JPH0435432A - Data ciphering system - Google Patents

Abstract

PURPOSE:To execute ciphering/decoding processings even if a data length is short by taking the exclusive OR of a result obtained by means of ciphering an initial chain value and plaintext data and setting plaintext data as cryptotext data. CONSTITUTION:The ciphering/decoding processings are executed with a data Encryption Standard (DES) arithmetic circuit 1 executing the operation of a DES system as a center. When the data length of plaintext data executing the ciphering processing is less than a block length, the initial chain value is ciphered and the exclusive OR between the ciphered initial chain value and inputted plaintext data is taken, whereby plaintext data is set to be ciphered data. Thus, even a short plaintext less than one block can be ciphered by taking the exclusive OR with data obtained by ciphering the initial chain value. Furthermore, a next ciphered block is read in advance and therefore the cryptotext block inputted from an opposite direction can successively be decoded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a data encryption method, and in particular, the present invention relates to a data encryption method, and particularly to data encryption methods that have an initial chain value, block data, and perform encryption processing for each block by block chaining. The present invention relates to a data encryption method that can perform encryption and decryption processing even when the data length is short.

[Conventional technology]

In the standard encryption method, the block chain encryption method is
For example, the International Standards Committee ISO/IEC
D I S 10116 ”1nfri+at
ion ProcessingMode of 0p
eration for an n-bit block
C B C (Cipher BlockCha
Ining) mote encryption methods are known.

FIG. 5 is a block diagram illustrating encryption processing in CBC mode. As shown in FIG. 5, the plaintext 51 to be encrypted is first divided into 8-byte blocks, including plaintext block O9, plaintext block 1, plaintext block 2, and so on.・、
Plaintext block n is defined as plaintext block (n+1). Therefore, the final plaintext block (n+1) may be less than 8 bytes. The encryption process uses plaintext blocks O
is subjected to an exclusive OR 53 with an initial chain value (ICV) 52, and this data is encrypted by an encryption circuit 54 to form a ciphertext block O. For the next plaintext block 1,
Exclusive OR 5 of plaintext block 1 and ciphertext block O
5 is taken, and this data is encrypted by the next encryption circuit 56 to form ciphertext block 1. This is performed sequentially, and the encryption process is performed for each block, so that the plaintext 5] becomes the ciphertext 57.

In this way, exclusive OR is performed on plaintext block 1 with the previous block, ciphertext block (i-1), and this data is encrypted to form ciphertext block 1. When the last plaintext block (n+1) is 8 bytes, processing is performed in the same manner as in the above method, and the encryption processing is completed. However, if the last plaintext block (n + 1) is less than 8 bytes, the previous ciphertext block n is encrypted again by the encryption circuit 58 to align the first bytes of the final plaintext block (n + 1). , the exclusive OR 59 of the length is taken, and this is defined as the final ciphertext block (n+1).

FIG. 6 is a block diagram illustrating the decoding process in the CBC mode. The decryption process is the reverse of the encryption process. That is, the ciphertext 61 to be decrypted is first
Blocked into 8-byte blocks, ciphertext block O9 ciphertext block 1. Ciphertext block 2. ..., ciphertext block D, ciphertext block (n+1). In decryption, after the ciphertext block 0 is decrypted by the decryption circuit 62, an exclusive OR 64 with the initial chain value (ICV) 63 is taken. As a result, IJ, this data becomes plaintext block O. Next, ciphertext block 1 is decrypted by a decryption circuit 65, and then an exclusive OR 66 with ciphertext block O is calculated. As a result, it is decrypted into a plaintext block]. Similarly, decryption processing is sequentially performed for each block, and the ciphertext 61 is converted into the plaintext 67. In this case, after decrypting the ciphertext block 1, the plaintext block 1 is restored by performing exclusive OR with the ciphertext block (i-1) of the previous block.

In addition, if the final ciphertext block (n+1) is less than 8 bytes, the encryption circuit 68 encrypts the ciphertext block n one before the last, and the first byte of this data and the final ciphertext block ( The final plaintext block (n+1) can be obtained by aligning the beginnings of the blocks (n+1) and calculating exclusive OR 69 for that length.

