Hi Luiz, On Mon, 2011-01-24 at 22:09 +0200, Luiz Augusto von Dentz wrote: > Hi, > > On Mon, Jan 24, 2011 at 9:03 PM, Brian Gix <bgix@xxxxxxxxxxxxxx> wrote: > > Hi Vinicius, > > [...] > > > > 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. > > But the point of MITM is man in the middle protection, so if we end up > with a key which is not MITM there is no protection why store the link > key? Actually if we do that we can end up in a situation where > insufficient security is always triggered and the other stack may > attempt to repair but with current code it will never succeed to > generate a valid MITM link key. Anyway I suppose supporting MITM is > mandatory so obviously the only possible fix for this is to support > MITM. The basic use case envisioned is that the two sides do not necessarily know what the other side can support or has available until it attempts this "pairing" operation. So we want to avoid this catch 22: 1. We support MITM but don't know if the other side does, nor if it requires it. With the code I just tested, the remote side (bluez) indicated that it doesn't not support MITM and therefore rejects pairing. 2. However, if we support MITM but don't know if the other side does and we *do not* request MITM, then a remote side that *requires* MITM should reject us for *not* requesting it. The solution is therefore to *always* request MITM, if you are capable of supporting it. If it turns out that neither side actually needs it, then there is no harm in having provided it. If one side does not support it (as bluez currently does not) and the other side requires it, then it is up to the side that *requested* MITM to reject the pairing attempt, if it determines that MITM is required. A low security device like the current bluez should *never* reject a pairing request because the other side needs MITM. It is up to the side that has the MITM requirement to issue the Security Failure packet. So until bluez can support MITM, it should *accept* remote requests for MITM, knowing that the remote side may reject it. As long as bluez advertises no OOB and NO_IN_NO_OUT, there will be no MITM. It should just not request MITM, and then provide no way to achieve it. [...] -- 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
