Author: David

My encryption code is now live on GitHub

My encryption code is now live on GitHub

Posted on by David
Crptography Word list
Image by tumbledore from Pixabay

I developed Pivot initially on Windows, (a Linux version will follow) though the differences are fairly small. I used the Windows _sopen_s for reading and writing files.  There shouldn’t be too much differen otherwise, though I guess I’ll find out when I compile it on Ubuntu or Raspberry Pi.

The program itself is around 450 lines of C in just one file. It can encrypt around 6 MB/s on my five year old i7 5930K PC and decrypt at around 10 MB/s.

If anyone could try this, I’d be very happy. It has one minor issue that I will resolve. Because it processes files in blocks of 64 bytes, it tends to round the output file when decrypting and adds a few 0s on the end. I will get it sorted

I’ve given it a very liberal MIT license, you can do what you want with it. Instructions on using it are provided on that link to GitHub.

This BTW is the encryption code at the heart of it.

        int bit = 128;
        for (int bi = 0; bi < 8; bi++) {
            for (int b = 0; b < NUMSTREAMS; b++) {
                dataout[b] = (dataout[b] >> 1) | (data[b] & bit);
                data[b] <<= 1;
            }
        }
             
        // Now alter the order of bytes according to the key
        for (int i = 0; i < NUMSTREAMS; i++) {
           data[i] = dataout[_key[i]];
        }

The first double for loop slices 64 bytes into 64 bit streams. It’s pivoting the bits if you like, hence the name. The second for loop is what does the donkey work of encrypting it. It uses a 64 byte key (made up of 64 numbers 0-63- shuffled). As there are 1.2688693e+89 different ways of arranging these 64 numbers, if you lose the key it might take you a while to brute force it!

So I believe that it is an original encryption algorithm, but I am not an expert in cryptography so I might be making a fool of myself! Whether there are any possible attacks against it, I don’t know, but it will be interesting to see!

Hex Editor for Raspberry-Pi

Hex Editor for Raspberry-Pi

Posted on by David

Hex Editor Raspberry PiSometimes you just need to view or maybe a binary file and here I’ve done that on the compiled file for asteroids.

I can’t recommend doing that, but I wanted to try hexedit on the Raspberry Pi. I ran it against the asteroids compiled program and found the text.

If you look I’ve changed the d in starfield (first line of text) to an e. Then I saved it. The program, not unreasonably crashed when run with an error in the errolog.txt file: Couldn’t open images/starfiele.png

You install hexedit with

sudo apt install hexedit

and run with the file you want to view/edit.

hexedit asteroids

To view all the command press F1. It displays the man page for hexedit. Have fun!

A fast random number generator in C

A fast random number generator in C

Posted on by David

Random numbersIf you are using RNGs (Random Number Generators) for cryptography then you need one that has been validated for sufficient randomness. For example the libsodium library.

But if you want a fast one for general purpose use, then xoshiro256++ is a fast one.  It’s actually that short that I can list it here. Just call next() and mod it (%) with the highest value+1. E.G. for a dice roll,

int diceroll= (next() %6) +1;

This algorithm is very fast, typically on the order of nano-seconds 10-9 seconds.

#include <stdint.h>
uint64_t rngstate[4];

static inline uint64_t rotl(const uint64_t x, int k) {
    return (x << k) | (x >> (64 - k));
}

// Returns a Uint64 random number
uint64_t next(void) {
    const uint64_t result = rotl(rngstate[0] + rngstate[3], 23) + rngstate[0];
    const uint64_t t = rngstate[1] << 17;
    rngstate[2] ^= rngstate[0];
    rngstate[3] ^= rngstate[1];
    rngstate[1] ^= rngstate[2];
    rngstate[0] ^= rngstate[3];
    rngstate[2] ^= t;
    rngstate[3] = rotl(rngstate[3], 45);
    return result;
}
Binary editors – Useful tools

Binary editors – Useful tools

Posted on by David

HxD - Binary editorAt some time or other you are going to need a binary editor, to let you look in files and see what they contain.

One I can recommend is HxD which is shown here.

This not only lets you look at the contents of a binary file (in hex and decoded as text)  but you can change them.

It also includes file tools so you can split files, combine them (i.e. append) and securely wipe them. And very handy, the ability to compare two binary files, shown below.

