以前被用于美国国防部的机密文件销毁算法

DDOSafeDelete.c

/*
*    File Destroyer 文件安全销毁
*
*    Copyright (C) 2015 Chaobs
*
*    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/>.
*
*    E-mail: chaobs@outlook.com
*    Blog: www.cnblogs.com/chaobs
*
*    用法: file-destroyer [filename1] <filename2>...
*
*    算法介绍：
*    基于美国国防部DOD5220.22M标准进行文件销毁，包括以下三步:
*    （1）将文件先用0x00覆盖，再用0x01覆盖，如此重复三次；
*    （2）将文件用一个随机值覆盖；
*    （3）将文件名改为一个单字符文件名，最后删除之。
*
*    算法可靠性验证：
*    此算法虽然已经不再被美国国防部采用，但也足够应付一般的环境，对于主流文件恢复软件恢复的可能性还有待验证。
*
*/

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


void notice(int i, char *s);    /* print short notice */


void wipe(FILE *f, char c);    /* core func */


long file_size(FILE *f);    /* get the size of a file */


int require(int c, char *s[]);


int main(int argc, char *argv[])
{
    int i, j;
    char ch;


    FILE *f;


    notice(1, argv[0]);


    if (argc < 2) {
        /* too few arguments */
        notice(2, argv[0]);
        exit(0);
    }


    if (!require(argc, argv)) {
        fprintf(stderr, "Cancel Operating.\n");
        exit(0);    /* cancel */
    }


    srand(time(NULL));    /* randomize */


    for (i = 1; i < argc; ++i) {
        /* process each file */


        if ((f = fopen(argv[i], "r+b")) == NULL) {/* fail to open file */
            fprintf(stderr, "Error when open %s:\n", argv[i]);
            exit(0);
        }


        for (j = 0; j < 3; ++j) {
            /* DOD5220.22M Step 1 */
            wipe(f, 0x00);
            wipe(f, 0x01);
        }


        wipe(f, rand() % 256);    /* Step 2 */


        if (rename(argv[i], "C")) {
            /* Step 3*/
            fprintf(stderr, "Error when rename %s\n", argv[i]);
            exit(0);


            /* XXX:文件名冲突的解决？可以考虑使用tmpnam()吗？*/
        }


        remove("C"); /* XXX:如果是一个符号连接怎样保证删除的是真正的文件？ */
        fclose(f);
    }


    printf("Done! Destroy %d files\n", argc - 1);


    return 0;
}


/* implementation */


void notice(int i, char *s)
{
    if (i == 1) {
        printf("\nFile Destroyer Copyright (C) 2015 Chaobs\n");
        printf("This program comes with ABSOLUTELY NO WARRANTY.\n");
        printf("This is free software, and you are welcome to redistribute under certain conditions.\n\n");
    } else {
        fprintf(stderr, "Usage: %s [filename1] <filename2> ...\n", s);
    }
}


void wipe(FILE *f, char c)
{
    long i;
    long len = file_size(f); /*获得文件长度*/


    for (i = 0; i < len; ++i)
        fwrite(&c, 1, 1, f);    /* overwrite */
}


long file_size(FILE *f)
{
    long len;
    fseek(f, 0, SEEK_END);    /* jump to the and of file */
    len = ftell(f);
    fseek(f, 0, SEEK_SET);    /* restore */
    return len; /*感谢网友冰尘醉*/
}


int require(int c, char *s[])
{
    int i;
    char ch;
    for (i = 1; i < c; ++i) {
        /* FIXME: the comfirm function can make mistakes and
        * it is not convenient even can't work in some cases.
        */
        printf("Do you want to destroy %s ?(y/n) ", s[i]);
        ch = getchar();
        getchar(); /* '\n' */
        if (ch == 'n')
            return 0;
    }


    return 1;
}