JP2008035305A - Encryption method and data concealing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the risk of information leak by shortening a time to be required for encryption and data concealing processing. <P>SOLUTION: A server device 1 generates a primary cipher text 103 by applying an exclusive OR operation to a plain text 101 and a first stream encryption key 102 by bit so as to primarily encrypt the plain text; generates a bit string 104 by applying an exclusive OR operation to the first stream encryption key and the second stream encryption key by bit, operating the bit string and the primary cipher text by bit, so as to secondarily encrypt the primary cipher text; and then transmits a secondary cipher text 105 generated by secondary encryption to a user device 2. The user device applies an exclusive OR operation to the secondary cipher text and a second stream encryption key 106 by bit, so as to decrypt the secondary cipher text. The different keys are used simultaneously for decryption and encryption. Consequently, high-speed re-encryption processing is attained, and the data are not restored to the plain text in re-encryption, so that the risk of the information leak is reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an encryption method and a data concealment method, and more particularly, to a data concealment method used when data on a server is encrypted and transmitted to a specific user.

  Converting communication contents such as document data so that it cannot be decrypted by anyone other than the parties is called encryption, and returning encrypted data to the original data is called decryption. The encrypted data is called ciphertext, the data before encryption, or the data after decryption is called plaintext. For encryption and decryption, a key is used together with an encryption algorithm, and in order to return a ciphertext to plaintext, it is necessary to decrypt using the same key as that for encryption.

  In general, ciphers can be classified into two types: block ciphers and stream ciphers. In the block cipher, data is divided into blocks of a certain size, and encryption is performed by converting the data for each block. Decryption is realized by performing the reverse conversion of encryption for each block that is the same as encryption. Since the data conversion / inverse conversion differs in processing depending on the key used, correct reverse conversion (= decryption) can be performed only with the same key used for conversion (= encryption).

  On the other hand, the stream cipher generates a random bit sequence called a key stream, and encrypts this by exclusive ORing the data and each bit. Decryption is realized by exclusive ORing the encrypted data with the same key stream as encryption. Different key streams are generated depending on the key used.

  Here, the exclusive OR for each bit will be briefly described. The exclusive OR of two bits is expressed as follows using the operator +.

  As is clear from the equations (a) to (d), when the same bits are exclusive ORed, the result is zero. Moreover, even if 0 is exclusive ORed to a certain bit, the same result as the original bit is obtained. The stream cipher uses this property. When a certain bit in the plaintext is p and the corresponding key stream and ciphertext are k and c, encryption and decryption are expressed as follows.

  When data that requires confidentiality is stored on a server, storing it in an encrypted state is one effective means. The key used for encryption for storing data must be unique to the server and should not be shared with multiple users who can access the server.

  In addition, when data is transmitted only to a specific user from the server, the stored data encrypted in advance using a key unique to the server is decrypted in order to prevent data leakage due to eavesdropping by a third party or impersonation. Then, it is common to encrypt the data again using a key shared only by the both sides of the decrypted data.

As an example of data encryption, Patent Document 1 discloses that random number generation is performed in order to make distribution of random numbers problematic when using a Burnham cipher that enables highly secure encrypted communication to be safe and efficient. A first random number is generated using a generator, and this is shared by both the sender and receiver of the ciphertext, and a second random number is generated using a random number generator, which is used for both encryption and decryption. The third random number is generated by adding the bit string of the first random number to the second random number by exclusive OR, and the third random number is delivered to the other party via the communication path. The other party receiving the third random number adds the bit string of the first random number to the exclusive random OR to restore the second random number, and when performing encrypted communication, the sending side sends a bit stream of information (plain text) The ciphertext is created by adding the bit string of the common key distributed earlier to the exclusive OR or A Vernam cipher that is transmitted to the other party via a communication path, and the receiving side restores the original information (plain text) by adding the bit string of the common key that has been received and restored to the cipher text bit stream by exclusive OR. A common key distribution method has been proposed.
JP 2002-217893 A

  As mentioned above, in order to send a part of the confidential data on the server to a specific user, the data encrypted with the key unique to the server is converted to the data encrypted with the common key with the specific user. However, in the method that is generally used at present, the following problems occur.

