Re: [TLS] Iotdir last call review of draft-ietf-tls-md5-sha1-deprecate-04
Sean Turner <sean@sn3rd.com> Fri, 29 January 2021 19:08 UTC
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From: Sean Turner <sean@sn3rd.com>
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Date: Fri, 29 Jan 2021 14:08:12 -0500
Cc: iot-directorate@ietf.org, last-call@ietf.org, draft-ietf-tls-md5-sha1-deprecate.all@ietf.org, TLS List <tls@ietf.org>
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To: Daniel Migault <mglt.ietf@gmail.com>
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Subject: Re: [TLS] Iotdir last call review of draft-ietf-tls-md5-sha1-deprecate-04
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> On Jan 21, 2021, at 16:50, Daniel Migault <mglt.ietf@gmail.com> wrote: > > Hi, > > First I deeply apologize for taking so long to respond, I just realized now these responses. No worries it does happen that I miss email from time to time too ;) > I do not believe a review of IoT protocol is needed, I am more thinking that TLS document should serve as a base guidance for TLS. Specific needs for IoT are addressed based on the generic guidances. In some cases specific extensions, cipher suites - not referenced by IANA as recommended - will be needed to address specific corner cases. I agree with you since the TLS RFC provides the general use case. Other RFCs can specify other use cases. The way we handled this for CCM_8 suites was to include the following note: Note CCM_8 cipher suites are not marked as "Recommended". These cipher suites have a significantly truncated authentication tag that represents a security trade-off that may not be appropriate for general environments. spt > Yours, > Daniel > > On Tue, Oct 27, 2020 at 11:32 PM Sean Turner <sean@sn3rd.com> wrote: > > > > On Oct 27, 2020, at 10:32, Daniel Migault <mglt.ietf@gmail.com> wrote: > > > > To address the comment below, keeping weak security is likely to weaken current and future IoT communications, so I do not think there is room for compromise with performance. Of course this is in a context of TLS. I expect protocol to leverage from TLS security, so the impact should be rather negligible. > > > > """ > > As those hash algorithms were 'cheap' for TLS 1.2, I would appreciate a review of impacted IoT protocols if those algorithms are deprecated. > > """ > > In terms of process, are you suggesting "a review of impacted IoT protocols if those algorithms are deprecated” MUST be completed prior to advancing this document to the IESG? > > spt > > > Yours, > > Daniel > > > > > > On Tue, Oct 27, 2020 at 10:21 AM Daniel Migault via Datatracker <noreply@ietf.org> wrote: > > Reviewer: Daniel Migault > > Review result: Ready with Nits > > > > Hi, > > > > > > I reviewed this document as part of the IoT Directorate's ongoing effort to > > review all IETF documents being processed by the IESG. These comments were > > written primarily for the benefit of the Security Area Directors. Document > > authors, document editors, and WG chairs should treat these comments just like > > any other IETF Last Call comments. > > > > Review Results: Ready with Nits > > > > Please find my comments below. > > > > Yours, > > Daniel > > > > > > Deprecating MD5 and SHA-1 signature hashes in TLS 1.2 > > draft-ietf-tls-md5-sha1-deprecate-04 > > [...] > > > > 1. Introduction > > > > The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is > > specified in [RFC5246]. MD5 and SHA-1 have been proven to be > > insecure, subject to collision attacks [Wang]. In 2011, [RFC6151] > > detailed the security considerations, including collision attacks for > > MD5. NIST formally deprecated use of SHA-1 in 2011 > > [NISTSP800-131A-R2] and disallowed its use for digital signatures at > > the end of 2013, based on both the Wang, et. al, attack and the > > potential for brute-force attack. In 2016, researchers from INRIA > > identified a new class of transcript collision attacks on TLS (and > > other protocols) that rely on efficient collision-finding algorithms > > on the underlying hash constructions [Transcript-Collision]. > > Further, in 2017, researchers from Google and CWI Amsterdam > > [SHA-1-Collision] proved SHA-1 collision attacks were practical. > > This document updates [RFC5246] and [RFC7525] in