What is the error in this?

function DECout = gf2dec(HA)
c=0:[(2^8)-1];
GFRefarray=gf(c);
for i=1:length(HA)
    for k=0:(2^8)-1
        temp=isequal(HAHA(i),GFRefarray(i));
        if (temp==1)
            DECout(i)=k;
        end
    end
end

The error is: >> gf2dec Error using gf (line 65) X must be between 0 and 2^m-1

Error in gf2dec (line 3) GFRefarray=gf(c); How to solve this??

The value of HA is:

HA = GF(2^8) array. Primitive polynomial = D^8+D^4+D^3+D^2+1 (285 decimal)

Array elements = 

           172
           106
           200
           187
            68
           251
           103
             2
           149
           131
            25
            55
           237
           110
           129
           231

I am trying to convert the galois polynomial, HA into a numeric value. I want to encrypt the data. So, how can I convert this ?

Answer 1

[Walter Roberson]

>> help gf
 gf  Create a Galois field array.

      X_GF = gf(X,M) creates a Galois field array from X in the field
      gf(2^M), for 1<=M<=16. The elements of X must be integers between 0
      and 2^M-1. [...]

     X_GF = gf(X) uses a default value of M = 1.

[Darsana P M]

Sir, I tried editing this line: c=0:[(2^8)-1]; replaced 8 by 1,because by default is 1. Even then i got an error stating, not enough arguments. Is that what you meant??

[Darsana P M]

Sir, i got the error rectified, but still conversion is not happening?? What might be the issue??

[Walter Roberson]

function DECout = gf2dec(HA)
N = 8;
c = 0 : (2^N)-1;
GFRefarray = gf(c, N);
for i = 1:length(HA)
    for k = c
        if isequal(HAHA(i),GFRefarray(i));
            DECout(i)=k;
        end
    end
end

... looks pretty inefficient to me.

[Darsana P M]

Sir, could you please help. I tried the above code too. I am still not able to convert the galois polynomial into a hexadecimal value. Could you please help with the correct code?

[Walter Roberson]

function DECout = gf2dec(HA)
N = 8;
c = 0 : (2^N)-1;
GFRefarray = gf(c, N);
for i = 1:length(HA)
    for k = c
        if isequal(HA(i),GFRefarray(k+1));
            DECout(i)=k;
        end
    end
end

[Darsana P M]

HA = GF(2^8) array. Primitive polynomial = D^8+D^4+D^3+D^2+1 (285 decimal)
Array elements = 
           172
           106
           200
           187
            68
           251
           103
             2
           149
           131
            25
            55
           237
           110
           129
           231

The error is : gf2dec Error using gf2dec (line 18) Not enough input arguments. line 18 is this : for i=1:length(HA) How to correct this sir?

[Walter Roberson]

You would get that error if you did not pass HA to gf2dec.

result = gf2dec(HA)

I would note that the code from the other thread, accessing the properties of the field, would be a lot more efficient.

[Darsana P M]

Yes, that is right sir. But HA is obtained from hash1(g) which is again a function. How to call a functon within a function??

[Darsana P M]

Very sorry Sir, now I got the error rectified. I made a mistake while calling functions. Thanks a lot sir.