Thread: one-time pad cryptor problem

Hi guys, plz help. I write simple cryptor:

Code:

#include <stdio.h>

int main(int argc, char* argv[])
{
    FILE *fp;
    int z,i=0;
    int rbyte;

    printf("One-time pad cryptor.\n");
    if (argc!=3) {printf("Usage: %s file cryptkey\n",argv[0]); return 0;}

    if (fp=fopen(argv[1],"rw")==0) { printf("Error opening file %s\n",argv[1]); return 0;}
    z=strlen(argv[2]);
    printf("%d\n",z);


    while ((rbyte=fgetc(fp)))
    {
    
        if (i<=z) i=0;
        rbyte=rbyte^argv[2][i];
        fputc(rbyte,fp);
        i++;
    }

    fclose(fp);
    return 0;
}

I got segmentation fault. What's the problem?

To add onto what laserlight already noted,

Code:

if (fp = fopen(argv[1] , "r+") == 0)

should be

Code:

if ((fp = fopen(argv[1], "r+")) == NULL)

You are right. I change

Code:

while ((rbyte = fgetc(fp)) != EOF)

and made
i==z
but still got segmentation fault.
Look:

Code:

while ((rbyte=fgetc(fp))!=EOF)
    {
        printf("Ok\n");
        if (i==z) i=0;
        printf("rbyte is %d, argv[2][i] is %d",rbyte,argv[2][i]);
        rbyte=rbyte^argv[2][i];
        fputc(rbyte,fp);
        i++;
    }

but i got "segmentation fault".


"Ok" didnt printf.
P.S. Sorry for my english.

Yes, Aslaville, you are right.
Now, next problem.

Code:

   if (i==z) i=0;
        rbyte=rbyte^argv[2][i];
        printf("rbyte is %d\n",rbyte);
        fputc(rbyte,fp);
        i++;

I write ./crypt test abc
test -> "testtesttest"

rbyte is 21
rbyte is 7
rbyte is 16
rbyte is 21
rbyte is 22
rbyte is 6
rbyte is 18
rbyte is 22
rbyte is 23
rbyte is 4
rbyte is 17
rbyte is 23

And...
cat test -> "testtesttest"

test file isn't changed!

Post your current code

Code:

#include <stdio.h>

int main(int argc, char* argv[])
{
    FILE *fp;
    int z,i=0;
    int rbyte;

    printf("One-time pad cryptor.\n");

    if (argc!=3) {printf("Usage: %s file cryptkey\n",argv[0]); return 0;}

    if ((fp=fopen(argv[1],"rw"))==NULL) { printf("Error opening file %s\n",argv[1]); return 0;}

    z=strlen(argv[2]);

    while ((rbyte=fgetc(fp))!=EOF)
    {

        if (i==z) i=0;
        rbyte=rbyte^argv[2][i];
        printf("rbyte is %d\n",rbyte);
        fputc(rbyte,fp);
        i++;
    }

    fclose(fp);
    return 0;
}

Originally Posted by surgeon

Code:

#include <stdio.h>

int main(int argc, char* argv[])
{
    FILE *fp;
    int z,i=0;
    int rbyte;

    printf("One-time pad cryptor.\n");

    if (argc!=3) {printf("Usage: %s file cryptkey\n",argv[0]); return 0;}

    if ((fp=fopen(argv[1],"rw"))==NULL) { printf("Error opening file %s\n",argv[1]); return 0;}

    z=strlen(argv[2]);

    while ((rbyte=fgetc(fp))!=EOF)
    {

        if (i==z) i=0;
        rbyte=rbyte^argv[2][i];
        printf("rbyte is %d\n",rbyte);
        fputc(rbyte,fp);
        i++;
    }

    fclose(fp);
    return 0;
}

Re-read post #2, your file opening mode is not correct.

i change opening mode to r+
cat "hello world" > test
./crypt test abc

program changed test file
then, i try to decrypt file with command
./crypt test abc

but file test doesn't changed