A SEMINAR REPORT ON

AES Implementation for Secure Wireless

Communication

SUBMITTED BY

ABINASH AGRAWAL

Regd.No.1205209042

In partial fulfilment for the award of the degree

Of

MCA

Silicon institute of Technology

Bhubaneswar

FEBUARY 2014

ACKNOWLEDGEMENT

Any achievement, be it scholastic or otherwise does not depend solely on the individual efforts but

on the guidance, encouragement and cooperation of intellectuals, elders and friends. A number of

personalities, in their own capabilities have helped me in carrying my seminar. I would like to take

this opportunity to thank them all.

First and foremost I would like to thank to my Seminar faculties Prof. Kasturi Dhal, Prof.

Niranjan Kumar Ray, Prof. Manoj Kumar Samantara and Prof. Sk. Kamaruddin without their

help this seminar would not have been a success. I would like to thank you all for giving me your

support & cooperation that was required and also, for being tremendous source of inspiration &

motivation.

I would also like to thank our H.O.D Prof. Aurabinda Misra for his co-operation and

support in making this seminar.

I will be failing in my duty, if I do not express my gratitude towards other staff members and

friends who have helped me to complete my seminar work successfully and in time.

ABINASH AGRAWAL

REGD. No: 1205209042

MCA 4th

SEMESTER

ABSTRACT

Data Security is plays a vital role every communication system. There are many ways to provide

security data that is being communicated. In order to protect data from malicious attacks we use

Cryptography. With increase in usage of wireless media for communication and increased

number of attacks on the same, there is a need to develop a viable cryptographic scheme. The

earlier encryption algorithm such as Data Encryption Standard (DES), triple DES which has

several loopholes such as small key size and sensible to brute force attack etc. and it cant

provide high level, efficient and exportable security. These loopholes overcome by a new

algorithm called as Advanced Encryption Standard (AES). Here implementation of AES

algorithm for encryption is described.

The Advanced Encryption Standard (AES) is a specification for the encryption of

electronic data established by the U.S. National Institute of Standards and Technology

(NIST) in 2001. It is based on the Rijndael cipher developed by two Belgian cryptographers, Joan

Daemen and Vincent Rijmen, who submitted a proposal to NIST during the AES selection process.

Rijndael is a family of ciphers with different key and block sizes. For AES, NIST selected three

members of the Rijndael family, each with a block size of 128 bits, but three different key lengths:

128, 192 and 256 bits.

Contents:

Topic Page No.

1 Introduction 1

2 Motivation 1-2

3 Methods of Encryption 2

4 AES Algorithm 2-4

5 Encryption Procedure in AES 4-8

6 Encryption Flow Chart 9

7 System Design and Flow Chart 10-11

8 Conclusion 12

9 References 13

1

Introduction

In todays world most of the communication is done using electronic media. Data Security plays a

vital role in such communication. Hence, there is a need to protect data from malicious attacks. This

can be achieved by Cryptography. The earlier encryption algorithm such as Data Encryption

Standard (DES), triple DES which has several loopholes such as small key size and sensible to brute

force attack etc. and it cant provide high level, efficient and exportable security. These loopholes

overcome by a new algorithm called as Advanced Encryption Standard (AES).

Advanced Encryption Standard (AES), also known as Rijndael, is an encryption standard

used for securing information. AES was published by NIST (National Institute of Standards and

Technology). AES is a block cipher algorithm that has been analysed extensively and is now used

widely. Rijndael is very secure and has no known weakness. Rijndael is conventional (symmetric

key) system and is relatively simple cipher in many respects. It takes an input block of a certain size,

usually 128, and produces a corresponding output block of the same size. The transformation

requires a second input, which is the secret key.

In this seminar work, the plain text of 128 bits is given as input to encryption block in which

encryption of data is made and the cipher text of 128 bits is throughout as output. The key length of

128bits, 192bits or 256bits is used in process of encryption. The AES algorithm is a block cipher that

uses the same binary key for both encryption and decryption of data blocks.

Motivation

The Advanced Encryption Standard, in the following referenced as AES, is the winner of the

contest, held in 1997 by the US Government, after the Data Encryption Standard (DES) was found

too weak. Fifteen candidates were accepted in 1998 and based on public comments the pool was

reduced to five finalists in 1999. In October 2000, one of these five algorithms was selected as the

forthcoming standard: a slightly modified version of the Rijndael.

The Rijndael, whose name is based on the names of its two Belgian inventors, Joan Daemen

and Vincent Rijmen, is a Block cipher, which means that it works on fixed-length group of bits,

which are called Blocks. It takes an input block of a certain size, usually 128, and produces a

corresponding output block of the same size. The transformation requires a second input, which is

the secret key. It is important to know that the secret key can be of any size (depending on the cipher

used) and that AES uses three different key sizes: 128, 192 and 256 bits.

