KR100259836B1 - A n-round round output feedback block cipher/decipher method - Google Patents

Abstract

In the present invention, the concept of time is introduced into the existing structure of Feistel, and the N-round round output statement (ROF-N) used for encryption / decryption of the current block by returning the round output statement of the previous block of the current block to be encrypted / decrypted. Provides a block encryption / decryption method.

The ROF-N block encryption / decryption method of the present invention includes: initializing a n-th plaintext / ciphertext block to be encrypted / decrypted into two subblocks with respect to one plaintext / ciphertext block sequence in which input data is grouped by M bits; Encrypting / decrypting the nth plaintext / ciphertext block by applying g (.) And f (.) Functions to the left and right round output statements of the initialized subblock, respectively; and n-1 in step 2 Generating a ciphertext / decryption sentence by inputting the left and right round output statements generated by the cipher / decryption block to a round of the ciphertext / decryption block of the nth subblock to generate a ciphertext / decryption block; The f (.) And g (.) Functions of the encryption / decryption step are Boolean functions composed of permutations and permutations as round functions, and the f (.) Function is a plaintext / encryption text to be encrypted / decrypted. And a key as input, and the g (.) Function is a function of inputting a left and right round output statement and a key of a block immediately before the current block to be encrypted / decrypted.

Description

N-round round output statement feedback block encryption / decryption method

The present invention relates to a N-round round-output feedback (ROF-N) block encryption / decryption method, which is a new secret key block encryption method. In particular, the concept of time in the existing Feistel structure By introducing a round output statement of the immediately preceding block of the current block to be encrypted / decrypted to use the same for encrypting / decrypting the current block, a higher degree of confidentiality is achieved than the conventional data encryption standard (DES) block encryption method. It relates to an N-round round output statement feedback block encryption / decryption method that can maintain.

In general, there are two broad categories of encryption methods used in remote data transmission and digital computer applications.

One is a stream cipher and the other is a block cipher.

The stream encryption method is an encryption method that operates in real time on a plain text by generating a bit string by a key irrespective of plain text and converting and encrypting the plain text and the generated bit string by an operation such as modulo 2 addition.

On the other hand, the block encryption method is a method of mapping a plain text block space having a predetermined size to a cipher text block space and encrypting the plain text block under the control of a key having substantially the same size as the encrypted plain text block. If the block size is n bits, the plaintext block space (i.e. range of plaintext block values) and ciphertext block space (i.e. range of cipher block values) are 2 ⁿ respectively.

The conventional DES block encryption method, which is one of the block encryption methods, basically operates on 64-bit blocks and uses 56-bit keys. The 56-bit key parameterizes the DES block encryption method of defining permutations in a 64-bit block space. Each bit of the round output for the current block to be encrypted is the result of the function by each bit of the key and each bit of the output statement generated in the previous round of the current round to be encrypted.

In general, in a block encryption / decryption algorithm, an encryption key for encrypting an input plaintext block is the same as a decryption key for decrypting an encrypted plaintext block. Similarly, a block encryption algorithm using an encryption key is an algorithm corresponding to a block decryption algorithm using a decryption key, and the encryption algorithm and the decryption algorithm are forward and backward relations with each other using the encryption key and the decryption key as parameters.

1 is a block flow diagram illustrating an example of a conventional 16-round DES block encryption method. As shown, the 16-round DES block encryption method according to the configuration of FIG. 1 is implemented by the following algorithm.

That is, a step of initializing the plaintext block to be divided into subblocks, performing encryption by applying a constant function and a key to each of the initialized plaintext blocks, and subblocking the blocks output by the encryption performing step. It is composed of the step of generating a cipher text by inputting to the cipher text block.

This will be described in more detail with reference to FIG. 1 as follows.

1) Initialization stage

First, the nth plaintext block to be encrypted is divided into two subblocks. Let P ⁿ = (P ⁿ _L , P ⁿ _R ). After that,

Is done.

2) Steps to Perform Encryption

For each round, do the following:

L ⁿ _i = R ⁿ _i-1 ,

f(Rⁿ _i-1,K_i), i = 1, ... , 15R ⁿ _i = L ⁿ _i-1

f (R ⁿ _i-1 , K _i ), i = 1, ..., 15

And

Is done.

3) Ciphertext Generation Steps

Divide the ciphertext block into two subblocks. Let C ⁿ = (C ⁿ _L , C ⁿ _R ). Then, the ciphertext C ⁿ = (C ⁿ _L , C ⁿ _R )

Becomes

2 is a block flow diagram illustrating a conventional 16-round DES block decoding method. As shown, the 16-round DES block decoding method according to the configuration of FIG. 2 is implemented by the following algorithm.

