Design and Implementation of a Document Encryption Convergence

Program Selecting Encryption Methods, and Integrating the Program

into the Existing Office System

Hong-Jin Ryu

and Samuel Sangkon Lee

Dept. of Computer Engineering, Jeonbuk National University, Jeonju, Chonbuk, South Korea

Dept. of Computer Science and Engineering, Jeonju University, Jeonju, Chonbuk, South Korea

Keywords: Ancient Cryptography, Modern Cryptography, Shift Encryption, Poly-Alphabetic Substitution, Transposition

Cipher, Nihilist Encryption, DES and AES Encryption, MVVM.

Abstract: The article explores the limitations of current encryption methods and proposes a new encryption system that

combines ancient and modern cryptography through software engineering. The article also discusses the

history of cryptography, from simple substitution encryption methods to more complex mathematical

algorithms. The proposed encryption system fuses several ancient ciphers with AES-256 encryption, creating

a more secure and stronger password that is difficult to decrypt. This paper suggests the usefulness and

reliability of cryptographic algorithms, such as virtual currency and blockchain fields, and could be used

easily by the general public in electronic devices.

1 INTRODUCTION

Cryptography has played an important role in safely

storing and transmitting information. Today, many

researchers are trying to enhance existing encryption

algorithms more sophisticated and powerful. These

encryption techniques also contributed to the creation

of modern cryptosystems. Special institutions have

used encryption for storage for information protection

or transmission of information between institutions.

However, with the spread of Internet technology,

encryption technology has begun to be required for

information transmission between individuals.

However, programs that allow individuals to easily

generate their own ciphertext through encryption

algorithms have not been common until now.

Encryption is a security device that makes it

unreadable by anyone other than the person

concerned. It is a kind of information hiding using a

computer algorithm. This aims to prevent

unauthorized third parties from obtaining or viewing

one's information. However, the public usually does

not know how to securely encrypt their data or which

encryption methods are safe to use. Therefore, it is not

https://orcid.org/0000-0003-2042-8330

https://orcid.org/0000-0001-9965-8387

easy to encrypt documents for personal purposes.

Most applications are at the level of preventing others

from easily opening them by putting a password on

them. For this reason, even intermediate level users

often store important documents without encryption.

Information protection mainly consists of three types:

preventing anyone from entering, preventing the

information inside from leaving, and making the

information useless even if it flows out. This paper

intends to strengthen information protection through

the third case.

In this research, we deal with the direction that a

third party can never decrypt when a user's data is

transmitted. We are planning to design and

implement a new encryption system that combines

ancient and modern cryptography through software

engineering. It aims to make such an encryption

program easy to use.

Advances in encryption technology mean that

passwords may be cracked by third parties. Therefore,

if the vulnerability of the currently used password is

found, a better encryption method has to be

developed. Through such efforts, encryption

technology has been continuously developed from

452

Ryu, H. and Lee, S.

Design and Implementation of a Document Encryption Convergence Program Selecting Encryption Methods, and Integrating the Program into the Existing Ofﬁce System.

DOI: 10.5220/0012124000003541

In Proceedings of the 12th International Conference on Data Science, Technology and Applications (DATA 2023), pages 452-459

ISBN: 978-989-758-664-4; ISSN: 2184-285X

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

ancient times to modern times. At first, it started with

a substitution encryption method that simply replaces

letters with other letters. Over time, a method of

changing the order and position of letters at the same

time and a transposition cipher that moved them to a

different position were developed. Using the

incredible power of modern computers, ancient

passwords were easy to crack. Therefore, in order to

deal with this, cryptography using mathematical

methods was created. As computer performance

increases, not only encryption methods become more

difficult, but also decryption technologies. The

developed encryption technology has evolved and is

highly dependent on the development of computer

performance. As the computer processes calculations

that humans can do at a very high speed, the

encryption technology using it is great, but as the

performance of the computer improves, the current

encryption technology cannot help but become weak.

This can be seen as a limitation of the generation of

cryptographic algorithms that depend on computer

performance. The more difficult the algorithm used

for encryption, the higher the computer performance

required. To decipher it, a computer with a higher

specification is required.

