I just realized that we never replied publicly. Jeff and I had a phone chat with Cullen (and Alexey) about this before the holidays, and we plan to submit a revised I-D this week. Cullen raised some very good points, which we've attempted to address in the forthcoming version. On 12/16/10 8:22 AM, Peter Saint-Andre wrote: > 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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