Encryption Methods and Algorithms Based on Domestic Standards in

Open-Source Operating Systems

MADJIT MALIKOVICH KARIMOV1, NIZOMIDDIN NAJMIDDIN UGLI OCHILOV1,

ABDIQAHHAR EGAMOVICH TANGIROV2

1State Testing Center under the Cabinet of Ministers Republic of Uzbekistan,

12 Bagishamol St., Yunusabda paradise,100084, Tashkent,

REPUBLIC OF UZBEKISTAN

2Department of "Mathematics and Informatics", Tashkent Institute of Textile and Light Industry,

5 Shokhjakhon St., Yakkasaray paradise, Tashkent,

REPUBLIC OF UZBEKISTAN

Abstract: - The paper describes the principles and methods underlying the creation of an application in secure

operating systems, which provides reliable data encryption. The research aims to analyze and indicate the

specifics of encryption methods and algorithms based on domestic standards in open-source operating systems.

Cryptanalysis was used in the article, as this avoids vulnerabilities identified in previously created

implementations. In the article, the authors draw attention to the fact that 7-Zip uses CBC

encryption (concatenation of encrypted text blocks), but the Counter Mode is supported. The same support was

provided in the encrypt implementation. Since the key expansion function initially fills the special array created

by p7zip with round keys using a unique property of the domestic standard, only one round encryption function

was created (performed both during encryption and decryption). This method is also used in various modes. In

many cases, initialization time deviations depending on the selected mode are insignificant. The created

cryptographic module was tested to meet the domestic standard, which contains several test cases. It was

confirmed during the tests that the created module implements the algorithm of the domestic standard. The

article shows a way to implement a fairly convenient graphical interface for accessing the cryptographic

module, which enables the user not to call the command line and remember the sequence and types of

parameters passed to p7zip. This implementation also takes into account the verification of the correctness of

decryption and the reading of other error codes.

Key-Words: - lossless compression, cryptanalysis, concatenation of ciphertext blocks, initialization vector.

Received: April 22, 2022. Revised: December 13, 2022. Accepted: January 22, 2023. Published: February 20, 2023.

1 Introduction

The open-source operating system ensures the

protection of processed and stored data through

Security Policies, kernel settings, and additional

software. One of the requirements is to support

encryption in accordance with the law. It was

required to create an application that performs

encryption following the domestic standard, the

only encryption algorithm allowed for use when

working with information containing state

secrets, [1], [2].

However, the lack of open-source software available

in the public domain that performed the assigned

tasks, while having sufficient performance, with

open source, necessitated the development of a

cryptographic module.

2 Analysis of Research on Encryption

Methods and Algorithms in Open-

Source Operating Systems

The main problem in creating a cryptographic

application is to provide all verification procedures

— splitting the data stream into blocks, padding to

the desired length, and creating a pseudo-random

sequence initializing vector (IV). As a result, it was

decided to use ready-made software, in which these

procedures were successfully implemented, [3], [4],

[5], [6], [7].

For block ciphers, the use of IV is described by

modes of operation. Randomization is also required

for other primitives such as generic hash functions

and derived message authentication codes. An

initialization vector (IV) is introduced in CBC,

CFB, and OFB encryption. Moreover, both the

sender and the receiver must have the same IV at the

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Madjit Malikovich Karimov,

Nizomiddin Najmiddin Ugli Ochilov,

Abdiqahhar Egamovich Tangirov

E-ISSN: 2224-3402

Volume 20, 2023

beginning of the communication session. The IV

does not have to be secret at all and can be

transmitted along with the first ciphertext block.

What’s important is that this value should be

unpredictable in CBC and CFB modes and unique in

OFB mode. Unpredictability in CBC and CFB

modes can be achieved in several ways. For

example, the value of a counter (say a message

counter) can be converted using the same function.

GPC can also be used to generate a pseudo-random

sequence of the desired length.