In other words, the steps of decoding a block to be decoded into sub-blocks are initialized, a step of performing decryption by applying a constant function and a key to each of the initialized blocks, and the blocks output by the decrypting step are subblocks. Inputting a decoded block to generate a decoded sentence.

This will be described in more detail with reference to FIG. 2 as follows.

1) Initialization stage

First, the n-th block to be decoded is divided into two subblocks. Let C ⁿ = (C ⁿ _L , C ⁿ _R ). After that,

Is done.

2) Decryption Step

For each round, do the following:

L ⁿ _i-1 = R ⁿ _i ,

f(Rⁿ _i,K_i), i = 16, ... , 2R ⁿ _i-1 = L ⁿ _i

f (R ⁿ _i , K _i ), i = 16, ..., 2

And

Is done.

3) Decoding door generation step

Divides the decryption block into two subblocks. Let P ⁿ = (P ⁿ _L , P ⁿ _R ).

After that, the decryption statement P ⁿ = (P ⁿ _L , P ⁿ _R )

Becomes

In Equations 1 to 6, n denotes the sequence number of the plaintext / ciphertext block sequence to be encrypted / decrypted, i denotes the round sequence number among the 16 rounds, and f (.) Function inputs the plaintext / ciphertext and key as input. Round function.

The conventional DES block encryption / decryption method is a block encryption / decryption algorithm based on a Feistel involution, and the present study on the DES block encryption / decryption method is based on illegal access attempts of non-authorized users. The focus is on the design of f (.), A safe round function, and increased stability by increasing block length and increasing key length.

However, in the conventional DES block encryption / decryption method, an increase in the block length or key length causes an increase in the number of operations and key management of the block encryption / decryption algorithm for implementing the DES block encryption / decryption method. In addition, the secure design of the safe round function f (.) Poses a problem that must objectively demonstrate the stability of the designed f (.) Function.

Accordingly, the present invention is to overcome the above-mentioned disadvantages, and by changing the existing Feistel structure, the block encryption / decryption algorithm is based on the conventional round function f (.) Without increasing the block length or key length. The purpose is to provide a ROF-N block encryption / decryption method with improved confidentiality.

1 is a block flow diagram showing an example of a conventional DES block encryption method.

2 is a block flow diagram showing an example of a conventional DES block decoding method.

3 is a block flow diagram illustrating a N-round round output statement feedback block encryption method of the present invention.

4 is a block flow diagram illustrating a N-round round output feedback feedback block decoding method of the present invention.

ROF-N block encryption / decryption method of the present invention comprises the steps of: initializing the n-th plaintext / ciphertext block to be encrypted / decrypted into two sub-blocks for one plaintext / ciphertext block string grouping the input data by 64 bits; Encrypting / decrypting the nth plain / ciphertext block by applying g (.) And f (.) Functions to the left and right round output statements of the initialized subblock, respectively; A ciphertext / decryption text is generated by inputting the left and right round output statements generated by the encryption / decryption of the plaintext / ciphertext block into the ciphertext / decryption text block of the n-1 th subblock.

The f (.) And g (.) Functions of the encryption / decryption performing step are round functions, which are Boolean functions composed of permutations and permutations, and the f (.) Function is an input of a plaintext / cipher text and a key to be encrypted / decrypted. Generate a ciphertext, and the g (.) Function is a function of inputting a left and right round output statement and a key of a block immediately before the current block to be encrypted / decrypted.

The newly designed ROF-N encryption / decryption method requires 64 * N bits of memory and more computation than the conventional DES method. On the other hand, with the same plaintext length and secret key length as the conventional method, it can maintain a higher degree of secrecy.

Now, the ROF-N block encryption method and decryption method of the present invention will be described in more detail with reference to FIGS. 3 and 4.

3 is a block flow diagram illustrating a ROF-N block encryption method of the present invention. As shown in FIG. 3, the algorithm for implementing ROF-N block encryption according to the configuration of FIG. 3 performs encryption on one plaintext block having 64-bits of input data as follows.

1) Initialization stage

First, the nth plaintext block to be encrypted is divided into two subblocks.

Let P ⁿ = (P ⁿ _L , P ⁿ _R ). After that

Is done.

