Encrypting conversion apparatus, decrypting conversion apparatus, cryptographic communication system, and electronic toll collection apparatus

Information

  • Patent Grant
  • 6683956
  • Patent Number
    6,683,956
  • Date Filed
    Tuesday, June 1, 1999
    25 years ago
  • Date Issued
    Tuesday, January 27, 2004
    20 years ago
Abstract
An encrypting conversion apparatus, a decrypting conversion apparatus, a cryptographic communication system and an electronic toll collection apparatus are provided which are capable of changing algorithms of cryptographic conversion to hide the algorithm in use from a third party so that the apparatuses and system are resistant against a cryptographic attack from the third party and can operate at high speed. In the cryptographic communication system.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to techniques for encrypting/decrypting digital data transferred among computers, household information processing appliances, and electronic toll collection apparatuses.




2. Description of the Related Art




Enciphering techniques for preventing an illegal copy of digital data are essential for digital household information processing appliances. For example, if digital visual data received by a digital broadcasting receiver is digitally recorded in a digital video recorder and the digital visual data has a copyright, both the receiver and digital video recorder are required to have a function of protecting the copyright. In order to realize such a copyright protection system, it is necessary to prevent alteration and illegal copying of digital data by means of setting a limitation to digital data copying, device authentication, and cryptographic techniques such as real time cryptograph of digital data.




An example of conventional cryptographic techniques may be a symmetric key or common key algorithm, typically DES cryptograph disclosed in U.S. Pat. No. 3,962,539. Most of common key algorithms are characterized in a complicated cryptogram formed by repeating a simple conversion. Various approaches have been tried in order to improve security of cryptograms. For example, a cryptographic attack can be made difficult by increasing the number of repetitions of simple conversions to further disturb statistical characteristics of cipher texts.




However, if the number of conversion repetitions is increased, the processing time required for cryptographic conversion becomes long. Therefore, a security reinforcing countermeasure through an increase in the number of repetitions of simple conversions is not suitable for real time cryptograph in the copyright protection system.




In an electronic toll collection system (ETC) of a toll speed-way which has lately attracted attention, a real-time cryptographic processing is required, so that the problem as mentioned above arises.




The electronic toll collection system represents a system which is capable of collecting a toll based on an electronic transaction through a wireless communication between an antenna provided at a toll collecting station and an on-board equipment mounted on a car when the car passes through the toll collecting station, the details of which are described in for example, a Japanese magazine “Card Wave” published by C-Media, March, 1999, pp42-45. In the referred-to system, a real-time cryptographic processing is indispensable in order to send and receive exchange data at real time and protect the exchange data from bugging and unauthorized alteration.




SUMMARY OF THE INVENTION




It is an object of the present invention to provide an encrypting conversion apparatus, a decrypting conversion apparatus, a cryptographic communication system and an electronic toll collection apparatus capable of changing algorithms of cryptographic conversion to hide the algorithm in use from a third party so that the apparatuses and system are resistant against a cryptographic attack and can operate at high speed.




According to one aspect of the present invention, there is provided an encrypting conversion apparatus for inputting at least one cipher key, at least one algorithm parameter, and plain text data and outputting cipher text data, the apparatus comprising: a plurality stage of encrypting conversion means for executing each of an exclusive logical sum operation, a cyclic shift operation and an addition operation at least once, wherein: the encrypting conversion means includes at least one of each of first to third operation means, the first operation means executes either an exclusive logical sum operation or an addition operation of input data and a portion of data generated from data of the cipher key, the second operation means executes either an exclusive logical sum operation or an addition operation of input data and a portion of data determined by the algorithm parameter, and the third operation means cyclically shifts input data by the number of bits determined by the algorithm parameter; and conversions which use combinations of a plurality stage of consecutive encrypting conversion means optionally selected from all of the encrypting conversion means and use the same input data and the same algorithm parameter, are all different.




According to another aspect of the present invention, there is provided a decrypting conversion apparatus for inputting at least one cipher key, at least one algorithm parameter, and cipher text data and outputting plain text data, the apparatus comprising: a plurality stage of decrypting conversion means for executing each of an exclusive logical sum operation, a cyclic shift operation and an addition operation at least once, wherein: the decrypting conversion means includes at least one of each of first to third operation means, the first operation means executes either an exclusive logical sum operation or an addition operation of input data and a portion of data generated from data of the cipher key, the second operation means executes either an exclusive logical sum operation or an addition operation of input data and a portion of data determined by the algorithm parameter, and the third operation means cyclically shifts input data by the number of bits determined by the algorithm parameter; and conversions which use combinations of a plurality stage of consecutive decrypting conversion means optionally selected from all of the encrypting conversion means and use the same input data and the same algorithm parameter, are all different.




