ocr: a'(x)= (Objx + (Od)r+ (09jx+ (0e). (5.9) As described in Sec. 4.3, this can be written as a matrix multiplication. Let s(1)=a"(m)@s(): [Oe Ob Od 0,c 09TSae Sic 09 - Oe Ob Od - Sie forOSc<Nb. (5.10) S2,c Od 09 Oe Ob S2e S3.c LOb Od 09 Oe JLSsc Asa result ofthis multiplication, the four bytes in a column are replaced by the following: Soc = (£0e) Soc)e(fObj* Si)e(od) d 5,)0(09)e5) Sie = (£09) - S0c)0 (0e, Si2)0(f0b; e 52)0(od)*: S3e) S2c = (10d) . Soz)e(109)* Si)e(0e)* S,)e(0b)es,) S3c =l (0b) . Su)e(fod) . 118403-,)0408-)
(.png)
