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a self-checking program in standard C

P: n/a
Do you know how to write a self-checking program in standard C?
Do I can think that if I write in a file.c
static g[100]="1234567";
in the file.exe (or file) there is in some place
1234567'\0''\0''\0''\0''\0''\0''\0'...'\0'

This is my first attempt:

/* file.c -> file.exe */
#include <stdio.h>
#include <string.h>

char* estr(char* nome)
{
char *a = nome, *b;
char c;
if(nome == 0)
return 0;
while( 1 )
{b = a;
while( (c = *a) && c != '\\' && c != '/' )
++a;
if(c == 0) break;
++a;
}
return b;
}

int main(int c, char** argv)
{
(void) c;
printf("I'm a self-checking program\n");
if(strncmp("dc.exe", estr(argv[0]), 6) != 0)
{printf("File corrupted\n"); return 0;}
printf("Continue\n");
return 0;
}

Nov 14 '05 #1
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6 Replies


P: n/a
RoSsIaCrIiLoIA wrote:
Do you know how to write a self-checking program in standard C?
Do I can think that if I write in a file.c
static g[100]="1234567";
in the file.exe (or file) there is in some place
1234567'\0''\0''\0''\0''\0''\0''\0'...'\0'

I think you can. But it is out of Standard C scope.

This is my first attempt:

/* file.c -> file.exe */
#include <stdio.h>
#include <string.h>

char* estr(char* nome)
{
char *a = nome, *b;
char c;
if(nome == 0)
return 0;
while( 1 )
{b = a;
while( (c = *a) && c != '\\' && c != '/' )
what about c != '\0'
++a;
if(c == 0) break;
++a;
}
return b;
}

int main(int c, char** argv)
{
(void) c;
printf("I'm a self-checking program\n");
if(strncmp("dc.exe", estr(argv[0]), 6) != 0)
{printf("File corrupted\n"); return 0;}
Why do you think this garanties that file is corrupted? Why user
shouldn't rename files? If he shouldn't then you must consider that file
may had more than one name in some environments (hard and symbolic links).
printf("Continue\n");
return 0;
}


How does this code relate with your proposal made in the begining.

Anyway all of this is offtopic here.

vir

Nov 14 '05 #2

P: n/a
On Wed, 14 Apr 2004 15:26:47 +0400, Victor Nazarov <vv*****@mail.ru>
wrote:
RoSsIaCrIiLoIA wrote:
Do you know how to write a self-checking program in standard C?
Do I can think that if I write in a file.c
static g[100]="1234567";
in the file.exe (or file) there is in some place
1234567'\0''\0''\0''\0''\0''\0''\0'...'\0'

I think you can. But it is out of Standard C scope.


But are there any system where this is not true?

This is my first attempt:

/* file.c -> file.exe */
#include <stdio.h>
#include <string.h>

char* estr(char* nome)
{
char *a = nome, *b;
char c;
if(nome == 0)
return 0;
while( 1 )
{b = a;
while( (c = *a) && c != '\\' && c != '/' )


what about c != '\0'


ok (c = *a)!=0
++a;
if(c == 0) break;
++a;
}
return b;
}

int main(int c, char** argv)
{
(void) c;
printf("I'm a self-checking program\n");
if(strncmp("dc.exe", estr(argv[0]), 6) != 0)
{printf("File corrupted\n"); return 0;}


Why do you think this garanties that file is corrupted? Why user
shouldn't rename files? If he shouldn't then you must consider that file
may had more than one name in some environments (hard and symbolic links).


I'm thinking some of this type:

/* my1.c */
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#define UNS unsigned

char* estr(char* nome)
{
char *a = nome, *b;
char c;
if(nome == 0)
return 0;
while( 1 )
{b = a;
while( (c = *a)!=0 && c!='\\' && c!='/' )
++a;
if(c == 0) break;
++a;
}
return b;
}
int info_p(char* );

int main(int c, char** argv)
{
if(c != 2)
{
if( c==0 || !argv[0] )
printf("Use:> this_prog prog\n");
else printf("Use:> %s prog[.exe]\n", estr(argv[0]));

return 0;
}
if( info_p( argv[1] )==0 )
{ printf("Not signed %s\n", estr(argv[1])); return 0;}

printf("Ok signed %s\n", estr(argv[1]));
return 0;
}

void printu(char* a)
{
int i;
for( i = 0; i < sizeof(UNS); ++i)
printf(" %d ", (int) a[i]);
}
int f(const char* a, FILE* fp)
{
int i, j;
for( i= 0, j= EOF + 1 ; i < sizeof(UNS) && j!=EOF; ++i)
j= fputc(a[i], fp);
return j;
}

int info_p(char* as)
{int c, r, k, cp;
FILE *fp;
unsigned count= 0, rox= 0, sum= 0, *p1, buffer= 0;
char acount[ sizeof(UNS) + 8 ] = {0},
arox [ sizeof(UNS) + 8 ] = {0},
asum [ sizeof(UNS) + 8 ] = {0};
char *pc1 = acount, *pc2 = arox, *pc3 = asum;
long ove;