According to another aspect of the present invention, there is provided a cryptographic communication system with a common key algorithm for communication between a transmitter apparatus and a receiver apparatus having a same cipher key, the transmitter apparatus encrypting a plain text by using the cipher key to acquire and transmit a cipher text, and the receiving apparatus decrypting the received cipher text by using the cipher key to recover the plain text, wherein: the transmitter apparatus includes encrypting conversion means and first algorithm key storing means; the receiver apparatus includes decrypting conversion means and second algorithm key storing mean; a conversion algorithm to be executed by the encrypting conversion means of the transmitter apparatus is determined by a first parameter stored in the first algorithm key storing means of the transmitter apparatus; a conversion algorithm to be executed by the decrypting conversion means of the receiver apparatus is determined by a second parameter stored in the second algorithm key storing means of the receiver apparatus; and the cipher text encrypted by the transmitter apparatus by using the cipher key can be correctly decrypted by the receiver apparatus by using the cipher key, only if the cipher key as well as the first and second parameters used by the transmitter and receiver apparatuses is same.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a block diagram showing a cryptographic communication system having a transmitter and a receiver according to an embodiment of the invention.





FIG. 2

is a block diagram of an encrypting conversion unit shown in FIG.


1


.





FIG. 3

is a block diagram of a key conversion means shown in FIG.


2


.





FIG. 4

is a block diagram of a substitution/permutation conversion means shown in FIG.


2


.





FIG. 5

is a block diagram of a bit train conversion unit shown in FIG.


4


.





FIG. 6

is a block diagram of a decrypting conversion unit shown in FIG.


1


.





FIG. 7

is a block diagram of a substitution/permutation conversion means shown in

FIG. 6

according to another embodiment of the invention.





FIG. 8

is a block diagram of a key conversion means according to another embodiment of the invention.





FIG. 9

is a block diagram of a substitution/permutation means according to another embodiment of the invention.





FIG. 10

is a block diagram of a bit train conversion unit according to another embodiment of the invention.





FIG. 11

is a block diagram showing an electronic toll collecting system as another embodiment of cryptographic communication of the invention.





FIG. 12

is a chart illustrating communication flows of the electronic toll collecting system.





FIG. 13

is a chart illustrating cryptographic communication of the electronic toll collecting system.











DETAILED DESCRIPTION OF THE EMBODIMENTS




Embodiments of the invention will be described with reference to the accompanying drawings.





FIG. 1

is a block diagram showing the configuration of a cryptographic communication system in which a data transmitter equipped with an encrypting conversion apparatus of the invention cryptographically communicates with a data receiver equipped with a decrypting conversion apparatus of the invention. Referring to

FIG. 1

, the data transmitter


1


has an encrypting conversion unit


11


, a key sharing unit


12


, a data processing unit


13


, a communication processing unit


14


, and a key length data storage means


15


. The data receiver


12


has a decrypting conversion unit


31


, a key sharing unit


32


, a data processing unit


33


, and a communication processing unit


34


. The data transmitter


1


may be a digital broadcasting receiver. The data receiver


2


may be a digital video recorder. In this case, the data processing units


13


and


33


process digital program data of, for example, MPEG2-TS (Transport Stream) distributed by digital broadcasting services. The data processing unit


13


performs a reception process, a multiplex/separation process, an expansion process, and a transmission process, respectively of digital program data, whereas the data processing unit


33


performs a reception process, an expansion process, and a storage process, respectively of digital program data.




The data transmitter


1


and data receiver


2


share data called a cipher key necessary for data encrypting and decrypting in order to start cryptographic communication. Sharing this cipher key is realized by a message exchange between the key sharing unit


12


of the data transmitter


1


and the key sharing unit


32


of the data receiver via the communication processing units


14


and


34


. In this case, the key length is determined in accordance with key length data stored in a key length data storage means


15


of the data transmitter


1


. It is desired that the cipher key shared by the data transmitter


1


and data receiver


2


is changed each time data is transferred. This is because since a generated cryptogram is different if the cipher key is different, a cryptographic attack to a cryptogram by a third party becomes difficult. There are various methods of sharing a cipher key. For example, key exchange in a key distribution system by Diffie-Hellman may be used which is detailed, for example, in “Current Cryptograph” by Tatsuaki Okamoto, et al, published by Sangyo Tosho Kabushiki Kaisha, at pp. 200 to 202. With this key exchange, it is very difficult for a third party to infer a cipher key from a tapped message which was exchanged for sharing the cipher key, and it is possible to share a cipher key in high secrecy each time data is transferred.




After the cipher key is shared, the data processing unit


13


of the data transmitter


1


supplies the encrypting conversion unit


11


with data to be transmitted. Data supplied from the data processing unit


13


is still not encrypted, and such data is called hereinafter a “plain text”. The encrypting conversion unit


11


is constituted of an encrypting conversion means


20


, a key conversion means


23


and an algorithm key storage means


24


. The key conversion means


23


generate a plurality set of data called a conversion key in accordance with the cipher key and key length data. The key length data represents the length of a cipher key determined by cipher key sharing. The algorithm key storage means


24


stores a plurality set of data called an algorithm key. An encrypting conversion algorithm to be executed by the encrypting conversion means


20


is determined by the algorithm key. By using the conversion key generated by the key conversion means


23


and the algorithm key stored in the algorithm key storage means


24


, the encrypting conversion means


20


encrypts the plain text and outputs a cipher text. The cipher text generated by the encrypting conversion unit


