Kerberos for Windows 2.1.1

Release Notes

October 9, 2001

Table of Contents


Kerberos for Windows (or KfW for short) is the integrated release of Kerberos version 4 and Kerberos version 5 (or Kerberos 4 and Kerberos 5 for short -- also Kerberos v4 and Kerberos v5).

Kerberos 4 and Kerberos 5 refers to the versions 4 and 5 of the Kerberos protocol. (A protocol refers to how data is transmitted on a network.) KfW includes both of these. KfW 2.1.1, in particular, includes the MIT Kerberos v5 Release 1.2.2 and KfW's own release of Kerberos v4.

What's New

KfW 2.1.1

KfW 2.1

Known Issues

Building the Sources

Building KfW is supported on Windows NT 4.0, Windows 2000, and Windows XP. While buildin on Windows 9x/Me might work, it is not supported.

First, make sure that you have Microsoft Visual C++ 6.0, a recent release of the Microsoft Platform SDK (July 2000 or higher is known to work), ActiveState Perl (build 517 or higher), sed, gawk, cat, and rm in your PATH. You can get sed, gawk, cat, and rm from the Cygwin distribution. Also make sure that your INCLUDE path includes the Microsoft Platform SDK before the Microsoft Visual C++ include files and that perl has been installed so that .pl files are automatically executed with perl. You will probably also need to be using the default system shell (cmd or command, depending on whether you're running NT/2000 or 9x/Me) so that the Makefiles work properly.

Then, go into the athena directory and type

..\scripts\ --softdirs
to build everything with debug information. For a release build, run
..\scripts\ --softdirs NODEBUG=1
For help, do
..\scripts\ -?
..\scripts\ --docs
[NOTE: does not work in 9x/Me]
If you are running 9x/Me, you will need to invoke the script using perl. For example:
perl ..\scripts\ [args]
If krb5 does not build properly, it is probably because sed/gawk were not in your path. To fix this, delete athena/auth/krb5/src/Makefile, fix your PATH, and try again.

To make your life easier, you might try putting the scripts directory in your path. (Under 9x/Me, that will not help you since you always need to invoke the script through perl.)

If you use the script, the targets should get copied into the target directory at the same level as the athena directory. You can go into target\bin\i386\dbg (replacing i386 with the right CPU and dbg with rel if building release targets), and run the binaries. The debug symbols for the debug build also get placed there in case you need to debug.


Table of Contents


We recommend to developers that the binaries have a single Kerberos directory that is in the PATH.

Kerberos Configuration Files

Kerberos 5 needs a single configuration file: krb5.ini. You can put it in the same directory as the DLL and everything will work fine. You can also put it in the Windows directory. You can even point to an arbitrary file by setting the KRB5_CONFIG environment variable.

Kerberos 4 needs two configuration files, typically called krb.con and krbrealm.con. You can put these files in the same directory as the DLL and everything should work. You can also set KRB4_KRB.REALMS or KRB4_KRB.CONF to override each file. Or you can set KRB4_CONFIG to force Kerberos 4 to look for both files in a particular directory. If you do none of these, this is where Kerberos 4 will search:

  1. %NDIR%\kerb\
  2. The current directory
  3. The Windows directory
  4. The Windows system directory
  5. The directory containing the executable file for the current task
  6. The directories in the path (*)
  7. The list of directories mapped in a network
  8. %NDIR%\
  9. %ETC%\

(*) Note: If you put the files in the DLL's directory, this part of the search is what will take you there. If you have another config file earlier in the search, that will take precedence, so be careful.

Modifying Kerberos 4 Configuration Files

Note: You can use Leash32 to edit the Kerberos 4 configuration files.

It is anticipated that most sites using Kerberos version 4 on Windows also will have an existing UNIX Kerberos infrastructure. For that reason, we kept the format of the krb.con identical to the UNIX krb.conf and the format of krbrealm.con identical to the UNIX krb.realms. For many users, the easiest way to configure these files for use at their local sites will be to ftp the corresponding files from a local UNIX machine that is already properly configured.

