JP4249166B2 - Stream cipher method and apparatus - Google Patents

Description

  The present invention relates to a stream encryption method and apparatus that includes a linear feedback register, generates a key stream by performing a nonlinear function operation on the output of the linear feedback register, and calculates and encrypts the key stream and plaintext.

In recent years, various services using computers have been provided. In many services, encryption is used to conceal communication. The most common encryption method is a common key encryption method that performs encryption / decryption with a single key. This common encryption method is divided into a block encryption method and a stream encryption method. Broadly divided.
The former is the method that is most commonly used, but the latter has been attracting attention in recent years because it is superior in processing speed.

An example of a method and apparatus for generating the above-described stream cipher is disclosed in the following patent document.
Special Table 2002-536912

  By the way, the above-described stream cipher has a problem that it takes time for the initialization process. “Initialization” here refers to determination of the internal state (pseudo-random number) of the stream cipher by the built-in key schedule algorithm, and input of this internal state to the linear feedback register (LFSR), and then multiple rotations. This refers to the initial stirring process to be performed.

  The initialization process described above must be re-executed from the beginning every time the initial value (initial vector IV) input from the outside is changed. Therefore, this problem cannot be avoided and cannot be ignored in terms of system performance.

  The present invention has been made based on the above circumstances, and a stream cipher method capable of realizing initialization processing safely and at high speed even when using stream ciphers in an environment where initial values are frequently updated. And an object to provide an apparatus.

  In order to solve the above problems, the present invention includes a linear feedback register, generates a key stream by performing a non-linear function operation on the output of the linear feedback register, and encrypts an input plaintext using the key stream. An encryption method, receiving the key information and the initial value from the outside in a predetermined cycle, inputting the internal state of the stream cipher determined according to a predetermined algorithm into the linear feedback register and performing initial stirring, An initialization processing step for storing the internal state after the completion of the initial stirring in an internal state memory, and an initial value that arrives in a cycle shorter than the cycle in the initialization processing step are received and stored in the initial value and the state memory The internal state after the completion of the initial stirring is calculated and the result is stored in the internal state memory. Performing a simple initialization process step, and generating a key stream using the internal state stored in the internal state memory, calculating the key stream and plain text input from outside, and performing encryption, An encryption processing step for dynamically updating the state, and when encryption by the encryption processing unit is completed or the initial value is input, the internal state held in the internal state memory is erased, and And a post-processing step of repeatedly executing the processing steps after the simple initialization processing step based on the internal state after the completion of the initial stirring stored in the internal memory.

  Further, the present invention is a stream encryption device that includes a linear feedback register, generates a key stream by performing a non-linear function operation on the output of the linear feedback register, and calculates and encrypts the key stream and plaintext. Receiving the key information and the initial value from the outside in a predetermined cycle, inputting the internal state of the stream cipher determined according to a predetermined algorithm to the linear feedback shift register, performing initial stirring, and after the initial stirring A first internal state generation unit that stores an internal state in an internal state memory; and an initial value that arrives at a cycle shorter than the predetermined cycle, and the initial stirring is completed and the initial stirring is stored in the state memory A second internal state generation unit for calculating a subsequent internal state and holding the result in the internal state memory; and the internal state memory An encryption processing unit that generates a key stream using the held internal state, performs encryption by calculating the key stream and plaintext input from the outside, and dynamically updates the internal state; When the encryption by the encryption processing unit is completed or the initial value is input, the internal state stored in the internal state memory is erased, and after the initial agitation end stored in the internal state memory And an internal state restoring unit for restoring the internal state.

  According to the present invention, the internal state where the normal initialization process is completed and the internal state during the encryption process are independently managed, and the simple initialization process added by the present invention is executed during the encryption process. After updating the internal state, perform encryption processing, erase the internal state after the end of encryption processing, and restore the internal state at the end of normal initialization, so that the initial value is updated frequently. However, a high-speed and secure stream cipher can be realized.