It also lets you export binary files as data  for any of these languages (Pascal,C C#, Java, VisualBasic.net, HTML, rich text and some other formats). Here’s what the top file looks like exported into C.

/* D:\development\pivot\pivot\Debug\l.key (11/05/2020 12:03:32)
StartOffset(h): 00000000, EndOffset(h): 0000003F, Length(h): 00000040 */

unsigned char rawData[64] = {
0x18, 0x3C, 0x2B, 0x11, 0x24, 0x1E, 0x17, 0x26, 0x1C, 0x15, 0x04, 0x19,
0x23, 0x28, 0x08, 0x07, 0x35, 0x0F, 0x34, 0x37, 0x32, 0x05, 0x20, 0x27,
0x3E, 0x0A, 0x3B, 0x2E, 0x1F, 0x29, 0x21, 0x25, 0x2F, 0x14, 0x2D, 0x1A,
0x1D, 0x0C, 0x33, 0x01, 0x39, 0x2A, 0x1B, 0x00, 0x36, 0x06, 0x22, 0x31,
0x38, 0x3A, 0x3D, 0x2C, 0x16, 0x0D, 0x03, 0x00, 0x09, 0x12, 0x13, 0x02,
0x0B, 0x0E, 0x30, 0x10
};

In truth there are many binary file editors. You can find them under hex editors as well. But this is a particularly nice one; recommended.

A remarkable piece of C code

A remarkable piece of C code

Posted on by David

What do you think this outputs?

unsigned char c = 241;
long bits = (c * 01001001001ULL & 042104210421ULL) % 017;
printf("Bits = %lu\n",bits);

Remarkably it calculates the number of bits in c and should output “Bits = 5”.

If you don’t believe me, try this program to show all 256 values and the count. If you use c in the for loop instead of i, it never finishes. Well not with Visual C++ 2019!

#include <stdio.h>

int main()
{
    for (int i = 0; i < 256; i++){
        unsigned char c = i % 256;
        long bits = (c * 01001001001ULL & 042104210421ULL) % 017;
        printf("c %d #Bits = %lu\n",c, bits);
    }
    return 0;
}

You can try this out online on one of the various online C compilers.
Count bitsHere’s it on repl.it.

Build Android apps in C

Build Android apps in C

Posted on by David
Android phone image
Image by mohamed Hassan from Pixabay

Now this isn’t something I’m going to do but I thought it worth the mention. Android development is done in Java mostly but increasingly in Kotlin. But someone has figured out how to do it in C and published it on GitHub.

You still need to install the free Android Studio to get this to work and I’m not really sure I’d want to write a complete mobile app in C, but it would probably outperform many Java/Kotlin apps.

Using printf type variable parameters in your function

Using printf type variable parameters in your function

Posted on by David

The C programming languagI needed this in a bit of debug code. I wanted it to work like printf where there’s a format string containing one or more % format specifications and then write this into a buffer and dump it where ever.

C has a library stdarg which lets you do this. It’s not the most intuitive but it’s definitely worth understanding.

What I’m wanting to do is a function that does something like this (assume s1,s2 and s3 are char *).

sprintf(buffer,"Some string values %s %s %s",s1,s2,s3);
doSomething(buffer);

But in my own function and with the ability to have 0,1,2 or how ever many parameters without having to write a separate function for each. Kind of what printf does.

Here’s the code:

 

#include <stdarg.h>
void op(char* s, ...) {
	char buffer[50];
	va_list argptr;
	va_start(argptr, s);
	vsprintf_s(buffer,sizeof(buffer),s,argptr);
	OutputDebugStringA(buffer);
	va_end(argptr);
}

The … represent the variable number of parameters. it’s called the variadic operator. To access the actual parameters needs the various va_ macros and types. For instance va_list is a type that manages the list of parameters. The va_start macro takes the list and the parameter before the list. vsprintf_s is the Microsoft secure version of vsprintf. Both are the variable parameter equivalent of sprintf/sprintf_s.

OutputDebugString is the Windows debug string function. Finally the va_end tidies up everything.

So you use this just like printf, except the output goes to the Debug channel and can be picked up in Visual Studio (if debugging) or by running the SysInternals free DebugView utility.

Note, the original version of this used OutputDebugString but I found it was outputting gibberish. I correctly guessed that it was linking to OutputDebugStringW ; the MBCS version and changing it to OutputDebugStringA (the ASCII version) fixed it. Something to watch out for on Windows. 

