A new project i'm undertaking...

Hey everyone!

I've been really bored lately and i want some programming to do! haha so i asked my mom if she wanted me to make her a program to keep track of her grades at school. She uses a gradebook and spends hours calculating final grades and such so i figured i'd make her life easier.

Okay so i've been writing everything down and all to get organized, i need to have everything together before i even put down a single line of code, ha.

One thing i encountered was this, i wanted to do a basic encryption on the grade files. I know no one is ever gonna try to mess with the files but i figured it would add an extra challenge and aspect to the program to keep me busy. I was thinking of using the hash of the user password (to get into the program) the only problem is that i would have to store this number somewhere and it would be easy for someone to get to it and decrypt the files using it.

So what should i do? I'm not looking for code right now just suggestions.


Thanks!


PS- Maybe a hash of the hash? i dunno.

Quote:

---

One thing i encountered was this, i wanted to do a basic encryption on the grade files. I know no one is ever gonna try to mess with the files but i figured it would add an extra challenge and aspect to the program to keep me busy. I was thinking of using the hash of the user password (to get into the program) the only problem is that i would have to store this number somewhere and it would be easy for someone to get to it and decrypt the files using it.

---

This is how Linux and UNIX password systems work. The password is encrypted with some encryption mechanism, and the encrypted version is stored somewhere (usually in /etc/shadow). Then, when someone types a password, that password is encrypted and compared with the encypted version. If they match, the password is correct.

The nice thing about that scheme is that you never store the unencrypted password, nor do you actually even need to use an algorithm that can be decypted. You can use a "one-way" algorithm, and in fact many programs do.

I don't know if that helps. Unfortunately I don't know of any one-way (trapdoor) algorithms.

[edit] BTW, you could write the plaintext version first, and then, if you write it well and modular-ily, modify it to use encryption with little hassle. [/edit]

Yeah one way hash functions :)

But yeah, i figured out not to store the unencrypted password a while ago, i used to (*try to*) do a lot of that stuff.

It's just how do i encrypt the files? That's what i wonder, i cant use and irreversible algorithm for that cause you gotta be able to reopen the files ;) haha so i dunno what to do. I'll do that part of the program last but its the one pitfall i can really think of right now.


Thanks!

Well, it depends on how secure you want those files to be. For very simple encryption you could just use CBC, Cipher Block Chaining encryption. It's very easy to crack (this is a first-hand experience), but someone who just opens the file by accident won't be able to read it.

For CBC, basically you take the key and XOR it with the first byte; this byte is written to the file. Then you use the generated byte for the next key.

I did a study on CBC once, a long time ago. You can improve its encryption somewhat (very slightly) by using two keys. (It's still a very bad encryption algorithm.) Perhaps you could have the password as two bytes, then split that in half and use each half as one of the keys.

Your best best for "unbreakable" encryption is probably AES (it is a standard, after all). I'm sure you can find plenty of implementations on the web.

I'll look into CBC, AES is overkill ;) haha, no ones ever really gonna open the files directly, lol, so i just need sometihng basic, like CBC, thanks though!


Oh and nother quick quesiton, i feel like an idiot cause i asked this a long..... time ago and i forget now, how do i make a folder from the program? Do i have to use a batch-file type command or is there something in C++ i can use?


Thanks!

Quote:

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Oh and nother quick quesiton, i feel like an idiot cause i asked this a long..... time ago and i forget now, how do i make a folder from the program? Do i have to use a batch-file type command or is there something in C++ i can use?

---

POSIX has a function called mkdir() (in <unistd.h>, I think) but it isn't standard (though omnipresent on Linux systems). You'd need to use system() for windows:

Code:

---

system("mkdir directory");

---

I suggest using "mkdir" instead of "md", because "mkdir" is the right command on both Windows and Linux.

Thanks!

Hey guys, i gotta problem =(

In my program i have a function to encrypt a file (using what i think is the CBC mentioned earlier). But when i pass the filename to ofstream and ifstream it tells me that it cannot convert a string to a const char *.