The krb.con file contains configuration information describing the Kerberos realm and the Kerberos key distribution center (KDC) servers for known realms.

krb.con contains the name of the local realm in the first line, followed by lines indicating realm/host entries. The first token is a realm name, and the second is a hostname of a host running a KDC for that realm. The words "admin server" following the hostname indicate that the host also provides an administrative database server which is contacted when changing a user's password. For example:

ATHENA.MIT.EDU admin server
LCS.MIT.EDU admin server

If this were your krb.con file and you wanted to change the default local realm to CIT.CORNELL.EDU you would edit it to look like:

CIT.CORNELL.EDU admin server
ATHENA.MIT.EDU admin server
LCS.MIT.EDU admin server

The krbrealm.con file is the host-to-Kerberos realm translation file. This provides a translation from a local hostname to the Kerberos realm name for the services provided by that host.

Each line of the translation file is in one the following forms (domain_name should be of the form .XXX.YYY, e.g., .LCS.MIT.EDU):

	host_name kerberos_realm
	domain_name kerberos_realm

If a hostname exactly matches the host_name field in a line of the first form, the corresponding realm is the realm of the host. If a hostname does not match any host_name in the file, but its domain exactly matches the domain_name field in a line of the second form, the corresponding realm is the realm of the host.

If no translation entry applies, the host's realm is considered to be the hostname's domain portion converted to uppercase.

Modifying Kerberos 5 Configuration File

Note: Leash32 can be used to edit the Kerberos 5 configuration file.

See the Kerberos 5 documentation in athena/auth/krb5/doc for further documentation on Kerberos 5.

Services File

The Kerberos DLLs need to know what port to use to talk to the Kerberos server. Kerberos 4 now defaults to ports 750 (kerberos 750/udp kdc) and 751 (kerberos-master 751/tcp) if there are no kerberos or kerberos-master entries in the services file. Kerberos 5 also has proper defaults (port 88 with a fallback to 750) in case the services file is missing the entries for kerberos and kerberos-sec.

If your site uses non-standard ports, you will still need a services file appropriate for your site.

Ticket Cache

The new default for Kerberos 4 and 5 is to store their tickets in memory.

You can specify the name of the ticket file and the directory in which it is stored via the environment variables KRBTKFILE (krb4) and KRB5CCNAME (krb5). The krb4 credentials always go into memory. The ticket string you see always has an "API:" in front of it.

There are also registry settings for these locations. Playing with Leash32 will reveal where they are (look in HKCU\Software\MIT\Kerberos4 and Kerberos5). You can set machine-wide values by playing with these settings in HKLM.

Kerberos 5 does support using file-based tickets, but we do not recommend this, as it is less secure.

Date and Time issues

Why Kerberos cares what time it is...

Kerberos authentication uses time stamps as part of its protocol. When the clocks of the Kerberos server and your computer are too far out of synchronization, you cannot authenticate properly. Both the Kerberos server and the Kerberos client depend on having clocks that are synchronized within a certain margin. This margin is normally 5 minutes.

The date and time on the machine running Kerberos must be "accurately" set. If the date or time is off "too far", Kerberos authentication will not work.

You can synchronize your clock using Leash32. It allows you to set the name of the host to which you will synchronize. It saves this information in the registry (under HKCU\Software\MIT\Leash32 -- you can set machine-wide defaults in HKLM).

By default, the server that the libraries contact when synchronizing the time is time. The domain name has been left off on purpose. If local system administrators create a machine with a CNAME of time within the local domain the clients will contact this machine by default.

If local system administrators are opposed to doing this for some reason, you can edit the resource LSH_TIME_HOST in the leashw32.dll to the name appropriate for your local site. You can also edit the header files from the source distribution and recompile for your local site. However, this is not recommended. You can also tweak the registry setting Leash32 uses.

