# Method of block encryption of binary information

(57) Abstract:

The invention relates to the field of telecommunications and computing, and more particularly to the field of cryptographic methods and devices for data encryption. The technical result achieved by the invention is to increase the speed of encryption in the software implementation. 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. New in the present method is that before performing the two-place operations on the i-th sub-block and the data over the connection perform the substitution operation, depending on the j-th sub-blocks, where j i. New is also the fact that, as performed on the data substitution operation, depending on the j-th sub-block, using the substitution operation that depends on the encryption key. 1 C.p. f-crystals, 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 combination of features of the proposed method are used slotmacine of data signals; the encryption key is a replaceable part of the cipher and is used to convert the message or the set of messages; the encryption key must be known only to the legitimate user;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;

- binary vector is a sequence of zero and a unit of bits, for example 101101011; the specific structure of the binary vector can be interpreted as a binary number, if we assume that the position of each bit corresponds to a binary digit, i.e., the binary vector can be mapped to a numerical value that is determined uniquely by the structure of the binary vector;

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 known what I; 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 the cryptogram, when knowledge of the conversion algorithm, but without knowledge of the encryption key.Known methods of block encryption of binary information, 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. Protection mechanisms 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 under the key.However, the known methods analogs are not sufficiently resistant to known differential Cree is adnych data blocks for a given conversion step uses the same connection intact.The closest in technical essence to the present method of encryption of binary data, a method described in the Russian standard for cryptographic protection of data [the Standard of the USSR GOST 28147-89. The information processing system. The cryptographic protection. The cryptographic transformation] . Prototype method includes forming the encryption key in 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 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 () with the OK 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 performing the substitution operation. Just running a 32 similar step changes of sub-blocks, and for all of the converted input data blocks 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) Mick is and the format of the data representation in the computer.The basis of the invention is to develop a method of block encryption of binary data 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 differential cryptanalysis, which increases the speed of encryption in the software implementation.This object is achieved in that in the method block encryption of binary information, including the formation of the encryption key in a set under the keys, partitioning 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 substitution operation, depending on the j-th sub-blocks, where j i.

This solution structure under the keys 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 different mo is toanalyze while reducing the number of operations performed conversion, and enhance the speed of cryptographic transformation.New is also the fact that, as performed on the data substitution operation, depending on the j-th sub-block, using the substitution operation that depends on the encryption key.This solution provides additional increase encryption strength while maintaining a high speed encryption.Below the essence of the invention is explained in more detail by examples, with reference to the accompanying drawing.The invention is illustrated a generalized diagram of the cryptographic transformation of data blocks on the basis of the proposed method, which is shown in the drawing, where S is the block substitution operation that depends on the value of one of the transformed sub-blocks; 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 of the operation of summation modulo 2

^{n}. Operational block S performs a lookup operation on the plug K

_{2R}K

_{2R-1}depending on the control signal on the control bus, shown in broken Inu 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 specific implementation of the block controlled substitutions and the desired speed of the transformations can be set from 8 to 20 or more rounds.Under the substitution operation we mean the replacement operation on the binary values of the signal at the input of the operational block S to the other binary value (determined at the output of the operational block S), which is selected depending on the values at the input of the block S in accordance with some replacement table. Can be implemented two variants lookup:

(1) n-bit binary input vector is replaced by the n-bit output binary vector, with different input binary vectors correspond to different output binary vector;

(2) n-bit binary vector is replaced by the m-bit binary vector, where m n, and various input binary vectors may correspond to how different and the same output binary vectors.The lookup operation of both types can be set depending on a control signal, i.e., given a binary vector at the input can be changed to different the second method uses the value of one of the transformed sub-blocks.Explain the task based substitution operation of the first type of sub-block data to be converted. Let the substitution operation is performed on binary vectors of length n bits, where n is an integer. Then to determine the substitution operation of size nxn (designation nxn means that the input for the substitution operation is a data block of size n bits and the output block is a binary vector of length n bits) is needed to use a table containing two rows of numbers:

< / BR>

where N = 2

^{n}. In this table, in the bottom row contains all possible values of n-bit block exactly once, but in a random order. The sequence of the numbers in the bottom row defines a specific version of the lookup table, and hence the specific variant substitution operation performed using this table. The operation of substitution is as follows. Select the top line number that is equal to the value of the input block. Under this number is in the bottom row is taken as the output unit. Thus, the lookup table can be placed in the operative memory of the computer as a serial write n-bit computingnow binary vector K is used to calculate the address of w

_{0}+ K words, which is taken as the output of the binary vector. This way of representing a lookup table requires the use of memory equal to 2

^{n}n bits. Select the number of lookup tables, is 2

^{L}(required space will be a 2

^{L}Nn bit) and place lookup tables continuously one after another. As the address of table v we take the address value of w