2

Rijndael was designed to have the following characteristics:

Resistance against all known attacks.

Speed and code compactness on a wide range of platforms.

Design Simplicity.

Methods of Encryption

Although there can be several pieces to an encryption method, the two main pieces are the

algorithms and the keys. As stated earlier, algorithms are usually complex mathematical formulas

that dictate the rules of how the plaintext will be turned into cipher text. A key is a string of random

bits that will be inserted into the algorithm. In some encryption methods, the receiver and the sender

use the same key and in other encryption methods, they must use different keys for encryption and

decryption purposes. The following sections explain the difference between these two types of

encryption methods.

Symmetric key Cryptography

Symmetric cryptography uses the same secret (private) key to encrypt and decrypt its data. It requires

that the secret key be known by the party encrypting the data and the party decrypting the data.

Asymmetric key Cryptography

Asymmetric uses both a public and private key. This allows for distribution of your public key to

anyone with which they can encrypt the data they want to send securely and then it can only be

decoded by the person having the private key.

AES Algorithm

The AES is an iterated symmetric block cipher, which means that,

AES works by repeating the same defined steps multiple times.

AES is a secret key encryption algorithm.

AES operates on a fixed number of bytes

AES as well as most encryption algorithms is reversible. This means that almost the same steps

are performed to complete both encryption and decryption in reverse order. The AES algorithm

operates on bytes, which makes it simpler to implement.

3

Specification

For the AES algorithm, the length of the input block, the output block and the State is 128 bits. This

is represented by Nb = 4, which reflects the number of 32-bit words (number of columns) in the

State. The length of the Cipher Key, K, is 128 bits. The key length is represented by Nk = 4, which

reflects the number of 32-bit words (number of columns) in the Cipher Key.

For the AES algorithm, the number of rounds to be performed during the execution of the

algorithm is dependent on the key size. The number of rounds is represented by Nr, where Nr = 10

when Nk = 4.

Description

The AES is an iterated block cipher with a fixed block size of 128 and a variable key length. The

different transformations operate on the intermediate results, called state. The state is a rectangular

array of bytes and since the block size is 128 bits, which is 16 bytes, the rectangular array is of

dimensions 4x4. The basic unit for processing in the AES algorithm is a byte, a sequence of eight

bits treated as a single entity. The input, output and Cipher Key bit sequences which are processed as

arrays of bytes that are formed by dividing these sequences into groups of eight contiguous bits to

form arrays of bytes.

Rijndaels round

At a basic level the Rijndael algorithm uses a number of rounds to transform the data for each block.

The number of rounds used is 6 + the maximum of Nb and Nk. Following from the previous example

of AES-128, the number of rounds is 10. This is calculated from 6 plus the maximum of (4,4). Since

Nb and Nk are both 4, the number of rounds is 6 + 4 = 10

The figure 1 shows the top level blocks available in the AES algorithm. Also the basic inputs to

the system and the outputs from the system were clearly represented. As per the standard, 10 rounds

for 128 bits key length were carried out in which the last round will be performed separately. For

both its Cipher and Inverse Cipher, the AES algorithm uses a round function that is composed of four

different byte-oriented transformations:

Byte substitution using a substitution table (S-box)

Shifting rows of the State array by different offsets

Mixing the data within each column of the State array

Adding a Round Key to the State

4

Above mentioned functions were carried out for every individual round and in the last round

the third function, that is, Mixing the data within each column of the State array will not be

performed. Hence the last round is carried out separately. Based on the key provided, the new set of

keys will be generated in the Key Expansion block and is given to the each round as input.

Fig. 1: Block diagram of AES Algorithm

Encryption Procedure in AES

At the start of the Encryption or Cipher, the input data and the input key were copied to the State

array using the conventions. Initially the XOR operation should be performed between each byte of

the input data and the input key and the output will be given as the input of the Round-1. After an

initial Round Key addition, the State array is transformed by implementing a round function 10

times, with the final round differing slightly from the first Nr1 rounds. The final State is then

copied to the output. The round function is parameterized using a key schedule that consists of a one-

dimensional array of four-byte words derived using the Key Expansion routine.

The individual transformations that carried out are listed below.

SubBytes

ShiftRows

MixColumns

AddRoundKey

Round 1

Cipher key

Round 2

Round 10

Round key 1

Round key 0

Round key 2

Cipher text block

Round key 10

Plain text block

. ..

