CHIFFREMENT DE VIGENERE

/*
  Name: vigenere
  Copyright: Mars 2011
  Author: Lajouad Rachid
  Date: 06/03/11 22:00
  Description: cryptage et décryptage par la méthode de viginère
  avec une ligne de commande
*/

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

char Crypt(char,char*);
char Decrypt(char,char*);

int main(int argc,char *argv[]) {
    if(argc < 4) {
            printf("syntax error : \n"
                   "Syntaxe de la commande : \n\n\t"
                   "%s -{c|d} -pwd NomFichier\n",argv[0]);
                   getchar();
            exit(1);
            }
    if(strcmp(argv[1],"-c") == 0) {
         FILE *fs, *fd;
         char fname[200],pwd[10];
         char c;
         fs = fopen(argv[3],"rb+");
         if(fs == NULL) {
               printf("syntax error : \n"
                   "Syntaxe de la commande : \n\n\t"
                   "%s -{c|d} -pwd NomFichier\n",argv[0]);
               printf("\n\n fichier inexistant ... Retype command ... ");
               getchar();
               exit(1);
               }
         strcpy(fname,argv[3]);
         fname[strlen(argv[3])-3] = 'v';
         fname[strlen(argv[3])-2] = 'i';
         fname[strlen(argv[3])-1] = 'g';
         fd = fopen(fname,"wb+");
// sauvegarder l'extension à l'interieur du fichier crypté
         fprintf(fd,"%c",argv[3][strlen(argv[3])-3]);      
         fprintf(fd,"%c",argv[3][strlen(argv[3])-2]);
         fprintf(fd,"%c",argv[3][strlen(argv[3])-1]);
         while( !feof( fs ) ) {
                fscanf(fs,"%c",&c);
                fprintf(fd,"%c",Crypt(c,argv[2]));
                }
         fclose(fs); fclose(fd);
    }
    
    else if(strcmp(argv[1],"-d") == 0) {
         FILE *fs, *fd;
         char fname[200],pwd[10];
         char c;
         int j = 0;
         fs = fopen(argv[3],"rb+");
         if(fs == NULL) {
               printf("\n\n fichier inexistant ... Retype command ... ");
               exit(1);
               }
         strcpy(fname,argv[3]);
         //rerstauration de l'extension du fichier
         while( !feof( fs ) ) {
                if( j < 3) {
                    j++;
                    fscanf(fs,"%c",&c);
                    fname[strlen(argv[3])-4+j] = c;
                     }
                else {
                  if(j == 3) fd = fopen(fname,"wb+");
                  j++;
                  fscanf(fs,"%c",&c);
                  fprintf(fd,"%c",Decrypt(c,argv[2]));
                  }
                }         
         fclose(fs); fclose(fd);
    }
    else {
         printf("commutateur inconnu ...\n\n");
            printf("syntax error : \n"
                   "Syntaxe de la commande : \n\n\t"
                   "%s -{c|d} -pwd NomFichier\n",argv[0]);
            exit(1);         
         }
    printf("\n\n\t\t\tsuccess ... cryptage terminé");getchar();
    }


char Crypt(char c,char *pwd){
     static int i;
     if(++i >= strlen(pwd)) i = 0;
     return (c + (pwd[i] - '0'));     
     }
     
char Decrypt(char c,char *pwd){
     static int i;
     if(++i >= strlen(pwd)) i = 0;
     return (c - (pwd[i] - '0'));  
     }