Modiﬁcation of Advance Encryption Standard(AES) and

Rivest–Shamir–Adleman(RSA) Algorithms for Data Authentication on

Study Results Card

Karina Andriani

, Roslina

and B. Herawan Hayadi

Computer Science, Main Potential University, Medan, Indonesia

Department of Computer Engineering, Politeknik Negeri Medan, Medan, Indonesia

Keywords:

AES and RSA Algorithms, Data Authentication.

Abstract:

Authentication is a process carried out to validate the authenticity of data and the owner of the data. The

method used to form an authentication system is cryptography. One of the cryptographic algorithms that

are often used is the Advance Encryption Standard (AES) because it has been tested for its resistance to all

kinds of attacks on data. Not only is it able to encrypt or encode data, but the AES algorithm is also able

to decrypt or restore encrypted data so that the data can be read or understood again. Besides that, the RSA

algorithm is a cryptographic algorithm that is often used for authentication. The RSA algorithm has a private

key concept where the encryption and decryption keys are different so that it is stronger to serve as a data

security algorithm. Therefore, modiﬁcations to the AES and RSA algorithms were made to produce a better

authentication system. In this study, modiﬁcations were made to the AES and RSA algorithms for data security

authentication on the study results card.

1 INTRODUCTION

In the digital era, it is convenient to falsify data and

the identity of the data owner. Counterfeiting is car-

ried out for various interests that beneﬁt the perpetra-

tor. Therefore, security is the solution to the threat of

data forgery and the identity of the data owner by us-

ing modern security techniques such as cryptography.

One of the data security techniques in the form of data

authenticity validity is a digital signature. Digital Sig-

nature can be applied in verifying the authenticity of

data and authenticating the authenticity of the owner

of the data. Digital Signature is a cryptographic value

that depends on the message and the sender. The

way a Digital Signature works is almost the same as

how a regular document ”signature” works (Amik and

Cipta, 2021).

There are two algorithms in the Digital Signature

system, namely the signing algorithm to sign a doc-

ument M and generate a signature (sign) ρ, and the

verify algorithm that returns true if the signature ρ

belongs to the signer and for document M (Waruwu

et al., 2020).

RSA is a cryptographic algorithm that is often

used for making Digital Signatures because this al-

gorithm produces two keys that are mathematically

connected. Where the public key is used for the en-

cryption process while the private key is used for

the decryption process(Ahmed, 2022).RSA is a pop-

ular public-key cryptographic algorithm. This algo-

rithm was found by three researchers from MIT (Mas-

sachusetts Institute of Technology) in 1976: Rivest,

Shamir, and Adleman. The RSA algorithm uses a

public key and a private key, where the public key

can be known by many people to encrypt messages,

while the private key can only be known by certain

parties to decrypt messages. The security of this algo-

rithm lies in the difﬁculty of factoring large integers

into prime factors. This factoring decrease to obtain

the private key. RSA’s operating mechanism is conve-

nient to understand and simple, but powerful (Parid-

dudin and Syawaludin, 2021).

AES Method The Advanced Encryption Standard

(AES) method is an encryption method that uses a

symmetric key with a key length of 128, 192, and 256

bits to encrypt and decrypt data in 128-bit blocks. The

AES method that uses a block cipher system can per-

form symmetric key encryption operations with oper-

ating modes. In addition, AES has advantages in se-

curity, speed, and characteristics of the algorithm and

Andriani, K., Roslina, . and Hayadi, B.

Modiﬁcation of Advance Encryption Standard (AES) and Rivest–Shamir–Adleman (RSA) Algorithms for Data Authentication on Study Results Card.

DOI: 10.5220/0012447000003848

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 3rd International Conference on Advanced Information Scientiﬁc Development (ICAISD 2023), pages 211-217

ISBN: 978-989-758-678-1

211

its implementation (Allan, 2020).

With the collaboration of the Hybrid Cryptosys-

tem, the RSA-AES algorithm can increase the effec-

tiveness and capabilities of the algorithm in secur-

ing data, especially in producing Digital Signatures

which function to maintain the authenticity of Study

Result Card data.

2 METHOD

2.1 Stage of Research

At this stage of the study, which starts from the anal-

ysis of problem how to modiﬁed AES and RSA to se-

cure the data of study result card, then conducted lit-

erature studies to modify the two algorithms, namely

as follows:

Figure 1: Stages of research.

From these results, it can be seen what the con-

clusions of the combination of these 2 algorithms are

in authenticating the authenticity of the data on the

study results card and the security of ownership of the

data. From the results of this combination, this algo-

rithm modiﬁcation can be used in other data security

to obtain a better level of security.