  First, with block ciphers that are generally used, the stored data must be decrypted with a key unique to the server, and the plaintext (unencrypted data) obtained must be re-encrypted with a common key. There was a problem that it took a long time.

  Second, since the encrypted data must be once decrypted, there is a problem in that there is a risk of information leakage. Although temporary, leaving important information such as personal information and business secrets unencrypted increases the potential for leakage, especially if the information is frequently distributed and collated. Therefore, it is desirable to avoid it as much as possible.

  Therefore, the present invention has been made in view of the problems in the conventional encryption method and data concealment method described above, and can reduce the processing time and the possibility of information leakage. And it aims at providing a data concealment method.

  In order to achieve the above object, the present invention provides an encryption method, which generates a first stream encryption key, performs an exclusive OR operation on the plaintext and the first stream encryption key bit by bit. The plaintext is first-encrypted to generate a primary ciphertext, a second stream encryption key is generated, and the first stream encryption key and the second stream encryption key are exclusive ORed for each bit. A bit string is generated, and the bit string and the primary ciphertext are exclusive ORed for each bit to secondary-encrypt the primary ciphertext.

  According to the present invention, since the plaintext decryption and encryption are simultaneously performed using the first stream encryption key and the second stream encryption key, the re-encryption process can be performed at high speed. Further, since decryption and encryption are performed at the same time, data does not return to plaintext during re-encryption, and the possibility of information leakage can be reduced.

  In addition, the present invention is an encryption device that performs an exclusive OR operation for each bit of a first encryption key generation unit that generates a first stream encryption key, plaintext, and the first stream encryption key. First encryption means for primarily encrypting the plaintext, second encryption key generation means for generating a second stream encryption key, the first stream encryption key and the second stream encryption key. Bit string generating means for generating a bit string by exclusive ORing for each bit, and a secondary for secondarily encrypting the primary ciphertext by exclusive ORing the bit string and the primary ciphertext for each bit And encryption means. By using this apparatus, as described above, it is possible to realize a high-speed re-encryption process and a reduction in the possibility of information leakage.

  Furthermore, the present invention is an encryption program, wherein the step of generating a first stream encryption key, the plaintext, and the first stream encryption key are exclusive-ORed bit by bit, and the plaintext is 1 A step of generating a primary ciphertext by performing next encryption, a step of generating a second stream encryption key, and exclusive ORing the first stream encryption key and the second stream encryption key bit by bit Generating a bit string, and performing an exclusive OR operation on the bit string and the primary ciphertext for each bit to secondary-encrypt the primary ciphertext. By using this encryption program, the possibility of information leakage can be reduced while realizing high-speed re-encryption processing as described above.

  The present invention is also a data concealment method used between a server device and a user device, wherein the server device generates a first stream encryption key, and a plaintext, the first stream encryption key, And the plaintext is first-order encrypted to generate a primary ciphertext, a second stream cipher key is generated, and the first stream cipher key and the second stream cipher A bit string is generated by exclusive ORing the key for each bit, the bit string and the primary ciphertext are exclusive ORed for each bit, and the primary ciphertext is secondarily encrypted, The secondary ciphertext generated by encryption is transmitted to the user device, and the user device performs an exclusive OR operation on the secondary ciphertext and the second stream cipher key for each bit, and The secondary ciphertext is decrypted.

  According to the present invention, in the server device, the secondary ciphertext generated by simultaneously decrypting and encrypting the plaintext with the first stream encryption key and the second stream encryption key is transmitted to the user device, Since the user apparatus can perform exclusive OR of the secondary ciphertext and the second stream cipher key for each bit, and decrypt the secondary ciphertext to obtain a plaintext. Data concealment processing can be performed at high speed, and therefore data concealment processing can be performed at high speed, and data does not return to plaintext during re-encryption, so data concealment processing is performed between the server device and the user device. Can reduce the possibility of information leakage.

