Thread: Problem with comparing hashes/substrings from 2 files

I have 2 files: shadow.txt and mytab2411.txt. "shadow.txt" contains password hashes while "mytab2411.txt" is a password lookup file containing passwords and their corresponding hashes. What I want to do is to use "mytab2411.txt" to find the passwords for "shadow.txt" by comparing hashes from both "shadow.txt" and "mytab2411.txt".


I have 2 problems:


1. I do not know how to obtain the password text from mytab2411.txt.


2. I get this output instead of the desired output:

Code:

user id: pyc 1 -password (NOT FOUND)
user id: pyc 2 -password (NOT FOUND)
user id: pyc 3 -password (NOT FOUND)
user id: pyc 4 -password (NOT FOUND)
user id: pyc 5 -password (NOT FOUND)
user id: pyc 6 -password (NOT FOUND)

shadow.txt

Code:

pyc1:$1$$Tnq7a6/C1wwyKyt0V/.BP/:17482:0:99999:7:::

pyc2:$6$$/xMg2/4CZwMUbah4IhNwCjqzZf0/OByfs6UHmq32jFbsdpbDw9bhLttC7n/bAVlM2NwJ7hBQ3d0H47leLXE6g1:17482:0:99999:7:::

pyc3:$1$$zZQKNjRd94GHyYOwXuStf0:17482:0:99999:7:::

pyc4:$6$iKYSRG68$STdY8TCgoCaNfSUcyCwSBlVekdjs0P3qXtwxSbgpQpMUnHJRRSHOT5amoR24IqZBTPNWuIfO.uhZEnGLuE4q/.:17482:0:99999:7:::

pyc5:$6$$FDqvMBbQOCyKP9uBL8E6TAEupCh72v.3/ow4fZ5HpZ/0NS7LBifFS9nJdzc/u2OEhUnRF9yC4Lw23hHjD1EmD.:17482:0:99999:7:::

pyc6:$6$$LfCuhKecDtIfX77LOTWD1PjhF1IC0hBzjxckEthmoT8mVbxKH3qJzFgEi/P9GN1mptR4WPiwuh69X/41M6pHW1:17482:0:99999:7:::

mytab2411.txt

Code:

apple:$1$$Tnq7a6/C1wwyKyt0V/.BP/

apple:$6$$vTqYXuMRNbK5N1xiTvUKcJuKVmEQyPtgUiyawaEBMwknJ3AQoOvPpr2RrANRxDTS.qo7rQuFvxZcUkT31W6uG/

banana:$1$$zZQKNjRd94GHyYOwXuStf0

banana:$6$$5iQBiKBv7vIGqC5iQJOVUpzgnSO0P.pMQ.Guwczcn9nQSu61IVKT9GU4IEYjb5WbsBLaIfZ3io59M4oac.W0/1
    
orange:$1$$Ro.kDk5GNLNQbdJyDEovy1
 
orange:$6$$/xMg2/4CZwMUbah4IhNwCjqzZf0/OByfs6UHmq32jFbsdpbDw9bhLttC7n/bAVlM2NwJ7hBQ3d0H47leLXE6g1

Desired output

Code:

user id : pyc1 – password found => apple   
user id : pyc2 –  password found => orange  
user id : pyc3 – password found => banana
Data Error: Invalid entry found in the shadow file. (skipped)
user id : pyc5 – password (NOT FOUND)
user id : pyc6 – password (NOT FOUND)

The main code

Code:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>


  int printDataError() {


    printf("Data error: Invalid entry found in the shadow file. (Skipped)\n");
  }


int main(void) {
    char buf[1024];
    char * * arr1 = NULL;
    char * * arr2 = NULL;
    int size1 = 0;
    int size2 = 0;
    FILE * f1, * f2;
    f1 = fopen("shadow.txt", "r");
    f2 = fopen("mytab2411.txt", "r");


    // Allocate memory for shadow.txt
    while (fgets(buf, 1024, f1)) {
      size1++;
      arr1 = realloc(arr1, sizeof(char * ) * size1);
      arr1[size1 - 1] = strdup(buf);
    }