Although most current encryption methods tend

to depend on mathematical encryption algorithms,

most of the algorithms are publicly available. The fact

that the encryption method is open means that anyone

can create an algorithm to decrypt it if they want. Of

course, even if it is a public algorithm, stability is

proven to the extent that it cannot be easily

deciphered. That's why the algorithms are still being

used. However, even proven algorithms may not be

stable anymore after the invention of future

computers. One of the ways to solve this problem is

to increase the length of the encryption key. However,

even if an encryption algorithm with a key length of

128 bits is used, decryption may be possible if

calculation is performed using a quantum computer.

Of course, quantum computers are not yet widespread

among ordinary users. However, it may be obvious

that as computer performance develops, there is some

risk that existing passwords can be cracked (Paar, and

Pelzl, 2010).

Moreover, the current issue is in the case of an

authentication method using biometric recognition

among encryption technologies. There is a weakness

that spoof authentication can succeed if a sufficient

number of attackers unite and attempt biometric

authentication (Richard, 2001). Therefore, in the case

of encryption using biometric authentication, it is

usually appropriate to mix other encryption methods.

In other words, so as to compensate for the weakness

of the currently used encryption algorithm, several

types of encryption methods must be mixed and used.

This idea is the main concept of this paper.

In this research, the existing algorithm is utilized,

but we will not rely solely on the existing algorithm.

We will focus on technologies that make it less likely

to be decrypted in the future. To create this, we need

to mix the classical and modern encryption methods

of human heritage. The best way to verify the

performance of an algorithm is to release it and test it.

Users can choose any of these proven algorithms to

mix ancient and modern cryptography. Thus, it can be

stored with multiple encryptions. Of course, to

decrypt, the user must know the encryption method

that combines up to 10 selected encryption methods

in reverse order. The values of each key must also be

known. There is an advantage in that a user performs

multiple encryptions in an encryption method

dependent on existing algorithm. Therefore, the

encryption strength is greatly increased compared to

the existing methods. Each encryption method is

described in the next section.

2 THEORETICAL

BACKGROUND

2.1 Ancient Ciphers

In the shift encryption method belonging to ancient

cryptography, cipher text is generated by shifting 26

letters of the English alphabet to the right or left as

much as the shift value (number) that becomes the

key. It seems relatively simple. 26 letters of the

English alphabet are shifted by 2 to the right. To use

this method, keys must be applied sequentially

throughout the input statement to complete. In this

paper, the shift encryption method, and it was

expanded to include 11,172 complete Korean

characters, special characters (44), and a total of 96

characters (44+26+26) of English uppercase and

lowercase letters (26+26). Related books published

on the market use only English letters to explain the

implementation principle (Paar, and Pelzl, 2010). In

contrast, in this paper, the public can take a look at

the encryption and decryption process, including

Korean. Special characters, uppercase/lowercase

English characters, and complete Korean characters

were converted into numeric values of ASCII code

and Unicode. After that, spaces between numeric

values were removed, and shift encryption was

applied. After that, the substitution operation was

performed as much as the value corresponding to the

Design and Implementation of a Document Encryption Convergence Program Selecting Encryption Methods, and Integrating the Program

into the Existing Ofﬁce System

453

blank between the numeric values removed before

encryption. It was implemented so that only the

characters within the range that can be input are

output normally. When entering a positive integer as

a key value, it is shifted to the right. When inputting

a negative integer, it is designed to be shifted to the

left.

According to scholars, the polyalphabetic

substitution method is called a ‘multi-character

cipher.’ A typical example is the Vigenere cipher.

This encryption method also belongs to the classical

encryption method like the previous studies described

above. In general, 26 English alphabets are filled in

horizontally and vertically (26×26) size blocks so that

one letter per column and row is moved. Then, the

document is encrypted by configuring the key used

for encryption and the input text to be encrypted in

horizontal and vertical coordinates, respectively (Lee,

Yeom, Song, and Kim, 2005).