Fixing an unbootable Raspberry Pi

Fixing an unbootable Raspberry Pi

Posted on by David
Raspberry-Pi
Image by Benjamin Nelan from Pixabay

Well to be fair, it was me that made it unbootable. I’d been reading this Wiki page on configuring the Pi. I’d told it to give the GPU almost a GB of RAM. The Pi is a 4 GB Pi 4B.  I did it last night and so this morning, I found it not working at all well.

My first thoughts were I’d messed up the Operating system and so I took the SD card put it in a holder and booted up my old laptop which has Ubuntu 18.04 LTS on it. This page on switchdoc suggested I could do a repair with these commands.

First lsblk to view attached devices. There was a /dev/sdc2 . There was also a /dev/sdc1

Then

sudo fsck -fy /dev/sdc1

That gave information about the drive but not the disk. That took

sudo fsck -fy /dev/sdc2

That took a few seconds and listed information, but still my drive wouldn’t boot back in the Pi.

Then I remembered I’d changed the boot config.txt and it was back with the SD card in the laptop and rebooted that. It showed two devices on the desktop (no need to mount anything) and clicking boot gave me a directory listing of /boot. I edited config.txt and changed the GPU Mem value to 256MB.

That fixed it and my PI is now booting quite happily again. I am now going to make a backup copy! It wouldn’t the end of the world if I had made it permanently unbootable, I’d just burn the OS again. It’s just the time wasted and minor hassles copying files, downloading and reinstalling software. Best avoided if possible!

 

 

Code::Blocks revisited

Code::Blocks revisited

Posted on by David

Code::Blocks SDL2 demoSo after yesterday’s post I also installed Code::Blocks on Ubuntu 20.04 LTS, the recent six monthly Ubuntu release. Guess what, it’s a much newer version of Code::Blocks that looks slightly different and does include SDL2. Although the demo program it creates is C++ not C (That coloured bar picture is the demo).  I haven’t used it enough to see what’s different between this and version 16.01.

The version of Code::Blocks on the 18.04LTS Ubuntu  was 16.01 and on Ubuntu 20.04 LTS it’s Code::Blocks 20.03. I keep my Ubuntus up to date but the 18.04 LTS hasn’t switched to the newer Code::Blocks which surprised me. I’m guessing that the maintainers of the 18.04 LTS Ubuntu repositories just haven’t updated their copy of Code::Blocks.

One thing I hadn’t explored in Code::Blocks is the debugging and this seems a lot more powerful than what you get in Visual Studio Code.   This screenshot below from version 20 shows it is more akin to Visual Studio debugging rather than Visual Studio Code debugging what with CPU registers, stack, memory dump and threads.

Code::Blocks Debugging Menu

 

So I thought I’d try Code::Blocks

So I thought I’d try Code::Blocks

Posted on by David

Code::blocks compiler options

Code::Blocks is an alternative cross-platform open source IDE for C/C++ (and Fortran!). It doesn’t include a compiler but can work with most of them.  It’s also written in C++ (you’d never guess from the name!) and so is fast.

Installing is just a

sudo apt install codeblocks

When you install it, it looks for installed compilers and gives you the choice of which is the default.

When you create a project there are a few types and one that got me excited was SDL. It creates a skeletal project and it was only when compiling that I realised it was for SDL1, not 2.  It’s the nature of open source that things take time to remedy. So don’t bother with it.

Anyway I copied in my source files and clang objected because it couldn’t find the SDL2 files. The fix isn’t too difficult. In Code::Blocks, navigate to Project Build Options then in Compiler settings > Other compiler options add these lines

-lSDL2

-lSDL2_image

-lSDL2_mixer

and in the Linker settings > Other linker options

-lSDL2

-lSDL2_image

-lSDL2_mixer

Note those are -l () not i or 1.

After that it compiled and linked ok. The compiled code is in the bin/Debug folder. However to get Asteroids to run you need to copy in the images, sounds, and masks folders and the highscore.txt file. After that it runs fine, but note when you compile it seems to delete everything in the folder.

So overall it wasn’t a difficult thing to do and I’m going to install it on a Raspberry Pi and see how that goes. I’ve already got Visual Studio Code installed on it and working but having a second IDE (both using the same compiler) is no bad thing.