aes write up

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MAULANA AZAD NATIONAL INSTITUTE

OF

TECHNOLOGY, BHOPAL

Year 2011-12

Write up

On

Advance Encryption Algorithm

Submitted to:- Submitted by:-

Proff. Namita Tiwari Amish Kumar

Dept of CSE & IT Sch no-102112204

M Tech (IS)



Motivation

Nowadays cryptography has a main role in transferring data. As

the number of devices and applications which send and receive data

are increasing rapidly, the data transfer rates are becoming higher. In

many applications, this data requires a secured connection which is

usually achieved by cryptography.

Many cryptographic algorithms were proposed, such as the Data

Encryption Standard (DES), the Elliptic Curve Cryptography (ECC), the

Advanced Encryption Standard (AES) and other algorithms. Many

researchers and hackers are always trying to break these algorithmsusing brute force and side channel attacks. Some attacks were

successful as it was the case for the Data Encryption Standard (DES) in

1993, where the published cryptanalysis attack could break the DES.

The Advanced Encryption Standard (AES) is considered nowadays

as one of the strongest published cryptographic algorithms, where it

was adopted by the National Institute for Standards and Technology

(NIST) after the failing of the Data Encryption Standard (DES).

Moreover, it is used in many applications such as in RFID cards, ATM

Machines, cell-phones and large servers.



Information Security and its Technique

Information security is the process of keeping the entire data safe

and secure from the reach of some unauthorized people or users.

The data and the information is not at all visible and disclosed to

anyone. The information that is to be fed on the system must be

readable, memorized, audible, and printable and hence must be

of electronic nature. The information must be protected in such a

way that is it not accessible to anyone. There is some sort of

confidentiality among the information systems and their security.

Characterization of Information security:

Confidentiality-

Ensuring that information is accessible only to those authorized to

have access.

Integrity-

Safeguarding the accuracy and completeness of information and

processing methods.

Availability-

Ensuring that authorized users have access to information and

associated assets when required.

Access Control-

Data should be accessed by authorized users only.



Methods Of Information security:

Cryptography tool

Digital Signature

Use Firewalls

Password protection



Definition and History of Cryptography

We refer to the word cryptography as the change of datarepresentation from its original form into another different form in

order to make it hidden and secured. Cryptography has two processes;

the first process is the encryption where the original data is converted

into secured form using certain steps. The second process is the

decryption, where the encrypted data is restored to the original form

by applying the inverse to the steps applied in the encryption process.

Classic Cryptography started thousands of years ago. All over the

history classic cryptography was used for secret communications

between people. This kind of cryptography is usually applied by

substituting the message letters by other letters using certain formula ,

for example substituting each letter in a message with the next letter in

the alphabets so that the word Test would become Uftu.

In modern ages, cryptography development has been a majorconcern in the fields of computer science and engineering. One of the

main classes in cryptography today is the symmetric-key cryptography,

where a shared key of a certain size will be used for the encryption and

decryption processes. Fig. 1 illustrates the concept of symmetric-key

cryptography and AES is one of the strongest asymmetric key

cryptography technique



The Advanced Encryption Standard (AES)

In the early 1970s, IBM developed the Data Encryption

Standard as a symmetric-key cryptography algorithm. This algorithm

was adopted by the National Institute of Standard and Technology(NIST) in 1977, where it was published in the Federal Information

Processing Standard (FIPS) Publication. The DES consists of 64 bits data

block with key size of 56 bits, where 16 encryption rounds will be

applied to the data to complete the encryption process. The DES

algorithm starts to fail after several published brute force attacks. The

linear cryptanalysis attack could break the DES and made it insecure

algorithm. The NIST started to search for another algorithm to replacethe DES, where the Rijndael cipher was selected as the new Advanced

Encryption Standard (AES).

The AES cipher is almost identical to the block cipher Rijndael. The

Rijndael block and key size vary between 128, 192 and 256 bits.



The number of internal rounds of the cipher is depends on the key

length, according to Table-

AES does not have a Feistel structure. Feistel networks do not encrypt

an entire block per iteration, e.g., in DES, 64/2 = 32 bits are encrypted

in one round. AES, on the other hand, encrypts all 128 bits in one

iteration. There are only three different types of layers. Each layer

manipulates all 128 bits of the data path.



