Low Level File I/O Compare Strings - c

Question

I'm writing a program that takes a file with the 3 lines of encrypted passwords and compares them to all 4 lower case letters from aaaa - zzzz. The only issue I am having is that I can't figure out how to go line by line of the file I input and how to compare it to the 4 letter words individually. It should then print the 3 decrypted 4 letter words that correlate to the passwords from the file. Also if there are any types on how to improve my code, please let me know. I'm a beginner at this so I need clear explanations and examples if possible. Thank you.
EDIT*****
The main problem is in the all function and main. I'm not wanting to print the aaaa, aaab, aaac, etc to the screen but I want to put it in an char array so that i can compare each individually to each line from the file using crypt. So I need advice on how to put all 456976 combinations into an array, compare it to each line of code, and print the solutions to the screen.
file looks like this:
$1$6gMKIopE$I.zkP2EvrXHDmApzYoV.B.
$1$pkMKIcvE$WQfqzTNmcQr7fqsNq7K2p0
$1$0lMKIuvE$7mOnlu6RZ/cUFRBidK7PK.
My code looks like this:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define BUFFER_SIZE 1024
int my_fgets(char* buf, int len, int f)
{
for (int i = 0; i < len; i++,buf++)
{
int count = read(f, buf, 1);
if (!count || (buf[0] == '\n'))
{
buf[0] = 0;
return i;
}
}
return 0;
}
int inc(char *c,char begin, char end){
if(c[0]==0)
return 0;
if(c[0] == end){ // This make the algorithm to stop at char 'f'
c[0]=begin; // but you can put any other char
return inc(c+sizeof(char), begin, end);
}
c[0]++;
return 1;
}
char all(int a, int n,char begin, char end){
int i, j;
char *c = malloc((n+1)*sizeof(char));
char result[] = "";
for(i = a; i <= n; i++)
{
for(j=0;j<i;j++) c[j]=begin;
c[i]=0;
do {
int k = sizeof(result);
for (int g = 0; g < k -1; g++)
{
result[g] = c;
}
} while(inc(c,begin,end));
}
free(c);
}
int main(int argc, char* argv[])
{
char *result;
char let[456976];
int f = open("pass.txt", O_RDONLY);
if (f < 0)
return 0;
char buf[1024];
while (my_fgets(buf, sizeof(buf), f))
{
let = all(4,4,'a','z');
int i = 0;
result = crypt((let[i+1]), buf);
int ok = strcmp (result, pass) == 0;
return ok ? 0 : 1;
all(4, 4, 'a', 'z');
}
close(f);
}

Answer 1

I think you need to reword the question. Maybe the code below is what you want. Let's say you have a password, and you have a file which contains a list of encrypted passwords (or hash usually), you want to see if password is right or wrong. You compare the hash of the password with hashes in the file. I haven't tested this code.
ps, let me know if I am way off, I'll delete the answer.
void crypt(char* hash, const char* password_test) {
//create hash from password, or encrypt it or something?
}
int test_password(const char *filename, const char *password){
FILE *f;
f = fopen(filename, "r");
if (!f) return 0;
char password_hash[256];
crypt(password_hash, password);
char hash[256];
char buf[1024];
while (fgets(buf, sizeof(buf), f) != NULL)
{
crypt(hash, buf);
if (strcmp(password_hash, hash) == 0)
return 1;
}
fclose(f);
return 0;
}
void main() {
int result = test_password("test.txt", "password");
if (result == 1)
printf("password is good\n");
}
Reading line by line using open/read/close
int my_fgets(char* buf, int len, int f)
{
for (int i = 0; i < len; i++,buf++)
{
int count = read(f, buf, 1);
if (!count || (buf[0] == '\n'))
{
buf[0] = 0;
return i;
}
}
return 0;
}
int main(){
int f = open("test.txt", O_RDONLY);
if (f < 0) return 0;
char buf[1024];
while (my_fgets(buf, sizeof(buf), f))
printf("%s\n", buf);
close(f);
}