[PATCH][SMB3.1.1] Add defines for new signing context

[Aurélien Aptel]

Patch LGTM

Reviewed-by: Aurelien Aptel <aaptel at suse.com>

Stefan Metzmacher via samba-technical <samba-technical at lists.samba.org>
> This isn't in MS-SMB2 yet.
>
> Is this AES_128?

This is returned in latest Windows Server Insider builds but it's not
documented yet.

https://www.microsoft.com/en-us/software-download/windowsinsiderpreviewserver

I've asked dochelp about it during the SDC plugfest and they gave me
this:

    The new ContextType is:
    SMB2_SIGNING_CAPABILITIES 0x0008
    The Data field contains a list of signing algorithms.
    •    It adds a new negotiate context, which enables SMB to decouple signing algorithms from dialects. E.g. if both client and server supports it, a session may use HMAC-SHA256 with SMB 3.1.1.
    •    It adds the AES-GMAC algorithm.
     
    SigningAlgorithmCount (2 bytes): Count of signing algorithms
    SigningAlgorithms (variable): An array of SigningAlgorithmCount 16-bit integer IDs specifying the supported signing algorithms.
     
    The following IDs are assigned: 
    0 = HMAC-SHA256
    1 = AES-CMAC
    2 = AES-GMAC


I've been CCed in a Microsoft email thread later on and it seems to be
unclear why this was missed/wasn't documented. Maybe this is subject to
change so take with a grain of salt.

Cheers,
-- 
Aurélien Aptel / SUSE Labs Samba Team
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