The encryption of the polyalphabetic cipher

method is generally made by adding 11,172 complete

Korean characters and 96 (=44+52) characters such

as special characters and English

uppercase/lowercase characters, like the shift cipher

above, based on the 26 characters of the English

alphabet. Each character in the input statement is

converted to Unicode value, and code values not used

within the program are excluded and arranged in

continuous sequence of numbers. The same operation

was applied to the key values as well. The value is

added to the calculated input statement, and it is

restored as a character. This restored character

becomes the ciphertext. In summary, in this paper, the

principle of the existing poly-alphabetic cipher text

produced only with English letters is used as it is.

However, additionally, an algorithm for generating a

password was implemented by extending it to

Korean, English, and special characters. In this way,

when encrypting the text in a document written by the

people, a program was developed that can encrypt all

characters normally.

Polyalphabetic cipher is a standard transposition

cipher belonging to the classical cipher, and can be

classified as a block cipher using blocks (Seo, 2017).

It is created by substituting the input text to be

encrypted into a block with as many columns as the

input key value, which must be numbers, in row units

and then outputting it in column units.

In the program designed in this paper, standard

transposition cipher is implemented and is operated in

the same way as mentioned above. The standard

transposition cipher, like other ciphers, is designed so

that it can be applied without error to documents

containing not only English but also complete Korean

and special characters. A key transposition cipher is

similar to a standard transposition cipher in that it

uses a block cipher. However, compared to the

existing standard transposition encryption where the

input key value was limited to numbers, the program

designed in this paper is different in that it allows text

key values as well. It provides improved encryption

by further increasing the interpretation strength. Key-

type transposition encryption has the advantage that

numbers, letters, or special characters can also be

used as key values. The encryption method creates a

block with as many columns as the length of the input

key value (characters) and substitutes the input text

like a standard transposition cipher. After that, the

key value (character) is replaced with the same

number as the alphabetical order, and the ciphertext

is completed by outputting the column with the

smallest number.

In the key transposition (key type transposition)

cipher, a block with as many columns as the length of

the key value is created, and then the input text to be

encrypted is substituted. After that, the key values are

output in column units in alphabetical order to

complete the ciphertext.

Among classical ciphers, the Nihilist cipher is a

type of transposition cipher and is a block cipher. It

uses an encryption method similar to a key-type

transposition cipher. The difference is that the

ciphertext is completed by applying the key value by

column unit and then applying the key value by row

unit (according to alphabetical order) and outputting

it. Therefore, ciphertext with higher strength than

standard transposition cipher or key-type

transposition cipher is generated. So far, the

implementation principles of five ancient ciphers

(Shift, PS; Polyalphabetic Substitution, STC;

Standard Transposition Cipher, KTC; Key

Transposition Cipher, and Nihilist) have been

described. The next section describes the design of

modern cryptography.

2.2 Modern Cryptography

In 1975, the National Bureau of Standards of the

United States established a kind of block (Seo, 2017)

encryption called DES (Data Encryption Standard) as

a standard for data encryption. It is a national standard

set by the US NBS (National Bureau of Standards,

now NIST). This technology is a symmetric-key

encryption method using a 56-bit key. We have been

using it for a while without any problems. However,

if the length of the key is too short and a backdoor is

included, it can be decrypted in a special way, which

raises several problems. Therefore, it was not long

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before DES was found to be weak and was replaced

by the modern AES (Advanced Encryption Standard)

encryption method.

AES-256 is the original name of the Rijndael

cipher. This is a type of modern cryptography. As

mentioned above, AES-256, the national standard

encryption method of the United States, was designed

to secure the vulnerability of DES, which was used as

the existing national standard encryption method. It is

known to be the strongest among currently used

encryption methods (Nakov, 2018). AES is a 128-bit

block encryption method newly developed to solve

the problems of DES encryption technology. AES

technology also uses a symmetric key method by

using the same key in the existing encryption and

decryption processes. It differs from DES in that

blocks of 128 bits can be processed with key lengths

of 128, 196, or 256 bits.