11


is transmitted from the communication processing unit


14


to the data receiver


2


,




The communication processing unit


34


of the data receiver


2


receives the cipher text and supplies it to the decrypting conversion unit


31


. The decrypting conversion unit


31


is constituted of a decrypting conversion means


40


, a key conversion means


43


and an algorithm key storage means


44


. The key conversion means


43


has a structure similar to that of the key conversion means


23


, and generates a conversion key in accordance with the cipher key and key length data. The algorithm key storage means


44


has a structure similar to that of the algorithm key storage means


24


, and stores an algorithm key. A decrypting conversion algorithm to be executed by the decrypting conversion means


40


is determined by the algorithm key. By using the conversion key generated by the key conversion means


24


and the algorithm key stored in the algorithm key storage means


44


, the decrypting conversion means


40


decrypts the cipher text. In this case, only if the decrypting conversion means


20


uses the same algorithm key as that used by the encrypting conversion means


20


, the decrypting conversion means


40


can decrypt the cipher text encrypted by the encrypting conversion means


20


into the original plain text. The plain text output from the decrypting conversion unit


31


is supplied to the data processing unit


33


to process data.




As described above, the data transmitter


1


and data receiver


2


can cryptographically communicate with each other only if they have the same algorithm key. Cryptographic communication with an authentication function can be realized by maintaining this algorithm key as secret information. Namely, if the correct algorithm key is held by only an authorized apparatus, cryptographic communication can be performed for only the authorized communication partner apparatus. In order to realize this, a key management facility


3


for generating algorithm keys and collectively managing them is provided as shown in FIG.


1


. As shown, authorized apparatuses (in this example, the data transmitter


1


and data receiver


2


) acquire the algorithm key from the key management facility


3


without being tapped by a third party. For example, an algorithm key managed by the key management facility


3


may be embedded in the algorithm key storage means


24


and


44


when the data transmitter


1


and data receiver


2


are manufactured. In this case, the data receiver


11


also acquires the key length data at the same time. In this manner, a cipher text transmitted from an authorized apparatus having a correct algorithm key can be decrypted only by an authorized apparatus having the correct algorithm key. In addition to the cipher key, the algorithm key is also secret information so that a cryptographic attack by a third party to a cipher text flowing on the communication path becomes more difficult.




Furthermore, since the data transmitter


1


generates a cipher key basing upon the key length data acquired from the key management facility


3


, the length of the cipher key can be renewed. For example, if renewed key length data is embedded in a newly manufactured data transmitter, cryptographic communication with the newly manufactured data transmitter can be performed by using a cipher key having the renewed length. Therefore, it is possible to elongate the key length of a cipher key in the future to thereby further improve security. The key length may be changed in each area where apparatuses are shipped.





FIG. 2

is a detailed block diagram showing an example of the encrypting conversion unit


11


. It is assumed that the encrypting conversion unit


11


receives a plain text of 64 bits, a cipher key of 40 or 64 bits and key length data of one bit, and outputs a cipher text of 64 bits. With reference to the key length data, the key conversion means


23


converts the cipher key into conversion keys K


1


and K


2


each having 32 bits. The key length data takes “0” if the cipher key has 40 bits, and “1” if the cipher key has 64 bits. Conversion by the key conversion means


23


will be later described. The encrypting conversion means


20


of the encrypting conversion unit


11


is constituted of N substitution/permutation conversion means


21




1


to


21




N


. A conversion algorithm to be executed by the substitution/permutation conversion means


21




n


(where 1≦n≦N) is determined by an algorithm key G


n


stored in the algorithm key storage means


24


.




A plain text is separated into upper 32 bits R


0


and lower 32 bits L


0


and input to the substitution/permutation conversion means


21




1


whereat a first encrypting conversion is performed by using the conversion keys K


1


and K


2


to output 32 bits R


1


and 32 bits L


1


. These bits R


1


and L


1


are input to the substitution/permutation conversion means


21




2


whereat a second encrypting conversion is performed by using the conversion keys K


1


and K


2


to output 32 bits R


2


and 32 bits L


2


. Such encrypting conversion is repeated N times and the last outputs of 32 bits R


N


and 32 bits L


N


are combined to obtain a cipher text of 64 bits. The total number N of encrypting conversion repetitions is called a round number.




Consider now the case wherein the cipher key is fixed and the same data is input to an optional combination of two or more consecutive substitution/permutation conversion means selected from all the substitution/permutation conversion means. In this case, the conversion result is determined by the algorithm keys Gn. In the encrypting conversion apparatus of this invention, it is assumed that only algorithm keys which provide different conversion results for all combinations are used. Namely, a periodicity does not appear on encrypting conversion which uses a plurality of substitution/permutation conversion means. In this way, secrecy of encrypting conversion can be improved.





FIG. 3

is a block diagram showing an example of the key conversion means


23


shown in FIG.


