# Method of block encryption of discrete information

(57) Abstract:

The invention relates to telecommunications and computing, and more particularly to cryptographic methods and devices for data encryption. The technical result achieved by the invention is to increase the speed of encryption. The method includes forming the encryption key as a set of plug, dividing the data block into N 2 sub-blocks and sequential conversion of sub-blocks by performing two-place operations on sub-blocks and connection. Differs from known methods that perform a double operation on the i-th sub-block and the data over the connection perform the operation of cyclic shift that depends on the j-th sub-blocks, where j i. 1 Il. The invention relates to the field of telecommunications and computing, and more particularly to the field of cryptographic methods and devices for encoding messages (or information). In the set of features proposed method uses the following terms:- the secret key is a combination of bits known only to the legitimate user;

- the encryption key is a combination of bits used in the encryption information soobshenia or a given set of messages; the encryption key is generated by the deterministic procedures for secret key; in some ciphers as the encryption key is a secret key;

the cipher is a set of elementary steps of converting input data using sherloch; cipher can be implemented as a software or as a separate electronic devices;

connection represents the portion of the encryption key used on the individual elementary steps encryption;

encryption is a process that implements some way of transforming the data using sherloch that translates data in the cryptogram represents a pseudo-random sequence of characters from which to obtain information without knowledge of the encryption key is impracticable;

- desifrovanie is the reverse process of the encryption process; decryption provides data recovery for the cryptogram with knowledge of the encryption key;

- cryptographic strength is a measure of the reliability of information protection and represents the complexity measured in the number of elementary operations that must be performed to recover information on reblockage data encryption, see, for example, U.S. standard DES [U. Diffie, M. E. Hellman. Security and infotouriste: Introduction to cryptography // TIER. 1979. So 67. N. 3. C. 87-89], the method of encryption for U.S. patent N 5222139 dated June 22, 1993, the cipher FEAL-1 and the cryptalgorithm B-Crypt [s Mattick. The mechanism of protection in computer networks. - M., Mir, 1993. S. 49-52]. In the known methods the encryption of data blocks is performed by generating the encryption key in the form of a set of plug, splits converted block data sub-blocks and alternating changes using operations substitution, permutation and arithmetic operations performed on the current sub-block and the current connection.However, the known methods analogs do not have sufficient resistance to differential cryptanalysis [Berson, T. A. Differential Cryptanalysis Mod 2

^{32}with application to MD5// EUROCRYPT'92. Hungary, May 24-28, 1992. Proceedings. P. 67-68], because for all the input blocks of data for a given conversion step uses the same connection intact.The closest in technical essence to the claimed method block encryption is the method that is described in the Russian standard for cryptographic protection of data [the Standard of the USSR GOST 28147-89. The information processing system. Protection cryptographically as a sequence of 8 plug with a length of 32 bits, splitting the input 64-bit data block into two 32-bit sub-blocks B

_{1}and B

_{2}the successive transformation of the sub-blocks. One step conversion of sub-blocks, for example of the subblock B

_{2}is the overlay of the current connection Q

_{i}, which is fixed for a given step, using the operation of addition modulo 2

^{32}(+) in accordance with the formula B

_{2}:= B

_{2}+ Q

_{i}where := - sign assignment operation, 1 i 8, and then on the resulting new value of the subblock B

_{2}perform the substitution operation, then the operation of cyclic shift to the left by eleven bits, i.e., at eleven binary bits toward the high-order bits, and then the obtained value of B

