I'm working on a project where we use JAAS/Krb5LoginModule with useTicketCache & doNotPrompt as well as the allowtgtsessionkey registry change to piggy back our authentication on the windows logon of the domain joined computer.
We then use jgss/kerberos to get a GSS API Kerberos Token (rfc1964) which we use to secure a SOAP Message using the WSS Kerberos Token Profile 1.1.1 when communicating with a service. This involves including the b64 encoded GSS Token in the Security element of the SOAP Envelope/Header and using the client/service sessionKey to sign a component of the element.
We are getting the client/sessionKey by querying the private credentials of the javax.security.auth.Subject which the JAAS/Krb5LoginModule returns and looking for a javax.security.auth.kerberos.KerberosTicket which matches our service peer name and invoking its getSessionKey().
All of this works fine in Java-6, however Java-7 clients are failing as there seems to have been a change in the Kerberos KRB_AP_REQ message that Java-7 creates. The Java-7 KRB_AP_REQ Authenticator contains a sub-key which is different to the sessionKey. Since the Kerberos specification (see excerpt below) says that this subkey supersedes the sessionKey then our Java-6 behaviour of using the sessionKey for signing is no longer correct.
RFC1510 - The Kerberos Network Authentication Service (V5)
subkey This field contains the client's choice for an encryption key which is to be used to protect this specific application session. Unless an application specifies otherwise, if this field is left out the session key from the ticket will be used.
I've not seen anywhere where this change is documented but have confirmed the behaviour at least in Java(TM) SE Runtime Environment (build 1.7.0_11-b21).
At this point unless I have missed something glaringly obvious (and I hope I have), our options seem to be:
- Change the Java-7 Kerberos Configuration to revert to Java-6 behaviour - unfortunately I've not seen anything in the docs that seems to suggest that this is possible.
- Find a way to get access to the subkey. For this options I have explored are:
- Decode the b64 encoded GSS Token, pull out the encrypted Authenticator, decrypt it using the sessionKey, decode the ASN.1 DER encoding and pull out the subkey.
- Use what appears to be non-standard GSS API Extensions and use theExtendedGSSContext.inquireSecContext() method with KRB5_GET_SESSION_KEY to get at the subKey.
Any suggestions/insight in to these or other possible options?