Question

I want use AES Algorithm.

I use this function on it

void SubBytes(char *SArr[4][4]){
int r,c;
char xlook[2];char ylook[2]; char hexStr[2]; char *Pad;
int intxlook,intylook;
char *temp;
int subbyte;
Pad = (char *)malloc (sizeof(char));
temp = (char *)malloc (sizeof(char));

for (r = 0; r < 4; r++)
  for(c = 0; c < 4; c++){
        strcpy(temp,"");
        strcpy(xlook,"");strcpy(ylook,"");
        strcpy(temp,SArr[r][c]);
        xlook[0] = temp[0]; xlook[1] = '\0';
        ylook[0] = temp[1];ylook[1] = '\0';
        intxlook = string_to_dec(xlook);
        intylook = string_to_dec(ylook);

     subbyte = SBox(intxlook,intylook);
     itoa(subbyte,hexStr,16);

     if (strlen(hexStr) < 2){
        strcpy(Pad,"");
        Pad = Padding(0,1);
        strcat(Pad,hexStr);  
        strcpy(SArr[r][c],Pad);
     }
     else
        strcpy(SArr[r][c],hexStr);

  }

  //free(temp); free(Pad);
}     //end 

but i get error

Stack around the variable ‘hexStr’ was corrupted in c

Answer 1

You forgot to null-terminate hexStr.

So when you do strcpy(SArr[r][c],hexStr);. it will attempt to copy into SArr[r][c] from hexStr until it reaches a '\0', which could be anywhere.