JPH04123625A - Block cipher generator - Google Patents

Abstract

PURPOSE:To enhance the cipher strength by coupling a linear arithmetic part and a non-linear arithmetic part in each cipher element in series. CONSTITUTION:In an LP encipherment cipher element 1 of a first stage, and in the LP ciphering cipher element 1 of a middle stage, a text T and a cipher sentence output C generated by the LP ciphering cipher element 1 of the pre- stage are inputted to a ciphering linear arithmetic part 2, respectively together with an L cipher key KL, and by this ciphering linear arithmetic part 2, an intermediate cipher sentence C' is generated. Subsequently, the intermediate cipher sentence C' generated by the enciphering linear arithmetic part 2 is inputted to a ciphering non-linear arithmetic part 3 together with a P cipher key KP, and by this ciphering non-linear arithmetic part 3, a cipher sentence C is generated, and this cipher sentence C is outputted to the ciphering cipher element 1 of the next stage or a decoding part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a simple block cipher generator used in cryptographic communication systems.

[Conventional technology]

As conventional block ciphers, NBS's DES cipher and NTT's FEEL cipher are famous, and since their algorithms have been made public, numerous studies have been conducted on their strength.

The block cipher is created by using the linear operation type cipher created using the linear feedback shift register shown in Japanese Patent Publication No. 50-22363 and the desired number of single character substitution tables. There is a nonlinear operation type P-cipher.

The L cipher is a block cipher that uses a 2n-stage linear feedback shift register to linearly convert an original text (n bits) into a ciphertext (n bits) using a key (n bits).
For example, a cipher prepares 16 substitution tables whose elements are integers from 0 to 15, divides the original text (64 bits) and key (64 bits) into 16 blocks of 4 bits each, and creates 4-bit tuples of the original text and key. 10 from 0 to 15
It is a block cipher that is expressed in base numbers and non-linearly transforms the original text into ciphertext using a selected substitution table matrix. This P cipher appears to be, but in the above example, the original text (64 bits) is used as the key (
It is a 64-bit block cipher that performs non-linear conversion into ciphertext (64 bits), but in reality,
This is a 4-bit block cipher that non-linearly converts the original text (4 bits) into ciphertext (4 bits) using a key (4 bits).

[Problem to be solved by the invention]

In this way, there are two types of block ciphers: the linear operation type Shicipher and the nonlinear operation type P cipher, but since the encryption operation of the L cipher is linear, if the pair of original text and ciphertext is leaked, There is a problem in that the key and the coefficients are solved algebraically, and since the P cipher is a nonlinear operation type, it basically has higher cryptographic strength than the L cipher. Due to the small block size, a chosen plaintext attack can easily restore the substitution table matrix and key, and if a sufficient number of pairs are leaked to a third party, a known plaintext attack can cause a similar situation. There is a problem.

Therefore, the present invention was devised to solve the above-mentioned problems in the prior art, and it strengthens the linearity weakness of the L cipher with the nonlinearity of the P cipher, and also improves the small block size of the P cipher. The technical challenge is to strengthen this weakness with the large block property of the L cipher, and the purpose is to provide a building block for a block cipher with significantly higher encryption strength.

[Means to solve the problem]

Means of the present invention for solving the above technical problem includes: having a linear calculation part using a linear feedback shift register; having a non-linear calculation part which selects and uses a desired number of single character substitution tables; These are: composing a cryptographic element by combining the nonlinear calculation parts; and combining this cryptographic element in multiple stages.

Note that the linear operation part for creating the L cipher and the nonlinear operation part for creating the P cipher in one cipherme may be combined in any order, but the linear operation part and the nonlinear operation part for each cipherme may The join order of is the same.

[Function and Examples]

Hereinafter, the operation of the present invention will be explained with reference to the drawings showing embodiments of the present invention.

FIG. 1 shows an encrypted cryptographic element 1 (hereinafter, this encrypted cryptographic element will be referred to as an LP encrypted cryptographic element), which is constructed by combining the output of an encrypted linear operation section 2 to be input to an encrypted nonlinear operation section 3. It is a schematic diagram of an encrypted part in which m stages of LP-encrypted cipher element 1-1 to LP-encrypted cipher element 1-m are combined.
In addition, FIG. 2 shows a decryption cipher element 1-1 (hereinafter referred to as this decryption cipher element) configured by combining the output of the decryption nonlinear calculation part 3-' to be input to the decryption linear calculation part 2-'. LP
LP decryption code (decoded in color) is LP decryption code 1-'-1
FIG. 3 is a schematic diagram of a decryption section in which m stages are combined from LP decryption cryptographic element 1-11.

