Metze, The product team confirmed that Windows servers always truncate session keys to 16 bytes for signing. As per previous e-mail, your SMB signing has to use entire 32 bytes of AES session key for signing. Do your newly found bugs affect this statement ?
Thanks ! Hongwei -----Original Message----- From: Stefan (metze) Metzmacher [mailto:[EMAIL PROTECTED] Sent: Wednesday, September 17, 2008 10:57 AM To: Hongwei Sun Cc: Andrew Bartlett; [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: Re: [cifs-protocol] Session keys are not always 16 bytes long Hongwei Sun schrieb: > Metze, > > When you tested SMB signing with 32 byte AES session key, did you test > Vista with Samba server , Samba client with Windows server or both ? Samba as client and Windows 2008 as server. I found a few bugs in Samba's smb signing implementation. Windows only signs the last session setup response and samba also signs the last session setup request. I have some hacks which fix samba, but I haven't done a clean implementation yet. The key thing is that the client needs to process the last session setup response first and then verify its signature after when the correct session key is avaliable. metze > > > -----Original Message----- > From: Stefan (metze) Metzmacher [mailto:[EMAIL PROTECTED] > Sent: Friday, September 05, 2008 3:25 PM > To: Hongwei Sun > Cc: Andrew Bartlett; [EMAIL PROTECTED]; [EMAIL PROTECTED] > Subject: Re: [cifs-protocol] Session keys are not always 16 bytes long > > Hongwei Sun schrieb: >> Metze/Andrew, >> >> The subkey in the EncAPRepPart of the AP-REP should be used as the session >> key when the mutual authentication is enabled(as described in RFC 4121). >> When DES and RC4 are used in Kerberos, the implementation is based on >> RFC1964 (instead of RFC4121). According to RFC1964, you can pick the subkey >> in AP_REQ as the session key as it is the same as the subkey in AP_REP, but >> this is not true when AES is used because both subkeys are different (again >> AES means RFC4121 being used, not RFC1964). This explains what you >> observed. We will add the information to [MS-KILE] to describe how the >> session key is selected. >> >> The session key returned from Kerberos package can be used for SMB >> signing as described in the section 4.3 of [MS-SMB]. You have to truncate >> the keys to 128 bits in your code because SMB does the truncation on the >> windows side. >> >> I ran the similar testing as you did. I had one Vista machine connected >> to Windows 2008 DC/KDC and configured AES256-CTS-HMAC-SHA1-96 as Kerberos >> encryption type with mutual authentication enabled. I cannot duplicate your >> SMB signing problem(see the network capture attached). It is working between >> Windows servers and clients. > > I got it working, the session key isn't truncated for the SMB signing. > > The problem was that we reseted the sequence number when updating the session > key from the initiator subkey to the acceptor subkey between the session > setup request and response. > > Also windows signs the response with the acceptor subkey, so that the client > needs to check the signature after processing the response. > > metze >
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