AES加密算法中的S盒及其C语言实现

详细叙述了算法中S盒的构造，并给出了其C语言实现的程序代码．S盒由有限域GF(2^8)上所有元素的乘法逆元及在域GF(2)上的仿射变换构成，经过S盒的非线性字节代换，密的差分均匀性和线性偏差都达到较理想的状态，提高了AES算法抗击差分密码分析及线性密码分析的能力．在AES算法中，Nr轮的加密过程都要对状态矩阵中的字节求其在有限域GF(2^8)上的乘法逆元和作GF(2)上的仿射变换，这些都要多次用到大运算量的非线性字节变换操作，为此可以通过一定的算法先算出GF(2^8)上所有元素的乘法逆元并作相应的仿射变换以形成对字节代换的代换表，即S盒，然后通过查表的方法进行加密过程中的字节代换，从而缩短明的加密时间，提高AES加密算法的整体效率．

S-box in AES encipher algorithm and its C language implementation

The paper described detailedly the construction of S box in AES and gave its source program code of C language. The S box was constituted with the multiplication inverse element affined transformation in GF(2) of all elements of limited field GF(28),with S box 's nonlinear byte changed,ciphered text attained the ideal status of the even of difference and the linear of deviation,and increased the capability of the AES algorithm of anti beating the difference cipher of analysis and linear cipher of analysis. In AES algorithm,the round of Nr of encipher procedure must compute the multiplication inverse element in limited field GF(28) and affined transformation in GF(2) to the byte of the status matrix,and these all needed to use many times the big quantity transform operation of nonlinear byte,for this,through the certain algorithm to calculate multiplication inverse element of all elements of the GF(28) and affined transformation forming the generation changes table to byte generation changes,it's S box,then through the method of the looking table to finish the byte generation changes of encrypt proceed,thereby shortened the encipher time of the plain text and increased the whole efficiency of AES encrypt algorithm.