On Tue, 2011-01-25 at 10:35 +0200, Luiz Augusto von Dentz wrote: > Hi Vinicius, > > On Mon, Jan 24, 2011 at 11:34 PM, Vinicius Costa Gomes > <vinicius.gomes@xxxxxxxxxxxxx> wrote: > > Hi Brian, > > > > On 11:03 Mon 24 Jan, Brian Gix wrote: > >> Hi Vinicius, > >> > >> I am sorry that it has taken so long to test the snapshot that you > >> placed on gitorious, but I have now done so. > >> > >> On Fri, 2010-12-03 at 19:05 -0300, Vinicius Costa Gomes wrote: > >> > Hi Brian, > >> > > >> > On 11:11 Fri 03 Dec, Brian Gix wrote: > >> > > > >> > > Hi Claudio, Johan & All, > >> > > > >> > > Is this LE capable kernel that Ville is working on, the development stream > >> > > for the LE Security Manager? And if so, is it in a partial fleshed out > >> > > state? > >> > > >> > There is a simple implementation of SMP here[1] on my "devel" branch. I am > >> > cleaning it up for sending it for review. > >> > > >> > If you want to help, have any comments or just want to tell us what you are > >> > working on, please drop by #bluez on freenode, or send an email. > >> > >> I have been able to verify that the Just Works negotiation of the Short > >> Term Key does work against an independent implementation of the LE > >> Security Manager, as long as I have requested no MITM protection. I > >> have the following comments: > >> > >> 1. You currently reject security if I *do* request MITM protection. > >> This should not be done. The correct functionality should be to > >> continue the negotiation. Even though I requested MITM, it will be > >> clear to both sides that JUST_WORKS methodology has been used, and so > >> when the Keys are generated and exchanged, both sides will indicate in > >> their Key Database that they are no-MITM keys. If I then actually > >> *needed* MITM protection, then whatever functionality requiring that > >> level of security will fail with an insufficient security error code. > >> However, security should *never* be rejected unless there is a > >> fundamental incompatibility such as no level of security actually > >> supported. This is the only functionality that I found to be actually > >> incorrect. > >> > > > > I was assuming that the meaning of setting the MITM protection bit, was that > > it was *requiring* MITM protection, and when that couldn't be fulfilled the > > Pairing Request should be rejected. > > > > So my assumption was incorrect, going to fix it soon. > > Well the spec says it is a requirement: > > "If the STK generation method does not result in an STK that provides > sufficient security properties then the device shall send the Pairing > Failed command with the error code âAuthentication Requirementsâ" - > 2.3.5.1 Selecting STK Generation Method - Page 608 >From Page 607: "If both devices have out of band authentication data, then the Authentication Requirements Flags shall be ignored when selecting the pairing method and the Out of Band pairing method shall be used. If both devices have not set the MITM option in the Authentication Requirements Flags, then the IO capabilities shall be ignored and the Just Works association model shall be used. Otherwise the IO capabilities of the devices shall be used to determine the pairing method as defined in Table 2.4." In the test case I ran, only One device (i.e. NOT BOTH) had the MITM option set. So my reading is that the IO Capabilities should be ignored, and JUST_WORKS used. Remember the phone use case: When it needs to pair with a remote device, it is usually a GATT client that can support any level of security. It does not know if this new remote device requires MITM security, or No security. However as the link Master and Initiator, it has to choose one. It Chooses MITM, and if the remote side supports MITM, then pairing proceeds with a resulting MITM protection level. If the remote device is a simple dumb device with no security, it also needs to proceed without failing, but this time it completes with NO-MITM as the protection level. If it fails because the remote doesn't require security, then there is a fundamental incompatibility between the devices, which in the SIG we have tried to avoid. > > In my interpretation this is exactly what should happen when MITM is > set but there is no way to generate an authenticated key as Table 2.4: > Mapping of IO Capabilities to STK Generation Method suggest, in other > words if one of sides has NoInputNoOutput and MITM is set we should > return "Authentication Requirements" error. > -- Brian Gix bgix@xxxxxxxxxxxxxx Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
