function [ a,Si ] = descramble( a,Si )
for i=1:length(a)
b(i)=xor(Si(4),Si(7));
b(i)=xor(b(i),a(i));
c(i)=a(i);
a(i)=b(i);
Si(2:7)=Si(1:6);
Si(1)=c(i);
end