs, one for each algorithm. Particularly, a portable transmitter of the keyless entry system needs to be compact and to exhibit rapid response, and therefore the capacity of the storage memory and the algorithms for scrambling the rolling code need to be small and simple, respectively.
The above problems are also encountered in keyless entry systems for use in houses or office buildings and keyless access systems for use in lockers of the type which uses encrypted access codes to for avoid unauthorized access.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a keyless entry system which is capable of producing rolling codes having a higher degree of security using a simple algorithm not requiring a large storage capacity.
According to one aspect of the present invention, there is provided a method of a rolling code producing method which comprises the steps of: (a) producing different rolling codes, in sequence, using an initial code variable according to a given algorithm; and (b) changing the initial code variable.
In the preferred mode of the invention, the changing changes the initial code variable after a given number of the rolling codes are produced.
The changing includes reading a given code variable out of an external storage medium to update the initial code variable.
According to another aspect of the invention, there is provided a security system which comprises: (a) a portable code transmitter producing a first rolling code using a first initial code variable according to a given algorithm and transmitting the first rolling code; (b) a receiver producing a second rolling code using a second initial code variable according to the given algorithm to compare the second rolling code with the first rolling code transmitted from the portable code transmitter, if the second rolling code matches the first rolling code, the receiver providing a security-releasing signal; and (c) a code changing circuit changing the initial code variables in the portable code transmitter and the receiver.
In the preferred mode of the invention, the security system further comprises: (d) a memory card storing therein a plurality of initial code variables; (e) a card reader responsive to input of the memory card to read one of the initial code variables out of the memory card; and (f) a means for providing the one of the initial code variables read out by the card reader to the portable code transmitter and the receiver as the first and second initial code variables, respectively.
The card reader reads the one of the initial code variables out of the memory card in a random access manner.
The security system further comprises a clock providing time information. The card reader reads the one of the initial code variables out of a memory location of the memory card corresponding to the time information provided by the clock.
The card reader is disposed within the receiver installed in a security object. The receiver includes a transmitter which transmits the initial code variable read out of the memory card to the transmitter as the first initial code variable.
The transmitter of the receiver is designed to establish electromagnetic coupling with the portable code transmitter for transmitting the one of the initial code variables read out by the card reader to the portable code transmitter.
The first and second initial code variables further include first and second subcodes, respectively. The portable code transmitter and the receiver perform a given operation on the first and second initial code variables and the first and second subcodes to produce the first and second rolling codes, respectively.
The first and second initial codes each consist of a plurality of bits. Each of the portable code transmitter and the receiver includes a first operation circuit dividing one of the first and second initial code into a higher-order bit group and a lower-order bit group, a second operation circuit performing a NOT operation on the sum of the higher-order bit groups, a third operation circuit performing an OR operation on the lower-order bit group and one of the first and second subcodes, a fourth operation circuit performing an exclusive-OR operation on a value resulting from the NOT operation on a value derive by the third operation circuit and the one of the first and second subcodes, a fifth operation circuit performing the exclusive-OR operation on a value resulting from the NOT operation on a value derived by the second operation circuit and the value derived by the third operation circuit, and a sixth operation circuit combining a value derived by the fourth operation circuit and a value derived by the fifth operation circuit as the higher-order bit group and the lower-order bit group, respectively, to produce one of the first and second rolling codes and to provide the one of the first and second rolling codes as one of the first and second initial code variables.
REFERENCES:
patent: 5185798 (1993-02-01), Hamada et al.
patent: 5369706 (1994-11-01), Latka
patent: 5412379 (1995-05-01), Waraksa et al.
patent: 5563600 (1996-10-01), Miyake
patent: 5600324 (1997-02-01), Miyake
patent: 5774550 (1998-06-01), Brinkmeyer et al.
patent: 6028527 (2000-02-01), Soenen et al.
patent: 6-239202 (1994-08-01), None
Furuta Noritoshi
Goto Masahiro
Hayes Gail
Nippon Soken Inc.
Pillsbury & Winthrop LLP
Song Ho S.
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