On Mon, Feb 10, 2020 at 11:44 AM Mohit Sethi M <mohit.m.se...@ericsson.com> wrote:
> > On 2/10/20 9:18 PM, Eric Rescorla wrote: > > > > On Mon, Feb 10, 2020 at 8:14 AM Mohit Sethi M <mohit.m.sethi= > 40ericsson....@dmarc.ietf.org> wrote: > >> Hi Sara, >> >> I understand the desire to get this done with. However, I have some >> further comments in-line: >> On 1/24/20 5:29 PM, Sara Dickinson wrote: >> >> Mohit, >> >> I’m out of the office next week so in order to try to move the draft >> along I have published an -08 version which I think addresses most of your >> comments (there were a few questions in my response below). Please let me >> know if any are still outstanding. >> >> Best regards >> >> Sara. >> >> On 17 Jan 2020, at 15:33, Sara Dickinson <s...@sinodun.com> wrote: >> >> >> On 29 Dec 2019, at 13:50, Mohit Sethi via Datatracker <nore...@ietf.org> >> wrote: >> >> Reviewer: Mohit Sethi >> Review result: On the Right Track >> >> I am the assigned Gen-ART reviewer for this draft. The General Area >> Review Team (Gen-ART) reviews all IETF documents being processed >> by the IESG for the IETF Chair. Please treat these comments just >> like any other last call comments. >> >> For more information, please see the FAQ at >> >> <https://trac.ietf.org/trac/gen/wiki/GenArtfaq>. >> >> Document: draft-ietf-dprive-bcp-op-07 >> Reviewer: Mohit Sethi >> Review Date: 2019-12-29 >> IETF LC End Date: 2020-01-02 >> IESG Telechat date: Not scheduled for a telechat >> >> Summary: >> This draft discusses privacy challenges for recursive DNS resolvers. It >> then >> describes policy and security considerations that DNS service providers >> can use >> for enhanced user privacy. The draft is 'On the Right Track' but not yet >> ready. >> >> >> Many thanks for the detailed review! Ben, Rob I hope theses fixes also >> address your comments. >> >> >> Major issues: >> >> I wonder if section 5.1.2.1/5.1.3.1 >> <https://protect2.fireeye.com/v1/url?k=91d59bed-cd5e90d7-91d5db76-86925ec6fd56-2a24500b228246a8&q=1&e=f2be251d-f590-4578-b7a9-ac8390a7396e&u=http%3A%2F%2F5.1.2.1%2F5.1.3.1> >> should also talk about recommending OCSP >> stapling (RFC 6066)? I looked at RFC 8310 and it mentions RFC 7525. Do >> you want >> to mention it here in section 5.1.2.1/5.1.3.1 >> <https://protect2.fireeye.com/v1/url?k=5f5ab97a-03d1b240-5f5af9e1-86925ec6fd56-8fb25ccf521d98d2&q=1&e=f2be251d-f590-4578-b7a9-ac8390a7396e&u=http%3A%2F%2F5.1.2.1%2F5.1.3.1> >> ? >> >> >> What exactly are you thinking of here - something that just says “Server >> operators should also follow the best practices with regard to OCSP as >> described in RFC7525”? If something more could you please suggest text? >> >> I was hoping that the text would be more precise rather than a cursory >> reference to another RFC. You could say something along the lines: 'The TLS >> client and server MUST use Certificate Status Requests [RFC6066] for the >> server's certificate chain and the client MUST treat a CertificateEntry >> (except the trust anchor) without a valid CertificateStatus extension as >> invalid and abort the handshake with an appropriate alert.'. In the same >> vein, I would expect that you would strongly mandate the use of TLS 1.3 >> with DoH and DNS over TLS? >> > Mohit: I actually don't think we should require OCSP at all. For instance, > most browsers are moving away from it. We should require or at least > strongly encourage revocation checking. > > And what is it being replaced with? i found this blog on OCSP stapling in > firefox: > https://blog.mozilla.org/security/2013/07/29/ocsp-stapling-in-firefox/. > Is there an updated blog post about new techniques for revocation checking? > https://blog.mozilla.org/security/2020/01/21/crlite-part-3-speeding-up-secure-browsing/ -Ekr --Mohit > > > -Ekr > > > >> >> In section 5.1.2.1, what is meant by 'authentication domain names'? >> Later, the >> text says 'authentication name for the service'. I guess you are implying >> the >> authentic domain name of the DNS resolver