//This program is free software: you can redistribute it and/or modify it under the terms #of the GNU General Public License as published by the Free Software Foundation, either #version 3 of the License, or (at your option) any later version.
//This program is distributed in the hope that it will be useful, but WITHOUT ANY #WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A #PARTICULAR PURPOSE. See the GNU General Public License for more details.
//You should have received a copy of the GNU General Public License along with this #program. If not, see <http://www.gnu.org/licenses/>
/* rot13.c */
/* Shift alphabetics by 13 positions */
/* Unless otherwise noted Copyright 1995 Willis E. Howard, III */
/* Willis E. Howard, III  email: WEHoward@aol.com  mail: POB 1473 Elkhart, IN  46515 */

/* under MSDOS, NMAKE /F ROT13.MAK all clean */

#include <stdio.h>
#include <stdlib.h>
#include "crypt.h"

#include <string.h>
#include <ctype.h>
#include <windows.h>

/*
  This routine uses the common interface to CRYPT.C.
  Generally, the name of this module becomes the name
  of the executable file.
*/

//static int key_defined_rot13 = 0;       /* Set to 1 after a valid key has been defined */
static int encrypt_or_decrypt_rot13 = ENCRYPTION_SELECT;

/*
   cipher_doc:
   This array of strings must have two sections:
   CIPHER that describes the cipher used and
   KEY that describes how the key is defined and entered.
*/

static char *cipher_doc[]=
{
  "CIPHER",
  "      The ROT13 cipher rotates letters 13 places to the",
  "      right mod 26.  Using the program twice restores the",
  "      original file.  This is often used on UNIX systems.",
  "",
  "KEY",
  "      No key is used by this function.",
  NULL
} ;

char **
crypt_help_rot13()
{
    return cipher_doc;         /* return a pointer to the help strings */
}

/*
   crypt_key:
   Get the key from the passed string (that may be a file name in some
   implementations) or from a key file name.  Return 0 on success but
   exit on error.
*/

int
crypt_key_rot13 ( int key_type, char *key_text )
{
    if (key_type == KEY_FILE)               /* a file name has been given */
    {
        return 0;
    }
    else if (key_type == KEY_IMMEDIATE)     /* a key string has been given */
    {
        if (!strcmp( key_text, "?" ))     /* prompt for key */
        {
            printf("No key needed\n");
        }
        return 0;
    }
    fprintf( stderr, "Error getting key\n" );
    exit( 1 );
}

/*
   crypt_key_erase:
   If a local copy of the key has been made, erase it from memory.
   This increases security that the key can not be obtained from
   an examination of memory.
*/

void
crypt_key_erase_rot13()
{
    return;
}

/*
    crypt_select:
    If encryption and decryption require different ciphers,
    this routine defines the direction.  Valid choices are
    ENCRYPTION_SELECT and DECRYPTION_SELECT.
*/

int
crypt_select_rot13( int selection )
{
    if ( selection == ENCRYPTION_SELECT )
        encrypt_or_decrypt_rot13 = ENCRYPTION_SELECT;
    if ( selection == DECRYPTION_SELECT )
        encrypt_or_decrypt_rot13 = DECRYPTION_SELECT;
    return encrypt_or_decrypt_rot13;
}

/*
    crypt_file:
    encrypt or decrypt the source to the destination file.
    Do not exit from this routine.  Return 0 on success
    and return 1 on error.  Use an fprintf(stderr, ... ) to
    report the nature of the error and close any open files.
    This allows the main routine to do some cleanup before
    exiting.
*/

int
crypt_file_rot13( char *source, char *dest )
{
    int c;
    FILE *infile;
    FILE *outfile;

    if ((infile = fopen( source, "rb" )) == NULL)
    {
        fprintf( stderr, "Can not open %s for reading.\n", source);
        return 1;
    }

    if ((outfile = fopen( dest, "wb" )) == NULL)
    {
        fprintf( stderr, "Can not open %s for writing.\n", dest);
        fclose( infile );
        return 1;
    }

    while ((c = fgetc(infile)) != EOF)
    {
        if ( c >= 'a' && c <= 'm' )
            c += 13;
        else if ( c >= 'n' && c <= 'z' )
            c -= 13;
        else if ( c >= 'A' && c <= 'M' )
            c += 13;
        else if ( c >= 'N' && c <= 'Z' )
            c -= 13;
        if (fputc(c, outfile) == EOF)
        {
            fprintf(stderr, "Could not write to output file %s\n", dest);
            fclose( infile );
            fclose( outfile );
            return 1;
        }
    }

    fclose( infile );
    fclose( outfile );
    return 0;
}