dvigenere.c

简单的vigenere解密及其解密功能实现代码

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

#include "dvigenere.h"

#define BASE 26

extern char *dvigenere_encrypt( char *p, char *k, int l )
{
	int i, keylen = strlen(k);
	char *c;
	
	c = (char *) malloc ( sizeof(char)*(strlen(p)+1) );
	if( NULL==c ) return (NULL);

	for( i=0; i<l; i++ )
	{
		if( blowerletter( *(p+i) ) ) 
			*(c+i) = ( *(p+i) - 'a' + getoffset(*(k+(i%keylen))) ) % BASE + 'A';
		else if( bpowerletter( *(p+i) ) )
			*(c+i) = ( *(p+i) - 'A' + getoffset(*(k+(i%keylen))) ) % BASE + 'a';
		else
			*(c+i) =  *(p+i);
//		printf( "encrypt [ %c ] with key [ %c:%d ] as the resule [ %c ]\n", *(p+i), *(k+(i%keylen)), getoffset(*(k+(i%keylen))), *(c+i) );
	}
	*(c+i) = '\0';
	return (c);
};


extern char *dvigenere_decrypt( char *c, char *k, int l )
{
	int i, j;
	char *p;
	
	p = (char *) malloc ( sizeof(char)*(strlen(c)+1) );
	if( NULL==c ) return (NULL);

	for( i=0; i<l; i++ )
	{
		if( blowerletter( *(c+i) ) ) 
			*(p+i) = ( *(c+i) - 'a' + BASE - getoffset(*(k+i%(strlen(k)))) ) % BASE + 'A';
		else if( bpowerletter( *(c+i) ) )
			*(p+i) = ( *(c+i) - 'A' + BASE - getoffset(*(k+i%(strlen(k)))) ) % BASE + 'a';
		else
			*(p+i) =  *(c+i);
	}
	*(p+i) = '\0';
	return (p);
};


extern int getoffset( char c )
{
	if( blowerletter(c) )
		return (c-'a');
	else if( bpowerletter(c) )
		return (c-'A');
	else
		return 0;
}


extern int blowerletter( char c )
{
	if( c>='a' && c<='z' )
		return 1;
	else
		return 0;
};


extern int bpowerletter( char c )
{
	if( c>='A' && c<='Z' )
		return 1;
	else
		return 0;
};