[il the invention tries to solve! Title]

By the way, the encryption process and the decryption process in the CBC mode are performed as if they were repeated twice.

When performing such encryption processing and decryption processing, the following problems arise. That is, (1) in CBC mote, if the length of the plaintext is less than the block length (8 bytes), encryption cannot be performed.

(2) Since the decryption process for each block uses the ciphertext block of the IN block, it cannot be decrypted from the reverse direction.

The present invention has been made to solve such problems.

An object of the present invention is to provide a data encryption method that can encrypt plaintext data even if it is less than the block length in a CBC mote data encryption method, and can also decrypt ciphertext blocks from the opposite direction. It is in.

[Means to solve the problem]

In order to achieve the above object, the data encryption method of the present invention has an initial sequence #1 value, blocks data, and performs encryption processing for each block by block chaining. If the data length of the plaintext data to be used is less than the block length, the result of encrypting the initial chain value and the plaintext data are exclusive ORed, and the plaintext data is used as the ciphertext data.

[Effect]

According to this, in the data encryption method, in the encryption process, if the data length of the plaintext data to be encrypted is less than the block length, the initial chain value of the CBC mote is encrypted, and the initial chain value of the CBC mote is encrypted. An exclusive OR is performed between the initial chain value and the input plaintext data, and the plaintext data is made into ciphertext data. In the CBC mote, the initial S value is data with a block length (8 bytes) created for plaintext. When this initial chain value is encrypted, a ciphertext block of block length (8 bytes) is obtained. therefore.

If we take the exclusive OR of the ciphertext block obtained by encrypting this initial chain value and the plaintext data shorter than the block length by the data length of the plaintext data, even if the plaintext data is shorter than the block length, the length of the plaintext data will be can generate ciphertext data.

In this way, plaintext data that is less than the block length can be made into ciphertext data, and by similar reverse processing,
Even ciphertext data that is less than the block length can be converted into plaintext data as is. In other words, for the ciphertext data that is less than the block length, if the initial chain value is exclusive-ORed with the encrypted ciphertext data and the data is only the data length of the ciphertext data that is less than the block length, then the plaintext data is・
- Can be decoded to data.

In this way, by converting ciphertext data smaller than the block length into plaintext data, the ciphertext data can be decrypted from the opposite direction as well. That is, in the decryption process, ciphertext data is divided into blocks, ciphertext blocks smaller than the block length are decrypted, the ciphertext block to be decoded is decrypted, the first ciphertext block is read in advance, and this Exclusive OR is performed on the ciphertext block and the plaintext block is decrypted. In CBC mode, the encrypted ciphertext data is input block by block in the reverse direction from the last ciphertext block to the first ciphertext block, and the input ciphertext data is input in order to obtain a plaintext block each time. Each plaintext block can be obtained by decrypting the blocks, including the ciphertext blocks smaller than the block length, and performing an exclusive OR with the ciphertext block inputted first. Due to this.

Encrypted data can also be decrypted from the opposite direction.

〔Example〕

Hereinafter, one embodiment of the present invention will be specifically described using the drawings.

FIG. 1 is a block diagram showing an encryption processing circuit that implements a data encryption method according to an embodiment of the present invention in one aspect. In Figure 1, 1 is DES (Data En
This is a DES arithmetic circuit that performs arithmetic operations based on the encryption (5 standard) method, and the DES arithmetic circuit 1 performs encryption and decryption processing. D.E.
The S arithmetic circuit 1 receives a code #KEY from the key register 2 to perform the arithmetic operation. In addition, an input register (IN) 4 for storing a plaintext block or a ciphertext block and an initial chain value register (ICV) 3 for storing an initial chain value are provided as input registers. An output register (OUT) 5 is provided to store the decoded output block.

The data output from input register 4 is input to input A register (
INA) 7, exclusive OR gate 10, and selector 1
4 is input. Further, the data output from the initial chain value register 3 is input to the selector 12. The data output of the input A register 7 is input to an input B register (INB) 8, and the data output from the input B register 8 is input to the selector 12. The output of the selector 12 becomes an input to the selector 13 and exclusive OR gate 11.

