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接着进行线性层运算，即将input数组右乘矩阵m_LinearTransMatrixBox（该矩阵的说明详见参考文献［１］），代码如下：
input[2] = (byte)((input[2] + input[0]) & 0xFF);
input[0] = (byte)((input[0] + input[2]) & 0xFF);
．．．．．．
temp = input[30];
input[30] = input[6];
input[6] = temp;
其实这段繁杂的代码就是一维数组input[]与一个二维数组m_LinearTransMatrixBox[][]的乘积，那么为什么不用以下更精炼的代码呢？
Byte[] temp = new byte[input.length];
For (j=0;j<16;j++)
For (k=0;k<16;k++)
{
Temp[2*j] +=(byte)(input[2*k] * m_nLinearTransMatrixBox[k,j]);
}
For (j=0;j<16;j++)
{
Input[2*j] = (byte)temp[2*j];
}
其中：
Static public byte[,] m_nLinearTransMatrixBox = newbyte[16,16]
{
{2,2,1,1,16,8,2,1,4,2,4,2,1,1,4,4},
{1,1,1,1,8,4,2,1,2,1,4,2,1,1,2,2},
{1,1,4,4,2,1,4,2,4,2,16,8,2,2,1,1},
{1,1,2,2,2,1,2,1,4,2,8,4,1,1,1,1},
{4,4,2,1,4,2,4,2,16,8,1,1,1,1,2,2},
{2,2,2,1,2,1,4,2,8,4,1,1,1,1,1,1},
{1,1,4,2,4,2,16,8,2,1,2,2,4,4,1,1},
{1,1,2,1,4,2,8,4,2,1,1,1,2,2,1,1},
{2,1,16,8,1,1,2,2,1,1,4,4,4,2,4,2},
{2,1,8,4,1,1,1,1,1,1,2,2,4,2,2,1},
{4,2,4,2,4,4,1,1,2,2,1,1,16,8,2,1},
{2,1,4,2,2,2,1,1,1,1,1,1,8,4,2,1},
{4,2,2,2,1,1,4,4,1,1,4,2,2,1,16,8},
{4,2,1,1,1,1,2,2,1,1,2,1,2,1,8,4},
{16,8,1,1,2,2,1,1,4,4,2,1,4,2,4,2},
{8,4,1,1,1,1,1,1,2,2,2,1,2,1,4,2}
}
很明显，因为这是模256的加法运算，所以只能采取在运算的每一步将部分和结果与0xFF做与（&）操作，从而保证其值介于0-255之间，因而不能采用通常意义上的二维数组乘法来进行处理。
接着进行一个输出变换，代码为：
input[0] = (byte)((input[0] ^ n_LocKeyExpandBox[16 * m_nChipherLen]));/* 此处不能做xFF */
input[2] = (byte)((input[2] + n_LocKeyExpandBox[16 * m_nChipherLen + 1]) & 0xFF);
input[4] = (byte)((input[4] + n_LocKeyExpandBox[16 * m_nChipherLen + 2]) & 0xFF);
input[6] = (byte)((input[6] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 3]) & 0xFF);
input[8] = (byte)((input[8] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 4]) & 0xFF);
input[10] = (byte)((input[10] + n_LocKeyExpandBox[16 * m_nChipherLen + 5]) & 0xFF);
input[12] = (byte)((input[12] + n_LocKeyExpandBox[16 * m_nChipherLen + 6]) & 0xFF);
input[14] = (byte)((input[14] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 7]) & 0xFF);
input[16] = (byte)((input[16] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 8]) & 0xFF);
input[18] = (byte)((input[18] + n_LocKeyExpandBox[16 * m_nChipherLen + 9]) & 0xFF);
input[20] = (byte)((input[20] + n_LocKeyExpandBox[16 * m_nChipherLen + 10]) & 0xFF);
input[22] = (byte)((input[22] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 11]) & 0xFF);
input[24] = (byte)((input[24] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 12]) & 0xFF);
input[26] = (byte)((input[26] + n_LocKeyExpandBox[16 * m_nChipherLen + 13]) & 0xFF);
input[28] = (byte)((input[28] + n_LocKeyExpandBox[16 * m_nChipherLen + 14]) & 0xFF);
input[30] = (byte)((input[30] ^ n_LocKeyExpandBox[16 * m_nChipherLen + 15]) & 0xFF);
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