Wi-Fi, which is the short-distance wireless

communication technology that we use the most, also

uses AES as one of the encryption methods. In the

case of Bluetooth, the SAFER+ encryption

technology was used up to the 3.0 standard, and the

AES standard is used from Bluetooth 4.0. In this

paper, DES and AES, which are modern encryption

methods, are implemented. For more effective and

accurate encryption program development and

convenient implementation, System.Security.Crypto-

graphy of the C# library was used. This library helps

to perform several tasks such as encoding/decoding

hashes, generating random numbers, and

authenticating messages. It also provides a way to

easily implement encryption methods including data.

In paper, AES-256 was applied and a key value of 256

bits.

3 ENCRYPTION DESIGN

The system uses a mix of classical and modern

ciphers to encrypt documents and store the ciphertext.

Conversely, it was designed with the goal of

decrypting the stored cipher text and restoring it to the

original document. The following Figure 1 shows the

overall system structure diagram. The function

requirements are as follows. The function of loading

a document enables a text file to be loaded and

displayed on the screen. After that, when selecting an

encryption method, up to 10 encryption methods used

are allowed to be duplicated, so that mixed encryption

methods can be selected. This method is a

convergence encryption method that allows a total of

seven types of ancient and modern passwords to be

duplicated up to 10 times. This paper is differentiated

from other papers in that it can combine various types

of encryptions in various forms.

When entering a key value to be used for

encryption, it is necessary to be able to input each key

value to be used according to the type of encryption.

Here, the type of encryption algorithm or key length

is an important factor in determining the security

level of the system. In particular, KISA (Korea

Internet & Security Agency) recommends that the

length of the private key must be 160 bits or more. It

is also recommended that the expiration date be up to

two years. The proposed method of this paper

contains seven encryption methods (Shift, PS

(Polyalphabetic Substitution), STC (Standard

Transposition Cipher), KTC (Key Transposition

Cipher), Nihilist, DES, and AES-256). In addition,

the above seven can be applied in combination, and

the order can be changed. Depending on the order in

which these applications are applied, the resistance to

decryption of ciphertext varies greatly. Functions

such as ciphertext output (encrypted text is displayed

on the screen), ciphertext storage (ciphertext can be

saved as a text file), and encrypted document

decryption (the original text is restored by decrypting

the ciphertext) are all included.

From the standpoint of software engineering, the

quality requirements of this program are as follows.

Input and output (retrieving and saving input text and

cipher text should work normally, and there should be

no data loss). It is designed to make decryption

impossible if the original text is modified even

Figure 1: Overall Control.

Design and Implementation of a Document Encryption Convergence Program Selecting Encryption Methods, and Integrating the Program

into the Existing Ofﬁce System

455

slightly. Figure 1 explained the flow chart of the

entire encryption/ decryption process of this program.

Next, the use case actor specification and outline

specification are expounded. As shown in Table 1,

this program has one actor, ‘user.’

Table 1: Specification of Use-case “Actor”.

From the user's point of view, use-cases are used

to easily explain the scope and function of the system,

which is called 'usage pattern' in Korean. A use case

is literally a “purpose that is used” to prevent chaos in

which two things are used at the same time. A use

case is a multi-purpose system created by gathering

the uses of the system. In this way, if use cases are

collected and connected to the system, users can

easily understand the development process. The use

cases of this program include 'document open',

'password selection/adding', 'key registration',

'document encryption', and 'document saving (Save)’

and 'Document Decryption (Decryption)' are added.

Sequence diagrams were created using Web

Sequence Diagrams

. Here, the sequence diagram

describes the sequence of message exchange between

objects of interaction. Presents a Unified Modelling

Language (UML) diagram. In particular, UML is

used for a model that conceptually and physically

expresses a system with vocabulary and rules for

creating software. It helps to solve problems of

system structure, communication within the project

team, and reuse of software structure. The design

details used in the program of this paper are shown.

The design details used in the program of this paper

are shown. As exhibited in Figure 2, it was designed

as a sequence diagram.

https://www.websequencediagrams.com/

Figure 2: Sequence Diagram.

