Re: [certid] Review of draft-saintandre-tls-server-id-check-12

[Peter Saint-Andre <[e-mail]>]

Done:

http://www.ietf.org/id/draft-saintandre-tls-server-id-check-13.txt

The diff from -12 is here:

http://tools.ietf.org/rfcdiff?url2=draft-saintandre-tls-server-id-check-13

Peter

On 1/3/11 4:14 PM, Peter Saint-Andre wrote:
> 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.
>>>