KR20190020988A - Computer-executable lightweight white-box cryptographic method and apparatus thereof - Google Patents

Abstract

According to an embodiment of the present invention, a computer-executable lightweight white-box cryptographic method and an apparatus thereof can easily reduce a number of rounds, thereby effectively improving a computation speed. The computer-executable lightweight white-box cryptographic method of the present invention comprises the steps of: (a) generating a plain text; (b) generating a white-box cryptographic generalized Feistel network (GFN) with a lookup table internally encoded with a round function as a round key; and (c) providing the externally encoded plain text to the white-box cryptographic GFN to provide a cipher text.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer-executable lightweight white-

The present invention relates to an encryption technique, and more particularly, to a computer-executable lightweight computer system capable of establishing a lightweight environment for Internet access and improving security through a white-box cryptography GFN (Generalized Feistel Network) White box encryption method and apparatus.

DES (Data Encryption Standard) based block cipher technology encrypts by applying cipher key and algorithm in data block unit to create ciphertext. More specifically, the DES-based block cipher technology applies the cipher text of the previous cipher block to the next block in order so that the same blocks of the plain text do not become the same cipher text in one message, By combining the initialization vector by the random number generator to the first block of the plaintext so that no ciphertext is generated, the next blocks can be different ciphertext blocks from the previous ciphertext block.

A block cipher based on a generalized Feistel networks (GFN) is a typical example. The block cipher uses a key to configure a block cipher, performs a network transformation, and performs a single round The encryption step is repeated several times and the encryption operation is performed by repeating the round function F in each round step. This will be described in more detail with reference to FIG.

1 is a diagram illustrating a generalized fiistel network. More specifically, Figs. 1 (a), 1 (b) and 1 (c) each show a block cipher technology using a generalized fiistel network of a first type, a second type and a third type, 1 (d) shows the encryption process of LEA (Lightweight Encryption Algorithm) which is one of the third type. A representative example of the first type (Type-I) in FIG. 1 (a) is the CAST-256 algorithm, and a typical example of the second type (Type-II) A representative example of the third type (Type-III) in Fig. 1 (c) is LEA.

Among them, the LEA is an algorithm for encrypting a 128-bit data block developed by the National Institute of Security and Technology. It is implemented in the form of ARX (Addition, Rotation, XOR) avoiding the use of S-BOX (Substitution-box) It provides faster computation speeds than the Advanced Encryption Standard (AES) and can provide a higher level of security than the HIGHT algorithm. The LEA algorithm encrypts keys 128, 192 and 256 bits for 128 bits, where each round is 24, 28, and 32 rounds.

In the left block diagram of Fig. 1 (d), the encryption process is performed as follows. In the operation of each round function, the input value is a 128-bit input value composed of four 32-bit internal state variables and a 192-bit round key, and the output value is an internal state variable of 128 bits. In the operation, the key is processed by the XOR process, and each block bit goes down in the direction of the arrow and goes through the addition process and the rotation process. 1 (d), ROR means right bit rotation and ROL means left bit rotation. The number displayed in each bit rotation means that the bit rotates by that number. After all operations are completed, each block moves to the left, and the block variable of the first position moves to the lowermost end, and the operation of the encryption round function is terminated. The decryption is performed in the same manner as the right block of FIG. 1 (d), and the calculation equation at this time is the same as encryption. However, since Addition is used in encryption, Subtraction is used in decryption.

Such a conventional generalized fistel network structure based encryption technique has a disadvantage that it is easy to implement, but still vulnerable to white-box attacks in the course of encryption and decryption.

The DES-based block ciphering technique described above is based on a black box cryptographic mechanism that operates under the assumption that cryptographic keys are securely maintained. White-box encryption technology, on the other hand, is based on a white-box cryptographic mechanism that prevents attackers from easily guessing encryption keys even when their internal behavior is exposed. This will be described in more detail with reference to FIG.

2 is a diagram for explaining the basic concept of white-box encryption.