4 IMPLEMENTATIONS

4.1 User Interface

The screen design was composed of a user-friendly

design. The menu is placed at the top, and the toolbar

below it is used to quickly access the menu. In the

window showing the result of the program, a window

for outputting the input text and a window for

outputting the converted ciphertext appear in pairs.

4.2 Structural Design

4.2.1 Architecture Model

An important design pattern in program development

was developed using the MVVM (Model-View-

ViewModel) model as shown in Figure 3 below. This

model is different from the existing MVC (Model-

View-Controller) or MVP (Model-View-Presenter)

patterns. As a software architecture pattern, the

development of a graphical user interface (view)

implemented in a markup language or GUI code is

separated from business logic or back-end

logic(model). This ensures that views are not tied to

any particular model platform. It is efficient for UI

accessibility or interpretation of program source code.

In the picture, INPUT means user's input or event.

The solid line means information exchange in a

general form, while the dotted line means that

information exchange is possible, but it is not

recommended for reasons of dependency between

models and security. In addition, since * means many

and 1 means one, MVC on the left means a many-to-

one relationship. MVP stands for one-to-one

Actor Description

User

 The user is the main agent who uses the

program.

 The user can use the program to open and

save text.

 The user can use the program to select or

add document encryption methods.

 The user can use the program to encrypt

documents.

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relationship. Finally, MVVM stands for one-to-many

relationship.

Figure 3: Design Patterns.

Figure 4: Example of MVVM.

In the existing MVC pattern, the controller

directly accesses the view and model and controls

them. Therefore, the model was able to access the

view indirectly. In the MVP pattern, the view and

model are accessed through the Presenter. However,

the MVVM pattern adopted in this program is

designed with three structures: View, Model, and

ViewModel, as shown in Figure 4. Design is designed

in the view, data is processed in the model, and data

is bound using model information in the view model.

The view is so controlled. When designing the view

on the left side of the figure, the UI (User Interface)

composed of XAML and the code composed of an

easy-to-develop language are designed on the code

behind to configure the User Interface Logic. The

notification in the middle of the picture operates the

view according to the instruction of the view model.

When this operation is performed, information is

exchanged in data binding between the view and the

view model. At the same time, commands are

executed. The view model corresponding to the

presentation logic controls the overall parts displayed

in the view. The model corresponding to Business

Logic and Data on the right side of the figure plays a

role in managing information storage, modification,

and deletion.

Figure 5: System Architecture.

Thus, the MVVM pattern is more modern than the

previous two design patterns. Efficiency can also be

achieved with a clear separation between the domain

logic and the presentation layer (separating the model

from the view obtained from the user's point of view).

MVVM provides clean separation of code and is

therefore maintainable. Separation of core logic parts

into external and internal dependencies, in other

words, it is easy to test unit module programs for core

logic. Reusing code, replacing code, or adding code

to the right place in the architecture is appropriate.

Abstraction can also be achieved with code-behind.

As described above, our program designed more

efficient program by using the MVVM model.

Figure 5 above shows the structure of this system.

First, we created the Main Window to be used as the

view. The source code was written using WPF's

XAML. I created a Main Window View Model for

the main window, which will be the view model. By

binding data with the main window, when data

changes occur in the main window view model, it is

implemented so that it can be immediately reflected

in the view. In addition, it is implemented so that each

function works well so that user commands are

transmitted between the view and the view model by

using a command. In the main window view model, a

text file corresponding to the model can be loaded or

saved. The Cipher on the right side of Figure 5 can be

accessed.

4.2.2 String Operations

This program uses regular expressions and string

internal operations to process strings using XAML

link in Section 4.2.1. In the case of the transposition

cipher, the input statement does not require any intra-

string operations. However, key values require

internal operation. In particular, the substitution is

Design and Implementation of a Document Encryption Convergence Program Selecting Encryption Methods, and Integrating the Program

into the Existing Ofﬁce System

457

required by internal string operation for both input

text and key values.

