function [r, i0, j0, sc]=rc4out(i0, j0, sc)
% next byte of rc4 output
% inputs: i0, j0 = indices; sc = key schedule
% outputs: r=random byte; i0, j0 = indices; sc = key schedule

i0 = mod( (i0+1), 256);
j0 = mod( j0 + sc(i0+1), 256);
tmp = sc(j0+1);
sc(j0+1) = sc(i0+1);
sc(i0+1) = tmp;
r = mod( tmp + sc(j0+1), 256);