In FIG. 2, the white-box encryption technique makes an algorithm a large look-up table and hides the encryption key in an obfuscation state with a software-implemented encryption algorithm, so that even if the attacker analyzes the internal operation, Avoid analogy. More specifically, the white box encryption technique internally performs encoding (Mi) and decoding (Mi) ^-1 on a separate table so that the intermediate value is not exposed, and as a result, The intermediate data and the key of the round operation can be safely hidden from the attacker.

Conventional white box encryption technology has a disadvantage in that it is difficult to implement a high security for a lightweight environment for the Internet or mobile devices because the size of the table is too large.

Korean Patent No. 10-1623503 (2016.05.17) relates to an apparatus and method for implementing a white-box encryption of an LEA block cipher. The encryption algorithm including the encryption key is composed of a plurality of tables, The present invention provides an apparatus and method for implementing a white-box cipher of an LEA block cipher that can prevent a cipher key from being searched for through a search of a plaintext input unit, a plain text input unit that receives an encoded plain text, A round function unit for receiving a result of the round function performed in the plain text or immediately before and performing a modular addition and a rotation operation based on the random table and outputting a result of the round key operation position dispersion processing using the linear transformation; The round function part for all the round keys among the output values processed in There is consists to the result of encoding including a ciphertext outputted cipher text output for outputting.

Korean Patent Laid-Open No. 10-2015-0090438 (May 2015.08.06) relates to a white-box encryption apparatus and method thereof, which includes an operation unit for performing encryption operations using a white-box cipher tables on a plurality of rounds, And a table-mixing unit for mixing an array of tables.

Korean Patent No. 10-1623503 (May 2015) Korean Patent Publication No. 10-2015-0090438 (2015.08.06)

One embodiment of the present invention provides a computer-executable lightweight white-box encryption method and apparatus that improves security through a white-box cryptography GFN (Generalized Feistel Network) structure that can establish a lightweight environment of the Internet of things .

One embodiment of the present invention provides a computer-executable lightweight white-box encryption method and apparatus that can be easily applied to a memory constrained environment by regulating the reuse of the lookup table to significantly reduce the total required table size .

An embodiment of the present invention is to provide a computer-executable lightweight white-box encryption method and apparatus capable of effectively controlling the reduction of the number of rounds and thereby improving the computation speed.

Among the embodiments, a computer-executable lightweight white-box encryption method comprises the steps of (a) outer encoding the plaintext, (b) generating a white-box cryptographic GFN (Generalized Feistel Network), which is generated as a lookup table internally encoded with a round- (C) providing the externally encoded plaintext to the white-box cryptographically GFN to provide a cipher text.

The step (a) may include performing the outer encoding based on an encoding table in which a plurality of encoding types are defined.

The step (a) may further include the step of dividing the externally encoded plaintext into internal state variables having n (where n is a natural number) m bits (where m is a natural number) bits.

The step (b) may include a step of performing an ARX (Addition, Rotation, XOR) operation on the round key to calculate the lookup table.

The step (b) includes the step of generating the lookup table for a single round by (n-1-t) (where n is the number of internal state variables and t is an integer of 0 or more as the number of reusable lookup tables) can do.

The step (b) may further comprise the step of keeping the t equal to each value of r (r is a natural number) rounds.

The step (b) may include the step of determining the total number N of round keys required and the number (m) of bits of the internal state variable by defining a stability index related to the white-box cipher type GFN.

The step (b) includes determining the number of round iterations (r), the number of internal state variables (n) and the number of reuse lookup tables (t) based on the total number N of round keys required .

The step (b) may include generating a secret key for white-box encryption by combining the total required round keys.

The step (c) may include performing external encoding on the cipher text to perform lightweight white-box encryption.

Among the embodiments, the lightweight white-box encryption apparatus includes a plain-text management unit that encodes a plain text, a white-box cipher-type GFN that generates a white-box cryptosystem GFN (Generalized Feistel Network) generated as a lookup table internally encoding a round function by a round- And a ciphertext providing unit for providing the ciphertext by providing the externally encoded plain text to the white-box cipher type GFN.