_{2}impose subsection B

_{1}using the bitwise sum modulo two) in accordance with the formula B

_{2}:= B

_{2}B

_{1}. The substitution operation is performed as follows. The sub-block is divided into 8 binary vectors of length 4 bits. Each binary vector is replaced by a binary vector of lookup tables. Selected from a lookup table 8 4-bit vectors are combined into a 32-bit binary vector, which is the output state of the sub-block after executing op input blocks of data at a fixed conversion step of sub-blocks use the same connection with the same value.However, the prototype method has drawbacks, namely in the software implementation it does not provide encryption speed of more than 1 Mbit/s [Andreev N. N. Some of the research directions in the field of information security // proceedings of the international conference "information Security". Moscow, 14-18 April 1997. M. 1997. S. 96], which does not allow to use it to encrypt data protection in real time. This disadvantage stems from the fact that in order to ensure resistance to differential cryptanalysis in the method-prototype uses a large number of lookup operations on 4-bit subblock transformed data block to perform each of which (in the software implementation), the microprocessor performs many basic commands, due to the mismatch of substitutions of this type with the format of the data representation in the computer.The basis of the invention is to develop a method of encryption in which the conversion of the input data would be carried out in such a manner that a decrease in the number of elementary operations conversion per one bit of the input data, while ensuring a high resistance to difference This object is achieved in that a method of block encryption of discrete information, including the formation of the encryption key as a set of plug, dividing the data block into N 2 sub-blocks and sequential conversion of sub-blocks by performing two-place operations on sub-blocks and connection, new according to the invention is that before performing the two-place operations on the i-th sub-block and the data over the connection perform the operation of cyclic shift that depends on the j-sub-blocks, where j i.Thanks to this solution the structure of the plug used at a given step of the encryption depends on the data to be converted and thus this step of conversion for different input blocks are used in various modified values of the plug, providing high resistance to differential cryptanalysis and simultaneous decrease in the number of operations transformation, and enhance the speed of cryptographic transformation.Below the essence of the invention is explained in more detail by examples, with reference to the accompanying drawings.The invention is illustrated by the generic scheme cryptographicexception is - the unit is controlled cyclic shift operation; A and B are converted n-bit sub-blocks; K

_{2r}, K

_{2r-1}elements of the encryption key (plug); the sign indicates the operation bitwise sum modulo two, the sign + is the operation of summation modulo 2

^{n}. Bold solid lines indicate the bus transfer n-bit signals, and the thick dashed line bus transfer n control signals, which are the bits of the transformed sub-blocks.The drawing shows one (the r-th round of the encryption. Depending on the desired speed of the transformations can be set from 8 to 30 or more rounds.Consider a specific example of implementation of the proposed method cryptographic transformation of binary data blocks.Example.In this example explains how to encrypt 64-bit blocks of data. The encryption key is generated in the form of 16 plug K

_{1}, K

_{2}, K

_{3}, ..., K

_{32}, each of which has a length of 32 bits. The input data block is broken into two 32-bit sub-blocks A and B. the Encryption input block described by the following algorithm:

1. Set the count of the number of rounds r = 1.2. To transform the sub-block B in accordance with virginjapanese over the subkey K

_{2r}.3. To transform the sub-block A in accordance with the expression

A := A + B,

where + is the operation of summing modulo 2

^{32}.4. To transform the sub-block A in accordance with the expression

A:= A(K

_{2r-1}< B),

where K

_{2r-1}<<< B denotes the operation of cyclic shift to the left by B bits to be performed on the connection K

_{2r-1}.5. To transform the sub-block B in accordance with the expression

B := B + A.If r 16, then increment the counter r := r + 1 and go to step 2, otherwise STOP.Modern microprocessors quickly carry out a cyclic shift operation depending on the value of a variable stored in one of registers. Thanks to the described algorithm provides encryption speed of about 30 Mbit/s for mass microprocessor Pentium/200.These examples show that the proposed method block encryption of discrete information technical feasibility and allows to solve the problem.The inventive method can be implemented, for example, in the form of computer programs that provide high-speed data encryption. Method of block encryption of discrete information, including the formation of the education sub-blocks by performing two-place operations on sub-blocks and connection, wherein before performing the two-place operations on the i-th sub-block and the data over the connection perform the operation of cyclic shift that depends on the j-th sub-blocks, where j i.

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