service that the client software >> should verify through the common name (CN) in the certificate? Some more >> explanation here would be beneficial. >> >> >> It is defined in the terminology section of RFC8310: >> >> "Authentication domain name: A domain name that can be used to >> authenticate a privacy-enabling DNS server. Sources of authentication >> domain names are discussed in Section 7." >> >> I have added a reference for RFC8310 after the first use of >> ‘authentication domain name’ and made sure every instance of >> 'authentication name' is updated to 'authentication domain name' for >> clarity. >> >> Personally, I find the phrase 'Authentication domain name' very unclear. >> From the phrase, it doesn't look like it has anything to do with DNS? On >> first reading, I interpreted it as the domain name where I should >> authenticate. Since the IESG let this through for RFC 8310, I guess we will >> have to live with this (poor) choice. >> >> >> >> In section 5.1.4, should 'DNS Roadblock avoidance' be 'DNSSEC Roadblock >> avoidance'? And please add a reference to RFC 8027 here if that is the >> case. >> >> >> Yes, good catch - will do. >> >> >> Section 5.1.7 says "discussion on the use of Bloom Filters in Appendix >> A". It >> is pointing to the wrong appendix. >> >> >> Fixed - thanks. >> >> Also, this section talks about implementing >> traffic monitoring by the DNS service provider. I would argue that in most >> deployments, the traffic monitoring is required (and implemented) by a >> different entity. Think of a home network router that has a parental >> control. >> Or an enterprise restricting employees from visiting certain sites (to >> prevent >> insider attacks)? The impact of encryption is more serious for them and >> less so >> for a DNS service provider. What is the BCP advice for them? >> >> >> You are correct that the there are differing concerns but I don’t believe >> this document should tackle that - the audience of the document is >> specifically operators of DNS privacy services, typically monitoring to >> prevent DDoS or similar, not network operators in general (although they >> may be both in some cases). For the more general case I think the impact is >> covered in RFC8404 'Effects of Pervasive Encryption on Operators’? >> >> I do notice a couple of places where just ‘operators’ is used in the text >> so could add ‘DNS Privacy Service’ before that to clarify? >> >> I leave it to Alissa and IESG to decide what they want here. >> >> >> Also, is it fair >> to say that this is a best current practice? It feels that we need more >> experience before we start recommending it as an optimization. >> >> >> Given the specific scope discussed above I think it is fair. The privacy >> policies of most of the public resolver operators and ISPs that offer >> encrypted DNS are pretty good today in terms of how they try to minimise >> the user data retained and I’m sure they all still have monitoring in >> place… >> >> My question was specifically about using Bloom filters? Which DNS >> operators are currently using it? Do we have sufficient evidence other than >> the research publication that this is 'Best Current Practice'? >> >> >> >> This comment applies to all 5.1.1-5.1.8. Each subsection starts rather >> abruptly >> by discussing threats. It would be nice if you add a sentence at the >> beginning >> of each sub-section telling the reader what are they heading into. This is >> probably most obvious from section 5.1.8. Without even telling the reader >> what >> is a pure TLS proxy, you start listing the DNS privacy threats. Only >> later on >> you mention option that operators may implement DNS-over-TLS using a TLS >> proxy. >> >> >> If we go down this road then I think to be consistent we would need to >> add text for all 16 sections 5.1.1 to 5.3.3. I could do this but I have a >> feeling it would be come quite repetitive with respect to the section title >> text and I think if we could get the titles correct (and possibly