On Wed, Apr 5, 2023 at 1:05 PM Rob Sayre <say...@gmail.com> wrote: > > > On Wed, Apr 5, 2023 at 12:53 PM Eric Rescorla <e...@rtfm.com> wrote: > >> >> >> On Wed, Apr 5, 2023 at 12:50 PM Rob Sayre <say...@gmail.com> wrote: >> >>> On Wed, Apr 5, 2023 at 12:26 PM Eric Rescorla <e...@rtfm.com> wrote: >>> >>>> Thanks for your feedback. Most of these are editorial comments and >>>> so I think they're my decision as editor about which ones to take >>>> absent some instruction from the chairs. >>>> >>> >>> I agree concerning most of them. One just finds nitpicks if you read the >>> whole thing carefully. >>> >>> The one thing I think is really substantive is the deprecation of TLS >>> 1.0 / 1.1, since you have a strange nesting of MUSTs. >>> >>> I think a descriptive "NOT RECOMMENDED" approach would be better here. >>> Then, describe that servers might choose to accept 1.0/1.1 if they don't >>> actually care whether the traffic is secure. This is a very common pattern. >>> I found a survey that showed popular public sites were likely to accept >>> almost anything (SSL3, unencrypted traffic, etc).* >>> >> >> I don't see how we can use NOT RECOMMENDED here, because we already have >> an RFC which prohibits the use of TLS 1.0 and TLS 1.1 and we're not >> contradicting >> that. The purpose of the text you highlight is to address people who are >> nonconformant >> with that RFC. >> > > I see your point. RFC8996 does say "MUST NOT", but that's not deprecation. > It's prohibition, as you say. So, the title of the document is confusing. > > I still think what it's in this document is confusing, because it says "if > you don't follow this MUST, you have to follow this MUST...". > > But I can see this situation is kind of messy, so I think it's editorial. >
Hi, sorry to be a pest here, but maybe this isn't editorial. First, one nit: "negotation" here: 4.1.3 Server Hello: > Note that [RFC8996] and Appendix E.5 forbid the negotation of TLS > versions below 1.2; implementations which do not follow that guidance > MUST behave as described above. Here's my effort, just to make it more than a complaint. I'm not attached to the exact wording: "In order to preserve the security properties enumerated in the Introduction, [RFC8996] and Appendix E.5 forbid the negotiation of TLS versions below 1.2. Implementations willing to accept obsolete TLS versions MUST behave as described above." Appendix E.5: > The security of SSL 2.0 [SSL2], SSL 3.0 [RFC6101], TLS 1.0 [RFC2246], > and TLS 1.1 [RFC4346] are considered insufficient for the reasons > enumerated in [RFC6176], [RFC7568], and [RFC8996] and they MUST NOT > be negotiated for any reason. Here, I would end with "...for any reason in applications that require a secure channel." > Implementations MUST NOT send an SSL version 2.0 compatible CLIENT- > HELLO. Implementations MUST NOT negotiate TLS 1.3 or later using an > SSL version 2.0 compatible CLIENT-HELLO. Implementations are NOT > RECOMMENDED to accept an SSL version 2.0 compatible CLIENT-HELLO in > order to negotiate older versions of TLS. Without the little trailing text I added above, this seems a little contradictory. The thinking here is the document says this is NOT RECOMMENDED, but it's something they MUST NOT do, unless you only mean TLS 1.2 here. thanks, Rob > > >> >>> I think this approach is more accurate, but also more critical in terms >>> of security than what you have now. >>> >>> thanks, >>> Rob >>> >>> * >>> "In fact, the top 100 sites were more likely to still support SSL 3, TLS >>> 1.0, and TLS 1.1 than servers with much less traffic." >>> < >>> https://www.f5.com/labs/articles/threat-intelligence/the-2021-tls-telemetry-report >>> > >>> >>> >>> >>>> On Tue, Apr 4, 2023 at 10:43 PM Rob Sayre <say...