As encryption in everyday work is more often

applied to text information, especially to documents

in DOC, and DOCX format, the presence of

standard expected sections in them creates a danger

in the reliability of the password used for

encryption. To eliminate this effect, it is

recommended to pre-compress the information, thus

reducing data redundancy. For this reason, the

archiver was chosen as the main application, [8],

[9].

The encryption algorithm in WinZip versions earlier

than 9 is not strong enough with the current

computing power, but it also has a 64-bit key size.

In this case, it is necessary to correct not only the

encryption module, but also key extensions, check it

for statistical properties, and so on. Moreover, the

encryption block is one byte, [10], [11].

The most popular archiver WinRAR is proprietary,

which means that it does not have open source,

thereby automatically excluding this software from

consideration.

7-Zip is a free, highly compressed file archiver. It

supports multiple compression algorithms and

multiple data formats, including the proprietary 7z

format with the highly efficient LZMA (Lossless

Compression Algorithm) compression

algorithm, [8]. The encryption algorithm used is

AES with a block size of 128 bits, and a key size of

256 bits. As a result, the p7zip version, developed

for the Linux OS family, was chosen (Table 1).

Table 1. Comparative table of archiver programs

7zip

ACE

WinZip

RAR

WinRAR

Squeeze

UHARC

Compressing

directories

Creation of self-

extracting

(SFX) archives

Changing the

contents of the

Archive

recovery

Breaking the

archive into

parts

Сonsole version

Graphic version

(GUI)

Asymmetry

RAM

requirements,

Available

3 Overview of Encryption Methods

and Algorithms in Open-Source

Operating Systems

Modifications and cryptanalysis. As the domestic

standard has the same key size as AES-256, it was

decided not to change the procedure for creating a

key from the password sequence. For this purpose,

p7zip repeatedly uses the SHA-2 algorithm, which

is used because of rather good statistics, [6], as a

pseudo-random sequence generator.

However, the procedure for expanding the key itself

is strikingly different for AES and the domestic

standard, so the entire module located in the AES.c

file was changed to the encrytp.c module. 7-Zip

itself performs text splitting into blocks of 128 bits

and padding to the desired length according to the

rules, [12], [13]. The encrytp.c implementation

resizes the block by 64 bits. As 128 is a multiple of

64, this transformation is done by simply changing

the constants, as well as doubling the number of

blocks.

7-Zip uses CBC mode encryption (ciphertext block

concatenation mode), but the Counter mode is

supported. The same support was provided in the

encrytp.c implementation. As the key expansion

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Abdiqahhar Egamovich Tangirov

E-ISSN: 2224-3402

Volume 20, 2023

function initially fills a special array created by

p7zip with round keys, using a unique property of

the domestic standard, only one round encryption

function was created (performed both during

encryption and decryption).

This method is also applied in various modes. In

many cases, the deviations in the initialization time

depending on the selected mode are negligible. The

initialization time increases in CBC and CFB

modes (ciphertext feedback mode) (see Figure 1).

Cryptographic strength is provided for this method

in cases of choosing encryption in the SHS mode,

[14], [15], [16].

Fig. 1: Results of measuring the algorithm

initialization time

4 Overview of the Results of the

Analysis of Encryption Methods and

Algorithms In Open-Source Operating

Systems

The first block of the message is IV — the

initialization vector (see Figure 2). When

encrypting, the first block is added to the second

block (bitwise by the module of 2). The resulting

block is encrypted and the result is stored as an

output second block (the first output block is still

IV). The output second block is added by the

module of 2 to the third block, the resulting third

block is encrypted and stored as the output third

block, etc. In the implemented module, the received

output blocks are stored in the same memory, in

which the input blocks with the same sequence

number were stored, [17], [18].

Fig. 2: Encryption process

When decrypting, the sequence is different:

The second block is decrypted (see Figure 3). The

result is added to the first block (IV) bitwise by the

module of 2, the resulting value is stored as the

second output block. In this case, the encrypted

value of the second block is stored in a temporary

variable. Then the third block is added to a

temporary variable bitwise by the module of 2,

decrypted, and saved as the third output block, and

the original encrypted value of the third block is

stored in a temporary variable, and so forth, [19].