add more >> text to section 5) this might be unnecessary. I suggest: >> >> Section 5: Add a first paragraph: >> “In the following sections we first outline the threats relevant to the >> specific topic and then discuss the potential actions that can be taken to >> mitigate them.”thorita >> >> And for section 5.1.8 change the title to “Limitations of fronting a DNS >> Privacy Service with a pure TLS proxy”. >> Happy to update any other headers you thought too vague. >> >> Would that address the issue or do you still think additional text is >> required? >> >> >> In section 5.3.2 'way and OUGHT obfuscate'. OUGHT is not part of RFC >> 2119/8174. >> Why is it capitalized? And, 'ought' ought to be followed by a 'to’. >> >> >> I was confused by this and then realised it is a hangover from a much >> earlier version of the draft that used EXPECTED/OUGHT/MIGHT keywords >> defined in the draft to described the various levels of actions….. so as you >> suggest: >> >> OLD: “For example, a resolver with a very small community of users risks >> exposing data in this way and OUGHT obfuscate this...” >> >> NEW: “For example, a resolver with a very small community of users risks >> exposing data in this way and ought to obfuscate this..." >> >> >> At the beginning of section 5, you describe three classes of actions. >> However, >> none of the subsections contain clear "Additional options" that operators >> need >> to follow for "maximal compliance”? >> >> >> Sections 5.3.1 and 5.3.2 do have them. In earlier versions several more >> sections but they have been removed. thorita >> >> Okay. Thanks. I hadn't seen this. I have a question related to the >> following text: >> >> o Aggressive Use of DNSSEC-Validated Cache [RFC8198 >> <https://tools.ietf.org/html/rfc8198>] and [RFC8020 >> <https://tools.ietf.org/html/rfc8020>] >> (NXDOMAIN: There Really Is Nothing Underneath) to reduce the >> number of queries to authoritative servers to increase privacy. >> >> Suppose I own the domain mydomain.com? My application requires clients >> to lookup for non-existent sub domains. So if a client sends a query to the >> local resolver for non-existent1.mydomain.com and >> non-existent2.mydomain.com, will both be sent to the authoritative >> server for mydomain.com? >> >> >> >> The document seems focused on TLS 1.2 (and does not talk about TLS 1.3). >> In >> fact, RFC 8446 is not even in the list of references even though section >> 5.1.3.1 mentions it. Similarly, Appendix A.2 mentions TLS session >> resumption >> without server-side state. How about servers using TLS 1.3 and PSK >> resumption? >> RFC 8446 has text on client tracking in appendix C.4: >> https://tools.ietf.org/html/rfc8446#appendix-C.4. >> >> >> A slight hangover from the fact the DNS-over-TLS spec was published in >> 2015 before TLS 1.3 was standardised (so it just says TLS 1.2 or later) and >> so most of the early DoT services used just TLS 1.2. >> >> Section 5.1.3.1 had the text ‘RFC8446’ but it wasn’t actually a reference >> so I’ve fixed that - thanks. >> >> I’ve added a bullet point to Appendix A.2 >> “RFC8446 Appendix C.4 describes Client Tracking Prevention in TLS 1.3" >> >> >> There is something wrong about the last sentence of Appendix A.2 'Note >> that >> depending on the specifics of the implementation [RFC8484] may also >> provide >> increased tracking'. You already mention RFC 8484 in Appendix A.1 as a >> means to >> increase privacy. Perhaps you wanted to cite a different RFC here? >> >> >> The point is that the use of HTTP headers in DoH can add additional >> privacy concerns over the other DNS transports, but that RFC8484 leaves >> that as an implementation decision. I suggest replacing the text with >> >> “Note that Section 8 of RFC8484 outlines the privacy considerations of >> DoH. Depending on the specifics of a DoH implementation there may be >> increased identification and tracking compared to other DNS transports." >> >> Think of the reader of this document. Appendix A.1 says that DoH