2


. Referring to

FIG. 3

, the key conversion means


23


is constituted of a register


26


of a 64-bit length, a multiplexer


27


and an addition operation unit


28


. A cipher key is first loaded in the register


26


. If the cipher key has 40 bits, it is loaded in the lower 40 bits of the register


26


, whereas if the cipher key has 64 bits, it is stored in all bits of the register


26


. The lower 32 bits of the register


26


are used as the conversion key K


1


. If the key length data is “0”, 32 bits of the register


26


from the lower 9-th bit to the lower 40-th bit are selected as an input to the multiplexer


27


. If the key length data is “1”, the upper 32 bits of the register


26


are selected as an input to the multiplexer


27


. An output of the multiplexer


27


is subjected to a 32-bit addition of K


1


at the addition operation unit


28


, the result being K


2


. A result of the 32-bit addition is a remainder of a usual addition result divided by 2 raised to a power of 32.





FIG. 4

is a block diagram of the substitution/permutation conversion means


21




n


shown in

FIG. 2

which executes the n-th (1≦n≦N) encrypting conversion.




Referring to

FIG. 4

, the substitution/permutation conversion means


21




n


is constituted of a bit train conversion unit


61


and an addition operation unit


62


. R


n−1


and L


n−1


are converted into R


n


and L


n


by using the conversion keys K


1


and K


2


. First, the substitution/permutation conversion means


21




n


inputs L


n−1


to the bit train conversion unit


61


. The conversion algorithm to be executed by the bit train conversion unit


61


is determined by the algorithm key G


n


. An input U to the bit train conversion unit


61


is related to an output Z from the unit


61


by the following equation:








Z=F




Gn


(


K




1


,


K




2


,


U


)






where the function F


Gn


, indicates a conversion by the bit train conversion unit


61


. The algorithm key G


n


is constituted of the following data:








G




n


=(


A




n




, B




n




, C




n




, P




n




, Q




n




, S




n


)






where A


n


, B


n


, and C


n


are 32-bit data, and P


n


, Q


n


, and S


n


are expressed by 1≦P


n


≦31, 1≦Q


n


≦31, and 1≦S


n


≦31. The values of the algorithm key G


n


may take different values at each n (1≦n≦N).




Next, R


n−1


is input to the addition operation unit


62


whereat a 62-bit addition of Z


n


is performed, the result being L


n


. L


n−1


is used as R


n


. The above-described conversion is summarized as in the following:







L




n




=R




n




+F




Gn


(


K




1


,


K




2


,


L




n−1


)








R




n




=L




n−1









FIG. 5

is a block diagram showing an example of the bit train conversion unit


61


shown in FIG.


4


. The bit train conversion unit


61


is constituted of five bit train converters


81


to


85


. The bit train converter


81


includes an exclusive logical sum (exclusive-OR) unit


94


. The bit train converter


82


includes an addition calculation unit


95


and a cyclic shift unit


91


. The bit train converter


83


includes an addition calculation unit


96


and a cyclic shift unit


92


. The bit train converter


84


includes an addition operation unit


97


. The bit train converter


85


includes an addition calculation unit


98


and a cyclic shift unit


93


.




The exclusive logical sum unit


94


of the bit train converter


81


executes an exclusive logical sum operation of two input values. Of the two input values, one is K


1


shown in FIG.


4


and the other is U shown in

FIG. 4

, i.e., an output value to the bit train conversion unit


61


or bit train converter


81


. A conversion by the bit train converter


81


is given by:








V=K




1


⊕U






where V is an output value of the bit train converter


81


and an expression of X⊕Y indicates an exclusive logical sum of X and Y.




The cyclic shift unit


91


of the bit train converter


82


cyclically shifts to the left only the data P


n


(1≦P


n


≦31) which is a fraction of the algorithm key G


n


. The addition operation unit


95


performs a 32-bit addition of three inputs. Of the three inputs, one is the data A


n


which is a fraction of the algorithm key G


n


shown in

FIG. 4

, another is an input value V to the bit train converter


82


, and the other is the data Pn to be cyclically shifted to the left. A conversion by the bit


10


train converter


82


is given by:








W=V+


(


V<<<P




n


)+A


n








where W is an output value of the bit train converter


82


and an expression of X<<<Y indicates a cyclic shift of X to the left by Y-bit.




The cyclic shift unit


92


of the bit train converter


83


cyclically shifts to the left only the data Q


n


(1≦Q


n


≦31) which is a fraction of the algorithm key G


n


. The addition operation unit


96


performs a 32-bit addition of three inputs. Of the three inputs, one is the data B


n


which is a fraction of the algorithm key G


n


shown in

FIG. 4

, another is an input value W to the bit train converter


83


, and the other is the data Pn to be cyclically shifted to the left. A conversion by the bit train converter


83


is given by:








X=W+


(


W<<<Q




n


)+B


n








where W is an output value of the bit train converter


83


.




The addition operation unit


97


of the bit train converter


84


performs a 32-bit addition of two inputs. Of the two inputs, one is K


2


shown in FIG.


2


and the other is an input X to the bit train converter


84


. A conversion by the bit train converter


84


is given by:








Y=K




2


+


X








where Y is an output value of the bit train converter


84


.




