Cant Use Reshape Function with Randi or Randperm

Hi,

I am trying to generate a random number vector and use it as shown in below:

plaintextsamples = randi(65535,1,1000);
for h = 1:1000
    %a = plaintextsamples(i);
    plaintexttemp = dec2bin(plaintextsamples(h),16);
        for k = 1:16
            temp = plaintexttemp(k);
            plaintext(k) = str2double(temp);
        end
    ciphertext = encrypt_func(plaintext);
  
    
   
    
    
  

In the 9th line, I call a function and this function contents another function with reshape operation:

function permboxout = permbox1func(permboxin_temp)
%%%%Block Cipher 1 Permutation
permutation1 = [1,5,9,13,2,6,10,14,3,7,11,15,4,8,12,16];
permboxin_temp = dec2bin(permboxin_temp);
permboxin = reshape(permboxin_temp',[1,16]);
for i = 1:16
    permboxout(permutation1(i)) = permboxin(i); 
end 

Basically, I am using the plaintext value in the first code as the input of the permbox1func and plaintext is a random value of the plaintextsamples which is created with an randi or randperm function.

When I run it an error message is shown:

Error using reshape

To RESHAPE the number of elements must not change.

Error in permbox1func (line 5)

permboxin = reshape(permboxin_temp',[1,16]);

Error in encrypt_func (line 21)

permboxround1 = permbox1func(sboxround1); %permutation 2

Error in decrypt (line 9)

ciphertext = encrypt_func(plaintext);

When I disable the randi function and using the loop value itself:

for h = 1:1000
    %a = plaintextsamples(i);
    plaintexttemp = dec2bin(h,16);
        for k = 1:16
            temp = plaintexttemp(k);
            plaintext(k) = str2double(temp);
        end
    ciphertext = encrypt_func(plaintext);

It works if h = 1:540 but the same error pop up if max limit of h is bigger than 550 or 560. I am really confused. Why the limit of a loop or randi function matters for reshape function? The shape should not change each time because I already declared that plaintext is a double vector with 16 elements.

Thanks for your help.

Answer 1

[MU]

I found the error.

permboxin_temp = dec2bin(permboxin_temp);

When this line is used with randi, a double array is created rather than a char array. And the function converts each value to a 16 bit value. So, at the end, permboxin_temp ends up with being a 4x16 char array (input is 4 decimal values). I fixed it with the following modification:

b = 1;
for a = 1:4
   permboxin_tempk(b:b+3) = dec2bin(permboxin_temp(a), 4);
   b = b + 4;
end

It may not be the optimal solution, but it works!

Answer 2

[James Tursa]

I'm guessing you need to tell this dec2bin call that it always needs to produce 16 digits also:

permboxin_temp = dec2bin(permboxin_temp,16);

[MU]

Well looks like I missed it. However the same error occurs for the same lines when I applied it.

[James Tursa]

Use the debugger. Type this in at the command line

dbstop if error

and then run your code. When the error occurs, the code will pause with all variables intact. Examine permboxin_temp to see what it is, and then backtrack in your code to figure out why it isn't what you expected.