JPH0591101A - Ciphering device and decoding device - Google Patents

Abstract

PURPOSE:To prevent a bit length of ciphering information from being longer than a bit length of input information. CONSTITUTION:A code converter 11 applies predetermined code conversion to information inputted from an input terminal 10. A comparator 12 compares the relation of quantity between a numeral A subject to code conversion and a numeral N given in advance and gives the result of comparison to a changeover device 14 as a control signal. On the other hand, a ciphering circuit 13 applies ciphering to an output of the code converter by a well-known method and gives the result to the changeover device 14. The changeover device 14 selects an output of the ciphering circuit 13 when the numeral A is smaller than the numeral N as the result of comparison and selects an output of the code converter 11 when the numeral A is not smaller than the numeral N as the result of comparison conversely and the selected output is outputted as ciphered information with respect to the inputted information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encryption device and a decryption device used in communication systems and computer systems.

[0002]

2. Description of the Related Art In a communication system or a computer system, in order to prevent unauthorized persons from obtaining information illegally, the information is converted into encryption (encryption) and restored (decryption) to the original information. In other words, this encryption / decryption method is basically the same as the input "information to be encrypted (source information)" or "encrypted information (encryption)". This is a method in which a remainder when the predetermined calculation is performed and the calculation result is divided by a predetermined numerical value is “encryption” or “original information”.

As a typical encryption / decryption method of this type, the RSA method has been widely known and used.
This was proposed by Rivest, Shamir, and Adelmann in 1978 (RLRivest, A.Shamirand
L. Addleman, “A Method forObtaining Digital Signat
ures and Public-key Cryptosystems, “Comm.ACM, Vo
L.21, No.2, pp.120-126, 1978), the acronym of the proposer was taken and it was named RSA method. Regarding the RSA method, for example, the book “Theory of Information and Code” (Miyakawa,
Harashima and Imai, published by Iwanami Shoten, 1983, 10th
There is a plain explanation in the chapter.

According to the above-mentioned document, an encryption device and a decryption device by a general encryption / decryption method including the RSA method are
Not only for the purpose of encrypting the information so that unauthorized persons can not peep at the information, but also to prevent fraud by denying that the person who sent the information later sent the information, It can also be used to prevent unauthorized persons from pretending to be false persons and transmitting false information, but for the sake of convenience in the following description, unauthorized persons will peek at the information. The case of encrypting information for the purpose of preventing the above will be explained by taking the RSA method as an example.

In the RSA encryption / decryption method,
A numerical value e is prepared in advance as an encryption key, a numerical value d is prepared as a decryption key, and a numerical value N is prepared in advance as a common key for encryption and decryption. These numerical values (e, d, N) are integers and are determined by the method described in detail in the book. In addition, the numerical representation P of the information to be encrypted is obtained by dividing the information represented by the bit sequence of "1" and "0" into bit strings of finite length. Therefore, in the following description, "information" and "numerical expression of information" are not distinguished unless there is confusion.

The encryption is performed by the operation of dividing the information P raised to the power of e by N and obtaining the remainder C as the encryption C, as shown in the following formula 1.

[0007]

[Equation 1]

Decryption is performed by multiplying the cipher C encrypted as described above to the d-th power by N, as shown in the following formula 2.
It is performed by an operation of dividing by and restoring the remainder P as the original information P.

[0009]

[Equation 2]

[0010]

As described above, when the encryption / decryption method, that is, the input information P is subjected to a predetermined operation and the operation result is divided by a predetermined numerical value N. In the method in which the remainder is encrypted or the original information, the remainder when divided by the common key N in the encryption process is calculated. At that time, the information whose numerical expression is P and the numerical expression is P + N
It is necessary to be able to distinguish it from the information of. However, the common key N is an arbitrary integer, but cannot be a convenient power of 2. In communication and computer, 2
The base system is used.

Therefore, in the conventional encryption / decryption method,
The information P is set to a value smaller than the common key N to enable the above distinction. Further, since the common key N does not take a convenient power of 2, the information P may be larger than the common key N if the bit lengths of the information P and the common key N are the same. Therefore, usually, the input information to be encrypted is divided and formed so that the bit length of the information P is shorter than the bit length of the common key N by 1 bit.

Then, since the bit length of the cipher is the same as the bit length of the common key N, the cipher becomes one bit longer than the information, and there is a problem that the transmission efficiency and storage efficiency of the information deteriorate.