The cyclic shift unit


93


of the bit train converter


85


cyclically shifts to the left only the data S


n


(1≦S


n


≦31) which is a fraction of the algorithm key G


n


. The addition operation unit


98


performs a 32-bit addition of three inputs. Of the three inputs, one is the data G


n


which is a fraction of the algorithm key G


n


shown in

FIG. 4

, another is an input value Y to the bit train converter


85


, and the other is the data Sn to be cyclically shifted to the left. A conversion by the bit train converter


85


is given by:








Z=Y+


(


Y<<<S




n


)+C


n








where Z is an output value of the bit train converter


85


.




As described above, the five bit train converters


81


to


85


of the bit train conversion unit


61


perform a bit train conversion by processing data to be converted. The order of processing data by the five bit train converters


81


to


85


of the bit train conversion unit


61


may be changed. This changed configuration is also included in the scope of the present invention. For-example, in place of the order of bit train converter


81





82





83





84





85


, the order of bit train conversion functions


84





83





81





85





82


may also be used. Although the five bit train converters


81


to


85


are constituted of one exclusive logical sum unit, three cyclic shift units, and four addition operation units, they may be constituted of at least one addition operation unit and at least one cyclic shift operation unit capable of executing substitution/permutation/mixture conversion, with similar expected advantages of the invention.





FIG. 6

is a block diagram showing the details of the decrypting conversion unit


31


shown in FIG.


1


. The decrypting conversion unit


31


decrypts a cipher text encrypted by the encrypting conversion unit


11


shown in

FIG. 2

into the original plain text. The decrypting conversion unit


31


receives a cipher text of 64 bits, a cipher key of 40 bits or 64 bits, and key length data of one bit, and outputs a plain text of 64 bits. The decrypting conversion means


40


of the decrypting conversion unit


31


is constituted of N substitution/permutation conversion means


41




n


to


41




n


. A conversion algorithm to be executed by the substitution/permutation conversion means


41


n (where 1≦n≦N) is determined by an algorithm by G


n


stored in the algorithm key storage means


44


.




A cipher text is separated into upper 32 bits RN and lower 32 bits L


N


and input to the substitution/permutation conversion means


41


, whereat a first decrypting conversion is performed by using conversion keys K


1


and K


2


to output 32 bits R


N−1


, and 32 bits L


N−1


. These bits R


N−1


and L


N−1


are input to the substitution/permutation conversion means


41




2


whereat a second decrypting conversion is performed by using the conversion keys K


1


and K


2


to output 32 bits R


N−2


and 32 bits L


N−2


. Such decrypting conversion is repeated N times and the last outputs of 32 bits R


0


and 32 bits L


0


are combined to obtain a plain text of 64 bits. Similar to the encrypting conversion, the total number N of decrypting conversion repetitions is called a round number.




Consider now the case wherein the cipher key is fixed and the same data is input to an optional combination of two or more consecutive substitution/permutation conversion means selected from all the substitution/permutation conversion means. In this case, the conversion result is determined by the algorithm keys Gn. In the encrypting conversion apparatus of this invention, it is assumed that only algorithm keys which provide different conversion results for all combinations are used. Namely, a periodicity does not appear on decrypting conversion which repetitively uses substitution/permutation conversion means.





FIG. 7

is a block diagram of the substitution/permutation conversion means


41




n


shown in

FIG. 6

which executes the (N+1−n)-th (1≦n≦N) decrypting conversion. Referring to

FIG. 7

, the substitution/permutation conversion means


41




n


is constituted of a bit train conversion unit


61


described with reference to

FIG. 5 and a

subtraction operation unit


72


. R


n


and L


n


are converted into R


n−1


and L


n−1


by using the conversion keys K


1


and K


2


. First, the substitution/permutation conversion means


41




n


inputs R


n


to the bit train conversion unit


61


. The conversion algorithm to be executed by the bit train conversion unit


61


is determined by the algorithm key G


n


. An input to the bit train conversion unit


61


is represented by U and an output from this unit


61


is represented by Z. Next, L


n


is input to the subtraction operation unit


72


to perform a 32-bit subtraction of Z, the result being R


n


. A result of the 32-bit subtraction is a usual subtraction result added to 2 raised to a power of 32, if the usual subtraction result is negative. Lastly, R


n


is used L


n−1


. The above-described conversion is summarized as in the following:







R




n−1




=L




n




−F




Gn


(


K




1


,


K




2


, R


n


)








L




n−1




R




n








This conversion is an inverse conversion of the substitution/permutation conversion means


21


n described with reference to FIG.


2


. If the decrypting conversion unit


31


has the same cipher key and algorithm key as those of the encrypting conversion unit


11


, the decrypting conversion unit


31


can decrypt data encrypted by the encrypting conversion unit


11


, in the manner described above.




The embodiment of the data transmitter


1


equipped with the encrypting conversion unit and the data receiver


2


equipped with the decrypting conversion unit have been described above in detail. It is obvious that a configuration partially changing the above-described configuration is included in the scope of the present invention. For example, although the cipher key has 40 bits or 64 bits and the key length data has one bit, the invention is not limited only thereto. For example, the cipher key may have the desired number of bits in the range from 40 to 128 bits and the key length data has 7 bits in order to identify each cipher key. In this case, the key conversion means is provided with a selector which selects a position where a cipher key is selected in accordance with the input key length data, in order to generate two conversion keys of 32 bits. Four conversion keys of 32 bits may be generated for a cipher key having 64 bits or more. In this case, N substitution/permutation conversion means are divided into two groups to each of which two conversion keys are supplied.




