Thanks for your comments. My co-author and I will need to confer before replying, and that might take a few days given the length of your review. Peter On 12/16/10 12:17 AM, Cullen Jennings wrote: > > So let me start with I think there is great information in here and I > think it should be published as a standards track RFC however I do > think there are some issues with the relation with this draft and the > realities of what would help improve security in deployment of SIP, > HTTP, IMAP, XMPP etc. > > There are many places where this draft makes choices to improve the > security from many current practices. At face value this seems like a > good thing but it's not always. The thing reducing the overall > security available to users of TLS is not if certs use CN-ID or > DNS-ID, it is that it's such a PITA to deploy a TLS server that > people choose to not use TLS at all. Everywhere there is a trade off > between making things marginally more secure, or making things > cheaper and easer to deploy, I think we need to seriously consider > the cheaper and easier approach. Yes, some things are just broken > even if they are easy and obviously we can't do those. Let me give an > example of this. I looked at the cert for the domains for the authors > of this draft. www.cisco.com has 3 DNS names even though as fas as I > can tell one of these are for something that would typically be used > in a ftp URI and the other HTTP URI. This is because it makes it > easier and cheaper for them to use TLS yet seems to go against the > recommendation of this "BCP". Then I went over the www.paypal.com > domain which uses, gasp, a CN-ID. Do we really believe that paypal is > seriously compromising their security by using a CN instead of > URI-ID? If so, how? I'm pretty sure the paypal guys know how to run a > secure web server. With the exception of Microsoft small business > server certificates (which are outrageously expensive by the way) it > pretty hard to get SRV name certs. In making these recommendations, > did the TLS WG consider the relative prices of various types of > certificates? Lets say I had a certificate for the domain example.org > because I was using it for email and it has a CN because I got it > years ago. Now lets say I am going to go deploy a SIP service on > example.org. My position is that best way to encourage the use of > security on the internet is to just reuse the certificate I have. It > cheap, it's easy, it secure enough even if it does make you feel a > bit dirty. I think Jeff disagrees w ith me, we argued for years about > this topic and my understanding is his position is that it would be > better to say that all new deployments MUST not use a CN name because > it's less secure. Give the prevalence of CN on the internet today, I > think it is fine to tell people how DNS-ID is better but I don't > think it's OK to tell them they should not use CN-ID and I definitely > don't think it is OK to tell implementors they don't need to > implement CN-ID. > > I encouraged Chris to write this draft long ago and what we had > discussed at the time was forming a RFC with one or more boiler plate > pieces of text that could be used in creation of the name matching > section of new protocols that got developed. I was thinking of > something similar to the way we use rfc 5226 for writing IANA > consideration section. Instead we have a document that is creating a > very complex situations about whats normative. This draft is a BCP > level, and it says you have to do everything in PKIX and PKIX takes > precedence. That is basically elevating PKIX to a BCP without > appropriate process review. Next this draft contradicts the > procedures in existing protocols and says that it does not apply to > the existing protocols but that it would take precedence over any > future updates of existing protocols that use TLS within the scope > specified here. I do not believe you have the consensus of the people > woking on SIP that the next time some specification is marked as an > UPDATE to 3261, that implementations need to implement the procedures > in this draft. Furthermore, I think that would be counter productive. > I think you should make it clear this guidelines for designers of new > protocol and people updating existing protocol and that these > protocols could make their own choices but would want to take into > account the information in this draft. When I read the sentence, > "However, the best current practices described here can be referenced > by future specifications, including updates to specifications for > existing application protocols if the relevant technology communities > agree to do so." I think that is exactly the right solution to the > problem. However, that not a BCP, thats a standards track spec. > Furthermore, I think this draft is going to have all the normal bugs > etc of any other spec that defines algorithms and such it should > proceed through the standards track process. If this draft is going > to go as a BCP, that text contradicts what a BCP is and needs to come > out and the rest of the draft be adjusted appropriately. My > preference would be that this draft be standards track. Its writing > exactly the same sort of normative algorithm text that we put in all > kinds of other thing like SIP, HTTP, and even TLS. They are all > standards track. This should be the same. > > Most RFCs today that use TLS have a page plus or minus that tells an > implementer what they need to know about matching names in certs. > This draft move that to 30 to 50 pages depending on how you count. > Most implementers are just going to ignore this thus worsening the > security situation. Think about why is the part implementers need to > read 10x longer than existing deceptions - this just seems wrong. Now > it's easy to blow off this type concern and say get over it, it's the > same number of lines of code they need to write. But the problem is > when an implementors goes to start doing this and encounters > something that is 50 pages long, they instantly decide this is a big > task and down it goes on the priority list of actually happening. The > other problem is that even thous it is long, it is still very > confusing on how to do things (such at URI). I'll provide more > detailed examples of this later in this email. If the document was > restructured to have all the normative text in one s hort simple > description and the rest moved to an appendix, it would be much > easier to get people to take this seriously and easier to review that > it was correct. > > My final big issue is the use of normative language. Lets say there > are two procedures A and B and we 100% consensus that B is better > than A but we still have to support A for existing deployment > reasons. To describe this, the text this draft would use is is MUST > do A and SHOULD NOT do B. Now reading 2119 it is pretty clear that > SHOULD NOT means you don't implement it unless there are real good > reasons to implement it. So on the things were we agree A is > preferred to B but you need both for backwards compatibility, this > draft needs to say MUST implement A and MUST implement B but > deployments are encouraged to use B as we are trying to move away > from A. I think the whole document needs a careful read checking for > this issue. You can insert the usual rant here about why SHOULD is a > awful word in specs 90% of the time it used because implementer > thinks it means "ignore rest of sentence". For example, section 5.4 > discusses they this spec continues to mandate protocols MUST suppo rt > CN yet this draft continually use "SHOULD NOT" when what it really > means is MUST implement. This is going to confuse implementors of > IETF specification and be ignored by operators. Given the goals of > this spec it would be much better if it was clearly defining what > IETF required implementers of protocols to do instead of confusing > that with how we wish security was deployed. > > > On to the nits. > > Take an applications like a web server. Is the preferred thing in a > cert a DNS-ID or a URI-ID. My reading of the 3.3 is that URI-ID is > preferred over DNS-ID yet the examples don't match that. I think > point 3 in section 3.1 tries to explain this away but I don't > understand that - clearly web browsers use a URI. > > The rules in section 3.1 don't make sense for a CA. How will the CA > know if the cert I want is going to be used for a protocol that uses > SRV? > > In section 3.2, in the imap example, you are saying that if I > configure my imap server to mail.example.com and it presents a > certificate with a DNS-ID of example.com that this is OK. That does > not sound OK to me but I don't know how IMAP works. In the SIP > example, the cert should have a SRV and DNS name too. As well as a CN > if you actually want it to work in the real world. > > In section 4.2.1 you have a long discussion on how the information > used must come from a way that can't be tampered with over the > internet. I generally agree with this but would like to point out > that protocols like LOST (see section 18 of rfc5222) specially do the > opposite of this and actually match the cert agains the output of > NAPTR process not the input to the NAPTR process. > > The example just seem plain wrong in some cases. Take for example > section 4.2.2 where the SIP example has only a URI reference > identifiers and no DNS yet the section right before this has said the > list MUST include a DNS-ID. This text has been through how many > reviews and Last Calls? The problem here is that this draft is too > long to review for stuff like this. Even after the IESG is done > reviewing it, statistics suggest it will still be littered with bugs > like this and implementors will use the examples to guide them. If > someone implements what is in the example, it will break in lots of > sip deployments. > > There is a whole algorithm about matching various ID types, but the > note about you ignore CN if you have other things is off in "Security > Warning" very much out of any flow of the algorithm description then > pointed out again in some other section. It's not wrong, but it's a > bit weird from an implementer point of view. > > Many applications do need to deal with IP matching as well as domain > names. The way this text is written here makes it harder to figure > out how and where to mix that in. I'd rather see it just dealt with > than instead of making it out of scope. Obviously it's not common on > internet but it is common on private networks and walled gardens > where many of the protocols were are talking about are deployed. Many > of the "internet of things" people I work with have no intention of > using DNS at all. I scoffed at multiple large service providers 10 > years ago when they said they were not using DNS with SIP but many > still use IPs. This sounds less insane when you consider the major OS > don't ship with an asynchronous DNS library. > > I'm baffled on why checking the service name in a SRV record is a > SHOULD not a MUST. Could you add text explain why and when one would > not check it. If you were in a really good mood you could do that for > all the SHOULDs. Actually, when I read section 4.5 carefully, I think > it literally says that when using a URI, checking the domain name is > a SHOULD not a MUST. Surely check the domain name matches is not a > SHOULD level sort of thing. > > Section 5.4. I have no idea why it matters that some major OS does > not support SNI. Even if that OS did support SNI, many many > applications running on that OS and the others would not support SNI. > It seems like it is the applications acting as TLS servers and > clients that are the important thing, not the OS. > > How you process URI-ID needs work. I could not figure out how to > implement given the text in the draft as is. Even ignoring the > special tar pit the SIP guys dug for themselves with tel URL > processing, just the normal sip, sips issues seems unclear. > > This seems like a long list of complaints delivered fairly late but, > once again, I really do like much of the information in here and > think it should be published as PS - it just would be significantly > improved with a bit of a re-factored and clean up. If this had been > run through the TLS working group, I would have caught all of this in > the WG LC. This is a draft that, as a BCP, profoundly effects many > of the protocols I work on including SIP but as far as I can tell has > not done much to gather the consensus of the people working on > protocol that this draft changes - I don't recall hearing about it > until after it went to the IESG so I'm pretty un apologetic about > providing these comments during IETF LC. > > In summary, I like the information in this but I think it still has > many small things that need fixing and needs to be changed to get > crisp about what implementors need to do and drop the confusing stuff > about how we wish operators and CA might use certificates. I also > feel strongly that the right way to look at this draft is, as that > draft says "practices described here can be referenced by future > specifications, including updates to specifications for existing > application protocols if the relevant technology communities agree to > do so" and that for that reason it has to be standards track not BCP. > If it was not being written and pushed by two IESG members, I don't > think we would even be discussing if it should be a BCP. >
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