base 64 encoding via c

Posted 07-25-2013 at 09:04 AM by sumeet inani

I came across some anti-virus in windows that detect programs like cmdow , fgdump etc. as threat & quarantine/remove it without asking.

So I wrote this c program that takes a byte from input-binary & writes it to ascii-hex-text-file while encoding .
In decoding takes two alphanumeric characters from input-text & writes it as single char to output-binary.

Compile it in your distro using
gcc program-file-name.c

Here is the code

Code:

#include"sys\types.h"
#include<fcntl.h>
#include<stdio.h>
#include"sys\stat.h"
#include<process.h>
#include<string.h>
char out_buffer[1028];
void encode(char *inp_buffer,int bytes)
{       int i;
	unsigned char b;
	for (i=0;i<bytes;i++)
	{	b=inp_buffer[i];
		switch((b/16))
		{	case 10:out_buffer[i*2]='a';break;
			case 11:out_buffer[i*2]='b';break;
			case 12:out_buffer[i*2]='c';break;
			case 13:out_buffer[i*2]='d';break;
			case 14:out_buffer[i*2]='e';break;
			case 15:out_buffer[i*2]='f';break;
			default:out_buffer[i*2]=(b/16)+48;
		}
		switch((b%16))
		{	case 10:out_buffer[(i*2)+1]='a';break;
			case 11:out_buffer[(i*2)+1]='b';break;
			case 12:out_buffer[(i*2)+1]='c';break;
			case 13:out_buffer[(i*2)+1]='d';break;
			case 14:out_buffer[(i*2)+1]='e';break;
			case 15:out_buffer[(i*2)+1]='f';break;
			default:out_buffer[(i*2)+1]=(b%16)+48;
		}
		printf("-%u=%c%c-",b,out_buffer[i*2],out_buffer[(i*2)+1]);
	}
}
void decode(char *inp_buffer,int bytes)
{	char ch;
	int i,tmp;
	printf("\n decoding begins");
	for(i=0;i<(bytes/2);i++)
	{	tmp=0;
		switch((char)inp_buffer[2*i])
		{	case 'a':inp_buffer[2*i]=10;break;
			case 'b':inp_buffer[2*i]=11;break;
			case 'c':inp_buffer[2*i]=12;break;
			case 'd':inp_buffer[2*i]=13;break;
			case 'e':inp_buffer[2*i]=14;break;
			case 'f':inp_buffer[2*i]=15;break;
			default://printf("\n:%d:%c:=inp_buffer[%d]\n",(char)inp_buffer[2*i],(char)inp_buffer[2*i],i);
				inp_buffer[2*i]=(char)inp_buffer[2*i]-'0';
				//printf("\nnow it has become %d",(char)inp_buffer[2*i]);
		}
		tmp=16*(char)inp_buffer[2*i];
		switch(inp_buffer[2*i+1])
		{	case 'a':inp_buffer[2*i+1]=10;break;
			case 'b':inp_buffer[2*i+1]=11;break;
			case 'c':inp_buffer[2*i+1]=12;break;
			case 'd':inp_buffer[2*i+1]=13;break;
			case 'e':inp_buffer[2*i+1]=14;break;
			case 'f':inp_buffer[2*i+1]=15;break;
			default:inp_buffer[2*i+1]=(char)inp_buffer[2*i+1]-'0';
		}
		tmp=tmp+inp_buffer[2*i+1];
		printf("\n%d=tmp",tmp);
		out_buffer[i]=(char)tmp;
		//printf("-%c%c=%u-",(char)inp_buffer[2*i],(char)inp_buffer[2*i+1],tmp);
		//out_buffer[i]=(char)tmp;
	}
	out_buffer[i]=0;
}

void main( int  argc, char  *argv[ ] )
{
	char  inp_buffer[ 512 ], source [ 128 ], target [ 128 ] ;
	int  inhandle, outhandle, bytes;
	if(argc<4)
	{	printf("\nCommand should be \"program source destination <switch>\"\nswitch=e,d\nBye!");
		exit(0);
	}
	printf ( "\nsource file name:%s:",argv[1] ) ;
	inhandle = open (argv[1], O_RDONLY | O_BINARY ) ;
	if ( inhandle == -1 )
	{
		puts ( "\nCannot open input file" ) ;
		exit(0) ;
	}
	printf ( "\ntarget file nam:%s:",argv[2] ) ;
	outhandle = open ( argv[2], O_CREAT | O_BINARY | O_WRONLY,S_IWRITE ) ;
	if ( outhandle == -1 )
	{
		puts ( "Cannot open output file" ) ;
		close ( inhandle ) ;
		exit(0) ;
	}
	do
	{
		bytes = read ( inhandle, inp_buffer, 512 ) ;
		if ( bytes > 0 )
		{       if(!strcmp(argv[3],"e"))
			{
				encode(inp_buffer,bytes);
				write ( outhandle, out_buffer, (bytes*2) ) ;
			}
			else
			{	if(!strcmp(argv[3],"d"))
				{	decode(inp_buffer,bytes);
					write ( outhandle, out_buffer, (bytes/2) ) ;
				}
				else
				{	printf("\ninvalid switch :%s:",argv[3]);
					close ( inhandle ) ;close ( outhandle ) ;
					exit(0);
				}
			}

		}
		else
			break ;
	}while(1);
	close ( inhandle ) ;
	close ( outhandle ) ;
}

This way I keep my original binary & double-sized-text-backup in my USB stick

USAGE
./application input-file output-file switch
e=encoding
d=decoding

TAKE CARE
use <=8 character filenames without absolute paths for safety

base 64 encoding via c

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