In order to generate a plurality of conversion keys, substitution/permutation conversion means used for encrypting conversion may be used. For example, a key conversion means for generating eight conversion key of 32 bits will be described.




Referring to

FIG. 8

, the key conversion means


23


is constituted of eight substitution/permutation conversion means


21




1


to


21




8


and an extension key storage means


100


. The extension key storage means


100


stores eight extension keys KE


1


to KE


8


having a 32-bit length to be used for conversion keys. A cipher key having 64 bits is sequentially converted by the eight substitution/permutation conversion means


21




1


to


21




8


. A conversion algorithm to be used by each substitution/permutation conversion means is determined by each algorithm key stored in the algorithm storage means


24


. Extension keys stored in the extension key storage means


100


are input to each substitution/permutation conversion means. For example, extension keys KE


3


and KE


4


are input to the substitution/permutation conversion means


21




2


.




By performing the conversion, outputs L


1


to L


8


of the eight substitution/permutation conversion means


21




1


to


21




8


are used as the eight extension keys.




The same extension keys stored in the extension key storage means may be used each time data is processed, or may be renewed by a method similar to the algorithm keys. A key sharing process may also be executed for the extension keys by a method similar to the cipher key. The key conversion means


23


described with reference to

FIG. 8

can use the substitution/permutation conversion means same as that used by encrypting conversion. Therefore, for example, if the encrypting conversion apparatus of the invention is implemented by hardware, encrypting conversion can be realized with a small circuit scale and with high security.




Next, the encrypting conversion apparatus and decrypting conversion apparatus according to another embodiment of the invention will be described.




The block diagram of the encrypting conversion apparatus of this embodiment is the same as that shown in

FIG. 2

of the first embodiment described earlier.





FIG. 9

is a block diagram of a substitution/permutation conversion means


21




1


of this embodiment in the encrypting conversion unit


11


shown in

FIG. 2

which executes the n-th encrypting conversion. Referring to

FIG. 9

, the substitution/permutation conversion means


21




n


is constituted of a bit train conversion unit


361


and an operation unit


362


. The operation unit


362


executes either an exclusive logical sum operation or an addition operation of two inputs. Which operation the operation unit


362


executes is determined by an algorithm key. The conversion process to be executed by the substitution/permutation conversion means


21




n


is the same as described with the first embodiment.





FIG. 10

is a block diagram showing an example of the bit train conversion unit


361


shown in FIG.


9


. The bit train conversion unit


361


is constituted of five bit train converters


81


to


85


. The bit train converter


81


includes an operation unit


394


. The bit train converter


82


includes an operation unit


395


, an operation unit


396


, and a cyclic shift unit


91


. The bit train converter


83


includes an operation unit


397


, an operation unit


398


, and a cyclic shift unit


92


. The bit train converter


84


includes an operation unit


399


. The bit train converter


85


includes an operation unit


400


, an operation unit


401


, and a cyclic shift unit


93


. Similar to the operation unit


362


shown in

FIG. 9

, each of the operation units


394


to


401


executes either an exclusive logical sum operation or an addition operation of two inputs. Which operation the operation units


394


to


401


execute is determined by an algorithm key. The bit train conversion unit


361


performs a bit train conversion by applying bit train converter


81


to


85


to data to be converted. As described above, in the encrypting conversion apparatus of this embodiment, the numbers of addition operations and exclusive logical sum operations can be determined by algorithm keys.




Next, a cryptographic communication system using the encrypting conversion apparatus and decrypting conversion apparatus according to an embodiment of the invention will be described.





FIG. 11

is a block diagram showing an electronic toll collection system. The electronic toll collection system can collect, through electronic account settlement, a toll from an IC card possessed by a driver of a car running on a toll road, at a road side equipment installed on the toll road, without stopping the car. Such an electronic toll collection system is expected to alleviate traffic congestion and improve user convenience through electronic account settlement with IC cards.




The electronic toll collection system shown in

FIG. 11

includes a car


200


, a road side equipment


201


, an on-board equipment


202


, an IC card


203


, and a key management facility


204


.




The car


200


has the on-board equipment


202


into which the IC card


203


is inserted while the car


200


is driven.




The road side equipment


201


is installed on the toll road and has a function of collecting a toll while the car


200


passes by.




The IC card


203


stores in advance contract information of the electronic toll collection system. While the car


200


passes by the road side equipment, the contract information is transferred by wireless communication from the on-board equipment


202


inserted with the IC card


203


, in order to receive routing information and account settlement information from the road side equipment


201


.




