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)
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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.
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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.
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Methods Of Information security:
Cryptography tool
Digital Signature
Use Firewalls
Password protection
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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
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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.
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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.
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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:
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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 .
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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.
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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
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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:-
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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
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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.
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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