An object of the present invention is to provide an encryption device and a decryption device which can improve the transmission efficiency and storage efficiency of information.

[0014]

In order to achieve the above object, the encryption device and the decryption device of the present invention have the following configurations. That is, the encryption device of the first invention is a code converter that performs a predetermined code conversion on the input information and outputs the coded information; an encryption circuit that performs an encryption process on the output of the code converter; A comparator that compares the magnitude relationship between the output value of the code converter and a predetermined value; either the output of the code converter or the output of the encryption circuit, depending on the comparison result of the comparator And a switch for selectively outputting one of the input information as encrypted information with respect to the input information.

A decoding device according to a second aspect of the present invention includes a decoding circuit for performing a decoding process on input information; a comparator for comparing the value of the input information with a numerical value given in advance. A switch for selectively outputting either the input information or the output of the decoding circuit according to the comparison result of the comparator; and a predetermined inverse code conversion for the output of the switch. An inverse code converter that outputs it as decoded information for the input information;
It is characterized by having.

The encryption device according to the third aspect of the present invention includes a first switching device that first selects and outputs the input original information according to a control signal given from the outside, and then selectively outputs information that has been subjected to a certain encryption process. A code converter that performs a predetermined code conversion on the output of the first switching device and outputs the converted code;
An encryption circuit for performing encryption processing on the output of the code converter; a comparator for comparing the magnitude relationship between the value of the output of the code converter and a predetermined numerical value; and a comparison result of the comparator. A second switch for selectively outputting either one of the output of the code converter and the output of the encryption circuit as the information subjected to the certain encryption processing;
It is characterized by having.

A decoding device according to a fourth aspect of the present invention includes a first switching device which, according to a control signal given from the outside, first selects and outputs the input original information, and then selectively outputs the information subjected to a certain decoding process. A decoding circuit that performs a decoding process on the output of the first switching device; a comparator that compares the value of the output of the first switching device with a predetermined value; a comparison of the comparators; A second switch that selectively outputs either the output of the first switch or the output of the decoding circuit according to the result; and a predetermined inverse code conversion for the output of the second switch. An inverse code converter which outputs it as the information subjected to the constant decoding processing;
It is characterized by having.

The encryption device of the fifth invention is the encryption device of the first invention or the third invention; the code converter outputs the input numerical value in a form in which the most significant bit thereof is inverted. It is what

The decoding device of the sixth invention is the decoding device of the second invention or the fourth invention; the inverse code converter outputs the input numerical value in a form in which the most significant bit thereof is inverted. It is a feature.

The encryption device of the seventh invention is the encryption device of the first invention or the third invention; the code converter has a negation circuit for inverting the most significant bit in the inputted numerical value;
A circuit for converting a numerical value composed of a plurality of lower bits in the input numerical value into a numerical value having a predetermined bit length; a plurality of upper bits excluding the most significant bit of the input numerical value, which are the same as the predetermined bit length An exclusive OR circuit that takes an exclusive OR of a numerical value consisting of a plurality of upper bits of a bit length and a numerical value consisting of the predetermined bit length; and an output of the NOT circuit and an output of the exclusive OR circuit. The plurality of lower-order bits and the remaining bits in the input numerical value are output from the code converter.

The decoding device of the eighth invention is the decoding device of the second invention or the fourth invention; the inverse code converter is a negation circuit for inverting the most significant bit in the inputted numerical values; A circuit for converting a numerical value consisting of a plurality of lower bits in the numerical value into a numerical value having a predetermined bit length; a plurality of upper bits excluding the most significant bit of the input numerical value and having the same bit length as the predetermined bit length An exclusive OR circuit that takes an exclusive OR of a numerical value composed of a plurality of upper bits and a numerical value having the predetermined bit length; and an output of the NOT circuit, an output of the exclusive OR circuit and the plurality of The lower bits and the remaining bits in the input numerical value are output from the inverse code converter.

[0022]

Next, the operation of the encryption device and the decryption device of the present invention configured as described above will be described. The encryption device and the decryption device of the present invention are intended to prevent unauthorized persons from peeping at the information, and deny that the person who has transmitted the information later transmitted the information, and thus fraud. It can be applied to both the purpose of preventing work and the purpose of preventing unauthorized persons from pretending to be false persons and transmitting false information. An example is used for the purpose of “preventing unauthorized persons from peeping at information”.