if( (fp = fopen( as, "r+b"))==NULL )
{printf("Problemi di apertura\n");
return 0;
}
r = 0; cp = 0;
label:
while( (c = fgetc(fp))!=EOF && !(cp=='1' && c=='2') )
{
sum += c; ++count;
cp = c;
buffer = (buffer << CHAR_BIT) | ((UNS)(unsigned char) c);
if(count % sizeof(UNS) ==0)
rox = rox ^ buffer;
}
if( c!=EOF && r==0 )
{k = 2;
while( (c = fgetc(fp))!=EOF && c-'0'== ++k )
{sum += c; ++count;
cp = c;
buffer = (buffer << CHAR_BIT) | (UNS)((unsigned char) c);
if(count % sizeof(UNS) == 0)
rox = rox ^ buffer;
} /*34567*/
if( k==8 && c!=EOF )
{
if((ove = ftell( fp ))== -1)
{ printf("Error\n"); exit(0); }
printf("Find\n");
r=1;
}
else if(c != EOF) goto label;
else goto fine;
while( (c = fgetc(fp))!=EOF && k!=512 ) ++k;
if(c !=EOF) goto label;
}
if(c == EOF) goto fine;
goto label;
fine:
*(UNS*) pc1 = count; *(UNS*) pc2 = rox; *(UNS*) pc3 = sum;
if(r == 1)
{
fseek(fp, ove, SEEK_SET);
clearerr(fp);
if(f(acount, fp)==EOF || f(arox, fp)==EOF || f(asum, fp)==EOF)
{r=0; printf("Error in writing\n");}
}
fclose(fp);
printf("count=%u rox=%u sum=%u\n", count, rox, sum );
printf("String=%s%s%s\nIn_num=", acount, arox, asum);
printu(acount); printf("M") ;printu(arox);printf("M");
printu(asum) ; printf("\n");
return r;
}
/*end my1.c*/
____________________

/* ali.c */
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>

#define UNS unsigned
char* estr(char* nome)
{
char *a = nome, *b;
char c;

if(nome == 0)
return 0;
while( 1 )
{
b = a;
while( (c = *a)!=0 && c!='\\' && c!='/' ) ++a;
if(c == 0) break;
++a;
}
return b;
}

int info_p(char* );

int main(int c, char** argv)
{
printf("Start \n");
if( c==0 || !argv[0] )
return 0;
if( info_p(argv[0]) == 0 )
{ printf("File corrupted\n"); return 0; }
printf("oK continue\n");
return 0;
}
void printu(char* a)
{
int i;

for( i = 0 ; i < sizeof(UNS) ; ++i)
printf(" %d ", (int) a[i]);
}

int f(const char* a, FILE* fp)
{
int i, j;

for( i = 0 ; i < sizeof(UNS) ; ++i)
{
if( (j = fgetc( fp ))==EOF ) return 0;
if( j != (unsigned char) a[i]) return 0;
}
return 1;
}

/* ###### HERE WE HAVE TO WRITE ###### */
char al[512] = "1234567 ";
int info_p(char* as)
{
int l, c, r, k, cp;
FILE *fp;
unsigned count = 0, rox = 0, sum = 0, *p1, buffer = 0;
char acount[ sizeof(UNS) + 8 ] = {0},
arox [ sizeof(UNS) + 8 ] = {0},
asum [ sizeof(UNS) + 8 ] = {0};
char *pc1 = acount, *pc2 = arox, *pc3 = asum;
long ove;

if((fp = fopen( as, "rb"))==NULL)
{
printf("Problemi di apertura\n");
return 0;
}
r = 0; cp = 0;
label:
while((c = fgetc(fp))!=EOF && !(cp=='1' && c=='2'))
{
sum += c; ++count;
cp = c;
buffer = (buffer << CHAR_BIT) | ((UNS)(unsigned char) c);
if(count % sizeof(UNS) ==0)
rox = rox ^ buffer;
}
if(c!=EOF && r==0)
{
k = 2;
while((c = fgetc(fp))!=EOF && c== ++k + '0' )
{
sum += c; ++count;
cp = c;
buffer = (buffer << CHAR_BIT) | (UNS)((unsigned char) c);
if(count % sizeof(UNS) == 0)
rox = rox ^ buffer;
} /*34567*/
if(k==8 && c!=EOF)
{
if( (ove = ftell(fp)) == -1)
{ printf( "Error\n" ); exit( 0 ); }
r = 1;
}
else if(c != EOF) goto label;
else goto fine;
while((c = fgetc(fp))!=EOF && k!=512) ++k;
if(c !=EOF ) goto label;
}
if(c == EOF) goto fine;
goto label;
fine:
*(UNS*) pc1 = count; *(UNS*) pc2 = rox; *(UNS*) pc3 = sum;
if(r == 1){
fseek(fp, ove, SEEK_SET);
clearerr(fp);
if( f(acount, fp)==0 || f(arox, fp)==0 || f(asum, fp)==0 )
r = 0;
}
fclose(fp);
return r;
}
/*end ali.c*/
__________________
C:\b>ali
Start
File corrupted

C:\b>my1 ali.exe
Find
count=59909 rox=3806249208 sum=5559428
String=?۰+T
In_num= 5 -22 0 0 M -8 -64 -34 -30 M -124 -44 84 0
Ok signed ali.exe

C:\b>ali
Start
oK continue
_______________

Are there errors?
Are there system where this doesn't run with success?