The disclosed technique may have the following effects. It is to be understood, however, that the scope of the disclosed technology is not to be construed as limited thereby, as it is not meant to imply that a particular embodiment should include all of the following effects or only the following effects.

The computer-executable lightweight white-box encryption method and apparatus according to an exemplary embodiment of the present invention can improve the security through a white-box cryptography GFN (Generalized Feistel Network) structure that is capable of building a lightweight environment for the Internet of objects, .

The computer-executable lightweight white-box encryption method and apparatus according to an embodiment of the present invention can significantly reduce the total required table size by regulating the reuse of the lookup table, and thus can be easily applied to a memory limitation environment.

The computer-executable lightweight white-box encryption method and apparatus according to an exemplary embodiment of the present invention can easily control the decrease in the number of rounds, thereby effectively improving the computation speed.

1 is a diagram illustrating a generalized fiistel network.
2 is a diagram for explaining the basic concept of white-box encryption.
FIG. 3 is a block diagram illustrating a configuration of a lightweight white-box encryption apparatus according to an embodiment of the present invention.
4 is a block diagram illustrating an embodiment of the structure of a white-box cryptographic GFN generated by the lightweight white-box cryptographic apparatus of FIG.
FIG. 5 is a view showing an embodiment of a process of generating a white-box cryptographic GFN for reducing the size of a total table by the lightweight white-box encryption apparatus shown in FIG.
FIG. 6 is a diagram illustrating embodiments in which the lightweight white-box encryption device of FIG. 3 performs computer-executable lightweight white-box encryption methods to significantly reduce the size of the aggregate table.
7 is a flowchart illustrating a lightweight white-box encryption method performed by the lightweight white-box encryption device of FIG.
8 is a graph showing a relationship graph between a ratio (t _r ) of a reusable lookup table and a number of round iterations (r) that can be derived in the process of generating a white box cryptographic type GFN by the lightweight white box encryption apparatus shown in FIG. 3 .

The description of the present invention is merely an example for structural or functional explanation, and the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, the embodiments are to be construed as being variously embodied and having various forms, so that the scope of the present invention should be understood to include equivalents capable of realizing technical ideas. Also, the purpose or effect of the present invention should not be construed as limiting the scope of the present invention, since it does not mean that a specific embodiment should include all or only such effect.

Meanwhile, the meaning of the terms described in the present application should be understood as follows.

The terms "first "," second ", and the like are intended to distinguish one element from another, and the scope of the right should not be limited by these terms. For example, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" to another element, it may be directly connected to the other element, but there may be other elements in between. On the other hand, when an element is referred to as being "directly connected" to another element, it should be understood that there are no other elements in between. On the other hand, other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

It is to be understood that the singular " include " or "have" are to be construed as including the stated feature, number, step, operation, It is to be understood that the combination is intended to specify that it does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In each step, the identification code (e.g., a, b, c, etc.) is used for convenience of explanation, the identification code does not describe the order of each step, Unless otherwise stated, it may occur differently from the stated order. That is, each step may occur in the same order as described, may be performed substantially concurrently, or may be performed in reverse order.

The present invention can be embodied as computer-readable code on a computer-readable recording medium, and the computer-readable recording medium includes all kinds of recording devices for storing data that can be read by a computer system . Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and also implemented in the form of a carrier wave (for example, transmission over the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used predefined terms should be interpreted to be consistent with the meanings in the context of the related art and can not be interpreted as having ideal or overly formal meaning unless explicitly defined in the present application.

FIG. 3 is a block diagram illustrating a configuration of a lightweight white-box encryption apparatus according to an embodiment of the present invention.

Referring to FIG. 3, the lightweight white-box encryption apparatus 300 may include a plain text management unit 310, a white-box cryptographic GFN generation unit 320, and a decryption unit 330.