  The present invention is also a data concealment system including an encryption device provided in a server device and a decryption device provided in a user device, wherein the encryption device generates a first stream encryption key. An encryption key generating means, a primary encryption means for performing a primary encryption on the plaintext by exclusive ORing the plaintext and the first stream encryption key bit by bit, and a second stream encryption key Second encryption key generating means, bit string generating means for generating a bit string by exclusive ORing the first stream encryption key and the second stream encryption key bit by bit, the bit string and the primary A secondary encryption means for performing a secondary encryption of the primary ciphertext by exclusive-ORing the ciphertext for each bit, and the decryption device stores the second stream encryption key And the received secondary ciphertext and the second ciphertext Characterized in that it comprises a decoding means for decoding of the stream cipher key by exclusive OR for each bit. By using this system, as described above, re-encryption processing and data concealment processing can be performed at high speed, and the possibility of information leakage is low when data concealment processing is performed between the server device and the user device. Become.

  Furthermore, the present invention is a data concealment program comprising an encryption program provided in a server device and a decryption program provided in a user device, wherein the encryption program generates a first stream encryption key; Plaintext and the first stream encryption key are exclusive-ORed bit by bit to perform primary encryption of the plaintext, generating a second stream encryption key, and the first stream Generating a bit string by exclusive-ORing the encryption key and the second stream encryption key bit by bit; and exclusive-ORing the bit string and the primary ciphertext bit by bit A step of secondarily encrypting a ciphertext, wherein the decryption program stores the second stream cipher key, the received second ciphertext, and the second stream. Characterized in that it comprises a step of decoding by exclusive OR encryption key for each bit. By using this program, as described above, high-speed re-encryption processing and data concealment processing are possible, and the possibility of information leakage in data concealment processing between the server device and the user device can be reduced. .

  The present invention is also a server device, wherein a first encryption key generation means for generating a first stream encryption key, a plaintext, and the first stream encryption key are exclusively ORed for each bit. Bits of primary encryption means for primarily encrypting the plaintext, second encryption key generation means for generating a second stream encryption key, the first stream encryption key and the second stream encryption key Bit string generating means for generating a bit string by exclusive ORing for each bit, and a secondary cipher that performs second-order encryption of the primary ciphertext by exclusive-ORing the bit string and the primary ciphertext for each bit And a means for generating. By using this server device, the re-encryption process can be performed at a high speed, and consequently the data concealment process with the user apparatus can be performed at a high speed. In addition, since data does not return to plaintext during re-encryption, the possibility of information leakage can be reduced when data concealment processing is performed between the server device and the user device.

  Furthermore, the present invention provides a control program for a server device, wherein a step of generating a first stream encryption key, a plaintext, and the first stream encryption key are exclusive ORed bit by bit. A primary encryption step, generating a second stream encryption key, and generating a bit string by exclusive ORing the first stream encryption key and the second stream encryption key bit by bit And a step of subjecting the bit string and the primary ciphertext to a bitwise exclusive OR to perform secondary encryption of the primary ciphertext. By using the control program of this server device, as described above, it is possible to reduce the possibility of information leakage while realizing high-speed re-encryption processing and data concealment processing.

  As described above, according to the present invention, the processing time for re-encryption and data concealment can be shortened, and the possibility of information leakage can be reduced.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a data concealment system according to the present invention. A server device 1 includes a key stream generator 11 and a storage 12, and plaintext encryption, storage, re-encryption, and user device 2. Send to. The user device 2 includes a key stream generator 21 and decrypts the ciphertext from the server device 1 to obtain a plaintext.

  FIG. 2 shows an embodiment of the key stream generator. The key stream generator 3 includes a generator 31, a generator 32, an adder 33, and a switch 34.

  The generators 31 and 32 generate key streams Ks and Kc, respectively. The adder 33 performs an exclusive OR operation on the key stream Ks and the key stream Kc for each bit to generate a key stream Ksc. The switch 34 switches ON / OFF of the input on the generator 32 side to the adder 33. When the switch 34 is ON, the output of the generator 32 is input to the adder 33. When the switch 34 is OFF, an all zero bit string is input to the adder 33.

  Next, the operation in the data concealment method according to the present invention will be described with reference to FIG.