The function looks like this:

Code:

---

...
void encryptFile(string filename)
{
    ...
    ofstream fout(filename);
    ...
}
...

---

Why wont it work? Its cause its beign passed to the function as a pointer probably right?

What can i do?


thanks!

filename.c_str()

i had a feeling that might be it ;) i'll give it a try, thanks!

Nope =( It still won't compile

Not sure what the problem might be, the below compiles fine as an example.

Code:

---

#include <iostream>
#include <string>
#include <fstream>

std::string testthis;
std::string testthat;

void encryptFile(std::string filename)
{
    filename.append(".txt");
    ofstream fout(filename.c_str(),ios::out);
    fout<<testthat;
}


int main()
 {
      testthat="Hello, thar";

          testthis="testthis";
          encryptFile(testthis);
     
      std::cin.get();
      return 0;
      }

---

i added the .c_str() in the wrong spot :( Lemme give it a try.

It works but i'm getting a seg fault i think with the strings, here's the code:

Code:

---

//Encryption Algorithm Start
        encrypted.at(0) = temp.at(0)^hPass;
        for(int i=1; i<temp.size(); i++)
        {
                encrypted.at(i) = encrypted.at(i-1)^hPass;
        }

---

encrypted is a string (not yet initialized) and hPass is an unsigned integer.


Anyone know why this is seg faulting? All the variables in the debugger look alright to me. =(

EDIT:

Nevermind, i used push_back() instead.

Never mind again ;)

EDIT

DWKS:

Is this the right way to go about this CBC thing? Cause it wont work right =(

Code:

---

//*****************ENCRYPT FILE FUNCTION*******************//
void encryptFile(string filename)
{
        //Get the contents of the file
        ifstream fin(filename.c_str());
        char ch;
        string temp;
        while(fin.get(ch))
        {
                temp += ch;
        }
        fin.close();
        //Encrypt
        string encrypted;
        string hPassword;
        //Get the hash value of the password
        unsigned int hPass;
        ifstream fin2(SETUP_FILE);
        string getTemp;
        while(fin2.get(ch))
        {
                getTemp += ch;
        }
        fin2.close();
        int j;
        for(int i=0; i<getTemp.size(); i++)
        {
                if(getTemp.at(i) == '\n')
                        j=(i+1);
        }
        for(j; j<getTemp.size(); j++)
        {
                hPassword += getTemp.at(j);
        }
        hPass = stringToInt(hPassword);
        //Encryption Algorithm Start
        encrypted.push_back(temp.at(0)^hPass);
        for(int i=1; i<temp.size(); i++)
        {
                encrypted.push_back(encrypted.at(i-1)^hPass);
        }
        //Encryption Algorithm End

        //Save to file
        ofstream fout(filename.c_str());
        fout<<encrypted;
        fout.close();
}

//**********************DECRYPT FILE FUNCTION************************//
void decryptFile(string filename)
{
        //Get the contents of the file
        ifstream fin(filename.c_str());
        char ch;
        string temp;
        while(fin.get(ch))
        {
                temp += ch;
        }
        fin.close();
        //Encrypt
        string decrypted;
        string hPassword;
        //Get the hash value of the password
        unsigned int hPass;
        ifstream fin2(SETUP_FILE);
        string getTemp;
        while(fin2.get(ch))
        {
                getTemp += ch;
        }
        fin2.close();
        int j;
        for(int i=0; i<getTemp.size(); i++)
        {
                if(getTemp.at(i) == '\n')
                        j=(i+1);
        }
        for(j; j<getTemp.size(); j++)
        {
                hPassword += getTemp.at(j);
        }
        hPass = stringToInt(hPassword);
        //Encryption Algorithm Start
        decrypted.push_back(temp.at(temp.size()-1)^hPass);
        for(int i=1; i < temp.size()-1; i++)
        {
                decrypted.push_back(decrypted.at(i-1)^hPass);
        }
        //Encryption Algorithm End

        //Save to file
        ofstream fout(filename.c_str());
        fout<<decrypted;
        fout.close();
}

---

How do i implement the CBC correctly?