The lightweight white-box encryption device 300 may correspond to a computing device capable of performing white-box encryption, and in one embodiment may be implemented as a desktop, tablet PC, notebook, or smart phone. In one embodiment, the lightweight white-box encryption device 300 may provide a security function based on a block cipher algorithm for establishing a lightweight environment of the object Internet to securely encrypt and decrypt data in a white-box attack.

The plain text management unit 310 encodes the plain text. More specifically, the plain text management unit 310 can generate the plaintext data as the encryption target, perform the outer encoding on the generated plaintext, and generate the white-box cipher-based ciphertext based on the outer-encoded plaintext . In one embodiment, the length of the plaintext block may be equal to the length of the ciphertext. The plain text management unit 310 can convert the plain text into the externally encoded plain text through the encoding function, and can provide the externally encoded plain text as an input to the white box cryptographically GFN generation unit 320. [ The plain text management unit 310 may perform outer encoding based on an encoding table in which a plurality of encoding types are defined. For example, the plain text management unit 310 can perform external encoding by selectively applying a specific encoding type among a plurality of encoding types included in the encoding table. Accordingly, various encoding methods can be used in the process of performing external encoding Therefore, the safety can be further enhanced.

The plain text management unit 310 may divide an externally encoded plaintext into internal state variables having n (n is a natural number) bits and m (m is a natural number) bits. In one embodiment, the plain text management unit 310 divides the externally encoded plain text into blocks having the same m-bit size to generate n internal state variables X ₁ , X ₂ , ... , X _n (see 410). For example, if the block size of the externally encoded plaintext is 40 bits, it is possible to divide the plaintext to generate five internal state variables each having 8 bits, And provide internal state variables as input to the white-box cryptographically GFN generator 320.

The white-box cipher type GFN generator 320 generates a white-box cipher-type GFN (Generalized Feistel Network) 400 (hereinafter referred to as " GFN ") generated as a lookup table 420 in which a round function is internally encoded with a round key ). This will be described with reference to FIG.

4 is a block diagram illustrating an embodiment of the structure of a white-box cryptographic GFN generated by the lightweight white-box cryptographic apparatus of FIG.

In Figure 4, the white-box cryptography GFN 400 comprises n internal state variables X ₁ , X ₂ , ..., n, which are divided from the plain text and each have m bits. (N-1) lookup tables T ₁ , T ₂ , ..., X _n 410 based on (n-1) round keys per single round as input to the first round 430 , T _{n -1} (420), and updates the internal state variables to be applied as input to the next round, by computing on the internal state variables received as inputs in the current round on a round-by-round basis. Here, round refers to a process that is repeated for encryption and decryption, round function refers to a function necessary for performing encryption and decryption, and a secret key refers to a function for encrypting and decrypting in a repeated round. It can be used as an argument.

The white-box cryptographic GFN generator 320 may generate a plurality of round keys from a secret key. The white-box cryptographic GFN generator 320 may generate round keys as many as the number of round functions F used per single round. In one embodiment, the white-box cryptographic GFN generator 320 may generate a plurality of round keys through block partitioning of the secret key, and in another embodiment, a key schedule ) Operation to generate a plurality of extended round keys. For example, the white-box cryptographic GFN generator 320 may set all of the required round keys as a secret key. If the size of the secret key is 16 bits, the white-key cryptographic GFN generator 320 performs key- can do.

In one embodiment, the white-box cryptographic GFN generator 320 is based on the structure of a generalized fiistel network (see Fig. 1) and includes a look-up table 420 internally encoded with round- Type GFN 400 and may be designed based on, for example, a second or third type of Pistel structure.

The white-box cryptographic GFN generator 320 may calculate an look-up table 420 by performing an ARX (Addition, Rotation, XOR) operation on the round key. More specifically, the white-box cipher-type GFN generator 320 may be configured to include at least one of addition, rotation, and exclusive-OR (XOR) operations that are relatively easy to implement the round function F, , And even if Xi is 8 bits, it is possible to perform a division operation in units of 4 bits.

