The meeting will be on Steganography (held over from last month) and some other coding such as modifying dates on Windows files that is not a facility normally available to users. There may also be some discussion and analysis of SBS's Myth Busters TV show on Monday nights at 7:30pm. Lots of good technology stuff done there.

We also have some very novel uses for wireless bridges that Rick is writing up for a magazine. We may have a look at wireless networks generally from a more practical point of view than we have done in the past.

Some source code to be talked about in the meeting follows;

alpha.c

//-------------------------------------------------------------------
//ALPHA.C reads a file byte-wise and writes it out to another file
//with all non-printing chars removed.
//-------------------------------------------------------------------

#include 
#include 

char c;

FILE *fi;
FILE *fo;

int main(int argc, char *argv[])
{
	if(argc<3)
	{ printf("Remove all non-printing characters\n");
		printf("\nUsage is:- ALPHA inputfile.ext outputfile.ext\n");
		exit(1);
	}

	if((fi = fopen(argv[1],"rb")) == NULL)
	{ printf("\nNo input file %s\n",argv[1]);
		exit(1);
	}

	if((fo = fopen(argv[2],"wb")) == NULL)
	{ printf("\nCan't open output file %s\n",argv[2]);
		exit(1);
	}

	while(feof(fi) == 0)
	{ c=fgetc(fi);

	 	//...insert a "filter" at this point
		if((c == 0xd) || (c == 0xa))
		{	fputc(c,fo);
			continue;
		}
		if((c < 0x20) || (c > 0x7d))
			continue;
		else
		fputc(c,fo);
	}

	fclose(fi);
	fclose(fo);
	printf("\a"); /* ring bell */
	exit(0);

datechg1.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 

main(int argc, char *argv[])
{	unsigned date;
	unsigned time;
	int fh;

	if(_dos_open(argv[1],O_RDONLY,&fh) != 0)
		perror("open error");
	else
		printf("open succeeded\n");

	_dos_getftime(fh,&date,&time);

	date = 16 + (8*32) + ((2005-1980)*512); //change date to 16/8/2005

	_dos_setftime(fh,date,time);
	printf("date changed\n");

	if(_dos_close(fh) != 0)
		perror("close error");
	else
		printf("file closed OK\n");
}

time2.c

//append time and date to a file.

#include 
#include 

FILE *fa;

int main()
{	char datebuf[20], timebuf[20];

	if((fa=fopen("time.lst","at")) == NULL)
		exit(1);

	_strtime(timebuf);
	_strdate(datebuf);
	fprintf(fa,"%s %s\n",timebuf,datebuf);

	fclose(fa);
	return 0;
}

steg-x.c

// ------------------------------------------------------------------
//STEG-x.C extracts hidden text from a steganography file.
//-------------------------------------------------------------------

#include 
#include 

int buff[4096];

FILE *fi;
FILE *ft;
FILE *fo;
int bitnum;
char ch;
char id[]="Rick was here";

//--------------- main ----------------
int main(int argc, char *argv[])
{ int n, num;

	if(argc != 3)
	{ printf("\nUsage is:- STEG-R inputfile.ext message.txt\n");
		exit(1);
	}

	if((fi = fopen(argv[1],"rb")) == NULL)	//inputfile.ext
	{ printf("\nNo input file %s\n",argv[1]);
		exit(1);
	}

	if((fo = fopen(argv[2],"wt")) == NULL)	//message.txt
	{ printf("\nCan't open output file %s\n",argv[2]);
		exit(1);
	}

	//skip 1st 1024 words
	if(fread(buff,sizeof(int),1024,fi) != 1024)
	{	printf("ERROR reading input file\n");
		exit(1);
	}

	while((num=fread(buff,sizeof(int),1024,fi)) > 0)
	{
		bitnum=0; ch='\0';
		for(n=0; n 7)
			{
				if((ch & 0xff) == 0xff)
					goto alldone;
        fprintf(fo,"%c",ch);
				bitnum=0; ch='\0';
			}
			else
				ch = (ch & 0xff) >> 1;
		}
	}

alldone:
	fclose(fi);
	fclose(fo);
	printf("\a"); /* ring bell */
	exit(0);
}

steg-h.c

//---------------------------------------------------------------------
//STEG-H.C uses steganography to HIDE a text file inside a picture file
//---------------------------------------------------------------------

#include 
#include 

int buff[4096];
char tbuff[4096];
FILE *fi;
FILE *ft;
FILE *fo;
int bitnum, bitval, endbits;
char ch;
char id[]="Rick was here!";


//------------ subroutines ------------
int getbit()
{
	if(bitnum == 0)
	ch=fgetc(ft);
	bitval = 1 & (ch >> bitnum);

	bitnum++;
	if(bitnum > 7)
		bitnum = 0;
	return bitval;
}

//--------------- main ----------------
int main(int argc, char *argv[])
{	int n, num;

	if(argc != 4)
	{	printf("\nUsage is:- STEG-H inputpicture.ext message.txt outputpicture.ext\n");
		exit(1);
	}

	if((fi = fopen(argv[1],"rb")) == NULL)	//inputpicture.ext
	{	printf("\nNo input file %s\n",argv[1]);
		exit(1);
	}

	if((ft = fopen(argv[2],"rt")) == NULL)	//message.txt
	{	printf("\nNo input file %s\n",argv[2]);
		exit(1);
	}

	if((fo = fopen(argv[3],"wb")) == NULL)	//outputpicture.ext
	{	printf("\nCan't open output file %s\n",argv[3]);
		exit(1);
	}


	//skip 1st 1024 words
	if((num=fread(buff,sizeof(int),1024,fi)) != 1024)
	{	printf("error reading input %s\n",argv[1]);
		exit(1);
	}
	fwrite(buff,sizeof(int),1024,fo);


	bitnum=0; endbits=8;
	while((num=fread(buff,sizeof(int),1024,fi)) > 0)
	{
		for(n=0; n 0)
				{ buff[n] = buff[n] | 1;
					endbits--;
				}
		}
    fwrite(buff,sizeof(int),1024,fo);
	}

	fclose(fi);
	fclose(ft);
	fclose(fo);
	printf("\a"); /* ring bell */
	exit(0);
}