_{0}the first n-bit words. Let the address of the table (v = 0 is a s. In this case, the address lookup table with any number v is equal to s+vN. If you have specified a control binary vector that determines the number of the current lookup tables v and the current input binary vector, the substitution operation is performed by replacing the current input block to the n-bit word located at address s + vN + K where K is the value of the input binary vector, which is the current substitution operation. Using this relation it is easy to select the lookup table with the number v and perform the substitution on the input binary vector with the value of K. In this case, the job according to the lookup tables from a control value of the binary vector and performing a substitution operation is carried out musannah parameters for host lookup tables requires 8 KB of RAM, what is acceptable, since modern computers have RAM on many orders of magnitude greater than this value (from 1 to 64 MB or more).Explain the task based substitution operation of the second type from the sub block converted data in the example lookup h specified using the numbered sequence of 32-bit binary vectors {Q

_{j}}, j= 0, 1, 2, . . . , 256. The sequence {Q

_{j}} it can be assumed known and related to the description of the encryption algorithm. In this case, it can be generated randomly, then it is recorded as part of the description of the encryption algorithm. Another option would specify the sequence {Q

_{j}} is it generating pseudo law depending on the encryption key. In this case, it is a secret, which further increases the cryptographic strength of the encryption. Converting 8-bit input binary vector (e.g., data) K is depending on the control binary vector (e.g., transform sub-blocks) B as follows:

(1) calculate the number of j

_{0}= (B + K) mod 256; (2) 8-bit binary vector K is replaced by a 32-bit binary vector

RAH">Example 1. In this example explains how to encrypt 64-bit blocks of data. The encryption key is generated in the form of plug 16 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-block A= A

_{4}|a

_{3}|a

_{2}|a

_{1}and B= b

_{4}|b

_{3}|b

_{2}|b

_{1}represented as the concatenation of the 8-bit sub-blocks of the a

_{i}and b

_{i}where i = 1, 2, 3, 4. Encryption input block described by the following algorithm:

1. Set the count of the number of rounds r = 1.2. To transform the sub-blocks In accordance with the expression

< / BR>

where denotes the substitution operation on connection K

_{8r}depending on subunit a

_{1}.3. To transform the sub-block A in accordance with the expression

A: = A + B (mod

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

< / BR>

where denotes the substitution operation on connection K

_{8r-7}performed depending on the sub-block b

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

B:=B+A(mod 2

^{32}).6. To transform the sub-block B in accordance with the expression

< / BR>

6. To transform the sub-block A in accordance with the expression

B:=B + A (mod 2

^{32}).9. To transform the sub-block B in accordance with the expression

< / BR>

10. To transform the sub-block A in accordance with the expression

A:=A + B (mod 2

^{32}).11. To transform the sub-block A in accordance with the expression

< / BR>

12. To transform the sub-block B in accordance with the expression

B:=B+A(mod 2

^{32}).13. To transform the sub-block B in accordance with the expression

< / BR>

14. To transform the sub-block A in accordance with the expression

A: = A + B (mod 2

^{32}).15. To transform the sub-block A in accordance with the expression

< / BR>

16. To transform the sub-block B according to the expression

B: = B + A (mod 2

^{32}).17. If r 4, then increment the counter r:=r+1 and go to step 2, otherwise STOP.As a lookup table used to perform a lookup in example 1 is used, the array is numbered 32-bit binary vectors { Q

_{j}}, j= 0, 1, 2,...,2048. To perform a lookup on connection K depending on subunit a

_{i}computes the number of j

_{a}in accordance with the formula j

_{a}=(K+a

_{i})mod 2

^{11}and is replaced by the value of K is Analytically it is written as

Brigetta up procedures, encryption based on the encryption key for a pseudorandom law. This can be done, for example, as follows. Take 1024 64-bit binary vector with numerical values 1, 2,..., 1024. Using the encryption key K

_{1}, K

_{2},...,K

_{32}using the RC5 encryption algorithm [B. Schneier. Applied Cryptography/John Wiley & Sons, Inc., New York, 1996. P. 344-345.] 'll encrypt the specified 64-bit binary vectors. The result will be a set of 64-bit blocks of data with pseudo-random values. Breaking each 64-bit block into two 32-bit sub-block will get a pseudo-random sequence {Q

_{j}}, j= 0, 1, 2,...,2048.In modern computers, the operation of extracting the binary vectors of RAM is available for a small number of machine cycles, thanks to the inventive method provides encryption speed from 10 to 30 Mbit/s (depending on the specific implementation) 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. 1. Method of block encryption of binary information, include the implementation of the operations of substitution and alternate conversion of sub-blocks by performing two-place operations on sub-blocks and connection, characterized in that the substitution operation performed on the data before performing the two-place operations on the i-th sub-block, and the substitution operation is performed in dependence on the j-th sub-blocks, where j i.

2. The method according to p. 1, characterized in that as performed on the data substitution operation using the substitution operation that depends on the encryption key.

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