JPH10303879A - Enciphering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform partial enciphering without being limited by the data of processing object. SOLUTION: The plane sentence of object is partitioned in the unit of 8 bytes. A plane sentence M0 and an initial vector V are exclusively ORed (T1) and DES enciphering is performed (T2). The enciphered result C0 is defined as an enciphered sentence C0 corresponding to the plane sentence M0 . Concerning following blocks, the plane sentence of relevant block and the plane sentence of preceding block are exclusively ORed without DES enciphering (T3 and T4) so that the enciphered sentence is provided. In order to provide the non- enciphered plane sentences of blocks after the 2nd one at the time of deciphering, concerning all the blocks preceding to the relevant block, it is necessary to successively provide plane sentences from the leading block and to repeat exclusive ORing. Namely, when deciphering any block, first of all, the DES deciphering of leading block (T5) is required at all the time. Besides, since data are enciphered for the unit of a block composed of fixed 8 bytes while using chain techniques, enciphering is not limited by the data type of processing object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encryption method, and more particularly, to an encryption method for dividing data into blocks having a predetermined data length and performing encryption using a chaining technique in block units.

[0002]

2. Description of the Related Art Conventionally, in a facsimile apparatus, data obtained by reading a document is encoded by MH encoding, MR encoding, or the like, and then the encoded data is transmitted to a target facsimile apparatus. . In such communication between facsimile apparatuses, a technique is known in which encoded data is further encrypted and transmitted to a target facsimile apparatus in order to prevent the original data from being decoded from the transmitted encoded data. .

The conventionally used cipher is a cipher which keeps all keys secret, and is called a conventional cipher. This conventional cipher is classified into a block cipher that encrypts each fixed-length data block of several tens of bits or more and a stream cipher that encrypts each small data block of 1 bit to several bits.

[0004] Among them, regarding the block cipher, in order to enhance the security of the block cipher and to use the block cipher as a stream cipher, the ciphertext obtained by encrypting the plaintext is input to the input side of the next encryption processing. A technique called a chain technique for feeding back is known and widely used.

By the way, in the conventional encryption processing, the encryption processing is performed on all the encoded data regardless of the type of the target encoded data. There is a problem that the encryption process takes a considerable amount of time, and the processing time of the entire facsimile transmission process including the encryption process becomes considerably long.

In order to solve this problem, a partial encryption technique has been proposed in which the processing target is narrowed down to a part of the data and encryption processing is performed while ensuring the confidentiality of all data.

As an example of this partial encryption technique, Japanese Patent Laid-Open Publication No. Hei 6-6615 discloses a partial encryption scheme in which only data of a part of scan lines is encrypted in units of scan lines when an original is read by a scanner. A processing technique is disclosed.

However, since the data amount is different for each scanning line, the data amount to be encrypted varies with the above technique. In this case, there is a problem that the above-mentioned block cipher for encrypting each fixed-length data block cannot be used.

On the other hand, in the conventional partial encryption technology,
The target is data coded by a so-called two-dimensional coding method (MMR coding method or the like) that refers to the previous line, and decoding is performed using the correlation between lines in the two-dimensional coding method at the time of decoding. . That is, the data encoded by the so-called one-dimensional encoding method (MH encoding method, etc.) that does not refer to the previous line cannot be partially encrypted, and the type of data to be processed is limited. , There was a problem.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an encryption method capable of performing partial encryption without being restricted by the type of data to be processed. The aim is to provide a method.

[0011]

In order to achieve the above object, an encryption method according to claim 1 divides data into blocks having a predetermined data length, and performs encryption using a chaining technique in block units. The encryption method is characterized in that only the odd-numbered blocks or even-numbered blocks from the beginning of the chain are encrypted.

An encryption method according to a second aspect is an encryption method in which data is divided into blocks of a predetermined data length and encryption is performed using a chaining technique in block units, and only the first block of the chain is used. Is encrypted.

In the encryption method according to the first aspect of the present invention, when data is divided into blocks of a predetermined data length, and encryption is performed using a chain technique in block units, an odd-numbered block or an even-numbered block from the head of the chain is used. Encrypt only the th block.