  The present invention is particularly effective when it is used for initialization processing of broadcast data encryption in which an initial value is transmitted at a fixed period and a user who has received it from the middle also restores it using stream cipher.

FIG. 1 is a flowchart showing a procedure of a stream encryption method according to an embodiment of the present invention.
Hereinafter, each processing procedure of the stream encryption method according to the embodiment of the present invention will be described in detail with reference to the flowchart shown in FIG.

  First, the normal initialization process (S11) will be described. A stream encryption apparatus according to an embodiment of the present invention is determined by first receiving a secret key (IK) and an initial value (IV) from the outside, and executing a built-in key schedule algorithm. The internal state is supplied to linear feedback registers (LFSR-A, LFSR-B) described later.

  Subsequently, the linear feedback registers (LFSR-A, LFSR-B) perform initial stirring processing that requires a relatively long time by performing idling a plurality of times. And the internal state after completion | finish of an initial stirring process is preserve | saved in the internal state memory mentioned later.

  Next, the simple initialization process (S12) added by the present invention is executed. In this simple initialization process, as shown in the flowchart in FIG. 2, first, the initial value (IV) is received at a constant cycle (S121, S122). Here, it is assumed that the initial value (IV) is frequently transmitted shorter than the period at the time of the initialization process, and has the same length of about 300 to 400 bits as the internal state.

  The initial value (IV) received here is added to the internal state after the completion of the initial stirring in the initialization process (S11) shown in FIG. 1, for example, by performing an XOR (exclusive OR) operation, and the internal state Is updated (S123). The internal state generated as a result of the XOR operation is temporarily stored in the internal state memory for encryption / decryption processing (S124). Here, the time-consuming stirring process as in the initialization process is not performed.

Returning to FIG. 1, the description will be continued. Following the simple initialization process (S12), the encryption / decryption process (S13) is executed.
In the encryption / decryption process (S13), plaintext or ciphertext is input, a key stream is generated using the internal state updated during the above-described simple initialization process (S12), and plaintext (ciphertext) Encryption (decryption) is performed by performing an XOR operation on the generated key stream. Here, the internal state is dynamically updated during the encryption (decryption) process, and is reflected in the internal state memory each time.

  Finally, post-processing (S14) will be described. The post-processing is started when the encryption (decryption) process is completed or when the initial value (IV) is changed, and the internal state held in the internal state memory is erased and stored in advance. Execute the process to restore the internal state after the initial stirring. Then, returning to the process of S12, the processes after the simple initialization process are repeated until the encryption (decryption) process ends or the initial value (IV) is changed.

  As described above, the stream encryption method of the present invention is characterized in that the internal state after the normal initialization process (S11) and the internal state at the time of the encryption process (S13) are managed independently. It is what. For this purpose, the simple initialization process (S12) is executed during the encryption process (S13), the internal state is updated, the encryption process (S13) is performed, and the internal state is deleted after the end of the encryption process. Each procedure for restoring the internal state at the end of normal initialization processing is executed.

  As a result, even in an environment where the initial value is frequently updated, high-speed stream cipher can be realized, and safety can also be realized by using a complete random number for the initial value (IV). It is.

FIG. 3 is a block diagram showing the internal configuration of the stream encryption apparatus according to the embodiment of the present invention.
The stream cipher apparatus according to the embodiment of the present invention includes an internal state generation unit 1, an LFSR-A (2), a clock controller 3, an LFSR-B (4), an internal state memory 5, and a nonlinear function generator. 6 and an internal state restoring unit 7.

  The internal state generation unit 1 includes first and second internal state generation units. The first internal state generation unit receives the secret key (IK) and the initial value (IV) from the outside at a predetermined cycle, and executes the internal key schedule algorithm to determine the internal state determined by the stream cipher. Input to each of LFSR-A (2) and LFSR-B (4) used for generating an internal state (pseudorandom number) to perform initial stirring, and the internal state after completion of the initial stirring is stored in the internal state memory 5 Save to.