In one embodiment, the white-box cryptographically GFN generator 320 calculates the lookup table 420 for a single round as (n-1-t) (where n is the number of internal state variables and t is the number of reuse look- ) Can be generated. More specifically, the white-box cryptographic GFN generation unit 320 can generate (n-1-t) round keys for use in a single round considering reuse, and generate (n-1-t) (N-1-t) lookup tables 420 may be generated for each round by using the round keys to reduce the size of the entire used table.

In one embodiment, the white-box cryptographically GFN generator 320 may maintain t at the same value in each round of r (r is a natural number) rounds. For example, if the total number of lookup tables 420 used in a single round is (n-1-t) and the number of lookup tables 420 in each round of r is reused, the total number of lookup tables 420 The number can be calculated as r * (n-1-t), and similarly, the total number N of round keys required can be calculated as r * (n-1-t).

In one embodiment, the white-box cryptographic GFN generator 320 defines the stability index S for the white-box cryptography GFN 400 to determine the total number N of round keys required and the internal state variables 410 (M) can be determined. For example, each of N and m can be calculated as an appropriate value from the stability index S based on the following equation (1).

[Equation 1]

S = N * m

In one embodiment, the white-box cryptographically GFN generator 320 calculates the round-robin number r, the number n of internal state variables, and the number of reuse look-up tables based on the total number N of round keys required (t) can be determined. For example, m, n, t, and r can be set to appropriate values depending on the environment based on the following equation (2).

&Quot; (2) "

N = r * (n-1-t)

For example, assuming that the block size of the plain text is 40 bits and the stability index S is set to 32, the white box cryptographic GFN generator 320 sets the size m of the internal state variable 410 to 8 (Bits), the number n of the internal state variables 410 can be calculated to be 5, and if the number of reuse look-up tables t is 2, the round repetition number r can be calculated to be 2. For example, when the size m of the internal state variable 410 is set to 4 (bits), the white-box cryptographic GFN generator 320 may generate the number n of internal state variables 410 The number of rounds of repetition r can be calculated to be 2 if the number of reuse lookup tables t is 4.

In another embodiment, the white-box cryptographic GFN generator 320 may determine the maximum stability that can be achieved from at least one of the number N of round keys and the number m of bits of the internal state variable 410 The remaining number of round keys N and the number of bits m of the internal state variable 410 may be determined so that the index S is calculated.

In one embodiment, the white-box cryptographic GFN generator 320 defines the size T of the total required lookup table 420 to determine the ratio t _r of the in-round reuse lookup table and the number of round iterations r, For example, r and t can be set to appropriate values according to the environment based on the following equation (3).

&Quot; (3) "

T = r * (n-1) * (1-t _r ) * 2 ^m * m

S = r * (n-1) * (1-t _r ) * m

(Where t _r corresponds to the ratio of the reuse look-up table that can be calculated as t / (n-1) on a round basis, 0 <t _r <1)

For example, the white-box cipher-type GFN generation unit 320 may limit the size T of the lookup table 420 requested to a total of 1 KB or less to the white-box cipher-type GFN 400 (M) of the internal state variable 410 is calculated as 4 according to T / S = 2 ^m = 8192/512 = 2 ⁴ , assuming that the stability index S (T _r ) of the in-round reuse look-up table according to the number n of internal state variables 410 based on the relational expression r * (n-1) * (1-t _r ) (See FIG. 8) between the number of rounds r and the number of times of rounds r can be derived. Thus, the ratio _r t of the lookup table and the number r of rounds can be set.

The white-box cryptographic GFN generator 320 may combine the total required round-down keys to generate a secret key for white-box cryptography. In the above example, the size of the secret key may be set to N * m bits. In one embodiment, the white-box cryptographic GFN generator 320 may determine the stability index S for the security level of the target white-box friendly algorithm as the size of the secret key, It can be set to a value suitable for the usage environment by the designer or the user.