For example, when encrypting only the odd-numbered blocks, an exclusive OR operation is performed between the plaintext of the first block and an arbitrary initial vector, and the operation result is encrypted to encrypt the first block. It is cipher data. For the second block, the adjacent plaintext block (eg,
An exclusive OR operation is performed between the plaintext of the first block and the exclusive vector of the initial vector) and the plaintext of the second block, and the operation result is used as encrypted data of the second block. For the third block, an exclusive OR operation is performed between an adjacent plaintext block (eg, the exclusive OR operation result in the second block) and the plaintext of the third block, and the operation result is encrypted. 3
The encrypted data of the second block.

Thereafter, for the odd-numbered block from the head of the chain, an exclusive OR operation is performed between the plaintext of the odd-numbered block and the adjacent plaintext block, and the operation result is encrypted. To obtain encrypted data. For even-numbered blocks, encrypted data is obtained by only performing an exclusive OR operation between the plaintext of the even-numbered block and the adjacent plaintext block.

When the encrypted data obtained as described above is decrypted, the encrypted data of the first block is decrypted, and the data obtained by this decryption and the initial vector are subjected to an exclusive OR operation to obtain the first encrypted data. Get the plaintext of the block. 2
For the second block, the plaintext of the second block is obtained by performing an exclusive OR operation on the encrypted data of the second block and the data obtained by the decryption in the first block. For the third block,
By decrypting the encrypted data of the second block and performing an exclusive OR operation on the data obtained by the decryption and the encrypted data of the second block, a plaintext of the third block is obtained.

Thereafter, for the odd-numbered block from the beginning of the chain, the encrypted data of the block is decrypted, and an exclusive OR operation is performed on the data obtained by the decryption and the encrypted data of the previous block. Get the plaintext by doing.
On the other hand, for even-numbered blocks, the plaintext is obtained by performing an exclusive OR operation on the encrypted data of the block and the data obtained by the decryption in the previous block.

As described above, in order to obtain the plaintext of the unencrypted even-numbered block, the data obtained by the decryption in the preceding odd-numbered block is required. That is, in any block, decryption is always required for decryption, so that sufficient confidentiality can be secured over the entire data.

On the other hand, also in the case of encrypting only the even-numbered block, in order to obtain the plaintext of the unencrypted odd-numbered block, the same even-numbered block is obtained by decoding the previous even-numbered block. Since data is required, sufficient confidentiality over the entire data can be ensured.

By the way, in the process of encrypting data in block units having a predetermined data length using the chaining technique as described above, there is no limitation on the data type to be processed. For example,
It is not necessary to detect the break of the scanning line when the original is scanned and read by a scanner or the like.

Thus, according to the encryption method of the first aspect, it is possible to perform partial encryption that can secure sufficient confidentiality without being limited by the type of data to be processed.

According to the encryption method of the present invention, when data is divided into blocks each having a predetermined data length, and encryption is performed using a chain technique in block units, only the first block in the chain is encrypted. .

Specifically, the exclusive (or) operation of the head (first) block and an arbitrary initial vector is performed, and the operation result is encrypted to obtain the encrypted data of the head block. For the second block, an exclusive OR operation is performed on the plaintext of the second block and an adjacent plaintext block (for example, the plaintext of the first block), and the operation result is used as the encrypted data of the second block. And As for the subsequent blocks, the plaintext of the block and the adjacent plaintext block (for example, the plaintext of the previous block) are subjected to an exclusive OR operation for the subsequent blocks, and the operation result is encrypted by the block. Data.

When the encrypted data obtained by such encryption is decrypted, the encrypted data of the first block is decrypted, and the data obtained by this decryption and the initial vector are subjected to an exclusive OR operation. , Get the plaintext of the first block. For the second block, the exclusive OR operation is performed on the encrypted data of the second block and the adjacent plaintext block (for example, the plaintext of the first block),
Get the plaintext of the second block. For the subsequent blocks, as in the second block, an exclusive OR operation is performed on the encrypted data of the block and an adjacent plaintext block (for example, the plaintext of the previous block), and the plaintext of the block is changed. obtain.