In the shift encryption method and the standard

transposition cipher (STC) method, the input text can

be in any form. However, since only numbers are

allowed as key values, the input key value must be

converted to an integer (int) type for calculation. In

addition, the key value of the shift cipher must receive

a plus (+)/minus (-) value indicating two directions

(right or left). After the input text is converted into an

ASCII code or a Unicode value, internal operations

are performed. This internal operation is implemented

when the cipher text is output after the encryption

process is finished or, conversely, numbers are

replaced with characters and output. Moreover, the

same process applies to the encryption process as well

as the decryption process.

4.2.3 Implementation and Function

Figure 6: Encryption of Text Files.

This section explains the menu composition in detail

and at the same time helps users understand each

encryption. When you press the combo box, a menu

composed of seven items such as Shift, PS, STC,

KTC, Nihilist, DES, and AES-256 appears. Prior to

selecting a password, the Open/Save toolbar menu is

empty. This program shows an example of choosing

four passwords. This is the screen where the currently

opened document is encrypted in the order of Shift,

PS, STC, and KTC. If you select a specific encryption

method from the combo box and select the Select

button, a button with the encryption written on it is

added. Up to 10 combinations of methods can be

selected. In the future, it will be upgraded to enable

changes (add/modify/delete) of the selection method.

The selected encryption is calculated in the same

reverse order in the encryption or decryption process.

If you click the Reselect button, all currently selected

and added encryption methods are cleared. Also, the

toolbar that outputs the password selected so far is

initialized at the same time. The shift encryption

method and the STC encryption method allow only

numbers to be entered as key values. The encryption

key is delivered to the other party through a secret

path and is used once more during decryption. The

user will have to properly resolve this error. The third

toolbar contains functions used for encryption and

decryption.

Figure 7: Description of Encrypted Text.

When encryption is complete, this progress bar

disappears. The [Input ← Output] button functions to

move the encrypted/decrypted text from the output

window to the input window. As the text moves to the

input window, the text in the output window is erased.

Decryption (Description) is performed in the reverse

order of the encryption method. In this program, if

you enter the same key value as the order of the

encryption method entered during encryption,

decryption proceeds in the reverse order of

encryption. All functions used in this program output

logs as shown so that the user can check the functions

he or she has used. More detailed logs can be output

for the encryption process. However, for information

security of the process, only the start and end logs are

shown to the user. When the program is started for the

first time, a log saying ‘Starting the program’ is

output. Each time you use a function of the program,

log messages such as ‘Loading a file’, ‘Loading

completed’, ‘Shift password added’, ‘STC password

added’ are added. Users can also check the encryption

method of their choice. Log messages are

continuously displayed in every process.

If you press the encryption button after registering

all key values, you can encrypt the input text as shown

in Figure 6. When all encryption is complete, you can

see the encrypted text in the output window. It is also

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possible to save the text displayed in the output

window and keep it safe in the form of an encrypted

file. When all input values are set normally,

decryption starts as shown in Figure 7 by clicking the

decryption button.

5 CONCLUSIONS

The encryption method presented in this paper is not

encryption by a single algorithm. Several types of

techniques that have already been verified are

converged. It is considered that it will be safely used

in fields that rely heavily on cryptographic algorithms

used in virtual currency and blockchain fields. In the

future, encryption-decryption will be more threatened

by easily accessible cloud computing than by

quantum computers. Later, through the combination

of various passwords, functions such as data

confidentiality and integrity, authentication and non-

repudiation (Nam, Kim, and Park, 2015), as well as

stability and robustness of cryptography (Kim, Kim,

and Kim, 2002; Song, Ko, and Chung, 2000; Abu-

Faraj, and Alqadi, 2020), resistance (Song, Kang, and

Sung, 2014; Jang, 2013; Kim, Jang, and Chang,

2014), and efficiency We will continue to study how

(Lee, You, and Yim, 2015; Lee, You, and Yim, K.

2016; Kwon, Kim, and Hong, 2014) is improved. In

addition, it would be a differentiated significance of

this thesis that encryption of documents was easily

realized not only in institutions and companies, but

also in electronic devices for the general public (Jeon,

Shin, Jung, Lee, and Yoo, 2015), which are already

becoming common.

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