DWKS or anyone for that matter ;) haha Thanks!

Sorry, I didn't get on CBoard yesterday . . .

No, it isn't, because it isn't working. :) I didn't explain CBC very well, because I didn't actually expect you to use it. :)

With CBC, each character is XORed with the IV (initialization vector) as well as the key. The IV is just some number -- you can pick it -- and for subsequent character, the previous enciphered character is the IV.

This is a great example -- a picture is worth a thousand words: http://upload.wikimedia.org/wikipedi...encryption.png
It's from this wikipedia entry, which is worth reading: http://en.wikipedia.org/wiki/Block_c...s_of_operation

[edit] Sections in for loops can be empty:

Code:

---

for(j; j<getTemp.size(); j++)

---

You don't really need to keep all of the information in a string. You could process it character by character, writing each character to the file once you're done with it. [/edit]

Okay, well this works but i know its not the CBC:

Code:

---

//*****************ENCRYPT FILE FUNCTION*******************//
void encryptFile(string filename)
{
        //Get the contents of the file
        ifstream fin(filename.c_str());
        char ch;
        string temp;
        while(fin.get(ch))
        {
                temp += ch;
        }
        fin.close();
        //Encrypt
        string encrypted;
        string hPassword;
        //Get the hash value of the password
        unsigned int hPass;
        ifstream fin2(SETUP_FILE);
        string getTemp;
        while(fin2.get(ch))
        {
                getTemp += ch;
        }
        fin2.close();
        int j;
        for(int i=0; i<getTemp.size(); i++)
        {
                if(getTemp.at(i) == '\n')
                        j=(i+1);
        }
        for(j; j<getTemp.size(); j++)
        {
                hPassword += getTemp.at(j);
        }
        hPass = stringToInt(hPassword);
       
        //Encryption Algorithm Start
        encrypted += (temp.at(0)^5)^hPass;
        for(int r=1; r<temp.size(); r++)
        {
                encrypted += temp.at(r) ^ hPass;
        }
        //Encryption Algorithm End

        //Save to file
        ofstream fout(filename.c_str());
        fout<<encrypted;
        fout.close();
}

//**********************DECRYPT FILE FUNCTION************************//
void decryptFile(string filename)
{
        //Get the contents of the file
        ifstream fin(filename.c_str());
        char ch;
        string temp;
        while(fin.get(ch))
        {
                temp += ch;
        }
        fin.close();
        //Encrypt
        string decrypted;
        string hPassword;
        //Get the hash value of the password
        unsigned int hPass;
        ifstream fin2(SETUP_FILE);
        string getTemp;
        while(fin2.get(ch))
        {
                getTemp += ch;
        }
        fin2.close();
        int j;
        for(int i=0; i<getTemp.size(); i++)
        {
                if(getTemp.at(i) == '\n')
                        j=(i+1);
        }
        for(j; j<getTemp.size(); j++)
        {
                hPassword += getTemp.at(j);
        }
        hPass = stringToInt(hPassword);
        //Decryption Algorithm Start
        decrypted += (temp.at(0)^5) ^ hPass;
        for(int r=1; r<temp.size(); r++)
        {
                decrypted += temp.at(r) ^ hPass;
        }
        //Decryption Algorithm End

        //Save to file
        ofstream fout(filename.c_str());
        fout<<decrypted;
        fout.close();
}

---

Thoughts?

How can i make a variable global (editable by ALL functions -- including those in other .cpp files)? I broke my project up into different header files, one for menu functions, one for secure functions, one for setup functions, etc. But there's this one variable i need some of those things in different header files to access. How do i do it?

I have one header file, called global.h which holds all of the the other include files and header files. I put the variable there and it compiles at first but it gets a linker error saying there's unresolved externals i think =(

Can anyone help me out here?

Thanks!

Perhaps you can do it as link your global to the header file which first uses the global, then so on and so forth.

