Click here to load reader
Upload
manjunath-badru
View
33
Download
2
Embed Size (px)
Citation preview
Image EncryptionSecurity and its problems security is automated tool for protecting files and other information stored on the computer. The major thing of the tools designed is to keep away the hackers is the computer security and internet security. How to overcome? Physical methods in earlier days Modern algorithms(DES and AES etc).
Introduction to AESAES acronym of advanced encryption
standard It was introduced in 2001 to increase the capacity of the keys by Rijndael Its an iterated process contents of AES Plain text Keys Cipher text(plain text+keys).
Over all AES structures
Plain text
Encryptio n algorithm
Decryption algorithm
Plain text
input output
AES evaluationSecurity Cost Algorithm and implementation charecteristics
AlgorithmDetails1.ADD ROUND KEY
Each of the 16 bytes of the state is xored with
each of the 16 bytes of the expanded key. The expanded key bytes are never reused . The next time add round key is called for the bytes 17 to 32.
2.AES SUB BYTE TRANSFORMATION
The xored data in the first step is
replaced by the bytes from the look up table. EXAMPLE: Let XORed data be EA(hex). This data is replaced by 87 from the look up table.This applies for all 4x4 matrix
3.SHIFT ROWS The state is arranged in 4x4 matrix
From: 1 5 9
To:no change
13 1 5 9 13 2 6 10 14 14 2 6 10 3 7 11 15 11 15 3 7
1 left shift
2 left shift
4.MIX COLOUM TRASNSFORMATIONThis step computes the new state matrix S0 by left
multyplaying S0=P*S where P is polynomial matrix S is current state matrix
.S0,j=(2*s0,j)xor(3*s1,j)xor(s2,j)xor(s3,j) S1,j=(s0,j)xor(2*s1,j)xor(3*s2,j)xor(s3,j) \This rule applies to all the rows and coloums
KEY EXPANSION
There are 4 steps in key 1.Rot word 2.Sub word 3.Rcon generator. 4.EK
expansion:
KEY EXPANSIONThe user supplied 16bytes long key are arranged in 4*4
matrix. Sub word is a function that takes a 4-byte input word and applies the s-box to produce an 4-byte output word. Rot word takes word from the input, performs a cyclic permutations and return the word. Rcon gen: This function return a 4-byte value based on the Rcon generator table. EK: This function will return 4-byte of the expanded key of the specified output.
DECRYPTION1. INVERSE ADD ROUND KEY:
The inverse add round key transformation is identical to the forward add round key transformation, because the xor operation is its own inverse. 2.INVERSE S-BOX TRANSFORMATION: The inverse substitute byte transformation make use of the inverse s-box as shown in the table below. The inverse s-box is constructed by applying the inverse of the transformation is bi=b(i+2) mod8 xor b(i+5) mod8 xor b(i+7) mod8 xor di
DECRYPTIONb0 |0 0 1 0 0 1 0 1 | b1 |1 0 0 1 0 0 1 0 | b2 |0 1 0 0 1 0 0 1 | b3 |1 0 1 0 0 1 0 0 | b4= |0 1 0 1 0 0 1 0 | b5 |0 0 1 0 1 0 0 1 | b6 |1 0 0 1 0 1 0 0 | b7 |0 1 0 0 1 0 1 0 | | bo | |1| | b1 | |0| | b2 | |1| | b3 | |0| | b4 | + |0| | b5 | |0| | b6 | |0| | b7 | |0|
DECRYPTIONDuring decryption each value of the state is replaced by the value in the inverse s-box.
DECRYPTION3.INVERSE SHIFT ROW TRANSFORMATION The inverse shift row transformation performs the circular shift in the opposite direction for each of the last three rows with one byte circular right shift for the second row and so on.
DECRYPTION4.INVERSE MIX COLUMN: The inverse mix column transformation can be defined by the following matrix multiplication on the state:0E 0B 0D 0909 0E 0B 0D0D 09 0E 0B 0B 0D 09 0E
Advantages of Hardware Implementation The cipher implementing in hardware is executed
approximately 23 times cipher implemented in software. The key expansion function implementing in hardware is executed 1.88 times slower than the key expansion implementation in software. The inverse cipher implementing in hardware is executed 29 times faster than inverse cipher implementing in software. The DMA(direct memory access)which is used to