Fig. 3: Decryption process

The only security issue may be changing the length

of the initialization vector from 128 bits to 64 bits.

To confirm the validity of this transition, the

following theorem was proved:

Theorem. If α_(m+n) – a random variable of length

m+n bits — is uniformly distributed, then α_m – a

random variable of length m bits, obtained from

α_(m+n) by discarding the last n bits, is also

uniformly distributed, [20], [21].

Proof. Suppose the opposite, α_m is unevenly

distributed. Take all possible sequences of length n

bits and denote them by β_n. Denote by η – a

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random variable obtained from a random variable

α_m by adding to it at the end of all possible β_n.

Since β_n is not a random variable, η will have the

same distribution as α_m. The resulting random

variable η will take values, among which the values

of the random variable α_(m+n). Then it is possible

to associate each value of α_(m+n) with the same

number of values of η, obtained by discarding the

random sequence and adding the same number of

deterministic different values. Therefore, we get a

contradiction, as α_(m+n) is uniformly distributed.

Therefore, the theorem is proved.

So, the generated random vector p7zip after

sprinkling 64 bits from the end has the same

uniform distribution function. That is, the durability

corresponds to that of AES. As the IV (initialization

vector) is not secret, the problem of reducing the

enumeration does not affect the robustness of the

algorithm.

Cryptanalysis by side channels was also taken into

account during the development. So, if the message

about the rejection of the correct password depends

on the stage at which it was found, the bits of the

correct encryption key can be found. In this

implementation, the refusal message is generated

only after the complete decryption of the message

using the entered password. The incorrect key is

identified by checking the last message block, which

is formed according to the established rules, [22],

[23]. If it does not correspond to those required for

the message of this structure (the number of blocks,

the number of added bits at the end of the message),

an error occurs.

5 Testing Encryption Methods and

Algorithms in Open-Source Operating

Systems

5.1 Adaptation for an Open-Source

Operating System

In operating systems of the Linux family, the super

user has unlimited rights. But the system

administrator may not have a sufficient level of

access to some information that is processed on

computers under his/her control. The developed

cryptographic module is used for this purpose, [24],

[25].

The developed module uses the get and set methods

that convert a 4-byte sequence into a 32-bit

unsigned number and a 32-bit unsigned number into

a 4-byte sequence, respectively. These methods are

also implemented in the developed module, they are

not considered external functions. The sequence of

writing bytes in a 32-bit number fully complies with

GOST 28147-89. 8-bit shifts are used to insert byte

data into an unsigned 32-bit integer.

It is mandatory to use cryptanalysis methods when

developing such modules, as this prevents the

detection of vulnerabilities in previously created

applications. Because of world practice, it is also

necessary to create uniform requirements for

checking such an implementation of symmetric

block data encryption algorithms and other

cryptographic algorithms.

5.1.1 Test no. 1

Description: Files are encrypted using the State

Standard 28147-89 algorithm based on the 7zip

archiver, in which the Aes.c. file is modified, [9].

Description: The file encryption function is

checked.

Preconditions:

1. The user is authorized in the system.

2. There is a non-empty text file in the user’s home

folder (for example, readme.txt).

Actions:

1. The user creates an archive with a password, into

which he places the file (in this case readme.txt, you

can specify a whole list of files together):

7za a –p arj.7z readme.txt

After pressing Enter, the archiver prompts you to

enter a password. After entering it and pressing

Enter, the archiver asks to repeat the password.

After entering the password again and pressing

Enter, the archiver creates the specified archive.

2. The user copies the archive to another folder (say

archtest): cp arj.7z archtest /

3. The user enters the specified folder:

cd archtest /

Postconditions:

1. The archtest folder contains the arj.7z archive, in

which the encrypted state is a file (readme.txt).