The output of the selector 13 serves as an input to the exclusive OR gate 10 and an input to the selector 14.

Further, the output from the exclusive OR gate 10 is as follows.

The input signal is input to the selector 14, and the output of the selector 14 is input to the input C register (INC) 6. The input C register 6 becomes the input register of the DES calculation circuit 1.
The output of the arithmetic circuit 1 is latched into an output C register (OUTC) 9. The output from this output C register 9 is the selector]3. Selector 15. and is input to exclusive OR gate 11. 411: The output of the algebraic OR gate 11 is input to the selector 15, and the output of the selector 15 is input to the output register (OUT) and output after being launched.

Next, using the encryption processing circuit configured as described above,
The operation of converting plaintext data into ciphertext data will be explained. In normal encryption and decryption processing, as explained in Figs. 5 and 6, plaintext data or ciphertext data is divided into blocks, and then encryption and decryption processing is performed for each block. This is done by

When performing encryption processing, when the plaintext block O is input to the input register 4, the 5 selector 12 and the selector 13 select the output of the initial chain value register (ICV) 3.

Therefore, the exclusive OR gate 0 performs the exclusive OR of the plaintext block O and the initial chain value, and the result is latched into the input C register 6 via the selector 14. DES
The arithmetic circuit 1 inputs the output of the input C register 6 to the key register 2.
The data of the ciphertext block is encrypted according to the KEY of , and the data of the ciphertext block is output to the output C register 9. At this time, selector ] 5
selects the output of output C register 9 and inputs encrypted text block 0 to output register 5.

Next, plaintext block j, (i=1 to n) is input to input register 4.
Since the selector 3 selects the output of the output C register 9, the exclusive OR gate 1o performs the exclusive OR of the plaintext block l and the ciphertext block (i-1). The output of this exclusive OR is selected by the selector 14, passes through the selector 14, and is latched into the input C register 6. The DES operation circuit encrypts the output data of the input C register 6 and outputs it to the output C register 9 as a ciphertext block. Selector 15 outputs C
The output of register 9 is selected and ciphertext block i is stored in output register 5. In this way, plaintext block 1
-Plaintext block n is encrypted, and ciphertext block 1 -ciphertext block n are generated.

Next, when the plaintext block (n+1) is input to the input register 4, the selector]-3 and the selector 14 output C
Select the output from register 9.

As a result, the input C register 6 contains the ciphertext block n
is set. During this time, the output from the input register 4 passes through the input A register 7 and is latched into the input B register 8. The DES arithmetic circuit 1 encrypts the output of the input C register 6 and outputs it to the output C register 9. Furthermore, since the selector 12 selects the output of the input B register 8, the exclusive OR gate 11 performs the exclusive OR of the output of the output C register 9 and the output of the input B register 8. The selector 15 selects the output of the exclusive OR gate 11 and stores the ciphertext block (n+1) in the output register 5.

When performing the decoding process, the decoding is performed by the DES arithmetic operation circuit post-encoding process and the exclusive OR operation of the exclusive OR gate 10.11 using the same selector selection operation.

First, when the ciphertext block O is input to the input register 4, the selector 14 selects the output of the input register 4 and launches the ciphertext block 0 to the input C register 6. During this time, the output of input register 4 is latched into input A register 7. The DES calculation circuit 1 uses *KE of the key register 2.
A decoding operation is performed according to Y, and the output is set in the output C register 9. In addition, the selector 12 selects the output of the initial chain value register 3, so the exclusive OR gate 1
1, the exclusive OR of the output from the output C register 9 and the output from the selector 12 is taken. At this time, the selector 15 selects the output of the exclusive OR gate 11, so that the decrypted plaintext block O is set in the output register 5.

Next, when the ciphertext block i (i=l to n) is input to the input register 4, the selector 4 outputs its output to the input C register 6. Thereby, the DES arithmetic circuit 1 decrypts the ciphertext block j and outputs the result to the output C register 9.