Internal Structure of AES:-

AES layers:-

Now understand how the data moves through AES, we first

imagine that the state A (i.e., the 128-bit data path) consisting of 16

bytes A0, A1, . . . , A15 is arranged in a four-by-four byte matrix:



Similarly, the key bytes are arranged into a matrix with four rows and

four (128-bit key), six (192-bit key) or eight (256-bit key) columns. Here

is, as an example, the state matrix of a 192-bit key:

And the operation that are performed on each round are:

1.Byte substitution

2.Shift rows3.Mix column

4.Key addition

Byte Substitution Layer:-

the first layer in each round is the Byte Substitution layer. The

Byte Substitution layer can be viewed as a row of 16 parallel S-Boxes. In

the layer, each state byte Ai is replaced, i.e substituted, by another byteBi :

S( Ai ) = Bi .



Lets assume the input byte to the S-Box is Ai = (C 2)hex , then the

substituted value is

S((C 2)hex ) = (25)hex .

Diffusion Layer:-

In AES, the Diffusion layer consists of two sublayers, the ShiftRows

transformation and the MixColumn transformation.

ShiftRows Sublayer:-

The ShiftRows transformation cyclically shifts the second row of the

state matrix by three bytes to the right, the third row by two bytes to

the right and the fourth row by one byte to the right. The first row is

not changed by the ShiftRows transformation. The purpose of the

ShiftRows transformation is to increase the diffusion properties of AES.



If the input of the ShiftRows sublayer is given as a state matrix

B = (B0,B1, . . . ,B15):

MixColumn Sublayer:-

The Mix Column step is a linear transformation which mixes each

column of the state matrix. Since every input byte influences four

output bytes, the Mix Column operation is the major diffusion element

in AES. The combination of the Shift Rows and Mix Column layer makes

it possible that after only three rounds every byte of the state matrix

depends on all 16 plaintext bytes.In the following, we denote the 16-byte input state by B and

the 16-byte output state by C :

Mix Column(B) =C ,

where B is the state after the ShiftRows operation .

Now, each 4-byte column is considered as a vector and

multiplied by a fixed 4×4 matrix. The matrix contains constant entries



The second column of output bytes (C 4,C 5,C 6,C 7) is computed by

multiplying the four input bytes (B4,B9,B14,B3) by the same constant

matrix, and so on.

Key Addition Layer

The two inputs to the K ey Addition layer are the current 16-byte state

matrix and a subkey which also consists of 16 bytes (128 bits). The two

inputs are combined through a bitwise XOR operation.

Key Schedule for 128-Bit Key AES:-



Literature Review

The Advanced Encryption Standard (AES) is the most widely

used symmetric cipher today. Even though the term Standard in its

name only refers to US government applications, the AES block cipher is

also mandatory in several industry standards and is used in many

commercial systems. Among the commercial standards that include AES

are the Internet security standard IPsec, TLS, the Wi-Fi encryption

standard IEEE 802.11i, the secure shell network protocol SSH (Secure

Shell), the Internet phone Skype and numerous security products

around the world. To date, there are no attacks better than brute-force

known against AES.

In this paper we have discuss:

1. Design process of the US symmetric encryption standard,AES

2. The encryption and decryption function of AES

3. The internal structure of AES, namely:

4. byte substitution layer

5. diffusion layer

6. key addition layer

7. key schedule8. Basic facts about Galois fields

9. Efficiency of AES implementations



Proposed Work

The proposed work is based on the implementation of AES-128

algorithm which will have:

1.high speed

2.high efficiency

And the AES 192,AES-256 can also be implemented for achieving high

speed and higher efficiency.



Reference

1- J. Daemen and V. Rijmen, AES Proposal: Rijndael , AES Algorithm

Submission,

September 3, 1999.

2- Advanced Encryption Standard (AES ), Nov. 26, 2001, Federal

Information Processing Standards publication 197. Federal Information

Processing Standards Publication

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