5.1.2 Test no. 2

Decrypting files

Description:

Checking the file decryption with the same

password as when entering. Demonstrates that the

file is restored after unzipping, [19].

Preconditions:

1. Complete Test # 1 completed

2. The user is in the archtest folder

Actions:

1. Enter in the console:

7za x arj. 7z

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At the invitation of the archiver to enter the

password, enter the correct password (the one that

was used for encryption).

Postcondition:

1. The archtest folder contains the source file

(readme.txt).

An attempt to access without a known password

Description:

The test verifies the validity of encryption

protection by the example of an attempt to enter a

different keyword.

Precondition:

1. Test # 1 completed

2. If Test # 2 was performed, delete the unzipped

file (readme.txt) from the archtest folder:rm

readme.txt

Actions:

1. Enter the command:

2. 7za x arj.7z

At the invitation of the archiver, enter a different

password (different from the one used for

encryption)

Postcondition:

1. The archiver gives an unzipping error.

2. The folder contains an empty file (readme.txt).

This item is optional.

As operations are performed on the entire volume of

input data in several cycles, this algorithm has a

linear complexity of O(n).

5.2 Checking the Compliance of the

Encryption Function with GOST 28147-89

Description: Checking whether the implemented

encryption function matches the test case given in

State Standard R 34.11-94 for the encryption

function specified by GOST 28147-89, [9]. Contains

two examples.

tests/p7zip_gost/c/test.cpp

test.cpp content

#include "Types.h"

#include "GOST.h"

#include <stdio.h>

int main()

{Byte key[32] = {0x33, 0x20, 0x6d, 0x54, 0x32,

0x6c, 0x65, 0x68, 0x20, 0x65, 0x73, 0x69, 0x62,

0x6e, 0x73, 0x73, 0x79, 0x67, 0x61, 0x20, 0x74,

0x74, 0x67, 0x69, 0x65, 0x68, 0x65, 0x73, 0x73,

0x3d, 0x2c, 0x20};

Byte key2[32] = {0xa4, 0x24, 0x87, 0x34, 0x67,

0x76, 0xa6, 0xc1, 0x59, 0xde, 0x3d, 0x15, 0x50,

0x42, 0x88, 0x33, 0x65, 0x8c, 0x24, 0xe3, 0x8c,

0x3b, 0x41, 0x7d, 0x9a, 0xa0, 0x9c, 0x1c, 0xcf,

0x68, 0xd9, 0x56};

Byte in[64] = {0}, out[64], iv[32] = {0};

size_t n = 1;

int i;

UInt32 px[1000];

GOST_SetKey_Enc(px+4, key, 32);

printf("TEST1: input text = %8x %8x\n", get(in+4),

get(in));

GOSTCbc_Init(px, iv);

GOSTCbc_Encode(px, in, 1);

printf("Encryption: %x %x\n", get(in+4), get(in));

GOST_SetKey_Enc(px+4, key2, 32);

set(in+4, 0x561c7de3);

set(in, 0x3315c034);

printf("TEST2: input text = %8x %8x\n", get(in+4),

get(in));

GOSTCbc_Init(px, iv);

GOSTCbc_Encode(px, in, 1);

printf("Encryption: %x %x\n", get(in+4), get(in));

return 0;}

Precondition:

1. The tester is authorized as a user testmen.

2. The user is in his home directory. The pwd

command will issue: / home / testmen.

Actions:

Compile: make test-gost

Run: ./bin/test-gost

Result:

