美国国防部机密文件销毁算法

  1 /*
  2  *    File Destroyer 文件安全销毁
  3  *
  4  *    Copyright (C) 2015 Chaobs
  5  *
  6  *    This program is free software: you can redistribute it and/or modify
  7  *    it under the terms of the GNU General Public License as published by
  8  *    the Free Software Foundation, either version 3 of the License, or
  9  *    (at your option) any later version.
 10  *
 11  *    This program is distributed in the hope that it will be useful,
 12  *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 13  *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 14  *    GNU General Public License for more details.
 15  *
 16  *    You should have received a copy of the GNU General Public License
 17  *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 18  *
 19  *    E-mail: chaobs@outlook.com
 20  *    Blog: www.cnblogs.com/chaobs
 21  *
 22  *    用法: file-destroyer [filename1] <filename2>...
 23  *
 24  *     算法介绍：
 25  *     基于美国国防部DOD5220.22M标准进行文件销毁，包括以下三步:
 26  *     （1）将文件先用0x00覆盖，再用0x01覆盖，如此重复三次；
 27  *     （2）将文件用一个随机值覆盖；
 28  *     （3）将文件名改为一个单字符文件名，最后删除之。
 29  *
 30  *     算法可靠性验证：
 31  *     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。
 32  *
 33  */
 34 
 35 #include <stdio.h>
 36 #include <stdlib.h>
 37 #include <time.h>
 38 
 39 
 40 void notice(int i, char *s);    /* print short notice */
 41 
 42 void wipe(FILE *f, char c);    /* core func */
 43 
 44 long file_size(FILE *f);    /* get the size of a file */
 45 
 46 int require(int c, char *s[]);
 47 
 48 
 49 int main(int argc, char *argv[])
 50 {
 51     int i, j;
 52     char ch;
 53 
 54     FILE *f;
 55 
 56     notice(1, argv[0]);
 57 
 58     if (argc < 2) {
 59         /* too few arguments */
 60         notice(2, argv[0]);
 61         exit(0);
 62     }
 63 
 64     if (!require(argc, argv)) {
 65         fprintf(stderr, "Cancel Operating.\n");
 66         exit(0);    /* cancel */
 67     }
 68 
 69     srand(time(NULL));    /* randomize */
 70 
 71     for (i = 1; i < argc; ++i) {
 72         /* process each file */
 73 
 74         if ((f = fopen(argv[i], "r+b")) == NULL) {/* fail to open file */
 75             fprintf(stderr, "Error when open %s:\n", argv[i]);
 76             exit(0);
 77         }
 78 
 79         for (j = 0; j < 3; ++j) {
 80             /* DOD5220.22M Step 1 */
 81             wipe(f, 0x00);
 82             wipe(f, 0x01);
 83         }
 84 
 85         wipe(f, rand() % 256);    /* Step 2 */ 
 86         
 87         if (rename(argv[i], "C")) {
 88             /* Step 3*/
 89             fprintf(stderr, "Error when rename %s\n", argv[i]);
 90             exit(0);
 91             
 92             /* XXX:文件名冲突的解决？可以考虑使用tmpnam()吗？*/
 93         }
 94 
 95         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？ */
 96         fclose(f);
 97     }
 98 
 99     printf("Done! Destroy %d files\n", argc - 1);
100 
101     return 0;
102 }
103 
104 
105 /* implementation */
106 
107 void notice(int i, char *s)
108 {
109     if (i == 1) {
110         printf("\nFile Destroyer Copyright (C) 2015 Chaobs\n");
111         printf("This program comes with ABSOLUTELY NO WARRANTY.\n");
112         printf("This is free software, and you are welcome to redistribute under certain conditions.\n\n");
113     } else {
114         fprintf(stderr, "Usage: %s [filename1] <filename2> ...\n", s);
115     }
116 }
117 
118 void wipe(FILE *f, char c)
119 {
120     long i;
121 
122     for (i = 0; i < file_size(f); ++i)
123         fwrite(&c, 1, 1, f);    /* overwrite */
124 
125 }
126 
127 long file_size(FILE *f)
128 {
129     long len;
130     fseek(f, 0, SEEK_END);    /* jump to the and of file */
131     len = ftell(f);
132     fseek(f, 0, SEEK_SET);    /* restore */ 
133 }
134 
135 
136 int require(int c, char *s[])
137 {
138     int i;
139     char ch;
140     for (i = 1; i < c; ++i) {
141         /* FIXME: the comfirm function can make mistakes and
142          * it is not convenient even can‘t work in some cases.
143          */
144         printf("Do you want to destroy %s ?(y/n) ", s[i]);
145         ch = getchar();
146         getchar(); /* ‘\n‘ */
147         if (ch == ‘n‘)
148             return 0;
149     }
150 
151     return 1;
152 }