2.2 AES (Advanced Encryption

Standard) Algorithm

AES uses 5 units of data size: bits, bytes, words,

blocks, and states. The bit is the smallest unit of data,

namely the value of the binary system digits. While

bytes are 8 bits, words are 4 bytes (32 bits), blocks

are 16 bytes (128 bits) and the state is a block that is

arranged as a 4x4 byte matrix. The following image

describes the AES data unit(Siringoringo, 2020). The

following is the arrangement of the AES algorithm

steps(Azanuddin, 2022):

1. Transform plaintext and key into hexadecimal

numbers

2. Arrange the plaintext and key into a 4x4 state ar-

rays

3. Performs an expansion on the selected key

4. Do AES encryption transformation process with

SubBytes, ShiftRows, MixColumns, and Ad-

dRoundKey

5. To return the ciphertext to the original mes-

sage, decrypt it using the InvSubBytes, In-

vShiftRows, InvMixColumns, and InvAddRound-

Key processes.

The following is an overview of the encryp-

tion and decryption process with the AES algorithm

(Sodikin and Hidayat, 2020):

Figure 2: Encryption and decryption of AES.

SubByte doing by substituting each byte in the

Array state, the example, S [i, j] = xy is a hexadeci-

mal digit and the value is S [i, j], then the substitution

value expressed by S [i, j] is an element in the S-box

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212

that is the intersection of the x line with the y column

(Azhari et al., 2022).

Figure 3: SubByte transformation.

ShiftRow is a process in which each row of the sta-

tus matrix is given a cyclic shift to the right according

to its position (M et al., 2022).

MixColumn in the AES algorithm process by per-

forming polynomial multiplication between the last

state and the following matrix (Haris and Lydia,

2023):



















02 03 01 01

01 02 03 01

01 01 02 03

03 01 01 02



















AddRoundkey is performed by performing an

XOR operation on each value of the input block with

the value of the key block in the same position (Haris

and Lydia, 2023).

2.3 RSA (Rivest Shamir Addleman)

Algorithm

Rivest Shamir Adleman’s algorithm is a method that

has different keys (encryption and decryption keys).

The RSA method is known as a cryptographic method

that uses the concept of public key cryptography (Gea

et al., 2021). The following is a schematic of the RSA

algorithm (Kota and Aissi, 2022):

Figure 4: RSA Algorithm Schematic.

Following are the steps of the RSA algorithm:

1. Generate a public key (e) and a private key (d) by

choosing two very large primenumbers, the two

number = p and q

2. Multiply p and q, n = p * q .

3. Generate a public key, which is relatively prime to

the ”totient” function ϕ(n) = (p − 1)(q −1)

4. Generate a private key, which is the multiplicative

inverse of emod ϕ(n). Note that the public key is

< e, n > and private key is < d, n >

5. Encrypt a message with following formula:

c = memodn (1)

m = cdmodn (2)

6. Decrypt the cipher textwith following formula:

2.4 Authentication With Digital

Signature

The Digital Signature functions as a tool for the au-

thenticity of electronic information and veriﬁcation of

the identiﬁcation of the signer. Information and com-

munication technology has certainly changed the pat-

tern of people’s behavior and also human civilization

globally. In addition, the world has become border-

less because developments in the ﬁeld of information

technology have resulted in and also caused signif-

icant social changes to take place rapidly (Qisthina

and Neyman, 2021).

The scheme of the Digital Signature for the study

result card authentication is as follows:

1. Stages on digital signature

a. The data on the study results card is taken, for

example Name (secret)

b. Deﬁne a key, for example NIRM (secret)

c. The data is encrypted with the AES algorithm

d. The result of encryption (Cipherteks-AES) is

then encrypted again with RSA using the

private-RSA key. At this stage, an RSA pri-

vate key must be generated with the selected

data and an RSA Public key that is interrelated

with the private key

e. The result of encryption with RSA (this is the

Digital signature)

2. Veriﬁcation stage

a. Digital Signature taken

b. Then decrypt it using the RSA’s Public key

c. The result of this description is code

d. Code Decryption with AES: The results are in

the form of a name and Nirm

e. If Name and nirm = value on KHS then the

data is valid

Modiﬁcation of Advance Encryption Standard (AES) and Rivest–Shamir–Adleman (RSA) Algorithms for Data Authentication on Study

Results Card

213

3 RESULTS AND DISCUSSION

3.1 Message Encryption Process With

The AES Algorithm

In the AES algorithm, a ﬁle will ﬁrst be divided into

1 block of 128 bits to be processed ﬁrst with a key

length of 128 bits, 129 bits, or 256 bits, so that the

sizes of plaintext and ciphertext will be different be-

cause, during the encryption process, the division of

blocks is less of 128 bits will be padded to meet the

standard block size of the AES algorithm.