TEST1: input text = 0 0

Encryption: 42abbcce 32bc0b1b

TEST2: input text = 561c7de3 3315c034

Encryption: 3cd1602d dd783e86

TEST 3: input text = 2998 1748

Encryption: 59 f3 4a fd 2f 56 fc 03 ad cb 99 5d 64

d3 f2 77

TEST 4: input text =1111 1111

Encryption: ed 98 ec 4c 05 74 ef 0b 6b 23 ed a5 39

b7 2a 3b

TEST 5: input text =5 3

Encryption: 27 4a 47 31 42 95 90 38 2e 3f 18 0f a6

29 68 cf

TEST 6: input text =a2d1 b45d

Encryption: dd 19 87 e2 34 a1 9d 56 21 d0 e6 d0

c9 a3 06 4a

TEST 7: input text =10101010 10101010

Encryption: 68 ad 46 f8 e0 20 3c cc 68 ad 46 f8 e0

20 3c cc

TEST 8: input text =842a3 8f89c

Encryption: 22 4a f5 2e 86 12 f6 59 53 41 3b d4

d1 0f 12 23

TEST 9: input text =9583 fdeac

Encryption: 84 9a e1 e6 aa 96 12 dc 23 9c aa ad a6

91 95 a1

TEST 10: input text =1234 56789

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E-ISSN: 2224-3402

Volume 20, 2023

Encryption: bf d8 ff de b4 19 56 09 34 24 d6 d9 b7

a3 bd eb

The traditional data protection method has the

advantages of long average secrecy time and low

encryption efficiency, [26]. Because of this, many

researchers choose more modern encryption

algorithms. For example, the LRNG algorithm was

chosen for analysis in [27]. The researchers

determined that it is quite complex and includes a

large state from three different storage pools, a

complex mechanism for adding entropy from

system events, and an extraction algorithm based on

a shift register and several SHA-1 operations. This,

in turn, complicates the implementation but does not

prevent attacks on the direct security of LRNG. We

chose DST 28147-89 encryption algorithm for

research. It is a well-known 256-bit block cipher

that is a likely alternative to AES-256 and triple

DES, which, however, has a much lower

implementation cost, [28]. Moreover, it is currently

the only algorithm allowed to work with state

secrets, [2]. To use it, the 7zip archiver was

modified (with the AES encryption algorithm).

Changes have been made to allow the State

Standard algorithm to be implemented while

keeping the external parameters the same as in AES.

The created archiver successfully encrypts and

decrypts files. Simple encryption (no archiving) was

rejected due to the redundancy of symbolic

information. This redundancy significantly weakens

the properties of the algorithm. So, the first blocks

in a txt document are the same for documents

created on this computer by this user. Pre-archiving

(compression) can significantly reduce the

redundancy of files, and increase the statistical

spread of byte values, which enhances the strength

of the resulting cryptosystem. The user should be

able to conveniently initiate encryption (see Figure

4) and decryption (see Figure 5) of his/her files. For

this purpose, scripts have been created that draw a

graphical interface (after all, p7zip is a console

application).

Fig. 4. File Encryption GUI

Fig. 5: File decryption graphical interface

6 Conclusion

The created cryptographic module was tested to

meet the domestic standard, which contains several

test cases. It was confirmed during the tests that the

created module implements the algorithm of the

domestic standard.

The use of cryptanalysis in the development of such

modules is mandatory, as this avoids vulnerabilities

that were identified in previously created

implementations. It is also necessary to create

uniform requirements for checking such

implementations of both symmetric block data

encryption algorithms and other cryptographic

algorithms, taking into account world practice.

A fairly convenient graphical interface for accessing

the cryptographic module was implemented, which

enabled the user not to call the command line and

remember the sequence and types of parameters

passed to p7zip. This implementation also takes into

account the verification of the correctness of

decryption and the reading of other error codes.

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Abdiqahhar Egamovich Tangirov

E-ISSN: 2224-3402

Volume 20, 2023

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Abdiqahhar Egamovich Tangirov

E-ISSN: 2224-3402

Volume 20, 2023

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Madjit Malikovich Karimov,

Nizomiddin Najmiddin Ugli Ochilov,

Abdiqahhar Egamovich Tangirov

E-ISSN: 2224-3402

Volume 20, 2023

Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The authors equally contributed in the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflicts of interest to declare

that are relevant to the content of this article.

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(Attribution 4.0 International, CC BY 4.0)

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Creative Commons Attribution License 4.0

https://creativecommons.org/licenses/by/4.0/deed.en

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