As described above, in order to obtain the plaintext of the second and subsequent unencrypted blocks, it is necessary to decrypt the encrypted data of the first block. In other words, for any block, decryption of the encrypted data of the first block is always required, so that sufficient confidentiality over the entire data can be ensured.

Further, as described above, in the process of encrypting data in block units of a predetermined data length using the chaining technique, there is no limitation on the data type of the process target.

Therefore, even in the encryption method according to claim 2,
Partial encryption that can secure sufficient confidentiality can be performed without being limited by the type of data to be processed.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an encryption method according to the present invention will be described with reference to the drawings.

[Structure of Facsimile Machine for Executing Encryption Based on Encryption Method] First, the structure of a facsimile machine for executing encryption processing based on the encryption method according to the present invention will be described. As shown in FIG. 1, a facsimile apparatus 10 according to the present embodiment includes a CPU 12 for controlling the entire facsimile apparatus 10, a ROM 14 as a memory storing a program for operating the CPU 12, and a CPU 14.
R as a memory for storing data required for 12 operations
AM 16, an operation unit 18 for receiving input from an operator and displaying the status of the facsimile machine 10, a CCD
It is configured to include a document, etc.
Image reading unit 22 to be converted into a value, 2
An encoder 24 for compressing and encoding the valued image information and a memory are built in, and the image information encoded by the encoder 24 is written in the memory, and the image information is encrypted in cooperation with the CPU 12. A data processing unit 26, a decoder 28 for decoding the compression-encoded image information, an image recording unit 30 for printing out the image information on a recording sheet, etc. Modem line controller 3
2, and the image storage unit 20 for temporarily storing the image information read by the image reading unit 22 and the image information received by the modem line control unit 32, which are connected via the data bus 36. Interconnected.

[Transmitting / Receiving Operation of Facsimile Machine]
A basic transmission / reception operation of the facsimile machine 10 will be described.

First, the transmission operation will be described with reference to FIG. When a transmission instruction is received from the operation unit 18 in step 102 shown in FIG.
After the image information obtained by the reading is encoded by the encoder 24, the encoded image information is temporarily stored in the image storage unit 20.

In the next step 106, the image information stored in the image storage unit 20 is processed in 256-byte units into the data processing unit 2.
6 and performs partial encryption processing based on the partial encryption method described later. Then, the encrypted image information is transferred to the modem line control unit 32, and step 108
Then, the encrypted image information is transmitted by the modem line control unit 32 to the public line 34 in the ITU-T G3 facsimile error collect mode in 256-byte units. In this way, the image information is encrypted and transmitted to the intended facsimile machine.

Thereafter, steps 106 and 108 are repeated to encrypt all the image information and send it to the intended facsimile machine.

Next, the receiving operation will be described with reference to FIG. When the encrypted image information is received from the external facsimile machine in step 202 shown in FIG.
In 04, the received image information is converted into binary data by the modem line control unit 32 (that is, demodulated), and then transferred to the memory of the data processing unit 26.

In the next step 206, the data processing unit 2
In the memory of No. 6, partial decoding is performed on the demodulated image information by a predetermined data amount in a manner described later. And
In the next step 208, the decoded image information of the predetermined data amount is stored in the image storage unit 20.

Thereafter, steps 206 and 208 are repeated, and all the received image information is decoded and stored in the image storage unit 20. Decoding and image storage unit 2 for all received image information
When the storage of the image information is completed, the process proceeds to step 212 where the image information is taken out from the image storage unit 20 and decompressed by the decoder 28. Print out.

[Operation of this Embodiment] Now, as an operation of this embodiment, the first partial encryption method according to the invention of claim 1 and the invention of claim 2 will be described. The second partial encryption method will be described.

[First Partial Encryption Method] First, the first partial encryption method will be described with reference to FIG.

(1) A plaintext is divided into 8-byte units to obtain a plaintext M ₀ , a plaintext M ₁ , a plaintext M ₂ ...

