help with understanding code

[vbaswant]

Hello

Could anyone please explain to me the meaning of each line of the program below I marked with question marks (???). I copied it from a website. It encrypts and decrypts a password entered by the user using the crypt.h file.

The following program takes and sets a password entered by the user.

     #include <stdio.h>
     #include <time.h>
     #include <unistd.h>
     #include <crypt.h>
     
     int
     main(void)
     {
       unsigned long seed[2];
       char salt[] = "$1$........";
       const char *const seedchars =
         "./0123456789ABCDEFGHIJKLMNOPQRST"
         "UVWXYZabcdefghijklmnopqrstuvwxyz";
       char *password;
       int i;
     
       seed[0] = time(NULL);	// ??????????????
       seed[1] = getpid() ^ (seed[0] >> 14 & 0x30000);	// ??????????????
     
       
       for (i = 0; i < 8; i++)
         salt[3+i] = seedchars[(seed[i/5] >> (i%5)*6) & 0x3f];	// ??????????????
     
   
       password = crypt(getpass("Password:"), salt);	// ??????????????
     
  
       puts(password);
       return 0;
     }

And the following program verifies the password entered by the user.

     #include <stdio.h>
     #include <string.h>
     #include <unistd.h>
     #include <crypt.h>
     
     int
     main(void)
     {
      
       const char *const pass = "$1$/iSaq7rB$EoUw5jJPPvAPECNaaWzMK/";
     
       char *result;
       int ok;
     
       
       result = crypt(getpass("Password:"), pass);	// ??????????????
     
      
       ok = strcmp (result, pass) == 0;
     
       puts(ok ? "Access granted." : "Access denied.");
       return ok ? 0 : 1;
     }

Many thanks in advace

[johnnystarr]

<crypt.h> is provided by the standard C library.

It uses very complex algorithms such as hash functions http://en.wikipedia.org/wiki/Hash_function

The lines:

seed[0] = time(NULL);
seed[1] = getpid() ^ (seed[0] >> 14 & 0x30000);

Seem to initialize salt which is passed to crypt()

I am not certain about the implementation of crypt() however seeing the bitwise operations in advance I would assume it is very complex and precise.

[vbaswant]

Thanks johnnystarr for your reply