You can also avoid this problem by running a local, properly configured, NTP program on your machine.

Command Line Options to Leash32, kinit, klist, and kdestroy

The command line options for Leash32 are:

	-kinit, -i	only perform a kinit and then exit Leash

The options for kinit, klist, and kdestroy can be viewed by typing the name of the utility followed by -? (e.g., kinit -?).

To Do

Developer Notes


Below is Jeffrey Altmans's explanation of the problem. We put in a patch he submitted for the first 2 items in his 3-item solution below.

The design of the Kclient interface is so simplified that applications cannot easily get access to necessary information. This has resulted in the need for the Kerberos configuration page in Eudora which includes fields for:

  Realm:          CC.COLUMBIA.EDU
  Service name:   pop
  Service format: %1.%4@%3

The specification of a Realm here without a "Principal name" is interesting.

Some information on my system. The local realm is KRB5.COLUMBIA.EDU and the POP server is which is in realm CC.COLUMBIA.EDU. With a ticket manager I retrieve a TGT for CC.COLUMBIA.EDU. Kstatus.exe reports that I am authenticated. Kstatus uses the kclnt32.dll interface just as Eudora does. However, when I ask Eudora to check my mail an interesting thing happens:

GetTicketForService() is called which results in a dialog being displayed

    Please enter your Network ID and password.

    Network ID: jaltman

So I enter my password for CC.COLUMBIA.EDU and am told sorry but the password is incorrect.

What happened here?

First, Eudora does not include a field for the principal name to go along with the realm. So it does not call SetUserName() which should have been set to


to match the realm specified in Eudora for the POP host. Eudora needs the realm so it can construct the service ticket name


but without setting the username it has no mechanism to report the desired realm to kclnt32.dll.

GetTicketForService() calls an internal function to verify the TGT. But because no realm has been set and data is not shared between process boundaries this instance of kclnt32.dll has no idea that the ticket manager realm is CC.COLUMBIA.EDU. And instead of attempting to load the Ticket File Realm it calls krb_get_lrealm(). So it tries to verify a TGT


which does not exist. So it destroys the existing tickets and then attempts to get a new TGT for


in the default realm which again is KRB5.COLUMBIA.EDU. But of course kclnt32.dll does not display the realm in the dialog box so the user has no idea that kclnt32.dll is confused.

In order to correct this situation the following needs to be done to kclnt32.dll:

  1. all calls to krb_get_lrealm() should be preceded by an attempt to retrieve the realm from the ticket file with krb_get_tf_realm(). Only if krb_get_tf_realm() fails should krb_get_lream() be called.
  2. if a realm is specified in the GetTicketForService() request that realm should be used for the verification of the TGT.
  3. the dialog box displayed by UserInfo() should append the realm to the szNetID (if it is not already part of the string) when setting the default value for the box. This will indicate to the user which realm s/he is being authenticated against.

Then the author's of Eudora should add a principal name to the configuration for Kerberos and call SetUserName() to set the principal and realm to the values needed to authenticate against the POP server.

Registry and Environment Settings

Leash DLL timesync code:
   1. Use TIMEHOST environment value if defined.
   2. Otherwise, use value from registry 
      (HKCU\Software\MIT\Leash\Settings,timehost) if present.
   3. Otherwise, use value from registry 
      (HKLM\Software\MIT\Leash\Settings,timehost) if present.
   4. Otherwise, use resource string if present.
   5. Otherwise, default to #defined value "time".