In the encryption device of the first aspect of the invention, the input information to be encrypted (P for convenience) is subjected to a predetermined code conversion. Then, if the numerical value A obtained by the code conversion is smaller than a predetermined numerical value (corresponding to the common key N), the encryption is performed by the conventional encryption method (a known encryption method which is not limited to Equation 1). Then, the result is encrypted and output as a cipher. On the other hand, if the numerical value A is not smaller than the common key N, the numerical value A is directly output as a cipher.

Here, in the comparator, the numerical value A and the common key N
The information P to be encrypted has the same bit length as that of the common key N, since the size relationship between and is compared. The encryption method in the present invention is not limited to the RSA method, but if one property of the RSA method, that is, the key (e, d, N) is properly selected, the information that takes a value smaller than the common key N is obtained. Paying attention to the property that encryption can correspond to one-to-one, and processing as described above,
Since all the information whose effective bit length is not longer than the common key N and the cipher can be made to correspond one-to-one, the bit length of the cipher C can be encrypted so as not to be longer than the bit length of the information P. That is, the transmission efficiency and storage efficiency of information can be improved.

Further, in the decrypting apparatus of the second invention, the conventional decryption method (known decryption method not limited to the equation 2) is applied to the cipher obtained as described above (referred to as C for convenience). In parallel with the restoration, the magnitude relation between the cipher C and the common key N is compared. If the cipher C is smaller than the common key N, the cipher C is the common key N for the restored numerical value B.
If it is not smaller than the above, the code C is subjected to the inverse code conversion of the code conversion, and the code is used as the restoration information.

In the encrypting device of the third invention, the information P is first encrypted according to the first invention, and the cipher thus obtained is newly used as the information P '. Then, this is repeated a predetermined number of times to obtain a desired cipher. In the decoding device of the fourth invention,
Decrypt by the same method. Encryption of the first and second inventions
The decryption method is effective for applications where confidentiality is not sufficiently maintained.

The code converter and the inverse code converter "output the input numerical value in the form in which the most significant bit is inverted" so that the input and the output are in one-to-one correspondence.
Like (fifth and sixth inventions), or "inverted most significant bit in input numerical value, plural lower bits in input numerical value, and plural lower bits Exclusive of a value converted from a numerical value with a predetermined bit length and a plurality of high-order bits excluding the most significant bit in the input numerical value and having the predetermined bit length and a plurality of high-order bits of the same bit length The outputs obtained by taking the logical sum and converting and the remaining bits in the input numerical value "are configured (the seventh and eighth inventions).

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an encryption device according to the first embodiment of the present invention. This encryption device includes a code converter 11 and a comparator 1.
2, the encryption circuit 13, and the switch 14 are basically configured.

In FIG. 1, the code converter 11 performs a predetermined code conversion on the information to be encrypted (the above-mentioned information P) inputted from the input terminal 10, and the result is encrypted with the comparator 12. It outputs to the conversion circuit 13 and the switching device 14.

The comparator 12 compares the value of the output information of the code converter 11 (this is A) with a predetermined numerical value (the above-mentioned common key N), and the numerical value A is the common key. If it is smaller than N, "1" is given to the switch 14 as a control signal, and if the numerical value A is not smaller than the common key N, "0" is given.

On the other hand, the encryption circuit 13 includes the code converter 1
The output of 1 is subjected to a predetermined encryption by a conventionally known method, and the result is given to the switch 14.

As a result, the switcher 14 selects the output of the encryption circuit 13 if the output of the comparator 12 is "1", and conversely if the output of the comparator 12 is "0". 11
Output is output from the output terminal 15 as a code. When the output of the code converter 11 is output as a cipher, it is extremely small and does not pose a problem.

Next, FIG. 2 shows a decoding apparatus according to the second embodiment of the present invention. This decoding device basically includes a comparator 22, a decoding circuit 23, a switch 24, and an inverse code converter 21.

In FIG. 2, the encrypted information input from the input terminal 25, that is, the encryption, is the comparator 22.
Is supplied to the decoding circuit 23 and the switch 24. The comparator 22 compares the input cryptographic value with the numerical value (common key N) given in advance, and inputs “1” if the input cryptographic value is smaller than the common key N. If the value of the encrypted code is not smaller than the common key N, "0" is given to the switch 24 as a control signal.

On the other hand, the decryption circuit 23 performs a predetermined decryption on the input cipher by a conventionally known method, and supplies the result to the switch 24.