During this time, the output of input A register 7 is launched into input B register 8. Thereafter, ciphertext block 1 from input register 4 is latched into input A register 7. The selector 12 selects the ciphertext block (i
-1), so in the exclusive OR gate 11,
The output of the output C register 9 and the output of the input B register 8 are exclusive ORed, and the plaintext block l is decoded.

This is selected by the selector 15, and the decoded plaintext block l is latched into the output register 5. In this way,
Each block of ciphertext block 1 to @' ciphertext block n is decrypted into plaintext block 1 to plaintext block n.

Next, when the ciphertext block (n + 1) is set in the input register 4, the output from the input A register 7 (ciphertext block n) is manually input to the B register 8° selector 12.
Selector 13. It is latched into the input C register 6 via the selector 14. In this case, the DES arithmetic circuit 1 encrypts the output of the input C register 6 and sends the output to the output C.
Latch into register 9. During this time, the ciphertext block (n+1) output from input register 4 is transferred to input A register 7.
The input signal is latched into the input B register 8 through the input B register 8. Selector 12
selects the output of the input B register 8, and the exclusive OR gate 11 takes the exclusive OR of the output of the output C register 9 and the output of the input B register 8, decrypts it, and obtains the plaintext block (n+1). obtain. The plaintext block (n+1) output from the exclusive OR at this time passes through the selector 15 and is stored in the output register 5.

FIGS. 2 and 3 are block diagrams illustrating encryption processing and decryption processing, respectively, when the plaintext data to be encrypted is less than the block length of 8 bytes.

First, the encryption process will be explained with reference to FIG.

In the encryption process, as shown in Figure 2, plaintext data smaller than the block length is exclusive-ORed with the ciphertext block obtained by encrypting the initial sequence #J value, and the plaintext data is combined with the ciphertext data. be done.

When a plaintext block O of less than 8 bytes is input to the input register 4, the output from the initial chain value register 3 is sent to the selector 12. Selector 13. Through selector 14, input C
It is latched in the register 6 and encrypted in the DES arithmetic circuit 1 according to the key KEY of the key register 2. A ciphertext block obtained by encrypting this initial chain value is latched from the DES calculation circuit 1 to the output C register 9. During this time, the output of the input register 4 is latched into the input B register 8 via the input A register 7. The selector 12 selects the output of the input B register 8, and the exclusive OR gate 11 performs the exclusive OR of the output of the output C register 9 and the output of the input B register 8. The ciphertext block O which is the output of this exclusive OR gate 11 is selected by the selector 15 and output register 5
is stored in Next, the decoding process will be explained with reference to FIG. In the decryption process, as shown in Figure 3, similarly to the clearing process, the ciphertext data smaller than the block length is exclusive-ORed with the ciphertext block in which the initial chain value was encrypted, and the corresponding The ciphertext data is treated as plaintext data.

When a ciphertext block O of less than 8 bytes is input to the input register 4, the output from the initial chain value register 3 is sent to selector 12, selector 13, . It is latched into the input C register 6 through the selector 14, and the D
It is encrypted in the ES calculation circuit 1 according to IIIKEY of the key register 2. Then, the ciphertext block obtained by encrypting this initial chain value is latched into the output C register 9. During this time, the output of the input register 4 passes through the input A register 7 and is latched into the input B register 8. Next, selector 1
2 selects the output of input B register 8, exclusive OR gate 11 performs exclusive OR of the output of output C register 9 and the output of input B register 8, and this output, plaintext block 0, is Output register 5 via selector 15
is stored in

FIG. 4 is a block diagram illustrating processing when decrypting a ciphertext from the reverse direction. In this case as well, the ciphertext data to be decrypted is divided into blocks, and then the decryption process is performed in the reverse direction for each block.

This will be explained with reference to FIG. After blocking, the ciphertext block (n+1) that is less than 8 bytes is stored in the input register 4.
, the output of the input register 4 passes through the input A register 7 and is latched into the input B register 8. Next, when the ciphertext block is input to the input register 4, the output of the input register 4 is latched to the input A register 7. Furthermore, the output of the input register 4 passes through the selector 14 to the input C
It is latched in the register 6, and only this ciphertext block is encrypted in the DES calculation circuit 1 according to @KEY of the key register 2, and its output is latched in the output C register 9. The exclusive OR gate 11 takes the exclusive OR of the output of the input B register 8 selected by the selector 12 and the output of the output C register 9, and generates a plaintext block (n+1).
Decrypt as . Plaintext block (n+1) of this output
is output to the output register 5 via the selector 15.