  The second internal state generation unit receives the initial value (IV) that arrives at a shorter cycle than the above, and calculates the initial value and the internal state after the completion of the initial stirring stored in the internal state memory 5. The result is held in the internal state memory 5.

  Note that the key stream generated by the LFSR-B (4) is supplied as an input of the nonlinear function generator 6 that generates the key stream. Here, the nonlinear function generator 6 generates a new key stream by executing a certain nonlinear function calculation based on the input key stream and the internal state held in the internal state memory 5.

  On the other hand, the output of the nonlinear function generator 6 is also supplied to the internal state memory 5, and the updated output of the internal state memory 5 is fed back to the nonlinear function generator 6. The LFSR-A (2) outputs a key stream to the clock controller 3 that performs clock control. The clock controller 3 is configured to control the LFSR-B (4) by determining a clock (shift amount) according to the input key stream.

  Note that the key stream that is the output of the nonlinear function generator 6 is subjected to an XOR operation with a plaintext supplied from the outside, and outputs an encrypted text. Here, the nonlinear function generator 6 and the XOR operator are collectively referred to as an encryption processing unit. The encryption processing unit generates a key stream using the internal state held in the internal state memory 5, performs encryption by calculating the key stream and plain text input from the outside, and performs internal encryption. The internal state to be held in is updated dynamically.

  Further, when the encryption or decryption is completed or the initial value (IV) is input, the internal state restoring unit 7 erases the internal state held in the internal state memory 5 one by one, and the internal state memory 5 Restored to the internal state after completion of the initial stirring stored in

  Hereinafter, the operation of the stream encryption device shown in FIG. 3 will be described in detail. First, when setting the internal state in LFSE-A (2) and LFSR-B (4), a secret key (IK: Initial Key) and an initial value (IV: Initial Value) are input to the internal state generation unit 1. . At this time, the internal state generation unit 1 (first internal state generation unit) determines the internal state according to a predetermined key schedule algorithm, and the internal state (LFSR-A (2), LFSR-B (4)) The first pseudo random number sequence and the second pseudo random number sequence) are input to execute the initialization process. At this time, the determined internal state is stored in the internal state memory 5.

  Subsequently, the internal state generation unit 1 (second internal state generation unit) receives an initial value that arrives at a period shorter than the period in the initialization process described above, and is stored in the initial value and the internal state memory 5. The internal state after the completion of the initial stirring is calculated, and the result is stored in the internal state memory 5 for encryption processing and simple initialization processing is executed.

After the above-described simple initialization process, the stream cipher apparatus according to the embodiment of the present invention executes the encryption process according to the following procedure.
That is, the key stream output from the LFSR-B (4) is supplied as an input of the nonlinear function generator 6 through clock control by the clock controller 3 described later. The nonlinear function generator 6 generates a new key stream by executing a certain nonlinear function operation based on the input key stream and the internal state stored in the internal state memory 5. Then, the key stream generated by the non-linear function generator 6 is subjected to an XOR operation with a plaintext separately input, thereby generating an encrypted text.

  Note that the internal state is updated as appropriate during the above-described encryption process. That is, the output of the nonlinear function generator 6 is also supplied to the internal state memory 5, and the output of the internal state memory 5 whose contents are updated is fed back and input to the nonlinear function generator 6. The LFSR-A (2) outputs an internal state (pseudo-random number sequence) to the clock controller 3 that performs clock control.

  The clock controller 3 determines the clock according to the input key stream (pseudo random number sequence) and controls the LFSR-B (4). Specifically, here, LFSR-A (2) and LFSR-B (4) are operated for one cycle. At that time, the clock controller 3 performs bit shift of the feedback polynomial (connected portion in FIG. 3) of LFSR-B (4) according to the root α of the polynomial defining the Galois finite field (GF2 ^ N) of degree 2. Perform clock control (multiply α ^ n). Here, n is the number of clocks (shift amount) determined by the clock controller 3. As a result, clock control within one word is performed.

