Canonical/portable way to obtain long term key for a GSS security context (acceptor side)

[Osipov, Michael (IN IT IN)]

On 2024-05-06 16:32, Osipov, Michael (IN IT IN) wrote:
> Folks,
> 
> I have a GSS security context established and need to calculate a 
> signature on data received form the client. The client submits me a 
> forwarded signature calculated by the KDC (Active Directory) with the 
> server's long term key from the keytab.
> As far as I can see ExtendedGSSContext only exposes the server's session 
> key, but not the long term key used to accept this security context.
> The only way I have found working is either:
>> PrincipalName name = new PrincipalName("...", 
>> PrincipalName.KRB_NT_PRINCIPAL);
>> EncryptionKey[] encKeys = EncryptionKey.acquireSecretKeys(name, "...");
>> EncryptionKey encKey = 
>> EncryptionKey.findKey(serverSignature.getType().getEType(), encKeys);
> 
> which is ugly because these are really really private classes and the 
> key is disjoint with the context hoping that the KVNO matched with the 
> key I have here or I need to pull in a lot of dependencies from Apache 
> Kerby to get the key.
> 
> The signature calculation succeeds with additional private classes, but 
> that is another story.
> 
> Any tip would be helpful. In case you ask, I want to calculate: https:// 
> learn.microsoft.com/en-us/openspecs/windows_protocols/ms-pac/ 
> a194aa34-81bd-46a0-a931-2e05b87d1098
> 
> Ideal solution would be of course:
> Key longTermKey = (Key) 
> extGssContext.inquireSecContext(InquireType.KRB5_GET_LONG_TERM_KEY);
> 
> I am on Java 8+

While this is not the ideal situation this works:
> KeyTab keytab = KeyTab.getUnboundInstance(new File("..."));
> KerberosPrincipal principal = new KerberosPrincipal("...", KerberosPrincipal.KRB_NT_PRINCIPAL);
> KerberosKey[] keys = keytab.getKeys(principal);

The key still remains disjoint to the security context in terms of etype 
and kvno. I also noticed a possible bug in principal name comparison I 
need to check and will report separately.

Additional pointers still appreciated.

M