Key Expansion

5

Key Expansion

Prior to encryption or decryption the key must be expanded. The expanded key is used in the Add

Round Key function defined above. Each time the Add Round Key function is called a different part

of the expanded key is XORed against the state. In order for this to work the Expanded Key must be

large enough so that it can provide key material for every time the Add Round Key function is

executed. The Add Round Key function gets called for each round as well as one extra time at

beginning of the algorithm.

SubBytes Transformation

The SubBytes operation is a non-linear byte substitution, operating on each byte of the state

independently. Since the S-Box is independent of any input, pre-calculated forms are used, if enough

memory (256 bytes for one S-Box) is available. Each byte of the state is then substituted by the value

in the S-Box whose index corresponds to the value in the state. Figure 2 illustrates the effect of the

SubBytes transformation on the State clearly.

Fig. 2: SubBytes Operation of the State

The S-Box will be of a 16X16 matrix in which the row is represented as x and the column

is represented by y. The S-box used in the SubBytes transformation is presented in hexadecimal

form and hence the substitution value would be determined by the intersection of the row and the

column.

For example, if S1,1 = {53}, then the substitution value would be determined by the

intersection of the row with index 5 and the column with index 3. This would result in S1,1 having

a value of {ED}.

6

ShiftRows Transformation

Arranges the state in a matrix and then performs a circular shift for each row. This is not a bit wise

shift. The circular shift just moves each byte one space over. A byte that was in the second position

may end up in the third position after the shift.

Fig.3: ShiftRows Operation of the State

Figure 3 illustrates the ShiftRows transformation. The shifting operation will be carried out

horizontally as follows.

The 1st row is shifted 0 positions to the left.

The 2nd row is shifted 1 positions to the left.

The 3rd row is shifted 2 positions to the left.

The 4th row is shifted 3 positions to the left.

MixColumns Transformation

In MixColumns operation, parts of the state are multiplied against which parts of the matrix. The

transformation operates on the State column-by-column. The State is arranged into a 4 row table (as

described in the Shift Row function). The multiplication is performed one column at a time (4 bytes).

Each value in the column is eventually multiplied against every value of the matrix (16 total

multiplications). The results of these multiplications are XORed together to produce only 4 result

7

bytes for the next state. Therefore 4 bytes input, 16 multiplications 12 XORs and 4 bytes output. The

multiplication is performed one matrix row at a time against each value of a state column.

The pre-defined 4X4 matrix value and the first column of the ShiftRows state are represented as

follows, for the multiplication.

The first result byte is calculated by multiplying 4 values of the state column against 4 values

of the first row of the matrix. The result of each multiplication is then XORed to produce 1 Byte.

S0,c = ({02} S0,c) ({03} S1,c) S2,c S3,c

The second result byte is calculated by multiplying the same 4 values of the state column

against 4 values of the second row of the matrix. The result of each multiplication is then XORed to

produce 1 Byte.

S1,c = S0,c ({02} S1,c) ({03} S2,c) S3,c

The third result byte is calculated by multiplying the same 4 values of the state column

against 4 values of the third row of the matrix. The result of each multiplication is then XORed to

produce 1 Byte.

S2,c = S0,c S1,c ({02} S2,c ) ({03} S3,c)

The fourth result byte is calculated by multiplying the same 4 values of the state column

against 4 values of the fourth row of the matrix. The result of each multiplication is then XORed to

produce 1 Byte.

S3,c = ({03} S0,c) S1,c S2,c ({02} S3,c )

This procedure is repeated again with the next column of the state, until there are no more

state columns. Hence putting it all together, the first column will include state bytes 1-4 .

8

Fig.4: MixColumns operates on the State column-by-column

Figure 4 illustrates the MixColumns transformation. Hence the pictorial representation of the

MixColumns operation represented above gives the clear view on this transformation.

Add Round key

In the AddRoundKey transformation, a Round Key is added to the State by a simple bitwise XOR

operation. Each of the 16 bytes of the state is XORed against each of the 16 bytes of a portion of the

expanded key for the current round. The Expanded Key bytes are never reused. So once the first 16

bytes are XORed against the first 16 bytes of the expanded key then the expanded key bytes 1-16 are

never used again. The next time the Add Round Key function is called bytes 17-32 are XORed

against the state. This process will be continued until the operation ends. The graphical

representation of this operation can be seen below.

Fig.5: AddRoundKey Operation

The above figure 5 represents the clear view on the AddRoundKey transformation which takes place

between the results of MixColumns and KeyExpansion and gives the resultant matrix that is used as

the input to the next round.