(2) Plaintext M₀And exclusive with initial vector V
Logical OR operation (S1 in FIG. 4) and DES (US standard)
(Encryption method) (S2). This encryption result
Fruit C ₀The plaintext M₀Ciphertext C corresponding to₀And What
Note that the initial vector V has an initial value of 8 bytes for performing chaining.
Any value can be used as long as it is the same as that at the time of decoding. Ma
Also, the encryption key required for DES is preset from the panel etc.
However, it is not particularly shown. Of course, the same
The encryption key is set.

(3) The next plaintext M ₁ is not encrypted by DES, and the plaintext block adjacent to the plaintext M ₁ (= the value before the DES encryption for the plaintext M ₀ , that is, the initial vector V) by performing the exclusive OR operation result) the de XORed with the plaintext M ₀ (S3), to obtain the ciphertext C _1.

(4) For the next plaintext M ₂ , the plaintext M
_An exclusive OR operation was performed on ₂ and the ciphertext C ₁ (S4)
Then, by performing DES encryption (S5), the ciphertext C
_{Get 2}

(5) Next plaintext M₃About to DES
Without encryption, the plaintext M₃And the adjacent plaintext block
Ku (= plaintext M₂Value before DES encryption for
Sentence M ₂And ciphertext C₁Exclusive OR operation result)
By performing the logical OR operation (S6), the ciphertext C₃
To get

Thereafter, for the odd-numbered block (odd-numbered block) from the head of the chain, an exclusive-OR operation is performed on the plaintext of the odd-numbered block and the adjacent plaintext block, and the calculation result is obtained by DES. A ciphertext is obtained by encryption. On the other hand, with respect to the even-numbered block (even-numbered block), the ciphertext is obtained by performing only the exclusive OR operation of the plaintext of the even-numbered block and the adjacent plaintext block.

Next, the process of decrypting the ciphertext obtained above will be described. (1) Decryption is the reverse of encryption. For ciphertext C ₀ , DES is decrypted for ciphertext C ₀ (S 7), and an exclusive OR operation is performed on the decryption result and initial vector V. (S8). The original plaintext M ₀ is obtained as the result of this calculation.

(2) For the ciphertext C ₁ , the ciphertext C ₀
By performing an exclusive OR operation on the data obtained by performing the DES decryption process and the ciphertext C ₁ (S9),
Get the original plaintext M ₁ .

Thereafter, for the odd-numbered block, the ciphertext of the odd-numbered block is decrypted, and the original plaintext is obtained by performing an exclusive OR operation on the data obtained by the decryption and the adjacent plaintext block. obtain. For the even block, the original plaintext is obtained by performing an exclusive OR operation on the ciphertext of the even block and the adjacent plaintext block.

As described above, in order to obtain the plaintext of the unencrypted even block, it is necessary to decrypt the ciphertext of the adjacent odd block and obtain the plaintext of the adjacent odd block. That is, in any block, decryption is always required for decryption, so that sufficient confidentiality can be secured over the entire data.

By the way, as described above, in the process of encrypting data in units of 8 bytes using the chaining technique, there is no limitation on the data type to be processed. For example, it is not necessary to detect the boundaries of scanning lines when the document is scanned and read by the image reading unit 22.

As is clear from the above, according to the first partial encryption method, it is possible to perform partial encryption that can secure sufficient confidentiality without being limited by the type of data to be processed. it can. In addition, it is needless to say that the time required for the encryption can be greatly reduced because the encryption processing is about half that in the case of encrypting the entire data.

In the same manner as the first partial encryption method, the partial encryption method of encrypting only even blocks is also effective, and the same effect can be obtained.

[Second Partial Encryption Method] Next, the second partial encryption method will be described with reference to FIG.

(1) The plain text is divided into 8-byte units, and is defined as plain text M ₀ , plain text M ₁ , plain text M ₂ .

(2) An exclusive OR operation is performed on the plaintext M ₀ and the initial vector V (T1 in FIG. 5), and encryption is performed by DES (T2). The encryption result C _0, and the ciphertext C ₀ corresponding to the plaintext M _0. The initial vector V is
The initial value for chaining is 8 bytes, and any value may be used as long as it is the same value as when decoding. The encryption key required for the DES is set in advance on the panel or the like, and is not particularly shown. Naturally, the same encryption key is set at the time of decryption.