  Hereinafter, simply encrypting plaintext is primary encryption, re-encrypting the primary ciphertext with another key is secondary encryption, primary encryption key is the primary encryption key, A key for secondary encryption is defined as a secondary encryption key. The plaintext, ciphertext, and key stream are all n-bit data series.

  The server device 1 performs primary encryption on the plaintext 101 to form a primary ciphertext 103 and stores it in the storage 12. The primary encryption is performed by exclusive ORing the plaintext 101 and the key stream 102 for each bit. When the plaintext 101, the key stream 102, and the primary ciphertext 103 are P, Ks, and Cs, respectively, the primary encryption is expressed as follows.

  Here, pi and ksi (i = 1, 2,... N) are n pieces of bit data constituting the plaintext 101 and the key stream 102, respectively. The primary ciphertext 103 is stored in the storage 12 in an encrypted state.

  When transmitting the stored primary ciphertext 103 to the user device 2, the server device 1 performs secondary encryption on the ciphertext 103 to obtain a secondary ciphertext 105. Secondary encryption is performed by exclusive-ORing the ciphertext 103 read from the storage 12 and the key stream 104 for each bit. The key stream 104 is generated by the key stream generator 11 using the primary encryption key and the secondary encryption key. It is assumed that the secondary encryption key is shared by the server device 1 and the user device 2. If the key stream 104 and the secondary ciphertext 105 are Ksc and Cc, respectively, the secondary encryption is expressed as follows.

  Here, Kc is a sequence generated with the secondary encryption key by the key stream generator 11, and kci (i = 1, 2,... N) is n bit data constituting Kc. As can be seen from the above equation, the secondary encryption is a sequence (Ksc = Ks + Kc) in which two different key streams generated by the primary encryption key and the secondary encryption key are exclusive-ORed for each bit. This is performed by exclusive ORing the first-encrypted sequence (Cs = P + Ks) for each bit.

  Explaining in detail by taking the first bit as an example, the exclusive OR (ks1 + ks1) of the same value is 0 as shown in the following formula, and the exclusive OR with 0 can be ignored. And (p1 + kc1) that is the exclusive OR of the components of the key stream generated with the secondary encryption key remains, and the result is that plaintext 101 is encrypted only with the key stream generated with the secondary encryption key. Is equivalent to

  The user device 2 acquires the plaintext 107 by decrypting the received secondary ciphertext 105. Decryption is performed by exclusive ORing the secondary ciphertext 105 and the key stream 106 bit by bit. The key stream 106 is generated by the key stream generator 21 using the secondary encryption key. Decoding is represented by the following equation.

  Next, a method for generating a key stream in the data concealment method according to the present invention will be described with reference to FIG.

  In the case of primary encryption, the generator 31 is initialized with the primary encryption key prior to encryption, and the switch 34 is set to OFF. Therefore, the adder 33 performs exclusive OR for each bit of the key stream Ks and the all 0 series, and Ks = Ksc.

  In the case of secondary encryption, the generator 31 is initialized with the primary encryption key, the generator 32 is initialized with the secondary encryption key, and the switch 34 is set to ON prior to encryption. Since the primary encryption key and the secondary encryption key are different, Kc ≠ Ks, Kc ≠ Ksc, and Ks ≠ Ksc.

It is a figure which shows the flow of the process of the encryption concerning the data concealment method concerning this invention, re-encryption, and a decoding. It is a figure which shows the key stream generator in the data concealment method concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Server apparatus 11 Key stream generator 12 which a server apparatus has Storage 2 which a server apparatus has User apparatus 21 Key stream generator 101 which a user apparatus has Plaintext 102 Key stream 103 for primary encryption Primary ciphertext 104 Secondary encryption Key stream 105 for secondary encryption 106 key stream 107 for decryption (for secondary encryption) restored plaintext 3 key stream generator 31 generator 32 generator 33 adder 34 switch

Claims (8)