such a way that MD5 > > and SHA-1 MUST NOT be used for digital signatures. However, this > > document does not deprecate SHA-1 in HMAC for record protection. > > > > <mglt> > > RFC6194 may be mentioned as a reference for > > not deprecating HMAC-SHA-1 as well as an > > additional reference to [NISTSP800-131A-R2]. > > > > Reading the text the situation of HMAC with > > MD5 is unclear. Since we specify that SHA-1 > > is not deprecated for HMAC we may specify > > the status for HMAC with MD5. Given RFC6151 I > > hope the reason is that MD5 and HMAC-MD5 has > > already been deprecated but I have not found > > this. Maybe that would worth mentioning it > > is deprecated already. > > > > </mglt> > > > > [...] > > > > 2. Signature Algorithms > > > > Clients MUST NOT include MD5 and SHA-1 in the signature_algorithms > > extension. If a client does not send a signature_algorithms > > extension, then the server MUST abort the handshake and send a > > handshake_failure alert, except when digital signatures are not used > > (for example, when using PSK ciphers). > > > > <mglt> > > It seems to me that the server behavior might > > be defined as well. In our case this could be > > something around the lines the server MUST > > ignore MD5 and SHA1 values in the signature > > algorithm extension. > > > > </mglt> > > > > 3. Certificate Request > > > > Servers SHOULD NOT include MD5 and SHA-1 in CertificateRequest > > messages. > > > > <mglt> > > It seems to me that the same level of > > authentication should be provided for both > > peers and that server MUST NOT include MD5 > > or SHA-1. > > > > A SHOULD NOT status might be welcome for a > > smooth transition. At that time, collision > > for MD5 and SHA1 are known for years. It is likely > > that software that still need MD5 or SHA1 are > > likely to never upgrade, so I doubt a smooth > > path worth being taken. > > </mglt> > > > > 4. Server Key Exchange > > > > Servers MUST NOT include MD5 and SHA-1 in ServerKeyExchange messages. > > If a client receives a MD5 or SHA-1 signature in a ServerKeyExchange > > message it MUST abort the connection with the illegal_parameter > > alert. > > > > <mglt> > > As per section 2, the client has clearly > > indicated it does not support signature with > > MD5/SHA1, so Server Key Exchange should not > > end up with signature with SHA1/MD5. > > > > """ > > If the client has offered the "signature_algorithms" extension, the > > signature algorithm and hash algorithm MUST be a pair listed in that > > extension. > > """ > > > > It also seems to me that the constraint of > > including a MD5 and SHA-1 signature is > > related to the Certificate. I suspect that > > some clarification are needed here. > > > > Since the case where the extension becomes > > mandatory, the quoted text above of RFC 5246 > > might be updated as well, though this does > > not appear that necessary. > > > > </mglt> > > > > 5. Certificate Verify > > > > Clients MUST NOT include MD5 and SHA-1 in CertificateVerify messages. > > If a server receives a CertificateVerify message with MD5 or SHA-1 it > > MUST abort the connection with handshake_failure or > > insufficient_security alert. > > > > > > <mglt> > > > > 6. Certificate > > > > Unless I am missing something, it seems to me > > that signature may also be found in the > > Certificate messages for the chain as well in > > the restriction of the signature algorithm. > > The end certificate is associated to the peer > > while other certificate are related to a CA. > > > > It seems that client and server behavior may > > be specified. The quoted text below may be > > helpful to clarify. > > > > """ > > If the client provided a "signature_algorithms" extension, then all > > certificates provided by the server MUST be signed by a > > hash/signature algorithm pair that appears in that extension. > > """ > > > > </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. > > 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. > > """ > > > > Regarding the Note, it seems to be that the > > removal of support for MD5/SHA1 will result > > in interoperability issues. At this point, > > the issue is due to the obsolescence of the > > implementation as deprecation of SHA1/Md5 has > > started a long time ago. > > > > It is unclear to me how normative