[0055] (3) for the next plaintext M ₁ does not perform the encryption DES, performing an exclusive OR operation out with (before plaintext M ₀ of the block in this case) plaintext block adjacent the plaintext M ₁ by (T3), to obtain the ciphertext C _1.

(4) For the next plaintext M ₂ , the exclusive-OR operation is performed on the plaintext M ₂ and the adjacent plaintext block (here, the plaintext M _{1 of the} previous block) without encrypting by the DES. by (T4), to obtain the ciphertext C _2.

[0057] For subsequent blocks, as with the plain text M ₁ and plain text M _2, to obtain a ciphertext by performing an exclusive OR operation out with (previous plaintext block here) plaintext block adjacent the plaintext .

Next, the process of decrypting the ciphertext obtained above will be described. (1) Decryption is the reverse of encryption. For ciphertext C ₀ , DES decryption processing is performed on the ciphertext C ₀ (T5), and an exclusive OR operation is performed on the decryption result and the initial vector V. (T6). Obtain the original plain text M ₀ as the calculation result.

(2) For the next ciphertext C ₁ , the adjacent plaintext block (in this case, the plaintext M _{0 of the} previous block) and the ciphertext C ₁ are subjected to an exclusive OR operation (T
7) Obtain the original plaintext M ₁ .

[0060] (3) the next ciphertext C ₂ also, by performing an exclusive OR operation between the adjacent plaintext block (where the previous block plaintext M ₁₎ and the dark ciphertext C ₂ (T
8) Obtain the original plaintext M ₂ .

For the subsequent blocks, as in the case of the ciphertext C ₁ and the ciphertext C ₂ , an exclusive OR operation is performed on the ciphertext and an adjacent plaintext block (here, the plaintext of the previous block). Get the plaintext of.

As described above, in order to obtain the plaintexts of the second and subsequent unencrypted blocks, the plaintexts of all the blocks before the relevant block are sequentially obtained from the first block, and the exclusive OR operation is repeated. There is a need. That is, it is necessary to accurately decrypt the ciphertext of the head block to obtain the plaintext of the head block. Therefore, the decryption of the first block is required for the decryption of any of the blocks, so that sufficient confidentiality over the entire data can be secured.

As in the first partial encryption method, since the data is encrypted in 8-byte block units by using the chaining technique, there is no limitation on the data type to be processed.

As is clear from the above, according to the second partial encryption method, it is possible to perform partial encryption that can secure sufficient confidentiality without being limited by the type of data to be processed. it can. Also, since the entire data can be encrypted by one DES encryption, it goes without saying that the time required for the encryption can be greatly reduced.

In the above embodiment, 8 bytes are used as one block unit. However, this is an example, and another data amount (such as 256 bytes) may be used as one block unit.

In the above embodiment, an example in which the encryption method according to the present invention is applied to a facsimile machine has been shown.
The encryption method according to the present invention can be applied to all devices that transmit and receive data, in addition to facsimile devices.

[0067]

As described above, according to the present invention, it is possible to perform partial encryption that can secure sufficient confidentiality without being limited by the type of data to be processed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a facsimile apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing routine of a transmission operation in the facsimile apparatus of FIG. 1;

3 is a flow chart showing a processing routine of a receiving operation in the facsimile apparatus of FIG.

FIG. 4 is a diagram showing an outline of a first partial encryption method.

FIG. 5 is a diagram showing an outline of a second partial encryption method.

[Explanation of symbols]

 10 Facsimile machine 12 CPU 26 Data processing unit

Claims (2)

[Claims] 1. An encryption method for dividing data into blocks of a predetermined data length and performing encryption using a chain technique on a block basis, wherein only an odd-numbered block or an even-numbered block from the head of the chain is used. An encryption method characterized by performing encryption. 2. An encryption method for dividing data into blocks having a predetermined data length and performing encryption using a chain technique in block units, wherein only the first block of the chain is encrypted. Method.