[cifs-protocol] Session keys are not always 16 bytes long

Stefan (metze) Metzmacher metze at samba.org
Fri Aug 8 10:19:09 GMT 2008

I just found that the session key used to decrypt the password
attributes in the DsGetNCChanges() is not truncated.
And I need to use gsskrb5_get_subkey() instead of
gsskrb5_get_initiator_subkey(), when aes keys are used.

>>    In our last conference call, we talked about your question
>> regarding which of the numerous keys Kerberos produce is considered
>> the 'SMB session key'.  I had discussions with the product team to
>> find what or how should be documented.   You mentioned that you would
>> like to see the document to specify which GSSAPI call returns the
>> session key.   They would like to have a little more background
>> information, which you already talked about a little bit during our
>> conversation.  I just want to confirm so I can pass it accurately to
>> product team.  
>>     What do you mean by GSSAPI with CFX ? Do you mean the mechanism
>> conforming to RFC 4121 ?
> Yes.  (I should stop using that term, as it never made it into the RFC)
>>     What implementation are you using  for GSSAPI with CFX in Vista
>>  ?   Is it Heimdal’s implementation ?  
> Yes. 
>>     What is your expectation about how this detail should be included
>> in the document ?  Do you expect it to associate with specific GSSAPI
>> calls? 
> An indication of the (hopefully shared) MIT/Heimdal API would be very
> useful (as these are almost certainly the basis of any new
> implementations).
> However, this should be alongside a description of where in the kerberos
> protocol is is found:
> 'the session key generated on ... and encrypted in message ... as
> element ... from (client/server) to the (client/server) is also used as
> the SMB Session key' (for example)
>>    I hope that with the information we can have a resolution soon.
>> Thanks for your patience.
> No worries,
> Andrew Bartlett
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