    // Allocate memory for mytab2411.txt
    while (fgets(buf, 1024, f2)) {
      size2++;
      arr2 = realloc(arr2, sizeof(char * ) * size2);
      arr2[size2 - 1] = strdup(buf);
    }


    char line[1000]; //Allocate max number of characters in a line for shadow.txt
    char line2[1000]; //Allocate max number of characters in a line for mytab2411.txt


    char hash[1000]; //Allocate max number of characters in a hash (substring of a line) for shadow.txt
    char hash2[1000]; //Allocate max number of characters in a hash (substring of a line) for shadow.txt


    char md5[5] = "$1$$"; // Define string to be searched for md5
    char sha512[5] = "$6$$"; //Define string to be searched for sha512
    char * ret; // Used for shadow.txt
    char * ret2; //Used for shadow.txt
    char * ret3; //Used for mytab2411.txt
    char * ret4; //Used for mytab2411.txt


    // Read shadow.txt line by line
    for (int i = 0; i < size1; i++) {


      memset(hash, '\0', sizeof(hash));
      strcpy(line, arr1[i]);


      //Search for md5 in shadow.txt
      md5[4] = '\0';
      ret = strstr(line, md5);


      //Search for sha512 in shadow.txt
      sha512[4] = '\0';
      ret2 = strstr(line, sha512);


      // Copies md5 hash to the variable hash if md5 is detected in shadow.txt
      if (ret) {
        strncpy(hash, line + 5, 26);
        hash[26] = '\0';


      }


      // Copies sha512 hash to the variable hash if sha512 is detected in shadow.txt
      else if (ret2) {


        strncpy(hash, line + 5, 90);
        hash[90] = '\0';


      }


      // Read mytab2411.txt line by line
      for (int j = 0; j < size2; j++) {


        memset(hash2, '\0', sizeof(hash2));
        strcpy(line2, arr2[j]);


        //Search for md5 in mytab2411.txt
        md5[4] = '\0';
        ret3 = strstr(line2, md5);


        //Search for sha512 in mytab2411.txt
        sha512[4] = '\0';
        ret4 = strstr(line2, sha512);


        // Copies sha512 hash to the variable hash if md5 is detected in mytab2411.txt  
        if (ret3) {


          strcpy(hash2, & line2[strlen(line2) - 27]);


        }


        // Copies sha512 hash to the variable hash if sha512 is detected in mytab2411.txt
        else if (ret4) {


          strcpy(hash2, & line2[strlen(line2) - 91]);


          //printf("Line %d hash: %s\n", j+1,hash2);


        }


      } //End of "for(int j = 0; j < size2; j++)" loop


      // Compares the hash in shadow.txt (hash) and hash in mytab2411.txt (hash2).
      if (strcmp(hash, hash2) == 0)
        printf("user id: pyc %d - password found =>  \n", i + 1);


      else if (strcmp(hash, hash2) != 0)
        printf("user id: pyc %d -password <NOT FOUND>\n", i + 1);


      else
        printDataError();


    } //End of "for (int i = 0; i < size1; i++)" loop


    return 0;
  } //End of main

Originally Posted by wei

1. I do not know how to obtain the password text from mytab2411.txt.

From what I see, both files are colon-delimited, so you would use the same approach for mytab2411.txt as you would use for shadow.txt, e.g., use strchr to find the next ':', and from there determine the portion of the string that you wish to extract as the plaintext password or password hash in mytab2411.txt, and as the username or password hash in shadow.txt.

It seems to me that you don't have to care about the password hash algorithm, so your code shouldn't be trying to determine it as if you were say, trying to calculate the hash to confirm it.

EDIT:
You should break up your program into functions that do one thing and do it well. I would also declare two structures:

Code:

struct UsernamePasswordHashEntry {
    char username[1000];
    char passwordHash[1000];
};

struct PasswordLookupEntry {
    char password[1000];
    char passwordHash[1000];
};

This would make it easier for you to read the data and perform the matching.