As a result, the switch 24 selects the output of the decoding circuit 23 if the output of the comparator 22 is "1", and conversely, if the output of the comparator 22 is "0", the input terminal 25. Selects the cipher supplied from and outputs it to the inverse code converter 21.

The inverse code converter 21 is the switching device 2
4 is subjected to code conversion reverse to that of the code converter 11 and output from the output terminal 20 as restoration information for the cipher supplied from the input terminal 25. That is, the inverse code converter 21 has the same configuration as the code converter 11.

FIG. 3 shows an encryption device according to the third embodiment of the present invention. This encryption apparatus is the same as the first embodiment except that the (first) switch 31 is replaced by the code converter 11.
In front of. Hereinafter, description will be made focusing on the portion according to the third embodiment.

In FIG. 3, the switching device 31 has an input terminal 1
The information to be encrypted input from 0 and the (second) switch 14
Of the two inputs are selected in accordance with a control signal 30 from the outside, and the selected one is selected by the code converter 11
Give to.

Specifically, the control signal 30 becomes, for example, "1" at the timing when the information to be encrypted is input from the input terminal 10, and causes the switch 31 to selectively output the information to be encrypted from the input terminal 10. Then, at the timing when the switching device 14 outputs, it becomes "0", and the switching device 1 is switched to the switching device 1.
4 is selected, and thereafter, the state of “0” is maintained until the switch 14 outputs a predetermined number of times, and then becomes “1” at the timing when new information to be encrypted is input. is there.

In short, the apparatus of the third embodiment is an apparatus which performs the encryption process on the information to be encrypted a plurality of times and outputs the final value of each of the plurality of times as an encryption, and is capable of sufficiently maintaining confidentiality. To do. The decrypting device for the encrypting device according to the third embodiment is configured as shown in FIG.

That is, in FIG. 4, this fourth embodiment device has a (first) switch 41 at the input stage of the second embodiment device.
In front of. The switch 41 is the switch 31.
Similarly, according to the control signal 40 given from the outside,
Either one of the information to be decoded inputted from the input terminal 25 and the output of the inverse code converter 21 is selected and given to the comparator 22, the decoding circuit 23 and the (second) switch 24. Since the control signal 40 is a signal similar to the control signal 30, the final value of the decoding process of a plurality of times is output as the restoration information.

Next, the code converter and the inverse code converter will be described. Since they have the same configuration, they will be simply referred to as "converters" hereinafter. This converter has a configuration in which the input and the output are in one-to-one correspondence, and in this embodiment, the following two configurations were adopted.

The first configuration is such that "the input numerical value is output with its most significant bit inverted". When the most significant bit is inverted, a numerical value larger than the common key N is always converted into a smaller numerical value than the common key N.
Therefore, in the apparatus of the third embodiment, when encryption is repeatedly performed by using the code converter 11 having such a configuration, the switcher 14 causes the encryption circuit 1 to repeat the j-th time.
Even if the output of 3 is not selected, the output of the encryption circuit 13 is always selected in the (j + 1) th iteration.
The information to be encrypted input from 0 is encrypted by the encryption circuit 13 at least once. Therefore, the risk of decryption by a third party is reduced.

The second configuration is shown in FIG.
In FIG. 5, assuming that the numerical value input from the input terminal 50 is L bits, this converter uses a negation circuit 51 that inverts one bit of the most significant bit in the input numerical value, and the input numerical value. Of the hash function unit 53 for converting the numerical value consisting of the lower a bits of b to the numerical value of the b bit length, and the upper b excluding the most significant bit of the numerical value consisting of the output b bits of this hash function unit 53 and the input numerical value. Exclusive-OR circuit 52 that takes an exclusive-OR with a numerical value consisting of bits
And the output of the NOT circuit 51 (1 bit), the output of the exclusive OR circuit 52 (b bits), the lower a bits, and the remaining bits (L-a-b-1) of the converter. Is output from the output terminal 54.

Since the hash function is used in this embodiment, the bit length b of the output numerical value is shorter than the bit length a of the input numerical value, but the present invention is not limited to this. Of course, the conversion of the bit length in the circuit 53 is arbitrary.

In the above description, the use for the purpose of preventing unauthorized persons from obtaining the information was explained, but in the device of the present invention, in addition, the person who has transmitted the information can later obtain the information. It is also applied for the purpose of preventing fraud by denying that the sender has sent, and for preventing unauthorized persons from pretending to be false persons and transmitting false information. What can be done is apparent from the above-mentioned literature.