In one embodiment, the white-box cryptographic GFN generator 320 may set the round function F to be a small table if each of the internal state variables 410 is 4 or 8 bits in size.

The decipherer 330 provides an externally encoded plaintext to the white-box cryptography GFN 400 to provide a cipher text. In one embodiment, the decipherment unit 330 provides the input of the externally encoded plain text to the white-box cryptography GFN 400 generated by the white-box cryptographic GFN generation unit 320, And generate a ciphertext by performing a concatenation operation on data finally output from the white-box cipher type GFN 400. [ Here, the concatenation means concatenating at least two inputs bit by bit.

The decryption unit 330 may perform external encoding on the cipher text to perform lightweight white-box encryption. In one embodiment, the decryption unit 330 may perform an outer encoding on the cipher text generated through the white-box cryptography GFN 400 based on an encoding table in which a plurality of encoding types are defined.

FIG. 5 is a view showing an embodiment of a process of generating a white-box cryptographic GFN for reducing the size of a total table by the lightweight white-box encryption apparatus shown in FIG.

5, the lightweight white-box encryption apparatus 100 is a variable for decreasing the total number of lookup tables 420 required in the process of encryption and decryption, as described above. The number of internal state variables 410 (n), the number of reuse lookup tables (t), the number of round keys required per single round (n-1-t), and the number of round iterations (r) The number N of round keys can be set to r * (n-1-t).

The lightweight white-box encryption apparatus 100 can calculate r = 128 (= 256 / (5-1-2)) by setting n = 5 and t = 2 when N = 256. The white-box cipher type GFN 500 as shown in FIG. 5 can be generated based on the respective variables.

More specifically, the lightweight white-box encryption apparatus 100 can reuse the reusable lookup tables T ₁ and T ₂ one time each twice, using the two round keys for use in the first round, It is possible to reuse the reuse lookup tables T ₃ and T ₄ one time each twice using the other two round keys not used in the previous round, and this process can be repeated for 128 rounds. Accordingly, the lightweight white-box encryption apparatus 100 can prepare for a white-box attack through white-box encryption, and can significantly reduce the total number of required tables through the reuse of the look-up table.

FIG. 6 is a diagram illustrating embodiments in which the lightweight white-box encryption device of FIG. 3 performs computer-executable lightweight white-box encryption methods to significantly reduce the size of the aggregate table.

More specifically, Fig. 6 (a) shows an embodiment in which the lightweight white-box encryption apparatus 300 constructs the white-box cryptograph GFN 400 without reusing the lookup table 420, and Fig. 6 (b) FIG. 6 (c) shows one embodiment in which the lookup table 420 is reused to construct the white-box cryptographically GFN 400. FIG.

FIGS. 6A to 6C show how the total number of lookup tables 420 required can be significantly reduced according to the presence or the reuse degree of the reuse lookup table. Here, for the configuration of the white-box cipher type GFN shown in Figs. 6 (a) to 6 (c), the environmental conditions of the block size 40 (= m * n) .

6 (a) shows a case where the lookup table 420 is not reused. The lightweight white box encryption apparatus 300 sets the total size of the table to be 32,768 bits (= 16 * 2 ⁸ ) by setting the size m of the internal state variable 410 to 8 bits and the round repetition number r to 4, * 8). Here, the round key 16 bits can be extended to 128 bits through a secret key and a key-schedule.

6 (b) to 6 (c) show a case in which the lookup table 420 is reused, each of which reduces the memory usage while satisfying the stability index S of the white-box cipher type GFN 400 as 32 . 6 (b), the lightweight white-box encryption apparatus 300 can derive S = r * (n-1) * (1- _tr ) * m = 32 based on Equation The number n of internal state variables 410 can be calculated to be 5 by setting the size m of the internal state variable 410 to 8 bits and the ratio t _r of the reuse look- , And the round number of times of repetition r can be calculated to be 2. In this case, since the lightweight white-box encryption apparatus 300 calculates the total required table size as 8,196 bits (= 4 * 2 ⁸ * 8), the size of the total required table is about 1 / 4 times.

