[cifs-protocol] SMB2 signing

[tridge at samba.org]

Folks,

I'm trying (and failing) to get SMB2 signing implemented in
Samba. Looking at the MS-SMB2 docs some things are not at all clear:

 1) section 3.1.4.1 refers to MS-MWBE for SHA-256. I can't see
 anything in MS-MWBE that is relevant. What is that reference for?

 2) I interpret step 2 as meaning that we concatenate the session key
 with the packet, with the session key being put in front of the
 packet in the concatenated buffer. Is that right?

 3) It isn't clear if the buffer should include the 4 byte NBSS
 length. I think not, but I think that should be made clear

 4) step for talks about "high order 16 bytes". Do you mean the first
 16 bytes? What is "high order" in a 32 byte buffer, which is what
 SHA-256 gives.

 5) what is the "big endian" thing about? SHA-256 gives a 32 byte
 buffer. It does put the bytes in there in BE format, but what does it
 mean to put the resulting 16 bytes in the packet in big endian
 format?

Pu another way, I'm implementing it like this:
 
     SHA256_CTX m;
     uint8_t res[32];
     memset(sig_in_packet, 0, 16);
     SHA256_Init(&m);
     SHA256_Update(&m, session_key, 16);
     SHA256_Update(&m, packet, length);
     SHA256_Final(res, &m);
     memcpy(sig_in_packet, res, 16);

Using SHA-256 from Heimdal, which you can see here:

    http://samba.org/ftp/unpacked/samba_4_0_test/source/heimdal/lib/hcrypto/sha256.c

But I'm finding the signatures don't match what windows produces. I've
tried quite a few combinations (like including the 4 byte header, or
doing the packet before the session key). No luck. Any clues?

Cheers, Tridge

PS: I also submitted this to the file services forum, but am
resubmitting to dochelp as a CAR, and also CCing the
cifs-protocol at samba.org public list to try to kick start some public
discussion on SMB2