[0048]

As described above, according to the encryption device and the decryption device of the present invention, the input information has the same bit length as the common key, and the effective bit length is longer than that of the common key. One-to-one with all missing input information and encrypted information
In this case, since the encryption information can be encrypted so that the bit length of the encrypted information does not become longer than the bit length of the input information, the information transmission efficiency and the storage efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an encryption device according to a first embodiment of the present invention.

FIG. 2 is a configuration block diagram of a decoding device according to a second embodiment of the present invention.

FIG. 3 is a configuration block diagram of an encryption device according to a third embodiment of the present invention.

FIG. 4 is a configuration block diagram of a decoding device according to a fourth embodiment of the present invention.

FIG. 5 is a configuration block diagram of a code converter and an inverse code converter.

[Explanation of symbols]

 11 Code Converter 12 Comparator 13 Encryption Circuit 14 Switcher 21 Inverse Code Converter 22 Comparator 23 Decoding Circuit 24 Switcher 31 Switcher 51 Negative Circuit 52 Exclusive OR Circuit 53 Hash Function Unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04L 9/10 9/12

Claims (8)

[Claims] 1. A code converter that performs predetermined code conversion on input information and outputs the coded information; an encryption circuit that performs encryption processing on the output of the code converter;
A comparator for comparing the magnitude relationship between the output value of the code converter and a predetermined numerical value; either the output of the code converter or the output of the encryption circuit according to the comparison result of the comparator A switching device for selectively outputting one of them as encrypted information for the input information, and an encryption device. 2. A decoding circuit for decoding input information; a comparator for comparing the value of the input information with a predetermined numerical value; a comparison result of the comparator A switch that selectively outputs either one of the input information and the output of the decoding circuit according to
And a reverse code converter for performing a predetermined reverse code conversion on the output of the switch and outputting the reverse code conversion as decoded information for the input information. 3. According to a control signal given from the outside,
A first switching device that first selects and outputs the input original information, and then selects and outputs information that has been subjected to certain encryption processing;
A code converter that performs predetermined code conversion on the output of the first switching device and outputs the code; an encryption circuit that performs encryption processing on the output of the code converter; and a value of the output of the code converter A comparator for comparing the magnitude relation with a given numerical value; the certain encryption processing for either one of the output of the code converter and the output of the encryption circuit according to the comparison result of the comparator A second switching device for selectively outputting as the information obtained by the above; 4. According to a control signal given from the outside,
A first switching device which first selectively outputs the input original information and then selectively outputs information that has been subjected to a certain decoding process;
A decoding circuit that performs a decoding process on the output of the first switching device; a comparator that compares the value of the output of the first switching device with a predetermined numerical value; a comparison result of the comparator A second switch that selectively outputs one of the output of the first switch and the output of the decoding circuit according to
And a reverse code converter for performing a predetermined reverse code conversion on the output of the second switch and outputting it as the information subjected to the constant decoding processing. 5. The encryption device according to claim 1 or 3, wherein the code converter outputs the input numerical value with its most significant bit inverted. .. 6. The decoding device according to claim 2 or 4, wherein the inverse code converter outputs the input numerical value with its most significant bit inverted. apparatus. 7. The encryption device according to claim 1, wherein the code converter includes a negation circuit that inverts the most significant bit of the input numerical value, and a plurality of input numerical values. A circuit for converting a numerical value consisting of lower bits into a numerical value consisting of a predetermined bit length; a plurality of upper bits excluding the most significant bit of the inputted numerical value and consisting of a plurality of upper bits having the same bit length as the predetermined bit length An exclusive OR circuit that takes an exclusive OR of a numerical value and a numerical value having the predetermined bit length; and an output of the NOT circuit, an output of the exclusive OR circuit, the plurality of lower bits, and the input. And the remaining bits in the numerical value are output from the code converter. 8. The decoding device according to claim 2 or 4, wherein the inverse code converter includes a negation circuit that inverts the most significant bit in the input numerical value; A circuit for converting a numerical value consisting of a plurality of lower bits into a numerical value consisting of a predetermined bit length; a plurality of upper bits excluding the most significant bit in the input numerical value, the plural upper bits having the same bit length as the predetermined bit length An exclusive OR circuit that takes an exclusive OR of the numerical value and the numerical value having the predetermined bit length; and, the output of the NOT circuit, the output of the exclusive OR circuit, the plurality of lower bits, and the input. The remaining bits in the digitized numerical value are output from the inverse code converter.