@gmail.com> wrote: >>>> >>>>> Hi, >>>>> >>>>> I'm still not sure about the list/vector rename. Aside from that, >>>>> here's what I found: >>>>> >>>>> > It tightens some requirements and contains >>>>> > updated text in areas which were found to be unclear as well as >>>>> other >>>>> > editorial improvements. >>>>> >>>>> "It contains clarifications and tightened requirements." [let's assume >>>>> some things were unclear and that editorial improvements are >>>>> clarifications] >>>>> >>>> >>>> Not all editorial improvements are clarifications. >>>> >>>> >>>>> >>>>> > Forbid negotiating TLS 1.0 and 1.1 as they are now deprecated by >>>>> [RFC8996]. >>>>> >>>>> I know what's meant here, but deprecated does not mean forbidden. I >>>>> think you want to say "NOT RECOMMENDED" in RFC 2119 words, and give a >>>>> brief >>>>> reason for that. [but keep reading] >>>>> >>>> >>>> This isn't normative text. However 8996 is entitled "Deprecating TLS >>>> 1.0 and TLS 1.1" so I think this >>>> is fine. >>>> >>>> >>>> >>>>> > The protocol does not provide any forward secrecy guarantees for >>>>> this data. >>>>> > The server's behavior determines what forward secrecy >>>>> > guarantees, if any, apply (see Section 8.1). This behavior is >>>>> > not communicated to the client as part of the protocol. >>>>> > Therefore, absent out-of-band knowledge of the server's behavior, >>>>> > the client should assume that this data is not forward secret. >>>>> >>>>> Here, you use the term "out-of-band", but the PSK text replaced >>>>> "out-of-band" with "external[ly]". I can't tell whether this usage is >>>>> intentional. >>>>> >>>> >>>> It is. The PSKs here are resumption PSKs. They're not external. The out >>>> of band in >>>> question is knowledge about the server behavior. >>>> >>>> >>>> >>>>> >>>>> > Because TLS 1.3 forbids renegotiation, if a server has negotiated >>>>> TLS >>>>> > 1.3 and receives a ClientHello at any other time, it MUST terminate >>>>> >>>>> "TLS 1.3 forbids renegotiation. If a server has negotiated TLS 1.3 and >>>>> receives a ClientHello at any other time, it MUST terminate..." >>>>> >>>>> [No starting sentences with "Because"] >>>>> >>>> >>>> I believe this is editor discretion. >>>> >>>> >>>>> >>>>> > Note that [RFC8996] and Appendix E.5 forbid the negotation of TLS >>>>> > versions below 1.2; implementations which do not follow that >>>>> guidance >>>>> > MUST behave as described above. >>>>> >>>>> I think this makes my "NOT RECOMMENDED" suggestion above correct. A >>>>> forbidden "MUST NOT" wouldn't need this text. >>>>> >>>> >>>> I don't understand this argument. The point of this text is that people >>>> are forbidden >>>> to do previous versions by 8996, but we know some people won't so this >>>> is >>>> backup guidance. I think this is fine. >>>> >>>> >>>> >>>> >>>>> >>>>> > Unless otherwise specified, trailing data is forbidden. >>>>> > That is, senders MUST NOT include data after the structure in the >>>>> > "extension_data" field. >>>>> >>>>> This doesn't seem like "MUST NOT", since it could be "otherwise >>>>> specified". I think there needs to be a harsher choice made here, or just >>>>> leave it out. >>>>> >>>> >>>> This is actually fairly standard language. >>>> >>>> >>>> >>>>> > When processing an extension, receivers MUST >>>>> > abort the handshake with a "decode_error" alert if there is data >>>>> left >>>>> > over after parsing the structure. This does not apply if the >>>>> > receiver does not implement or is configured to ignore an extension. >>>>> >>>>> Again, doesn't seem like a "MUST". But the following text says "This >>>>> does not apply", without clarifying what "this" is. >>>>> >>>> >>>> I don't follow your argument here either. It's a MUST for any extension >>>> you understand. >>>> Obviously, if you don't understand it, you can't comply with this. I'll >>>> attempt to clarify. >>>> >>>> >>>>> > After checking ServerHello.random to determine if the server >>>>> > handshake message is a ServerHello or HelloRetryRequest, clients MUST >>>>> > check for this extension prior to processing the rest of the >>>>> > ServerHello. This will require clients to parse the ServerHello in >>>>> ... >>>>> >>>>> Another "this". Here, I think the text means "This requirement...", >>>>> but usually a rewrite can fix these ambiguities. >>>>> >>>> >>>> I don't think this one is unclear. >>>> >>>> >>>>> > In the absence of some other specification to the >>>>> > contrary, servers which are authenticating with an external PSK MUST >>>>> > NOT send the CertificateRequest message either in the main handshake >>>>> > or request post-handshake authentication. [RFC8773] provides an >>>>> > extension to permit this, but has not received the level of analysis >>>>> > as this specification. >>>>> >>>>> Another one of these "In the absence of..." paragraphs. Maybe these >>>>> are intentional? They still sound really redundant to me. >>>>> >>>> >>>> They're intentional because we know there is actually such an RFC, but >>>> you have to >>>> actually use it. >>>> >>>> >>>>> > With a 128-bit key as in AES-128, rekeying 2^64 times has a high >>>>> > probability of key reuse within a given connection. Note that >>>>> even... >>>>> >>>>> It's almost always possible to drop "Note that..." >>>>> >>>> >>>> It is possible, but I prefer to leave it as-is. >>>> >>>> >>>>> The rest of this paragraph is really heavy on em dashes, and needs to >>>>> be rewritten. Some of them seem to be parentheticals, but I would try to >>>>> rewrite it as short sentences. >>>>> >>>> >>>> I'll take a look. >>>> >>>> >>>> >>>>> > Note that it is common practice in some protocols to use the same >>>>> >>>>> Another "Note that" >>>>> >>>> >>>> See above. >>>> >>>> >>>>> >>>>> > Note that purely deterministic ECC signatures such as deterministic >>>>> ECDSA and EdDSA ... >>>>> >>>>> ... >>>>> >>>>> > If the resumption_master_secret has been >>>>> > compromised, a resumption handshake with EC(DHE) gives protection >>>>> > against passive attackers and a full handshake with EC(DHE) gives >>>>> > protection against active attackers. >>>>> >>>>> Here, you mean "resumption_secret". >>>>> >>>> >>>> Thanks. Good catch. >>>> >>>> >>>>> >>>>> > Note: This specification does not currently permit the server to send >>>>> >>>>> The old text was better. No "Note:". >>>>> >>>>> The "currently" part seems like the wrong thing to write in an >>>>> immutable document. Maybe "TLS 1.3 does not currently..."? >>>>> >>>> >>>> I don't think this is a problem. >>>> >>>> >>>>> >>>>> > In the absence of some other specification to the contrary, >>>>> implementations... >>>>> >>>>> I must be missing the conversation on this stuff. How could anyone >>>>> write a spec if every requirement was prefaced with "in the absence of >>>>> some >>>>> other specification to the contrary..." >>>>> >>>> >>>> The purpose of this text is to signpost that we know that there might >>>> be or >>>> in fact is is such a specification, as opposed to other requirements >>>> which >>>> we don't have any reason to think that about. >>>> >>>> >>>>> >>>>> > Amplifying existing information leaks caused by side effects like >>>>> > caching. An attacker... >>>>> >>>>> Not a complete sentence here. I think it's just a typo. >>>>> >>>> >>>> Thanks. Will fix. >>>> >>>> -Ekr >>>> >>>> >>>>> >>>>> thanks, >>>>> Rob >>>>> >>>>> >>>>> >>>>> On Tue, Apr 4, 2023 at 7:32 PM Stephen Farrell < >>>>> stephen.farr...@cs.tcd.ie> wrote: >>>>> >>>>>> >>>>>> Hiya, >>>>>> >>>>>> On 05/04/2023 02:47, Sean Turner wrote: >>>>>> > A post IETF 116 bump to make sure folks get their reviews in. If you >>>>>> > look at the diffs from RFC 8446 you can see not that much has >>>>>> > changed. We will also take “I read it and it looks good” response. >>>>>> >>>>>> I looked at the diff between 8446bis-07 and 8446 and it seems >>>>>> fine to me. My only comment is that C.4 says one "SHOULD NOT >>>>>> reuse a key share" - I'd be happier if that was a "MUST NOT" >>>>>> but understand if we stick with SHOULD NOT. If there were a >>>>>> good reference showing that it's quite feasible to never >>>>>> deliberately re-use a key share, even at scale, that'd be a fine >>>>>> addition. (I don't have such a reference to offer, >>>>>> sorry;-) >>>>>> >>>>>> Cheers, >>>>>> S. >>>>>> _______________________________________________ >>>>>> TLS mailing list >>>>>> TLS@ietf.org >>>>>> https://www.ietf.org/mailman/listinfo/tls >>>>>> >>>>> _______________________________________________ >>>>> TLS mailing list >>>>> TLS@ietf.org >>>>> https://www.ietf.org/mailman/listinfo/tls >>>>> >>>>
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