main.c

简单的vigenere解密及其解密功能实现代码

#include <stdio.h>
#include <string.h>

#include "dvigenere.h"
#include "dcaesar.h"

#define BASE 26
#define TOP 3
#define LEN 24

#define PRO_NAME "dvigenere-cracker"
#define PRO_VER "0.1"

static void display_usage( void );
static void display_logo( void );
static int getkey( unsigned long start, int len, FILE *in );
extern void encrypt( char c, int key, FILE *out );
extern void decrypt( char c, int key, FILE *out );

int main( int argc, char **argv )
{
	FILE *in, *out;
	char *infile, *outfile;

	char c;
	int i, j, len;
	int key[LEN];

	/**
	 * check whether enough parameters
	 **/
	if( 3!=argc && 2!=argc )
	{
		display_usage();
		return -1;
	}


	/**
	 * intput and output
	 **/
	infile = argv[1];
	in = fopen( infile, "rb" );
	if( NULL==in )
	{
		fprintf( stderr, "error: can not open file %s\n", infile );
		return -3;
	}
	if( 3==argc )
	{
		outfile = argv[2];
		out = fopen( outfile, "wb" );
		if( NULL==out )
		{
			fclose( in );
			fprintf( stderr, "error: can not create file %\n", outfile );
			return -4;
		}
	}
	else
		out = stdout;
	

	/**
	 * crack the length of the key
	 **/
	len = key[0] = 0;
	while( !(key[0]=getkey(0,len,in)) && len<=LEN )
	{
		len++;
	};
	if( LEN==len )
	{
		fprintf( stderr, "error: the length of the key is larger then %d\n", LEN  );
		return -5;
	}
	len++;
	if( 3==argc ) printf( "the length of the key : %d\n", len ); 


	/**
	 * crack all the keys
	 **/
	for( i=1; i<len; i++ )
	{
		key[i] = getkey( i, len-1, in ); // because auto-add-offset 1 when read a char
	}
	if( 3==argc ) 
	{
		printf( "the key : " ); 
		for( i=0; i<len; i++ )
			printf( "%c", key[i]+'a' );
		printf( "\n" );
	}

	/**
	 * output the result
	 **/
	fseek( in, 0l, SEEK_SET );
	i = 0;
	while( fread(&c,sizeof(char),1,in) )
	{
		decrypt(c,key[i%len],out);
		i++;
	}
	
	if( 3==argc ) fclose( out );
	fclose( in );

	return 0;
};




static void display_usage( void )
{
	printf( "%s v%s by dorainm, [e-mail]\n", PRO_NAME, PRO_VER );
	printf( "this is a free program; it used to encrypt or decrypt the string or file\n" );
	printf( "with the vigenere cipher, and current version only support all the letters\n" );
	printf( "\n" );
	printf( "usage :\n" );
	printf( "    %s infile <outfile> | -h\n", PRO_NAME);
	printf( "\n" );
	printf( "options :\n" );
	printf( "    infile               point out the file would be cracked\n" );
	printf( "    outfile              the file to save the result; if it hasn't be set,\n" );
        printf( "                            the cracked plain text will displayed on <stdout>\n" );
	printf( "    -h | --help          display this help\n" );
	printf( "\n" );
	printf( "report bugs to <[e-mail]>\n" );
	return;
};


static int getkey( unsigned long start, int len, FILE *in )
{
	int i, j, key = 0;
	int num[BASE], top[TOP];
	char c;

	fseek( in, start, SEEK_SET );

	/**
	 * count all the letter's displayed times
	 **/
	for( i=0; i<BASE; i++ ) num[i] = 0;
	
	while( fread(&c,sizeof(char),1,in) )
	{
		if( blowerletter(c) )
			num[c-'a']++;
		else if( bpowerletter(c) )
			num[c-'A']++;
		fseek( in, len, SEEK_CUR );
	}
	
	/**
	 * compute the top TOP letters
	 **/
	for( i=0; i<TOP; i++ )
	{
		top[i] = 0;
		for( j=0; j<BASE; j++ )
		{
			if( num[top[i]]<num[j] ) top[i] = j;
		}
		num[top[i]] = 0;
	}
	
	
	/**
	 * crack out the key's value
	 **/
	for( i=0; i<TOP-1; i++ )
	{
		for( j=1; j<TOP; j++ )
		{
			if( ((top[i]+'a'-'e'+BASE)%BASE)==((top[j]+'a'-'t'+BASE)%BASE) )
			{
				key = ((top[i]+'a'-'e'+BASE)%BASE);
			}
		}
	}

	return key;
}


extern void encrypt( char p, int key, FILE *out )
{
	if( blowerletter(p) )
		fputc( dcaesar_encrypt(p-'a',key,BASE,'A'), out );
	else if( bpowerletter(p) )
		fputc( dcaesar_encrypt(p-'A',key,BASE,'a'), out );
	else
		fputc( p, out );
	return;
};

extern void decrypt( char c, int key, FILE *out )
{
	if( blowerletter(c) )
		fputc( dcaesar_decrypt(c-'a',key,BASE,'A'), out );
	else if( bpowerletter(c) )
		fputc( dcaesar_decrypt(c-'A',key,BASE,'a'), out );
	else
		fputc( c, out );
	return;
};