Thereafter, ciphertext block n - ciphertext block O are input, and are decrypted into plaintext block n - plaintext block O by decryption processing in the reverse direction. The output of input A register 7 is latched into input B register 8, and then ciphertext block i
When (i = (n 1) ~ O) is input to the input register 4, the output of the input register 4 is latched to the input A register 7, and at the same time, the output of the input B register 8 is input to the selector 12° selector 3. ．． It passes through the selector 14, is latched into the input C register 6, and is decoded by the DES arithmetic circuit 1. The decoded output is latched into the output C register 9. At this time, the output of input A register 7 is input to input B.
It is latched into register 8. The selector 12 selects the output of the input B register 8 and inputs it to the exclusive OR game 1-11. As a result, in the exclusive OR gate 11, the manual B register 8 selected by the selector 12
The output of the output C register 9 is exclusively ORed with the output of the output C register 9, and the plaintext block (i+1) is decoded. The plaintext block (i+1) output from this exclusive OR is output to the output register 5 via the selector 15.

Further, in the case of 1;o, the decryption of the ciphertext block 1 is performed after the output of the input B register 8 is input to the selector 2. Selector 1; 3. selector] 4, is latched into the input C register 6, decoded by the DES arithmetic circuit 1, and then exclusive ORed with the initial chain value. When the output of the DES calculation circuit 1 is latched to the input C register 9, the exclusive OR gate 11 outputs the output of the initial chain value register 3 selected by the selector 12 and the output C
It is exclusive ORed with the output of register 9 and decoded into plaintext block O. The plaintext block O output from this exclusive OR is output to the output register 5 via the selector 15.

In this way, in a data encryption method that performs block chaining by exclusive ORing a ciphertext block and the next input block, the encrypted data is transferred in the reverse direction from the last cipher block to the cipher start block. Decrypt the input ciphertext block to be decrypted, and perform exclusive OR with the next input ciphertext block to decrypt the ciphertext block in the reverse direction and sequentially convert it into plaintext block data. be able to.

As described above, according to the present embodiment, it is possible to perform cryptographic processing even when 8 bytes of plaintext are missing, and the ciphertext blocks can be sequentially decrypted from the reverse direction.

The present invention has been specifically described above based on examples.
It goes without saying that the present invention is not limited to the above-mentioned embodiments, and can be modified without departing from the spirit thereof.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects are achieved.

(]) By exclusive ORing the initial chain value with the encrypted data, it is possible to encrypt even short plaintexts that are less than one block.

(2) By reading the next encrypted block in advance, it is possible to sequentially decrypt encrypted text blocks input from the opposite direction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an encryption processing circuit that implements a data encryption method in one aspect according to an embodiment of the present invention, and FIGS. 2 and 3 show the plain text to be encrypted. A block diagram illustrating the encryption process and decryption process when the data is less than the block length of 8 bytes; FIG. 4 is a block diagram illustrating the process when the ciphertext is decrypted from the reverse direction; FIG. 5 is a block diagram illustrating encryption processing in CBC mode, and FIG. 6 is a block diagram illustrating decryption processing in CBC mode. In the figure, 1--DES calculation circuit, 2--Key register, 3--
- Initial chain value register, 4... Input register, 5... Output register, 6... - Manual C register, 7... Input A register, 8... Input B register, 9... Power C register, 10 ...Exclusive OR gate, 11...Exclusive OR gate, 12...Selector, 13...Selector, 14...Selector, 15...Selector.

Claims (1)

[Claims] 1. In a data encryption method that has an initial chain value and blocks data and performs encryption processing for each block by block chaining, if the data length of the plaintext data to be encrypted is less than the block length, the initial A data encryption method characterized by performing an exclusive OR of the result of encrypting a chain value and plaintext data, and using the plaintext data as ciphertext data.