keytab for windows based services

[Guest lsniks]

Hi All,

 

We have an issue with generating a valid keytab for windows based

services which can be used on unix based machines to decrypt AP-REQ.

 

Following is our setup :

 

1. Windows XP cifs client

2. Windows 2003 KDC and domain controller 64 bit

3. Windows XP cifs server 64 bit.

4. Linux FC7 machine with MIT kerberos 1.6.3

 

We have the admin privileges for all the machines mentioned above.

 

What we are trying to do ?

 

1. We request a kerberized traffic from cifs client to cifs server

which we want to route through linux box.

 

2. We want to do some processing with the AP-REQ. Evidently for

which we need to authenticate the client in AP_REQ on linux machine.

 

3. Now to authenticate the client in AP-REQ on linux machine we

propose to use GSSAPI calls using corresponding service keytab.

 

The problem :

 

1. Our understanding is, all windows based services are registered

under corresponding computer name with their corresponding SPN.

 

2. This registration occurs whenever the machine joins the domain. So

basically , whenever the server is up and running and is in domain

all its services are registered with windows domain controller and

are mapped to its computer name.

 

3. The exchange of long term keys for service between service and KDC

occurs at the same time.

 

4. We understand the definition of ktpass is "To generate keytab for

UNIX based services " but with no other option to generate a keytab,

we run ktpass for this windows based service which creates a new

long term service key for the service which is not communicated back

to service.

 

When I use this keytab on linux machine through GSSAPI calls to

decrypt the AP-REQ , I get KRB5KRB_AP_ERR_BAD_INTEGRITY.

 

which is obvious since key used by KDC to encrypt the ticket for

service is different(Its the old key ) than what is in keytab.

 

Questions :

 

1. Is there a way to bring KDC and service in sync in terms of the

service key being used ? To be more precise , If I change the

service key for a service at KDC Is there a way to communicate

this back to service so that the service starts using this new key

for all further requests ?

 

2. We understand ktpass is a tool to generate a keytab for unix based

services. Do we have any similar tool for windows based services ?

 

3. Since windows based service SPN's are registered under computer name

at the time of logon It can be mapped to some other user as well without

creating a duplicate SPN. Is it possible for a service to run under

a user account and obtain a service key in windows ?

 

4. We understand "man in the middle" is not possible with kerberos but

when we own all components of traffic ( KDC , server , client , DC

with admin privileges ) should't I be allowed to extract a service key

for the given SPN from KDC without disturbing the existing setup ?

 

 

Any help is appreciated

 

--

Nikhil