The sequence of bits is numbered sequentially

from 0 to n-1 where n is the sequence number. The

data sequence of 8 bits sequentially is referred to as

a byte where this byte is the basic unit of operations

to be performed on a block of data. The number of

n-bits that exist depends on the key length = 128 bits,

0 ≤ n < 16; key length = 192 bits, 0 ≤ n < 24; key

length = 256 bits, 0 ≤ n < 32.

Each process in this algorithm will transform 10

rounds. Each round uses a different round key which

is obtained during the key expansion process. This is

intended to increase security so that this algorithm is

not easy to solve by cryptanalysts.

3.1.1 Key Expansion

In the process of encryption and description of the

AES algorithm, it is necessary to have 10 roundkey

keys for each round.In this case, key is taken from the

study results card, namely NIRM, then change the key

to hexadecimal form and arrange it into a 4 x 4 state

array as follows:

02 00 02 00

00 02 00 02

04 06 00 01

02 03 04 05

After the keys are arranged as above, the key ex-

pansion process will be carried out to get the round-

key state. Here is the process to get round 1 key:

a. Take the fourth column from RoundKey 0

b. The RotWord function is performed by moving the

top bit to the bottom bit.

c. SubBytes transformation is performed with s-

boxes

d. XOR with column 1 Roundkey 0

e. XOR with constant Rcon

In contrast to searching for results in column 1,

searching for results in columns 2, 3, and 4 only re-

quires an XOR process from the results of the previ-

ous column with the column values being searched.

And so on to produce Roundkey 1 as follows:

74 74 76 76

7C 7E 7E 7C

6F 69 69 68

61 62 66 63

To get the next RoundKey result, repeat the same

process as above. Because in this case using 128-bit

AES with a key length of 128 bits, 10 RoundKeys are

needed. The following are the search results for all of

the RoundKeys 1 to 10:

• RoundKeys 1

74 74 76 76

7C 7E 7E 7C

6F 69 69 68

61 62 66 63

• RoundKeys 2

66 12 64 12

39 47 39 45

94 FD 94 FC

59 5B 5D 3E

• RoundKeys 3

0C 1E 7A 68

89 CE F7 B2

26 DB 4F B3

90 AB F6 C8

• RoundKeys 4

33 2D 57 3F

E4 2A DD 6F

CE 15 5A E9

D5 7E 88 40

• RoundKeys 10

48 53 19 86

72 C4 76 98

D5 12 43 E2

EA 71 7B 6E

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3.1.2 Encryption

In the encryption process, the plaintext and key are

taken. In this case, the plaintext is taken in the form

of the name on the study result card and NIRM or

Roundkey 0.

Name : Khoril Khomis (Change to hexadecimal

4x4 state array):

48 68 6F 69

72 69 6C 4B

68 6F 6D 69

73 01 02 03

NIRM : 2020020246 (Change to hexadecimal 4x4

state array):

02 00 02 00

00 02 00 02

04 06 00 01

02 03 04 05

After getting the state of the plaintext and key, the

AddroundKey transformation process is carried out

by XOR it to get the State Initial Round. The follow-

ing is the result of the XOR process between plaintext

and RoundKey 0 :

49 68 6D 69

72 6B 6C 49

6C 69 6D 68

71 2 6 6

a. SubBytes Transformation

SubBytes are done by transforming the two num-

bers of hexadecimal digits with the S-box table :

Figure 5: S-Box.

The following is the result of the initial round state

transformation with the S-box :

3B 45 3C F9

40 7F 50 3B

50 F9 3C 45

A3 77 6F 6F

Then the results of SubBytes will then be pro-

cessed with shiftRow

b. ShiftRow

ShiftRow is a process in which each row of the sta-

tus matrix is given a cyclic shift to the right accord-

ing to its position. The following is the process for

getting the results of the ShiftrRow transformation.

The result of ShiftRow below will taken to next

step MixColumns:

3B 45 3C F9

7F 50 3B 40

3C 45 50 F9

6F A3 77 6F

c. MixColumns Process

MixColumns is done by multiplying polynomials

between Shift Row’s resulting states and predeter-

mined polynomial matrix :

1. {3B}x {02} = {X

+ X

+ X + 1}.{X}

= {X

+ X

+ X}

= 01110110

= 76

2. {7F}x{03}

= {x

+ x

+ x + 1}.{x + 1}

= {x

+ 1}

= 10000001

= 81

3. {3C}x1 = 3C

4. {6F}x1 = 6F

R1.0=76 XOR 81XOR3CXOR6F = A4

Do the next multiplication to get the MixColumn

result as follows:

A4 9C 12 BF

EE 89 CD 6

8D 63 3E E1

D0 87 D5 77

This state result to be continue for next step, Ad-

dRoundkey

d. AddRoundkey After getting the state from the

MixColumns transformation, the next step is to

carry out the AddroundKey transformation pro-

cess. AddRoundKey is done using an XOR opera-

tion between the resulting state of Mixcolumn and

Roundkey 1. This is the result of AddRoundkey :

After getting the value from the AddRoundkey

state, the SubBytes – ShiftRows – MixCollumns

process is carried out 9 times again bypassing the

Modiﬁcation of Advance Encryption Standard (AES) and Rivest–Shamir–Adleman (RSA) Algorithms for Data Authentication on Study

Results Card

215

D0 E8 64 C9

92 F7 B3 7A

E2 A 57 89

B1 E5 B3 14

state value from the AddroundKey which was ob-

tained from the process above. But in the 10th

round, the MixCollumns process is not used, just

do the SubBytes – ShiftRows – AddroundKey pro-

cess. The following is the result of the ciphertext

from the encryption process which is also the re-

sult of the 10th round Addroundkey process.

EB DD 9A BC

9B 86 EC 27

E4 C5 F9 B0

B0 82 AE 3D

The results of the message encryption with AES

will be modiﬁed with the RSA encryption algo-

rithm at a later stage.

3.2 Modiﬁcation AES With RSA

Algorithm

At this stage, the results of encryption with the pre-

vious AES algorithm will be encrypted with the RSA

algorithm. To do this, the Ciphertext resulting from

AES encryption must be converted to a decimal num-

ber ﬁrst.

Encrypted messages with AES:

AEBC193A19C7F7FCF8442777866FE97C

Message is converted to decimal:

1741882558251992472522486839119134111233124

Then, the message is processed with the RSA algo-

rithm. The following is the encryption process with

the RSA algorithm:

3.2.1 RSA Key Generator

• Take two prime numbers for the values of p and q

P = 137

Q = 131

• Calculate modulus value (n)

n = p x q

n = 137 × 131

n = 17947

• Calculate modulus value (m)

m = (p - 1) × (q - 1)

m = (137 - 1) × (131 - 1)

m = 136 × 130

m = 17680

• Choosing e which is relatively prime to m with the

condition that it meets the Greater Common Divi-

sor (GCD) means that the greatest dividing factor

for the values of e and m is one. To determine this

value, the Euclidean algorithm is used as follows:

• gcd(e,m)=1

Euclidean Algorithm Formula

= q

+ r

, 0 < r

< r

= q

+ r

, 0 < r

< r

= ...

gcd(e, 17680) = 1

• r

= 3, r

= 17680

= q

+ r

3 = 0.17680 + 3

= 17680, r

= 3

= q

+ r

17680 = 5893.3 + 1

= 3, r

= 1

= q

+ r

3 = 3.1 + 0

• then the value of e is 3, e = 3

• Determining the value of d : e×d mod m=1

3×11787 mod 17680=1

d = 11787

• Public Key

public

= (e, n)

public

= (3, 17947)

• Private Key

private

= (e, d)

private

= (3, 11787)

3.2.2 RSA Encryption

To encrypt messages with the RSA Algorithm,

the ﬁrst 3 digits of the message above are taken,

namely 174. Then, the plaintext is encrypted with the

following formula:

C = m

modn

C = 1743

mod17947

C = 9553

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216

3.2.3 RSA Decryption

Here is the result of the decryption of the message

above:

M = C

modn

M = 9553

11787

mod17947

M = 174

3.3 Authentication Message on Study

Result Card

The message that is used as a digital signature in

the form of a QR-Code is the name and registration

number (NIRM) which is encrypted with the AES

algorithm, then the results of the encryption are en-

crypted again with the AES algorithm using a public

keys. The message is placed on the study results card.

For authentication, the public key RSA algorithm is

used which generates the AES message again, then

decrypts it again to get the original message.

Figure 6: QR-Code On Study Result Card.

The following is a message that has been authenti-

cated by scanning the QR-Code that is already on the

study result card.

Figure 7: Date Veriﬁcation Of Study Result Card.

4 CONCLUSIONS

Modiﬁcation of the AES and RSA algorithms makes

it possible to authenticate data on study results cards.

This modiﬁcation is made to protect the data owned

by the card owner so that it cannot be modiﬁed. For

data authentication, decryption using RSA is a bit

complicated because of the large number of messages

resulting from AES encryption, which slows down the

decryption computation due to the large exponential

value. However, the security of this algorithm is very

strong because the message value cannot be predicted

easily.

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