Generating a first stream encryption key;
The plaintext and the first stream encryption key are exclusive-ORed bit by bit, and the plaintext is subjected to primary encryption to generate primary ciphertext,
Generate a second stream encryption key;
A bit string is generated by exclusive ORing the first stream encryption key and the second stream encryption key bit by bit;
An encryption method, wherein the bit string and the primary ciphertext are exclusive-ORed bit by bit and the primary ciphertext is secondarily encrypted. First encryption key generation means for generating a first stream encryption key;
Primary encryption means for subjecting the plaintext and the first stream encryption key to an exclusive OR for each bit to primarily encrypt the plaintext;
Second encryption key generation means for generating a second stream encryption key;
Bit string generation means for generating a bit string by exclusive ORing the first stream encryption key and the second stream encryption key bit by bit;
An encryption apparatus comprising: a secondary encryption unit that performs exclusive OR of the bit string and the primary ciphertext for each bit to perform secondary encryption of the primary ciphertext. Generating a first stream encryption key;
Generating a primary ciphertext by subjecting the plaintext and the first stream cipher key to an exclusive OR for each bit to perform primary encryption of the plaintext;
Generating a second stream encryption key;
Generating a bit string by exclusive-ORing the first stream encryption key and the second stream encryption key bit by bit;
An encryption program comprising: exclusive-ORing the bit string and the primary ciphertext for each bit to secondarily encrypt the primary ciphertext. A data concealment method used between a server device and a user device,
The server device generates a first stream encryption key, performs exclusive OR operation on the plaintext and the first stream encryption key for each bit, and generates the primary ciphertext by performing primary encryption on the plaintext. Generating a second stream encryption key, generating a bit string by exclusive ORing the first stream encryption key and the second stream encryption key for each bit, and generating the bit string and the primary encryption key. And the secondary ciphertext of the primary ciphertext by exclusive-ORing the text with each bit, and transmitting the secondary ciphertext generated by the secondary encryption to the user device,
The data concealment method, wherein the user device performs an exclusive OR operation on the secondary ciphertext and the second stream cipher key for each bit to decrypt the secondary ciphertext. A data concealment system comprising an encryption device provided in a server device and a decryption device provided in a user device,
The encryption device is:
First encryption key generation means for generating a first stream encryption key;
Primary encryption means for subjecting the plaintext and the first stream encryption key to an exclusive OR for each bit to primarily encrypt the plaintext;
Second encryption key generation means for generating a second stream encryption key;
Bit string generation means for generating a bit string by exclusive ORing the first stream encryption key and the second stream encryption key bit by bit;
A secondary encryption means for performing a secondary encryption of the primary ciphertext by exclusive ORing the bit string and the primary ciphertext for each bit;
The decoding device
Storage means for storing the second stream encryption key;
A data concealment system comprising: decryption means for performing exclusive OR operation on the received secondary ciphertext and the second stream encryption key for each bit. A data concealment program composed of an encryption program provided in the server device and a decryption program provided in the user device,
The encryption program is
Generating a first stream encryption key;
Primary encryption of the plaintext and the first stream encryption key for each bit by exclusive ORing;
Generating a second stream encryption key;
Generating a bit string by exclusive-ORing the first stream encryption key and the second stream encryption key bit by bit;
The bit string and the primary ciphertext are exclusive ORed for each bit to secondary-encrypt the primary ciphertext,
The decryption program is
Storing the second stream encryption key;
A data concealment program comprising: exclusive-ORing and decrypting the received secondary ciphertext and the second stream cipher key for each bit. First encryption key generation means for generating a first stream encryption key;
Primary encryption means for subjecting the plaintext and the first stream encryption key to an exclusive OR for each bit to primarily encrypt the plaintext;
Second encryption key generation means for generating a second stream encryption key;
Bit string generation means for generating a bit string by exclusive ORing the first stream encryption key and the second stream encryption key bit by bit;
A server apparatus comprising: a secondary encryption unit that performs exclusive OR on the bit string and the primary ciphertext for each bit to perform secondary encryption of the primary ciphertext. Generating a first stream encryption key;
Primary encryption of the plaintext and the first stream encryption key for each bit by exclusive ORing;
Generating a second stream encryption key;
Generating a bit string by exclusive-ORing the first stream encryption key and the second stream encryption key bit by bit;
A control program for a server device, comprising: exclusive-ORing the bit string and the primary ciphertext for each bit to perform secondary encryption of the primary ciphertext.

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