AW: Accepting secure context on Server without KDC-Login

[Seema Malkani]

The JAAS Krb5LoginModule allows to generate keys using passwords, which 
is when the server would need to contact the KDC. Currently, the JAAS 
Krb5LoginModule does not make the distinction of client/server, server 
can be an acceptor and initiator i.e. both, hence a TGT is acquired.

The usage option "isInitiator" allows to distinguish if are want the 
JAAS Krb5LoginModule to be an acceptor only or an initiator/acceptor 
i.e. both.

Seema

Olfmatic wrote:

>Hello Seema,
>
>Sorry, but this is important to me. Let us make this clear:
>
>JDK 1.4.2:
>Specifying the keytab-file in the LoginModule will make it look there for credentials. But the TGT is obtained from the KDC when login() is called.
>
>JAVA5:
>Specifying the keytab-file in the LoginModule will make it look there for credentials. If the option isInitiator is set true, it will NOT try to get the TGT from the KDC. No connection to the KDC will be established.
>Is that right?
>
>
>The point is, as far as I understand Kerberos, there should be no reason for the server application to call the KDC. So why does it do this? They shared a secret and that's enough to proove authenticity of service tickets. The server application should not need to have the TGT. At least that's what I thought.
>
>Thanks for your help.
>Florian
>
>
><<<<<<<<<<<<<<<<<<<
>
>This configuration option in JAAS Krb5LoginModule will be backported to 
>JDK 5.0 Update release, and JDK 1.4.2, don't have the exact release 
>details available as yet.
>
>No, server will acquire credentials from the keytab, if you provide the 
>configuration option to specify the keytab file. However, the JAAS 
>Krb5LoginModule will in addition acquire the TGT.
>
>Seema
>
>
>The default credential acquisition model for Java GSS-API requires 
>credentials to be present in the current Subject. Typically, the 
>credentials are placed there after a JAAS login by the application.
>
>Client and server applications typically perform JAAS authentication 
>using the Kerberos login module. Upon successful authentication the TGT 
>is stored in the Subject's private credentials set and the Kerberos 
>principal is stored in the Subject's principal set. At the server-end 
>the secret key is stored in the Subject's private credentials set.
>
>If there are no valid credentials in the current Subject, Java GSS 
>provider attempts to obtain new credentials by invoking a JAAS login 
>itself. This is when the default JAAS entries 
>"com.sun.security.jgss.initiate" and "com.sun.security.jgss.accept" are 
>read from the JAAS configuration file, using the desired configurations 
>that you provide, such as the keytab at the server-end.
>
>You can configure JAAS Krb5LoginModule to be an "acceptor" only at the 
>server-end. This option is available starting from Java SE 6, and will 
>be backported to earlier releases.
>
>For details on this option, check the javadoc on Krb5LoginModule:
>http://download.java.net/jdk6/docs/jre/api/security/jaas/spec/com/sun/security/auth/module/Krb5LoginModule.html
>
>Seema 
>
>Olfmatic wrote On 09/07/06 05:41,:
>
>  
>
>>Hello,
>>
>>Please help me, I still don't get it:
>>I want to accept a secure context on my server. As far as I learned, the server does not have to contact the KDC to do so, because the shared secret is stored in a keytab file created on the KDC and then stored at the server. But I made a different experience.
>>
>>This is my code:
>>
>>	Oid tKrb5Oid = new Oid("1.2.840.113554.1.2.2");
>>	GSSManager tGSSManager = GSSManager.getInstance();
>>	String tPrincName = "servicename/hostname at REALM";
>>	GSSName tServerName = tGSSManager.createName(tPrincName, GSSName.NT_USER_NAME);
>>	GSSCredential tServerCredential = tGSSManager.createCredential(tServerName,
>>		GSSCredential.INDEFINITE_LIFETIME, new Krb5MechFactory().getMechanismOid(),
>>		GSSCredential.ACCEPT_ONLY);
>>	GSSContext tSecureContext = tGSSManager.createContext(tServerName, tKrb5Oid, tServerCredential, GSSContext.DEFAULT_LIFETIME);
>>	byte [] tInToken = aToken;
>>	byte [] tOutToken = tSecureContext.acceptSecContext(tInToken, 0, tInToken.length);
>>
>>If I execute this code in a PrivilegedAction after loggin in to the KDC with the Krb5LoginModule, everything is fine. Now what I want is the server to accept the secure context WITHOUT trying to contact the KDC. Do I have to login with the Krb5LoginModule even though? Or can the above code also be executed without prior KDC-Login?
>>But then how do I tell the server application where to find the keytab file? As far as I know, the keytab file is configured in the configuration of LoginModules:
>>
>>JaasLogin {
>>   //Kerberos single-sign-on login module
>>   com.sun.security.auth.module.Krb5LoginModule required debug=true useKeyTab=true keyTab=C:/krb5.keytab ;
>>};
>>
>>
>>But if i never call
>>
>>   	LoginContext tLoginContext = new LoginContext("JaasLogin");
>>   	tLoginContext.login();
>>   	final Subject tSubject = tLoginContext.getSubject();
>>
>>then how can the application know that it shall use a keytab and where to find it?
>>
>>IF I login with the Krb5LoginModule, the server looks for the KDC which is not what I want.
>>IF I do not login with the Krb5LoginModule, I get the error message "Attempt to obtain new ACCEPT credentials failed", which seems clear to me because the server application doesn't know anything about the keytab file.
>>What do I have to do? Login or no Login?
>>
>>Thanks for any help.
>>
>>Florian
>>
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>> 
>>
>>    
>>