Re: [TLS] Iotdir last call review of draft-ietf-tls-md5-sha1-deprecate-04
Sean Turner <sean@sn3rd.com> Wed, 28 July 2021 16:41 UTC
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From: Sean Turner <sean@sn3rd.com>
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Date: Wed, 28 Jul 2021 12:41:47 -0400
Cc: iot-directorate@ietf.org, draft-ietf-tls-md5-sha1-deprecate.all@ietf.org, last-call@ietf.org
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To: Daniel Migault <mglt.ietf@gmail.com>, Loganaden Velvindron <loganaden@gmail.com>, TLS List <tls@ietf.org>
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Subject: Re: [TLS] Iotdir last call review of draft-ietf-tls-md5-sha1-deprecate-04
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Daniel, Thanks for following up on this (I meant to and dropped the ball). Triminng to the remaining issue. spt > </mglt> > >> >> > 6. Updates to RFC5246 > >> >> > > >> >> > [RFC5246], The Transport Layer Security (TLS) Protocol Version 1.2, > >> >> > suggests that implementations can assume support for MD5 and SHA-1 by > >> >> > their peer. This update changes the suggestion to assume support for > >> >> > SHA-256 instead, due to MD5 and SHA-1 being deprecated. > >> >> > > >> >> > In Section 7.4.1.4.1: the text should be revised from: > >> >> > > >> >> > OLD: > >> >> > > >> >> > "Note: this is a change from TLS 1.1 where there are no explicit > >> >> > rules, but as a practical matter one can assume that the peer > >> >> > supports MD5 and SHA- 1." > >> >> > > >> >> > NEW: > >> >> > > >> >> > "Note: This is a change from TLS 1.1 where there are no explicit > >> >> > rules, but as a practical matter one can assume that the peer > >> >> > supports SHA-256." > >> >> > > >> >> > > >> >> > <mglt> > >> >> > I am reading the Note as an explanation on > >> >> > why sha was taken as the default hash > >> >> > function with the following rules. > >> >> > > >> >> > """ > >> >> > If the client does not send the signature_algorithms extension, the > >> >> > server MUST do the following: > >> >> > > >> >> > - If the negotiated key exchange algorithm is one of (RSA, DHE_RSA, > >> >> > DH_RSA, RSA_PSK, ECDH_RSA, ECDHE_RSA), behave as if client had > >> >> > sent the value {sha1,rsa}. > >> >> > > >> >> > - If the negotiated key exchange algorithm is one of (DHE_DSS, > >> >> > DH_DSS), behave as if the client had sent the value {sha1,dsa}. > >> >> > > >> >> > - If the negotiated key exchange algorithm is one of (ECDH_ECDSA, > >> >> > ECDHE_ECDSA), behave as if the client had sent value {sha1,ecdsa}. > >> >> > """ > >> >> > > >> >> > The current document does not update the > >> >> > default hash function from sha to sha256 to > >> >> > avoid interoperability issue where one peer > >> >> > takes sha while the other one takes sha-256. > >> >> > >> >> You are right that this section, which is updating TLS1.2 [RFC5246], is not changing the default to SHA-256, but the recommendations for configuring TLS 1.2, which are provided in RFC 7525/BCP 195, is being updated to recommend SHA-256 in the very next section. > >> >> > >> > <mglt> > >> > Updating the update works. It believe that saying a section should be remove is not too hard, and it seems to me that mentioning the default behaviour is important. I would say that could get implementers confused to implement part of the specifications that do not hold any more. I would prefer to have this being addressed. > >> > > >> > I am reading RFC7525 as recommending a non default parameter while this document removed the support of default parameters. So to me the updating the status of the default parameters seems more updating the 5246 then 7525. > >> > </mglt> > >> > > >> >> > As a results, these rules and the "Note" may > >> >> > eventually all together be replaced by your > >> >> > text of section 2. > >> >> > > >> >> > The following text may also be removed: > >> >> > > >> >> > """ > >> >> > If the client supports only the default hash and signature algorithms > >> >> > (listed in this section), it MAY omit the signature_algorithms > >> >> > extension. > >> >> > """ > >> >> > >> >> So we might do it, but the question is whether implementers are going to be confused if we don’t do it. I think because s1 already says that client MUST send a signature_algorithms extension that we don’t have to indicate that that particular sentence be dropped/removed from the draft. I will admit this document mixes the two ways to do a bis document, i.e., old/new and describing blanket changes, but I think the intent is pretty clear based on the brevity of the draft. > >> >> > >> > > >> > <mglt> > >> > I agree we may be able to find all the dots. I think this provides more insight to clarify the reading of 5246. I agree the intend is clearly stated in the title and section 2 addresses most of it and I believe that some flexibility is permitted, but that is unclear to me where to put the bar. I still believe that could be easily be addressed. > >> > </mglt> > >> > > <mglt> > I think I have lost a bit where we are, but I tend to agree that clarification of 5246 would be clearer here. That is mentioning the text that needs to be removed / changed. > </mglt> > <mglt> > I do not see 07 mentioning the text to be removed - that is now dead text. I think that would be clarifying. > </mglt> To recap: You are suggesting that we add the following in s6 before the existing OLD/NEW, i.e., right after "due to MD5 and SHA-1 being deprecated.": In Section 7.1.4.1: the following text is removed: If the client supports only the default hash and signature algorithms (listed in this section), it MAY omit the signature_algorithms extension. Since it’s a MAY, I am a-okay with deleting. Anybody else see harm?
- [TLS] Iotdir last call review of draft-ietf-tls-m… Daniel Migault via Datatracker
- Re: [TLS] Iotdir last call review of draft-ietf-t… Daniel Migault
- Re: [TLS] [Last-Call] Iotdir last call review of … Michael Richardson
- Re: [TLS] [Last-Call] Iotdir last call review of … Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Daniel Migault
- Re: [TLS] Iotdir last call review of draft-ietf-t… Daniel Migault
- Re: [TLS] Iotdir last call review of draft-ietf-t… Loganaden Velvindron
- Re: [TLS] Iotdir last call review of draft-ietf-t… Daniel Migault
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Daniel Migault
- Re: [TLS] Iotdir last call review of draft-ietf-t… Daniel Migault
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] Iotdir last call review of draft-ietf-t… Sean Turner
- Re: [TLS] [Last-Call] Iotdir last call review of … Salz, Rich
- Re: [TLS] [Last-Call] Iotdir last call review of … Russ Housley
- Re: [TLS] [Iot-directorate] [Last-Call] Iotdir la… Hannes Tschofenig
- Re: [TLS] [Iot-directorate] [Last-Call] Iotdir la… Daniel Migault
- Re: [TLS] [Iot-directorate] [Last-Call] Iotdir la… Sean Turner
- Re: [TLS] [Iot-directorate] [Last-Call] Iotdir la… Sean Turner
- Re: [TLS] [Iot-directorate] [Last-Call] Iotdir la… David Benjamin
- Re: [TLS] [Iot-directorate] [Last-Call] Iotdir la… Peter Saint-Andre