Kerberos 4:
A. location of krbrealm & krbconf:
   1. First, check for environment overrides:
      a. Use %KRB4_KRB.REALMS% as full filename for realms file if defined.
      a. Use %KRB4_KRB.CONF% as full filename for config file if defined.
      b. Otherwise, look for krbrealm.con and krb.con in dir %KRB4_CONFIG%.
   2. If nothing defined so far, look in registry:
      a. HKCU\Software\MIT\Kerberos4,krb.realms for realms full pathname.
      a. HKCU\Software\MIT\Kerberos4,krb.conf for config full pathname.
      b. HKCU\Software\MIT\Kerberos4,config as dir for both files.
      c. HKLM\Software\MIT\Kerberos4,krb.realms for realms full pathname .
      c. HKLM\Software\MIT\Kerberos4,krb.conf for config full pathname.
      d. HKLM\Software\MIT\Kerberos4,configdir as dir for both files.
   3. If any of the above are set, we use it even if the files are not there.
      If none of them are set, we use the old krb4 search.

B. ticket file
   1. %KRBTKFILE% if defined
   2. Registry setting, if setting is present
   3. Registry setting, if setting is present
   4. Otherwise, "API:krb4cc".
   If we ever support a file-based cache, we should use this:
   4. %TEMP%\ticket.krb, if var defined and dir exists
   5. %TMP%\ticket.krb, if var defined and dir exists
   6. c:\temp\ticket.krb if c:\temp exists
   7. c:\tmp\ticket.krb if c:\tmp exists
   8. GetWindowsDirectory()\ticket.krb as a last-ditch default?  It's
      either that or c:\ticket.krb!

Kerberos 5:
A. location of krb5.ini:
   1. %KRB5_CONFIG% if defined
   2. (HKCU\Software\MIT\kerberos5,config) if defined
   3. (HKCU\Software\MIT\kerberos5,config) if defined
   4. Otherwise, use GetWindowsDirectory()\krb5.ini
   (do this instead of OpenFile to make things more explicit/simple)

B. credentials cache
   1. %KRB5CCNAME% if defined
   2. (HKCU\Software\MIT\kerberos5,ccname) if defined
   3. (HKLM\Software\MIT\kerberos5,ccname) if defined
   4. If RegKRB5CCNAME is set under [Files] in kerberos.ini,
      look at that path in the registry (code already in krb5 for compat
      with Gradient DCE installations, I believe).
   5. Otherwise, if using CCAPI, default to "API:krb5cc".
                 if no CCAPI, use "FILE:" with:
      a. %TEMP%\krb5cc, if var defined and dir exists
      b. %TMP%\krb5cc, if var defined and dir exists
      c. c:\temp\krb5cc if c:\temp exists
      d. c:\tmp\krb5cc if c:\tmp exists
      e. GetWindowsDirectory()\krb5cc as a last-ditch default?
         it's either that or c:\krb5cc!

Using DNS Lookups for Kerberos Configuration

What is it?

DNS Lookups provide Kerberos the ability to determine the Kerberos Realm that a host belongs to and to find the servers associated with a given Realm by using the Domain Name Service instead of or in addition to local configuration files.

When are DNS Lookups used?

DNS Lookups are used under two circumstances:

  1. No krb.con file is found for Kerberos 4 or no krb5.ini file is found for Kerberos 5.
  2. The krb.con file or krb5.ini file contains a command to activate DNS Lookups and the lookup cannot be answered by data found in the appropriate configuration file.

To activate DNS lookups in a krb.con file place a line that reads:


as one of the Realm to Host entries. When DNS Lookups are used the first line may be left blank to indicate that the default realm should be determined by a DNS Lookup.

To activate DNS lookups in a krb5.ini file place:

dns_fallback = true

into the [libdefaults] section. If a "default_realm" entry is not provided, a DNS lookup will be performed to determine the default realm.

What entries go into the DNS?

Host to realm lookups are performed using DNS TXT records. Example records are:  IN TXT "KRB5.COLUMBIA.EDU"                IN TXT "CC.COLUMBIA.EDU"

Realm to server lookups are performed using DNS SRV records. Example records are:

_kerberos._udp.KRB5.COLUMBIA.EDU.    IN SRV 0 0 750
_kerberos-adm._tcp.KRB5.COLUMBIA.EDU IN SRV 0 0 749
_kpasswd._udp.KRB5.COLUMBIA.EDU      IN SRV 0 0 464

Some older notes from prior releases...

