srm.dod.c

/*******************************************
 * srm-dod v. 1.0                          *
 * Description: Implementation of the DoD  *
 * secure erase algorithm with a couple of *
 * modifications for extra obscurity       *
 * Author: Michael Warren                  *
 * Date: January 8 & 17 2019               *
 *******************************************/

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

int main( int argc, char **argv ){
    FILE *fp;
    for( int i = 1; i < argc; i++ ){
        if( !(fp = fopen( argv[i], "r+" )) ){
            // Error handling section:
            char errorstring[strlen( argv[0] ) + strlen( argv[i] ) + 3];
            sprintf( errorstring, "%s: %s", argv[0], argv[i] );
            perror( errorstring );
            exit( errno );
        }
        // Determine file length:
        fseek( fp, 0, SEEK_END );
        long file_length = ftell( fp );
        rewind( fp );

        // Proceed with DoD algorithm:
        srand( time( NULL ) );
        char c = rand() % 256;
        for( int i = 0; i < file_length; i++ ){
            fputc( c, fp );
        }
        rewind( fp );
        c = ~c;
        for( int i = 0; i < file_length; i++ ){
            fputc( c, fp );
        }
        rewind( fp );
        for( int i = 0; i < file_length; i++ ){
            fputc( rand() % 256, fp );
        }
        rewind( fp );

        // Two extra zero passes to conceal the
        // fact that data was securely erased:
        for( int i = 0; i < file_length; i++ ){
            fputc( '\0', fp );
        }
        rewind( fp );
        for( int i = 0; i < file_length; i++ ){
            fputc( '\0', fp );
        }

        // Truncate:
        fclose( fp );
        fp = fopen( argv[i], "w" );
        fclose( fp );

        // Change filename and delete:
        char newname[TMP_MAX];
        for( int i = 0; i < TMP_MAX; i++ ){
            newname[i] = rand() % 26 + 'A';
        }
        if( rename( argv[i], newname ) ){
            printf( "%s: Error renaming file %s\n", argv[0], argv[i] );
            printf( "Error code: %d\n", errno );
            exit( errno );
        }
        remove( newname );
        fclose( fp );
    }
    return 0;
}