Something like; first.h ->include globals.h, second.h-> include first.h, main.cpp->include second.h.

It's actually rather difficult to visualize....

yeah... ha, you lost me there.

There's a header called global.h, it holds All of the other header files and includes, as well as the using namespace std; bit. Now i also put the global variable (unsigned int hp;) in there as well, hoping that all of the other files that include that file (global.h) would have access to it.


I dunno if i'm coming across well either =P haha

EDIT-----------

Here's the code for global.h:

Code:

---

//Standard Include Files
#include <iostream>
#include <fstream>
#include <ctime>
#include <vector>
#include <string>

//Global Variables
unsigned int hp;

//Namespaces
using namespace std;

//Custom Include Files
#include "setup.h"
#include "secure.h"
#include "menus.h"
#include "grades.h"

---

Unfortunately, you may need someone smarter than I to help you. About your code above though, is it valid to declare variables before including your header files? For some reason, that seems a rather odd thing to do. Or is that simply a typed-in typo?

Quote:

---

Originally Posted by Junior89

Here's the code for global.h:

Code:

---

//Standard Include Files
#include <iostream>
#include <fstream>
#include <ctime>
#include <vector>
#include <string>

//Global Variables
unsigned int hp;

//Namespaces
using namespace std;

//Custom Include Files
#include "setup.h"
#include "secure.h"
#include "menus.h"
#include "grades.h"

---

---

That kinda looks like the classic "what not to do" approach. Seems dandy when you've gone beyond the simple; looks, well, like what not to do, later on.

Quote:

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Originally Posted by Junior89

I've been really bored lately and i want some programming to do! haha so i asked my mom if she wanted me to make her a program to keep track of her grades at school. She uses a gradebook and spends hours calculating final grades and such so i figured i'd make her life easier.

---

[aside]Spreadsheets do such things nicely.[/aside]

I've tried the spreadsheet thing before but the grading system at her school requires a more 'powerful' scripting, to put it that way.

A c++ program is the way to go. And what's wrong with my approach with the global.h? This is the first time i've ever used my own header files and such cause this project is so big.

What should i do instead of that?

EDIT--------

I moved the global variable down after the includes and i still get the same errors =(

Quote:

---

Originally Posted by Junior89

And what's wrong with my approach with the global.h?

---

In general you shouldn't be putting using namespace std; in any header ever*. And each header should only contain the necessary #includes to declare such things as the header does.

The panacea approach always introduces more problems than it is worth, IMO.

*Yeah, yeah, yeah.

Quote:

---

And what's wrong with my approach with the global.h? This is the first time i've ever used my own header files and such cause this project is so big.

---

1. Generally, it is better to avoid using such a global variable. Also, if you do insist on using it, I think it should be declared extern in the header file.
2. "using namespace std;" in a header file defeats the point of namespaces.
3. You may include header files that you do not need for a given source file.

If you are interested in a more in-depth look at block cipher modes of operation, I've written a tutorial about it not so long ago. There's also a section dedicated to CBC. All you have to do is remove the call to aes_encrypt(), since you don't apply a block cipher to your plaintext.

So what you guys are saying is to take all the stuff in global.h and move it to the main?

My only question is that wouldn't i then have to put all those includes in the other includes as well? Cause some of the header files functions rely on other header file functions =(

Probably not the way header files are supposed to work but i used this to keep all my functions sorted neatly so i knew if i needed to look up the encrypt() function for example i could do so in the secure.h and secure.cpp header files.


And thanks for that article KONI, it was interesting, my problem is that i'm always the one who wants to 'reinvent the wheel' by writing my own algorithm. =( haha

Quote:

---

Originally Posted by Junior89

I've tried the spreadsheet thing before but the grading system at her school requires a more 'powerful' scripting, to put it that way.

A c++ program is the way to go.

---

That's like saying "I need to get to the second floor of this building. A Saturn rocket is the way to go." I think it's great that you want to write a C++ program for this task, and I think you should for the sake of experience, but be realistic: what you are doing is WAY overkill.

