Menu
Home
Log in / Register
 
Home arrow Computer Science arrow Hardware Security and Trust: Design and Deployment of Integrated Circuits in a Threatened Environment
Source

SubBytes Operation

The SubBytes operation is a nonlinear function which replaces one byte by a different predefined byte, given

where b-1 is the г'-th bit of the multiplicative inverse of the input byte b [19]. For efficiency purposes, the SubBytes function is often replaced by an equivalent 256- byte lookup table, designated as SBox. Alternatives to the implementation of this byte substitution considering composite fields also exist [3, 24, 26].

ShiftRows Operation

The ShiftRows operation, as the name implies, is a permutation of the 2nd, 3rd and 4th rows of the State matrix, 1,2, and 3 positions to the left, respectively. The inverse operation used in decryption, InvShiftRows, is the direct undoing of the former shifting, with the permutations of the same rows 1, 2, and 3 positions to the right. The 1st row of the State matrix does not suffer any changes in either one of these operations. Both operations are depicted in Fig. 1.2.

AES ShiftRows and InvShiftRows operations

Fig. 1.2 AES ShiftRows and InvShiftRows operations

Table 1.1 Byte-by-byte GF(28) multiplication

2n multiplication

Non 2n multiplication

01 x B = (B < 0)mod(0x11B)

03 x B = 02 x B ф 01x B

02 x B = (B < 1)mod(0x11B)

05 x B = 04 x B ф 01 x B

04 x B = (B 2)mod(0x11B)

07 x B = 04 x B ф 02 x B ф 01 x B

08 X B = (B < 3)mod(0x 11B)

  • 0F x B =
  • 08 x B ф 04 x B ф 02 x B ф 01 x B
 
Source
Found a mistake? Please highlight the word and press Shift + Enter  
< Prev   CONTENTS   Next >
 
Subjects
Accounting
Business & Finance
Communication
Computer Science
Economics
Education
Engineering
Environment
Geography
Health
History
Language & Literature
Law
Management
Marketing
Mathematics
Political science
Philosophy
Psychology
Religion
Sociology
Travel