Nov 14 '05 #3

P: n/a
In <hc********************************@4ax.com> RoSsIaCrIiLoIA <n@esiste.ee> writes:
Do you know how to write a self-checking program in standard C?
I don't know what a self-checking program is in the first place.
Do I can think that if I write in a file.c
static g[100]="1234567";
in the file.exe (or file) there is in some place
1234567'\0''\0''\0''\0''\0''\0''\0'...'\0'
Not necessarily. Long sequences of null bytes are so common that some
linkers compress them.
This is my first attempt:

/* file.c -> file.exe */
#include <stdio.h>
#include <string.h>

char* estr(char* nome)
{
char *a = nome, *b;
char c;
if(nome == 0)
return 0;
while( 1 )
{b = a;
while( (c = *a) && c != '\\' && c != '/' )
++a;
if(c == 0) break;
++a;
}
return b;
}

int main(int c, char** argv)
{
(void) c;
printf("I'm a self-checking program\n");
if(strncmp("dc.exe", estr(argv[0]), 6) != 0)
{printf("File corrupted\n"); return 0;}
printf("Continue\n");
return 0;
}


Let's try it:

fangorn:~/tmp 371> gcc test.c
fangorn:~/tmp 372> ./a.out
I'm a self-checking program
File corrupted

Which file is corrupted and why? And how can you determine whether a
file is corrupted or not by examining argv[0]?

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Nov 14 '05 #4

P: n/a
Da*****@cern.ch (Dan Pop) wrote in message news:<c5**********@sunnews.cern.ch>...
In <hc********************************@4ax.com> RoSsIaCrIiLoIA <n@esiste.ee> writes:
Do you know how to write a self-checking program in standard C?


I don't know what a self-checking program is in the first place.
Do I can think that if I write in a file.c
static g[100]="1234567";
in the file.exe (or file) there is in some place
1234567'\0''\0''\0''\0''\0''\0''\0'...'\0'


Not necessarily. Long sequences of null bytes are so common that some
linkers compress them.
This is my first attempt:

/* file.c -> file.exe */
#include <stdio.h>
#include <string.h>

char* estr(char* nome)
{
char *a = nome, *b;
char c;
if(nome == 0)
return 0;
while( 1 )
{b = a;
while( (c = *a) && c != '\\' && c != '/' )
++a;
if(c == 0) break;
++a;
}

return b;
}

int main(int c, char** argv)
{
(void) c;
printf("I'm a self-checking program\n");
if(strncmp("dc.exe", estr(argv[0]), 6) != 0)
{printf("File corrupted\n"); return 0;}
printf("Continue\n");
return 0;
}


Let's try it:

fangorn:~/tmp 371> gcc test.c
fangorn:~/tmp 372> ./a.out
I'm a self-checking program
File corrupted

Which file is corrupted and why? And how can you determine whether a
file is corrupted or not by examining argv[0]?

Dan

A lot of work along these lines has already been done. A company that
I used to work for had visual studio add-in tools. See the page:
http://www.arxan.com/home/index.php

Paul
Nov 14 '05 #5

P: n/a
RoSsIaCrIiLoIA wrote:
C:\b>ali
Start
File corrupted

C:\b>my1 ali.exe
Find
count=59909 rox=3806249208 sum=5559428
String=?۰+T
In_num= 5 -22 0 0 M -8 -64 -34 -30 M -124 -44 84 0
Ok signed ali.exe

C:\b>ali
Start
oK continue
_______________

Are there errors?
Are there system where this doesn't run with success?


This is not portable anyway. Really It depends on the executable format.
Executables often get comressed. Try another newsgroup...

vir

Nov 14 '05 #6

P: n/a
[comp.lang.c, sci.crypt]
On Wed, 14 Apr 2004 +0400, Victor Nazarov <vv*****@mail.ru> wrote:
This is not portable anyway. Really It depends on the executable format.
Executables often get comressed. Try another newsgroup...


yes compressed or *encrypted*
If the OS has a database of all the public key of software houses,
if M.exe is a encrypted program of Company XX
the loader of the OS could take the public key of Company XX
encrypt it [on the fly] and jump on it.

If a crakker want to crack M.exe he has to know the secret key of
Company XX or change the code in the memory space of that running
program.(in many OSes seems to me that the memory space of a program
is closed to other process)

Regarding Internet **why** OSes seems to have the default in allowing
*every* FTP-telnet-http-all *fu?king* protocol- IN EXIT for the
home-PC ( and change it in a world server of resources) ???
__________________
Il popolo dell'iraaq non vuole eserciti oppressori sia onu o altro
(se non ci credete fate un referendum)
Come ragionate con i piedi?
Nov 14 '05 #7

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