  Finally, when the encryption process is completed or a new initial value (IV) is input, the internal state restoration unit 7 erases the internal state held in the internal state memory 5 and stores it in the internal state memory 5. Based on the stored internal state after the completion of the initial stirring, an instruction is given to repeatedly execute the processes after the simple initialization process.

  As described above, the present invention independently manages the internal state after normal initialization processing and the internal state during encryption processing, and executes the above-described simple initialization processing during encryption processing. After updating the internal state, perform encryption processing, erase the internal state after the end of encryption processing, and restore the internal state at the end of normal initialization, so that the initial value is updated frequently. However, a high-speed and secure stream cipher is realized.

  The present invention is particularly effective when it is used for initialization processing of broadcast data encryption in which an initial value is transmitted at a fixed period and a user who has received it from the middle also restores it using stream cipher. In addition, it can be widely applied to the evaluation of various stream ciphers, and can be applied to a broadband business using stream ciphers and system construction in mobile communications including mobile phones.

It is the flowchart quoted in order to demonstrate each execution procedure of the stream darkening method concerning embodiment of this invention. It is the flowchart quoted in order to demonstrate the detailed procedure of the simple initialization process added by this invention. It is a block diagram which shows the internal structure of the stream darkening apparatus concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal state production | generation part (1st, 2nd internal state production | generation part) 2, 4 ... Linear feedback register (LFSR-A, LFSR-B), 3 ... Clock controller, 5 ... Internal state memory, 6 ... Non Linear function generator (encryption processing unit), 7 ... internal state restoration unit

Claims (2)

A stream encryption method comprising a linear feedback register, performing a non-linear function operation on an output of the linear feedback register to generate a key stream, and encrypting an input plaintext with the key stream;
The key information and the initial value are externally received at a predetermined cycle, and the internal state of the stream cipher determined according to a predetermined algorithm is input to the linear feedback register to perform initial stirring, and after the initial stirring is completed. An initialization process step to store the internal state in the internal state memory;
An initial value that arrives in a cycle shorter than the cycle in the initialization process step is received, and the initial value and the internal state after the completion of the initial stirring stored in the internal state memory are calculated and stored in the internal state memory A simple initialization process step to hold,
A cipher that generates a key stream using an internal state held in the internal state memory, performs encryption by calculating the key stream and plain text input from the outside, and dynamically updates the internal state Processing step,
When the encryption is completed or the initial value is input, the internal state stored in the internal state memory is deleted, and the internal state after the completion of the initial stirring stored in the internal memory is restored. A post-processing step for repeatedly executing the processing steps after the simple initialization processing step;
A stream encryption method characterized by comprising: A stream encryption device comprising a linear feedback register, performing a non-linear function operation on an output of the linear feedback register to generate a key stream, and encrypting an input plaintext with the key stream;
The key information and the initial value are received from the outside at a predetermined cycle, and the internal state of the stream cipher determined according to a predetermined algorithm is input to the linear feedback shift register for initial stirring, and after the initial stirring is completed. A first internal state generator for storing the internal state in an internal state memory;
An initial value that arrives at a cycle shorter than the predetermined cycle is received, the initial value and the internal state after the completion of the initial stirring stored in the internal state memory are calculated, and the result is stored in the internal state memory A second internal state generation unit to hold;
A cipher that generates a key stream using an internal state held in the internal state memory, performs encryption by calculating the key stream and plain text input from the outside, and dynamically updates the internal state The processing unit,
When the encryption by the encryption processing unit is completed or the initial value is input, the internal state held in the internal state memory is deleted, and after the initial agitation stored in the internal state memory is completed An internal state restoration unit for restoring the internal state of
A stream cipher apparatus comprising:

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