In order to maintain security and reliability of such processes, it is necessary to verify authentication of contract information, routing information and account settlement information and to prevent illegal alteration and tapping of the information. Between the IC card and on-board equipment


202


and between the on-board equipment


202


and road side equipment, it is necessary to execute an authentication process for a communication partner, a sharing process of sharing a cipher key to be used for encrypting/decrypting exchange data, and a cryptographic communication using the shared cipher key. To these third party authentication process, cipher key sharing process and cryptographic communication, the encrypting and decrypting conversion apparatuses of the invention can be applied.




In order to realize the above-described processes, the on-board equipment


202


, IC card


203


and road side equipment


201


are required to store in advance a shared algorithm key and a license key issued by the key management facility


204


. For example, these keys may be embedded during manufacture.




The details of the algorithm key and encrypting and decrypting conversions set by the algorithm key have been given above.




The license key is embedded in an authorized equipment as secret information and is used for reliably executing the authentication process and cipher key sharing process. Consider for example that an equipment B confirms whether or not an equipment A is an authorized equipment, in order to communicate with the equipment A. In this case, the equipment A provides the equipment B with certification that the license key of the equipment A is correct. Since the license key is secret information, the equipment A is required to provide the equipment B with certification that the license key is correct, without making open the license key. This certification can be realized by utilizing cryptographic techniques. For example, a symmetric key algorithm is described in ISO 9798-2 which is international specifications for security mechanism. As a specific example of the symmetric key algorithm, the encrypting and decrypting conversion apparatuses of the invention can be used.




Elements constituting the apparatuses shown in

FIG. 11

will be described.




The road side equipment


201


is constituted of a wireless communication unit


232


, an encrypting/decrypting process unit


230


, a partner authentication/key sharing process unit


233


, a main control unit


235


, and a data storage unit


234


.




The on-board equipment


202


is constituted of a wireless communication unit


212


, an encrypting/decrypting process unit


210


, an IC card communication unit


211


, a partner authentication/key sharing process unit


213


, a data storage unit


214


, and a main control unit


215


.




The IC card


203


is constituted of an IC card communication unit


221


, an encrypting/decrypting process unit


220


, a partner authentication/key sharing process unit


223


, a data storage unit


224


, and a main control unit


225


.




The encrypting/decrypting process units


210


,


220


and


230


have the encrypting and decrypting conversion apparatuses of the invention described previously and can encrypt and decrypt data.




The IC card communication units


211


and


221


are used for communication between the on-board equipment


202


and IC card


203


.




The wireless communication units


212


and


232


are used for wireless communication between the on-board equipment


202


and road side equipment


201


.




The encrypting/decrypting process units


210


,


220


and


230


execute the authentication process of confirming whether a communication partner is authorized and a sharing process of sharing a cipher key to be used for data encryption and decryption. The partner authentication/key sharing process unit


213


uses an encrypting/decrypting conversion function supplied from the encrypting/decrypting process unit


210


in order to execute the partner authentication and key sharing process. In order to realize similar functions, the partner authentication/key sharing process unit


223


uses the encrypting/decrypting process unit


220


. Similarly, the partner authentication/key sharing process unit


233


uses the encrypting/decrypting process unit


230


.




The data storage units


214


,


224


and


234


store the algorithm key and license key acquired from the key management facility


204


, and may also store contract information, routing information and account settlement information.





FIG. 12

is a flow chart illustrating communications to be executed by the electronic toll collection system shown in FIG.


11


.




In the flow chart shown in

FIG. 12

, a partner authentication/key sharing process


240


is first performed between the IC card


203


and on-board equipment


202


when the IC card


203


shown in

FIG. 11

is set to the on-board equipment


202


. After the partner authentication/key sharing process


240


is succeeded, the IC card


203


performs a cryptographic communication


241


to transfer contract information to the on-board equipment


202


. Upon reception of the contract information from the IC card


203


, the on-board equipment stores in secret the contract information in the data storage unit


214


(FIG.


11


).




Next, a partner authentication/key sharing process


250


is performed between the on-board equipment


202


and road side equipment


201


while the car


200


shown in

FIG. 11

passes by the road side equipment


201


. After the partner authentication/key sharing process


250


is succeeded, the on-board equipment


202


performs a cryptographic communication


251


to transfer the contract information supplied from the IC card to the road side equipment


201


. This cryptographic communication


251


is also used for transferring routing information and account settlement information from the road side equipment


201


, to the on-board equipment


202


.




Next, the on-board equipment


202


performs a cryptographic communication


261


to transfer the routing information and account settlement information acquired from the road side equipment


201


, to the IC card


203


.




Account settlement for road toll is made between the IC card


203


and road side equipment


201


. However, communication between the IC card


201


and road side equipment


201


is required to use the on-board equipment


202


. In this case, if the on-board equipment


202


make an illegal process, an illegal account settlement may be performed. In order to avoid such a process, it is necessary for the road side equipment


201


to identify the on-board equipment


202


used with the IC card


203


for account settlement. For example, the onboard equipment


202


is assigned an identification number and transfers it to the IC card


203


during the partner authentication/key sharing process


240


with the IC card.