=

9

Encryption Flow Chart

Fig.6: Encryption Flow chart

In the flow chart of AES encryption algorithm round counter for 128 bit is 10. Then all other

operation like key addition, S-Table Substitution, Row Shift, MixColumn is performed. The figure 6

illustrates the whole encryption procedure that is conversion of plain text into the cipher text.

start

Round Counter = 10

Round_con = 1

Key addition

S Table Substitution

Encode Row Shift

Round counter = 1?

Key addition

Encode key schedule

Encode mix column

Round counter - 1

Round counter= 0?

End

True

False

10

System Design

Fig.7: Block diagram of system

Data is transmitted from transmitter to receiver and vice versa when data is given through the

keyboard scan code of keyboard is used. If data is given through the PC then prolific USB to

UART IC pl2303 is used.

Given data is load in At Mega 16 using emulator. Then data is transmitted from transmitter to

receiver through the wire antenna. Prolific pl2303 is used for Communication interface between

USART based serial port of microcontroller and USB port of computer. Visual basic based GUI

makes it easy to pre-store the response of transmitter user.

The PL-2303 operates as a bridge between one USB port and one standard RS232 Serial port.

This device is also compliant with USB power management and remote wakeup scheme. Only

minimum power is consumed from the host during suspend. By integrating all the functions into the

SSOP- 28 package, this chip is suitable for cable embedding. Users just simply hook the cable into

PC or hubs USB port, and then they can connect to any RS-232 devices. The figure 7 illustrates

the block diagram of the system to be used.

At Mega

16Atmel AVR

PC Prolific

USB to

USART

RF

MODEM

TX-RX

PC Ps2

KEYBOARD

LCD

11

System Flow chart

Fig.8: Flow chart of system

The input data is given through the PC. For that Visual Basic Graphical interface is used. When

data is given through the PC USB to UART converter IC pl2303 is used. Then data is loaded in

At Mega16.For the security of data cryptography algorithm is used. After that encrypted data is

displayed on LCD. When data is given through the keyboard scan code is used. For the data

communication 433Mhz frequency is used. The figure 8 shows the details implementations of AES

in the system.

AES is successfully implemented in the above discussed system and data is transmitted up to

a maximum distance of 100m at 4.6 Kbps, which is quite enough for wireless communication. But

on increasing the distance data transmission rate decreases.

USB INTERFACE

PROFOLIC USB TO USART

CONVERTER

PC/PS2 KEYBOARD

INTERFACE

AVR 8 BIT RISC PROCESSOR

CRYPTOGRAPHY

ALGORITHM

VB 6.0 GRAPHICAL USER

INTERFACE

POWER SUPPLY UNIT

ALPHANUMERIC LCD DISPLAY

PC HARD DRIVE

433 Mhz RF

MODEM/TRANSCIVER

WIRELESS DATA ERROR

CHECK

12

Conclusion

With increase in usage of wireless media for communication and increased number of attacks on the

same, there is a need to develop a viable cryptographic scheme.

Earlier schemes such as DES and Triple DES couldnt suffice the needs of wireless

communication, a stronger encryption technique was needed.

Rijndael appears to be consistently a very good performer in both hardware and software

across a wide range of computing environments regardless of its use in feedback or non feedback

modes. Its key setup time is excellent, and its key agility is good. Rijndaels very low memory

requirements make it very well suited for restricted-space environments, in which it also

demonstrates excellent performance.

There are many unknowns regarding future computing platforms and the wide range of

environments in which the AES will be implemented. However, when considered together,

Rijndaels combination of security, performance, efficiency, implementability, and flexibility make it

an appropriate selection for the AES for use in the technology of today and in the future.

13

References:

1. G.H.Karsanbhai and M.G.Shajan, Published in: Emerging Trends in Networks and Computer

Communications (ETNCC), 2011 International Conference, Page(s):497 501.

2. Tsang-Yean Lee, Huey-Ming Lee, Homer Wu, Jin-Shieh Su, DataTransmission Encryption

and Decryption Algorithm in Network Security.

3. Pekka Riikonen .RSA algorithm. Nov. 2002

4. Bruce Schneier. Applied Cryptogrphy Second adition (Chapter 12)

5. Diaa Salama Abdul. Elminaam, Hatem M. Abdul Kader and Mohie M.

6. Hadhoud, Performance Evaluation of Symmetric Encryption Algorithms on Power

Consumption for Wireless Devices, oct. 2009

7. William Stallings, Cryptography and Network Security: Principles and Practices,

International Edition, Third Edition 2003 by Pearson Education, Inc. Upper Saddle River, NJ

07458.

8. National Institute of Standards and Technology (NIST). NIST FIPS PUB 185, Escrowed

Encryption Standard, February 1994.

report1.pdfreport2.pdf