How to do: Multiple Row Allocation within a for loop for a Variable in GF (2^m)

Hello all,

Recently, I started working on a ECC implementation in Matlab to model the ECDH (elliptic curve diffie-hellman key exchange) algorithm. Everything was going great until I wanted to allocate each point on the curve starting from my base point i.e. P1 (base), P2, P3, P4, ... etc. I thought that a simple for loop would do the trick like this...

    m = 9;
    x1=6;
    y1=298;

    % Input GF allocation for EC in GF(2^m) --> first point (Base point)
x0 = gf(x1,m);
y0 = gf(y1,m);

 A = [x0,y0]           % 'A' is to show that without a for loop, the allocation works as expected and shown in the output

 for i = 1 : 2         % Test loop, in my code I have while 1 and a break to work with the rest of my code accordingly

    if i == 1
        B(i) = [x0,y0] % <------------'B(i)' won't allocate correctly
    end

 end

But to my surprise I was stuck with the following error... I don't know if this is a problem with the internal Matlab function gf() or if there is a specific way to do this allocation. I cannot allocate each point by brute-force because there will be MANY points, therefore I need to use a loop.

I want to thank you in advance for your time, explanation, and efforts in helping me tackle this problem I am facing; have a fantastic day!

- Dylan R.

[Walter Roberson]

Has B been given a value before that point, or is it undefined at the time the problem occurs?

[lalonded]

B hasn't been defined or given a value before that point. It is just a arbitrary variable to help illustrate my problem. Thanks for commenting!

Answer 1

[Thorsten]

I would guess that the following works

B{i} = [x0, y0];

[lalonded]

This runs properly, thank you!

Is there a reason why it needs to be a cell for this allocation to work properly? I'm genuinely interested...

[Thorsten]

B(i) can just store a single element, but not two, [x0, y0];

 B(i,:) = [x0, y0]

may also work, if x0 and y0 have the same size for each i.

[RESHMA]

can you please suggest me to encrypt an image using matlab