The IC card


203


generates a digital signature for both the identification number of the on-board equipment


202


and account settlement history of the IC card


203


and returns them to the on-board equipment


202


. The onboard equipment


202


transfers the identification number and the digital signature acquired from the IC card


203


, to the road side equipment


201


during the partner authentication/key sharing process


250


. Thereafter, the road side equipment


201


verifies the digital signature generated by the IC card


203


to check the time when the on-board equipment


202


was used.




It is also necessary to prevent a third party to alter encrypted data flowing on a communication path during the cryptographic communication


241


,


251


and


261


. In order to realize this, it is necessary to perform a message authentication capable of judging whether the received message is correct. In order to perform the message authentication, a transmitter and a receiver shares in advance a message authentication key which is kept in secret. Sharing the message authentication key is performed, for example, in the partner authentication/key sharing process


250


shown in FIG.


12


. The transmitter generates data called a message authentication code (MAC) from a message to be transferred and the message authentication key. The transmitter transmits the message together with the message authentication code to the receiver. The receiver verifies the received message authentication code by using the message authentication key. It is possible to judge from this verification whether the received message was altered. As the message authentication, for example, a method using a symmetric key algorithm is described in ISO 9797 which is international specifications for security mechanism. As a specific example of the symmetric key algorithm, the encrypting and decrypting conversion apparatuses of the invention can be used.





FIG. 13

is a detailed flow chart illustrating the cryptographic communication


241


as an example of a cryptographic communication including message authentication. Referring to the flow chart shown in

FIG. 13

, first the IC card


203


generates a message authentication code at an MAC generation process


261


. Next, the message to be transferred and the message authentication code are coupled at a coupling process


262


. Thereafter, data containing the coupled message and message authentication code is encrypted at an encrypting process


263


to form encrypted data.




Next, upon reception of the encrypted data, the on-board equipment


202


decrypts the data at a decrypting process


264


. Thereafter, at a separating process


265


, the message and message authentication code transferred from the IC card are recovered. Next, the recovered message authentication code is verified at a MAC verifying process


266


in order to verify the correctness of the received message.




In the above manner, data not permitted to be altered or tapped, such as toll information and routing information, can be exchanged with security.




With the above processes, a road toll can be charged to the IC card


203


and the toll information can be managed at the road side equipment


201


.




According to the present invention, it is possible to realize an encrypting conversion apparatus, a decrypting conversion apparatus, a cryptographic communication system and an electronic toll collection apparatus capable of changing algorithms of cryptographic conversion to hide the algorithm in use from a third party so that the apparatuses and system are resistant against a cryptographic attack and can operate at high speed.



Claims
  • 1. An encrypting conversion apparatus for inputting at least one cipher key, at least one algorithm parameter which is independent of said cipher key, and plain text data and outputting cipher text data, said encrypting apparatus comprising:a plurality stage of encrypting conversion means for executing each of an exclusive logical sum operation, a cyclic shift operation and an addition operation at least once, wherein: said encrypting conversion means includes at least one of each of first to third operation means, said first operation means executes either an exclusive logical sum operation or an addition operation of input data and a portion of data generated from data of the cipher key, said second operation means executes either an exclusive logical sum operation or an addition operation of input data and a determined by a portion of said algorithm parameter, and said third operation means cyclically shifts input data by the number of bits determined dynamically based on a portion of said algorithm parameter; and conversions which use combinations of a plurality stage of consecutive encrypting conversion means optionally selected from all of said encrypting conversion means and use the same input data and the same algorithm parameter, are all different.
  • 2. A decrypting conversion apparatus for inputting at least one cipher key, at least one an algorithm parameter which is independent of said cipher key, and cipher text data and outputting plain text data, the apparatus comprising:a plurality stage of decrypting conversion means for executing each of an exclusive logical sum operation, a cyclic shift operation and an addition operation at least once, wherein: said decrypting conversion means includes at least one of each of first to third operation means, said first operation means executes either an exclusive logical sum operation or an addition operation of input data and a portion of data generated from data of the cipher key, said second operation means executes either an exclusive logical sum operation or an addition operation of input data and a determined by a portion of said algorithm parameter, and said third operation means cyclically shifts input data by the number of bits determined dynamically based on a portion of said algorithm parameter; and conversions which use combinations of a plurality stage of consecutive decrypting conversion means optionally selected from all of said decrypting conversion means and use the same input data and the same algorithm parameter, are all different.
Priority Claims (1)
Number Date Country Kind
10-148712 May 1998 JP
CROSS-REFERENCE TO RELATED APPLICATION

This application relates to an application U.S. Ser. No. 09/130,529 filed on Aug. 4, 1998 by Makoto Aikawa et al entitled “DATA ENCRYPTING/DECRYPTING CONVERSION METHODS AND APPARATUSES AND DATA COMMUNICATION SYSTEM ADOPTING THE SAME” and assigned to the present assignee. The disclosure of that application is hereby incorporated by reference into the disclosure of this application.

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Number Name Date Kind
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4926479 Goldwasser et al. May 1990 A
5103479 Takaragi et al. Apr 1992 A
5193115 Vobach Mar 1993 A
5270956 Oruc et al. Dec 1993 A
5742678 Dent et al. Apr 1998 A