I highly doubt the grading system requires any processing more complicated than could be provided by VBA.

Probably, but i wanted something to program and learn from so here i am =)

Quote:

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Originally Posted by Junior89

Probably, but i wanted something to program and learn from so here i am =)

---

Again, I'm glad you're enthusiastic. Just make sure you can pull it off. You are, after all, dealing with the grades of REAL people here. Not only is this information very important to the individual students, it is protected by various privacy laws like FERPA.

Personally, I'd rather people gained their experience writing NON-mission-critical software. But of course in the real world most software is crap whether it is critical or not, so that's just wishful thinking :-)

Quote:

---

Originally Posted by Junior89

I've tried the spreadsheet thing before but the grading system at her school requires a more 'powerful' scripting, to put it that way.

---

Any examples you can share? To me it seems that a spreadsheet is still more suited to the task.

Quote:

---

Originally Posted by Junior89

So what you guys are saying is to take all the stuff in global.h and move it to the main?

---

Not exactly. A truly organized programming project would not need a global header file because
1. The project has already been divided into modules that can be compiled individually for unit testing.
2. All the modules can also be compiled together when the program is ready to be actually used.
3. The programmers know that global headers would increase the risk of unnecessary dependancies, code bloat, and extra long compile time.
4. The programmers know that forcing all classes under one namespace ( via using namespace vomit; ) is bad.
5. The programmers know that unnecessary global variables increase the risk of violating data integrity.

Pretty much what people told you, but no the answer is not "dump it into main.cpp"

Quote:

---

Originally Posted by brewbuck

Again, I'm glad you're enthusiastic. Just make sure you can pull it off. You are, after all, dealing with the grades of REAL people here. Not only is this information very important to the individual students, it is protected by various privacy laws like FERPA.

Personally, I'd rather people gained their experience writing NON-mission-critical software. But of course in the real world most software is crap whether it is critical or not, so that's just wishful thinking :-)

---

Well she does everything by the book now and she's gonna keep doing it that way In Addition to the program (if i can get it done anytime soon which is probably not gonna happen =P) so that's a backup.

Just some quickie tinkering, but why wouldn't something like this work?

I suppose it would but the whole *point* was to give me something to program ;)

I'll figure it out on my own i suppose, thanks for crushing my hopes and dreams! hahaha =P

But yeah, i'm doing it in C++ and i'm not changing my mind =D

Quote:

---

Originally Posted by Junior89

I suppose it would but the whole *point* was to give me something to program ;)

I'll figure it out on my own i suppose, thanks for crushing my hopes and dreams! hahaha =P

But yeah, i'm doing it in C++ and i'm not changing my mind =D

---

I'm not trying to crush your hopes or end your C++ practice exercises. I'm just paraphrasing an old adage of "when all you've got is a hammer, everything looks like a nail".

This plays perhaps a greater meaning than you take. That is, choose the correct tool for the job. Why spend months or years developing something that is already available to you for free and debugged and easy to use with wonderful choices for output? In another way, why try to run a 100-yard-dash wearing a 200-lb backpack if you have the choice of taking it off? The lesson to be learned is likely, "don't wear the 200-lb backpack".

What you intend can be done, and you will reinvent a decades-old wheel. The practice of programming has generally centered around making our lives easier by using appropriate tools. Ignoring them is a mistake that I feel should be pointed out.

I myself undertake such exercises regularly, and I usually end up with the finding that a better solution would have been to heed such advice in the first place. That is pretty much the reason I offer it.

But along the way, you do gain valuable knowledge before you inevitably (most likely, IMO) abandon the project unfinished. So it is in this spirit that I have offered my remarks.

We may stand on the shoulders of giants, but ...

[/rant=I'll just stop now]

Do continue with your project. Keep posting questions as they arise. It has drawn the interest of a number of folks already -- we wish you good results and will endeavor to assist you as best we can.

I hear what you're saying, and thank you =)

And yeah, the global variable is still the problem =(