2) Steps to Perform Encryption

For each round, do the following:

g(L^n-1 _i,R^n-1 _i,K_i)L ⁿ _i = R ⁿ _i-1

g (L ^n-1 _i , R ^n-1 _i , K _i )

f(Rⁿ _i-1,K_i), i = 1, ... , N-1R ⁿ _i = L ⁿ _i-1

f (R ⁿ _i-1 , K _i ), i = 1, ..., N-1

And

Is done.

3) Ciphertext Generation Steps

Divide the ciphertext block into two subblocks. Let C ⁿ = (C ⁿ _L , C ⁿ _R ). Then, the ciphertext C ⁿ = (C ⁿ _L , C ⁿ _R )

Becomes

4 is a block flow diagram illustrating a ROF-N block decoding method of the present invention. As shown in FIG. 4, the block decryption algorithm for implementing ROF-N block decryption according to the configuration of FIG. 4 performs decryption on one ciphertext block in which input data is 64-bit-bound as follows.

1) Initialization stage

First, the nth ciphertext block to be decrypted is divided into two subblocks.

Let C ⁿ = (C ⁿ _L , C ⁿ _R ). After that

Is done.

2) Decryption Step

For each round, do the following:

g(L^n-1 _i-1,R^n-1 _i-1,K_i)L ⁿ _i-1 = R ⁿ _i

g (L ^n-1 _i-1 , R ^n-1 _i-1 , K _i )

f(Rⁿ _i,K_i), i = N , ... , 2R ⁿ _i-1 = L ⁿ _i

f (R ⁿ _i , K _i ), i = N, ..., 2

And

Is done.

3) Decoding door generation step

Divides the decryption block into two subblocks. Let this be P ⁿ = (P ⁿ _L , P ⁿ _R ).

Thereafter, the decryption statement P ⁿ = (P ⁿ _L , P ⁿ _R )

Becomes

In Equations 7 to 12, n denotes the sequence number of the plaintext / ciphertext block to be encrypted / decrypted, and i represents the round sequence number of the nth plaintext / ciphertext block to be encrypted / decrypted among N rounds.

Here, the f (.) And g (.) Functions are Boolean functions composed of permutations and permutations as round functions. The f (.) Function is a function for generating a password by inputting a plain text and a key, and the g (.) Function is a function for inputting a round output statement and a key of a block immediately before the current block to be encrypted. That is, the g (.) Function serves as a stream encryption method for the current block to be encrypted, and the round output statement and the key of the immediately preceding block of the current block to be encrypted are keys of the g (.) Function.

Although not shown in FIGS. 3 and 4, each round output statement is placed as follows for the initial stage of n = 0, that is, the ROF-N encryption / decryption algorithm of the present invention.

Where IK _i is the initial value generated from the key and is independent of the sub key {K _i ).

Features of the ROF-N block encryption / decryption method of the present invention implemented as described above are as follows.

A) The increase in key length can be improved from the existing 64 bits to 128 bits. In the conventional DES block encryption method, when the key length is 128 bits, the algorithm stability is not practically guaranteed against illegal access attempts. However, in the ROF-N block encryption / decryption method of the present invention, even when the key length is 128 bits, the illegal access is illegal. The security of the algorithm that implements the ROF-N block encryption / decryption method for the challenge is practically guaranteed.

B) Since the increase in key length is achieved without substantial increase in key length, the complexity of key management can be maintained at the level of the conventional DES block encryption method.

C) The distribution method according to the key length performs key scheduling using the round output statement of the block immediately preceding the current block to be encrypted / decrypted.

R) The conventional DES block encryption method applies a key only to the generation of the right round output statement (R ⁿ _i ), whereas the ROF-N block encryption / decryption method of the present invention also generates a left round output statement (L ⁿ _i ). Apply the key. Therefore, randomization of each round output statement can be achieved, which increases the confidentiality of encryption / decryption.

ㅁ) The ROF-N block encryption / decryption method of the present invention is safe for differential encryption (DC) and linear cryptanalysis (LC) methods that are block encryption attack methods. The g (.) Function acts as a stream encryption / decryption method in the ROF-N block encryption / decryption method, and this stream encryption / decryption method is safe even when attacked by the differential decryption and linear decryption method.

Iii) The increase in memory size according to the ROF-N block encryption / decryption implementation of the present invention is a negligible size when implemented by an actual program or hardware.

G) The error size due to mistransmission of a ciphertext according to the ROF-N block encryption implementation of the present invention is negligible.

The ROF-N block encryption method of the present invention as described above can replace the conventional DES block encryption method.