6 (c), the lightweight white-box encryption apparatus 300 can derive S = r * (n-1) * (1- _tr ) * m = 32 based on Equation The number n of internal state variables 410 can be calculated to be 10 by setting the size m of the internal state variable 410 to 4 bits and the ratio t _r of the reuse look- , And the round number of times of repetition r can be calculated to be 2. In this case, the lightweight white-box encryption apparatus 300 calculates the total required table size to 640 bits (= 10 * 2 ⁴ * 4) / 51 times.

In one embodiment, the lightweight white-box cryptographic device 300 may thus adjust the parameters according to the environment to remove memory constraints, and may use the secret key as a round key to enhance security as the secret key size is increased As the safety is enhanced, the number of round iterations (r) can be reduced, and the encryption speed can be greatly improved.

7 is a flowchart illustrating a lightweight white-box encryption method performed by the lightweight white-box encryption device of FIG.

7, the plain text management unit 310 generates a plain text (step S710). The white-box cipher-type GFN generator 320 generates a white-box cipher-type GFN 400 generated as a lookup table 420 internally encoded with a round function as a round function (step S720). The decryption processor 330 provides the ciphertext by providing the externally encoded plaintext to the white-box cryptography GFN 400 (step S730).

In one embodiment, the white-box cryptographic GFN generator 320 reuses the lookup table 420 used for encryption and decryption on a round-by-round basis, thereby significantly reducing the number and size of tables required in the white-box encryption process And can be more suitably implemented in a lightweight environment based on the Internet of Things (IOT), which requires a limited memory and speed environment.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

300: Lightweight white box encryption device
310: plain text management unit 320: white box cryptographic GFN generating unit
330: Deciphered text
400: White-box cryptographic Generalized Feistel Network (GFN)
410: internal state variable 420: lookup table

Claims (11)

(a) outer encoding the plaintext;
(b) generating a white-box cryptosystem GFN (Generalized Feistel Network) generated as a look-up table internally encoding a round function with a round key; And
(c) providing the externally encoded plaintext to the white-box cryptographically GFN to provide a ciphertext.
The method of claim 1, wherein step (a)
And performing said outer encoding based on an encoding table in which a plurality of encoding types are defined.
3. The method of claim 2, wherein step (a)
Dividing the externally encoded plaintext into internal state variables having n (where n is a natural number) m bits (where m is a natural number) bits.
2. The method of claim 1, wherein step (b)
And performing an ARX (Addition, Rotation, XOR) operation on the round key to calculate the lookup table.
2. The method of claim 1, wherein step (b)
(N-1-t) (where n is the number of internal state variables, and t is an integer greater than or equal to 0 as the number of reuse look-up tables) per single round. A viable lightweight white-box encryption method.
6. The method of claim 5, wherein step (b)
further comprising the step of: maintaining said t at the same value in each round of r (r is a natural number).
2. The method of claim 1, wherein step (b)
Determining a total number of round keys (N) required and a number of bits (m) of internal state variables by defining a stability index for the white-box cryptographically GFN, Encryption method.
8. The method of claim 7, wherein step (b)
Determining the number of round iterations (r), the number of internal state variables (n) and the number of reuse look-up tables (t) based on the total number of round keys required (N) Possible lightweight white box encryption method.
9. The method of claim 8, wherein step (b)
And combining the total required round keys to generate a secret key for white box cryptography.
2. The method of claim 1, wherein step (c)
And performing external encoding on the cipher text to perform lightweight white box encryption.
A plain text management unit that encodes the plain text;
A white-box cipher type GFN generation unit for generating a white-box cipher-type generalized Feistel Network (GFN) generated as a look-up table internally encoded with a round function; And
And a ciphertext providing unit for providing the ciphertext by providing the externally encoded plain text to the white-box cipher type GFN.

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