  1. Modification of the Kerberos 4 credential cache:

    We encountered a problem at MIT that we felt needed to be addressed even though it broke some backwards compatibility. We found that if someone used a Kerberized application spanning multiple PPP sessions a Kerberos error would be generated and few applications would catch this error and try to get new tickets instead. E.g. Suppose a user starts a PPP connection and then starts Eudora, fetching mail. The user then decides to close down the PPP connection while they read their mail and compose responses. Next they initiate a new PPP connection and incorporate mail again. Note that the user never exited Eudora. Instead of prompting the user for their name and password Eudora will generate and error message. The only way for the user to recover the functionality would be to use Leash, Kview, or kdestroy to destroy their old tickets so that Eudora would get new tickets.

    This happened because many ISPs hand out a new IP address to a user each time that user reconnects to the system. Also a Kerberos ticket includes the machines local IP address in an encrypted form this is used by most severs to insure that the ticket has not been copied to another users machine.

    Since the local IP address is stored in the ticket it seems that it should be easy to compare this data to the machine's local IP address at the same time that an application is checking to see if the ticket has expired. Unfortunately the IP address in the ticket is encrypted in the server's session key and so is inaccessible to the local machine.

    Instead we borrowed an idea from Kerberos version 5 and decided to store the local IP address, unencrypted, in the credential which is cached in the local cache. Within the Kclient function IsCredExpired() or the krbv4wXX.dll function kchktkt we verify that the ticket has not expired and that the local IP address matches the IP address stored in the ticket.

    This implies that machines with multiple copies of kclnt32.dll or krbv4w32.dll, of different versions, may encounter unexpected errors when using Kerberized applications. The normal error message generated will be BAD_TKT_FILE_FORMAT or NO_TKT_FILE.

    Users of applications that use other vendors Kerberos implementations may also be affected. E.g. some software from FTP, Inc.

  2. Add a new function to the Kclient DLL. This function is SendTicketsForService(). It is basically a send_auth() type function. Before everyone complains please read the following explanation.

    Qualcomm has been working with Platinum on a 32-bit Kclient which would supports both Kerberos v4 and v5. From what I have heard this is a commercial implementation. It ignores GSS or other abstraction layers above the Kerberos layer that application developers should write to. It keeps its ticket cache in the DLL, as such it will not share the ticket cache with other Kerberos implementations that may reside on the user's system.

    Platinum and Qualcomm decide to add a new API call to the Kclient interface. Eudora uses this new function if it finds a KCLNT32.DLL. In this case it does not use the thunking application KERB16.

    We have duplicated this function in our release of KCLNT32 so that Eudora will not GPF. Please DO NOT WRITE APPLICATIONS TO THIS FUNCTION.

  3. We stole an idea from Cornell. If the clock is out of synch when we are trying to obtain a ticket we synchronize the clock and try again. We inform the user if this occurred.

  4. Fixed up some problems relating to DLL initialization. WSAStartup() will be called if necessary by a few functions. This was needed to handle some differences in DLL initialization under Win32 when multiple applications were using the DLL at the same time. Also fixed up some initialization of the com_err functions due to similar issues.

  5. Added two new functions to leashw32.dll. The first is Leash_set_help_file(char*szHelpFile) which allows an application developer to specify which help file to use from the dialog box presented when using the Leash_kinit() function. If the argument is NULL the function will check the environment variable KERB_HELP. If this is not set the hard coded value of kerberos.hlp will be used. The other function is Leash_get_help_file() which allows an application developer to determine the name of the help file being used. These are defined in lshfunc.c.

  6. Fix the send_auth so that we do not fail on a null realm. Also detects when an invalid socket descriptor has been passed. (Special thanks to Eudora 3.0 for providing a test case.)