can >> increase privacy. The Appendix A.2 says that with DoH 'identification and >> tracking may be increased' Should I use DoH or not? I recommend to >> re-phrase the text in A.2 along the lines 'While DoH can increase privacy, >> section 8 of RFC 8484 outlines potential mechanisms that can nonetheless be >> used by on-path adversaries for correlation and tracking. As recommended in >> RFC 8484, DNS resolvers that offer DoH need to consider the benefit and >> privacy impact of these features, and their deployment context when >> deciding what features are enabled. Resolver implementations are advised to >> expose the minimal set of data needed to achieve the desired feature set..' >> >> >> >> Minor issues: >> >> Nits/editorial comments: >> >> There is mixed usage of Anonymisation (in Table 1) vs Anonymization. The >> same >> with Pseudoanonymisation (in Table 1) vs pseudonymization in text. Please >> check >> with the RFC editor on what is expected and use that consistently. Also >> noticed >> optimisation. >> >> >> Thanks - have fixed. I have now used the American English forms (z not s) >> throughout. >> >> >> In Table 1, Crytpographic should be Cryptographic. >> >> >> Ack. >> >> >> Maybe you could use an Oxford comma when using lists of items. >> >> >> Had it some places, but not all - should be fixed now. >> >> >> In section 5.1.2.1, there is stray space character at the end of the >> bullet on >> "Follow the guidance in Section 6.5 of [RFC7525] with regards to >> certificate >> revocation .” >> >> >> Perhaps expand DNSSEC on first usage: Domain Name System Security >> Extensions >> (DNSSEC). >> >> In section 5.1.6 'in terms of such options as filtering' should instead >> be 'in >> terms of options such as filtering'. >> >> In section 5.1.8 'a DNS aware proxy such as [dnsdist] which offer custom >> (similar to that proposed in'. Consider using 'offers' instead of 'offer' >> and >> 'similar to those proposed in' instead of 'similar to that proposed in'. >> >> In section 5.2.2 'presents and overview' should be 'presents an overview'. >> Consider rephrasing 'the better to resist brute force'. Also, in 'agreed >> solution or any Standards to inform', why is standards capitalized? >> >> In section 5.2.4 'queries on multiple TCP session' should be 'queries on >> multiple TCP sessions'. Please expand CPE on first usage. >> >> In section 6.3 'This is by analogy with e.g. several TLS or website' could >> instead be 'This is analogous to several TLS or website'. >> >> In Appendix A.1 'documents apply to recursive to authoritative DNS' >> shouldn't >> there be an 'and’? >> >> >> All fixed - thanks. >> >> >> In Appendix C.1, consider changing the format for the sub bullets of >> '2.. Data >> collection and sharing.'. Instead of numbering them with 1/2/3, perhaps >> use >> a/b/c. >> >> >> I’m currently using markdown which won’t let me do that…. :-( I do think >> that would be better so I suggest adding a note that this is done at RFC >> editor time….? >> >> Yes, please do. It will help with readability. >> >> Thanks for the rest of the changes. >> >> --Mohit >> >> >> >> In Appendix C.1 'of use of system' could be 'of system use'.. Also why is >> there >> a line break between 'items that are' and 'included'? There is an >> extraneous >> 'the' in 'available with the our threat intelligence'. Consider re-wording >> parts of paragraph '3. Sharing of data. '. At one place you say 'with our >> threat intelligence partners' and a few words later you say 'with its >> threat >> intelligence partners’. >> >> >> Fixed. >> >> >> In Appendix C.1 'In the event of events or observed behaviors' is a bit >> hard to >> parse. Consider rephrasing the 'event of events' part. >> >> >> Replaced events with actions. >> >> Best regards >> >> Sara. >> >> >> >> >> _______________________________________________ >> dns-privacy mailing list >> dns-priv...@ietf.org >> https://www.ietf.org/mailman/listinfo/dns-privacy >> >
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