LP encryption cipher 1, a building block
As shown in Figure 3, the encryption algorithm in
In step ■, the original text T is generated in the LP-encrypted cipher element l of the first stage, and the cipher text output C created with the LP-encrypted cipher element 1 of the previous stage is generated in the LP-encrypted cipher element 1 of the intermediate stage. is input to the encrypted linear operation section 2 together with the L encryption key, and the intermediate ciphertext C is generated in the encrypted linear operation section 2.

EC' = L (T, Kt)) is created, and in step ■, the intermediate ciphertext C created in the encrypted linear operation part 2
° is input into the encryption nonlinear calculation part 3 together with the P encryption key, and in this encryption nonlinear calculation part 3, the ciphertext C (C=
P (C'', KP)] is created, and this ciphertext C is output to the encrypted cipherme 1 or decryption part of the next stage.

As shown in FIG. In the LP decryption cipher element t-', the ciphertext C from the encrypted part is transmitted, and in the LP decryption cipher element 1-1 in the middle stage, the LP decryption cipher element 1- in the previous stage is transmitted.
The original text output T created in step 1 is input to the decryption nonlinear calculation section 3-1 together with the P encryption key Kp, and the intermediate ciphertext C'[C''=P-'
(C.

K.
It is input to the decoding linear calculation part 2-1 together with KL, and in this decoding linear calculation part 2-' the original text T ('r=t,
-'(c', KL)], and this original text T is output as the received output as it is in the case of the final stage decrypted cipher element 1-', and in the case of the intermediate decrypted cipher element 1-1. is output to the next stage decrypted cryptographic element 1-.

In addition, in FIG. 3 and FIG. 4, L, PIL-' and P-' indicate the encryption function and decryption function of the L cipher and the P cipher, respectively. Furthermore, if a ciphertext is created using only one cipherme, there is a risk that this ciphertext will be solved algebraically by a known plaintext attack or a chosen plaintext attack.
Like EL cryptography, it is better to increase the encryption strength by combining cryptographic elements in multiple stages, and it is desirable to increase the number of stages as much as the conditions allow.

〔Effect of the invention〕

Since the present invention has the above-described configuration, it has the following effects.

Since the cipher prime was constructed by serially combining Ll14j and the P cipher, the linearity weakness of the L cipher can be reinforced with the nonlinearity of the PII cipher, and on the contrary, the small block size of the P cipher can be strengthened. Weaknesses can be reinforced by the large block size of the L cipher, thereby making it possible to create a cipher with significantly higher strength.

Each cipherme is simply a series combination of a linear operation part that is a known cipher algorithm and a nonlinear operation part that is a P cipher algorithm, and the entire device is also just a series combination of these ciphermes. , it is possible to have an extremely simple configuration.

The strength of the created cipher can be freely changed by changing the number of cipher primes that are combined in series, making it possible to easily obtain the cipher strength that meets the requirements, and also to change the cipher strength as necessary. It can be done easily and effortlessly.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an encrypted part multiplexed into m stages, showing an embodiment of the present invention. FIG. 2 is a schematic diagram of a decryption part corresponding to the encryption part of the present invention shown in FIG. FIG. 3 is a flowchart of encryption of one embodiment of the encrypted cryptogen according to the present invention. FIG. 4 is a decryption flowchart corresponding to the encryption flowchart of one embodiment of the encrypted cryptographic element of the present invention shown in FIG. Description of codes 1; Encryption cryptographic element, 1-1; Decryption cryptographic element, 2; Encryption linear operation part, 2-I; Decryption linear operation part, 3; Encryption nonlinear operation part, 3-1; Decryption nonlinear operation part,・
T: Original text, K, KL, KP: Key, C: Ciphertext, CI, intermediate ciphertext, L: Encryption function of L cipher, L-': Decryption function of L cipher, P: Encryption of P cipher Function, p-'; decryption function of p-cipher. Applicant 2 Co-Electronic Co., Ltd. Fig. 1 Fig. 2 Fig. 1 ---dJ4ctt4$ 1 above - age X'<4
t-a'ff Saimoto 2 -'e'ft't”<la ut etc.
]lL 舒文 2-'---tl'4 Iζku11 temporary expenses lie? Δt 3---"ν injection'); 4mu non-4■5. jar] (eclipse? 6t 3-"---fl Sai 4hi 4μ part brick warehouse thought? minutes y=-!叉K- 41(-wh%
fork

Claims (1)

[Claims] (1) A multi-stage cipherme (1) is constructed by combining a linear calculation part (2) using a linear feedback shift register and a non-linear calculation part (3) that selects and uses a desired number of single character substitution tables. A block cipher generator consisting of a combination of