With the same plaintext length and secret key length as the conventional DES block ciphering method, it is possible to implement encryption with improved confidentiality compared to the conventional DES block ciphering method, thereby increasing the key size. .

ROF-N block encryption method of the present invention can be easily applied to the field of authentication.

That is, in the conventional DES block encryption method, authentication has been performed using a message authentication code (MAC) to which a hash function is applied in ciphertext feedback chaninig (CBC) mode, but the ROF-N block of the present invention is used. The encryption method can easily authenticate the transmission data using a message authentication code made by applying a hash function directly without a separate operation mode.

The ROF-N block encryption method of the present invention is a block encryption method that can be extended to a block encryption method other than the conventional DES block encryption method.

In addition, according to the present invention, an independent subkey can be made using round thrust and a key, the subkey can be introduced into an existing Feistel structure, and the present invention can be used in a security device. It is also applicable to authentication devices.

Claims (6)

Dividing the plaintext to be encrypted into blocks of 2N bits, and dividing each 2N bit block into left (L) and right (R) blocks of N bits, respectively; In the (i) th round (i = 1 ~ n-1), the output value performing the first round function (f) by receiving the right block of the n th 2N bit block and the i th round key (Ki) and the n ORing the left block of the second 2N bit block to set the right block of the n-th 2N bit block of the next round; In the (i) th round (i = 1 to n-1), the second round function (g) is performed by receiving the right block and left block and the i th round key (Ki) of the n-1 th 2N bit block. Performing an OR operation on one output value and the right block of the nth 2N bit block to set the left block of the nth 2N bit block of the next round; Repeating the setting of the right and left blocks until n-1 round immediately before the last; Input the right block of the n-th 2N bit block and n-th round key (Kn) obtained as a result of n-1 rounds, and perform the first round function (f) and the left block of the n-th 2N bit block. Performing an OR operation to finally set the left block of the n-th 2N bit block; Obtained as a result of the n-1th round and the left block of the n-1th 2N bit block and the nth round key Kn, the output value of performing the second round function g and the result of the n-1th round and ORing the right block of the n-th 2N bit block and finally setting the block to the right block of the n-th 2N bit block. The method of claim 1, wherein the first round function receives a plain text and a round key to generate a cipher text, and the second round function receives a round output statement and a round key of a previous block to generate a cipher text. Round-output feedback block encryption method, characterized in that it is a Boolean function consisting of and permutation. 3. The left (L) and right (R) blocks of the N bits used in the first round, when the IK i is an initial value generated from the round key. L _i ^-1 = IK2 (i + 1) Round-output feedback block encryption method, characterized in that R _i ^-1 = IK2 (i + 1) +1 (i = 0,1,2, ....., N-1) . Dividing the cipher text to be decrypted into 2N bit blocks, and dividing each 2N bit block into N (left) and (R) blocks of N bits, respectively; In the (i) th round (i = 1 ~ n-1), the output value performing the first round function (f) by receiving the right block of the n th 2N bit block and the i th round key (Ki) and the n ORing the left block of the second 2N bit block to set the right block of the n-th 2N bit block of the next round; In the (i) th round (i = 1 to n-1), the second round function (g) is performed by receiving the right block and left block and the i th round key (Ki) of the n-1 th 2N bit block. Performing an OR operation on one output value and the right block of the nth 2N bit block to set the left block of the nth 2N bit block of the next round; Repeating the setting of the right and left blocks until n-1 round immediately before the last; Input the right block of the n-th 2N bit block and n-th round key (Kn) obtained as a result of n-1 rounds, and perform the first round function (f) and the left block of the n-th 2N bit block. Performing an OR operation to finally set the left block of the n-th 2N bit block; Obtained as a result of the n-1th round and the left block of the n-1th 2N bit block and the nth round key Kn, the output value of performing the second round function g and the result of the n-1th round and ORing the right block of the n-th 2N bit block and finally setting the right block of the n-th 2N bit block. The method of claim 4, wherein the first round function receives a cipher text and a round key to generate a decrypted sentence, and the second round function receives a round output statement and a round key of a previous block to generate a decrypted sentence. And a Boolean function consisting of permutations and permutations. 6. The left (L) and right (R) blocks of the N bits used in the first round, wherein the IKi is an initial value generated from the round key. L _i ^-1 = IK2 (i + 1) Round-output feedback block decoding method, characterized in that R _i ^-1 = IK2 (i + 1) +1 (i = 0,1,2, ....., N-1) .

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