is > > interpreted "can assume". Was the support of > > MD5/SHA1 a SHOULD or a MUST? In both case, if > > we were willing to maintain interoperability > > between software that only implemented > > MD5/SHA1, we should take a slower path and > > introducing SHA-256 and having were MD5/SHA1 > > kept for interoperability purpose before > > being deprecated. I do not think we should > > take that path as implementations that > > currently do not support SHA-256 are unlikely > > to be updated and that deprecation of > > SHA1/MD5 has started a long time ago. > > > > I would however mention the issue of > > interoperability in the section but not in > > the text to update. In the text to update I > > would maybe suggest that the support of > > SHA-256 comes with a normative MUST > > statement. > > > > > > </mglt> > > > > Velvindron, et al. Expires April 12, 2021 [Page 3] > > > > Internet-Draft draft-ietf-tls-md5-sha1-deprecate October 2020 > > > > > > 7. Updates to RFC7525 > > > > [RFC7525], Recommendations for Secure Use of Transport Layer Security > > (TLS) and Datagram Transport Layer Security (DTLS) recommends use of > > SHA-256 as a minimum requirement. This update moves the minimum > > recommendation to use stronger language deprecating use of both SHA-1 > > and MD5. The prior text did not explicitly include MD5 or SHA-1; and > > this text adds guidance to ensure that these algorithms have been > > deprecated.. > > > > Section 4.3: > > > > OLD: > > > > When using RSA, servers SHOULD authenticate using certificates with > > at least a 2048-bit modulus for the public key. In addition, the use > > of the SHA-256 hash algorithm is RECOMMENDED (see [CAB-Baseline] for > > more details). Clients SHOULD indicate to servers that they request > > SHA-256, by using the "Signature Algorithms" extension defined in TLS > > 1.2. > > > > NEW: > > > > Servers SHOULD authenticate using certificates with at least a > > 2048-bit modulus for the public key. > > > > In addition, the use of the SHA-256 hash algorithm is RECOMMENDED; > > and SHA-1 or MD5 MUST NOT be used (see [CAB-Baseline] for more > > details). Clients MUST indicate to servers that they request SHA- > > 256, by using the "Signature Algorithms" extension defined in TLS > > 1.2. > > > > <mglt> > > I understand the reason we do specify that > > hash algorithms that MUST NOT been used. This > > is fine in the context of this document, but > > it seems to me that if we were writing the > > updated specification we may have rather > > mentioned a minimum level of security hash > > function needs to be met - in our case > > SHA-256. I leave the co-authors make the > > appropriated choice. > > > > </mglt> > > > > > > 8. IANA Considerations > > > > The document updates the "TLS SignatureScheme" registry to change the > > recommended status of SHA-1 based signature schemes to N (not > > recommended) as defined by [RFC8447]. The following entries are to > > be updated: > > > > +--------+----------------+-------------+-------------------+ > > | Value | Description | Recommended | Reference | > > +--------+----------------+-------------+-------------------+ > > | 0x0201 | rsa_pkcs1_sha1 | N | [RFC8446][RFCTBD] | > > | 0x0203 | ecdsa_sha1 | N | [RFC8446][RFCTBD] | > > +--------+----------------+-------------+-------------------+ > > > > Other entries of the resgistry remain the same. > > > > > > <mglt> > > It seems to me that TLS 1.2 is using the TLS > > hash and TLS signature registry TLS signature > > registry and TLS 1.3 is using Signature > > Scheme. > > > > I suspect that TLS hash values for sha1 and > > md5 should be deprecated. And RFCTBD should > > be added for sha1 and md5. Note that the > > SHOULD NOT status for CertificateRequest > > may have prevented such deprecation. > > > > A side effect is these code points for > > signature scheme that were assigned for > > compatibility with legacy (TLS 1.2) > > signatures must not be used anymore - if > > there are no more valid with TLS 1.2. > > </mglt> > > > > > > > > > > _______________________________________________ > > TLS mailing list > > TLS@ietf.org > > https://www.ietf.org/mailman/listinfo/tls > > > > > > -- > > Daniel Migault > > Ericsson > > > > -- > Daniel Migault > Ericsson
- [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