Re: [Curdle] State of draft-ietf-curdle-ssh-kex-sha2?
denis bider <denisbider.ietf@gmail.com> Sun, 12 July 2020 12:05 UTC
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From: denis bider <denisbider.ietf@gmail.com>
Date: Sun, 12 Jul 2020 07:05:10 -0500
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To: "Mark D. Baushke" <mdb@juniper.net>
Cc: curdle <curdle@ietf.org>, curdle-chairs <curdle-chairs@ietf.org>
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Subject: Re: [Curdle] State of draft-ietf-curdle-ssh-kex-sha2?
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Hey Mark! It looks like I found the key thing I missed: Google did not show me RFC 8268 when I searched for "diffie-hellman-group14-sha256". It finds it now when I search for "rfc diffie-hellman-group14-sha256". I could have found it in the IANA registry but I trusted the lack of Google results in my first search. Alas. That resolves the key concern for me: that names like "diffie-hellman-group14-sha256" are authoritatively defined. I was looking for this reference for the SSH QUIC draft. With regard to MUST / MAY / SHOULD / etc assignments, I agree with all of these: > curve25519-sha256 SHOULD > curve448-sha512 MAY > diffie-hellman-group-exchange-sha1 SHOULD NOT > diffie-hellman-group-exchange-sha256 MAY > diffie-hellman-group1-sha1 SHOULD NOT > diffie-hellman-group14-sha1 SHOULD NOT > diffie-hellman-group14-sha256 SHOULD > diffie-hellman-group15-sha256 MAY I do not agree with this one: > diffie-hellman-group16-sha512 MUST I find this too computationally expensive to justify "MUST" for servers. Last time I checked, this costs about 100 ms in server CPU time, more on weaker CPUs, and makes it trivial to DoS a resource-constrained server - no DDoS needed. I agree with all of these: > diffie-hellman-group17-sha512 MAY > diffie-hellman-group18-sha512 MAY > ecdh-sha2-* MAY > ecdh-sha2-nistp256 SHOULD > ecdh-sha2-nistp384 SHOULD > ecmqv-sha2 MAY > ext-info-c SHOULD > ext-info-s SHOULD > gss-* MAY I conditionally agree on these: > gss-curve25519-sha256-* SHOULD > gss-curve448-sha512-* MAY > gss-gex-sha1-* SHOULD NOT > gss-group1-sha1-* SHOULD NOT > gss-group14-sha256-* SHOULD > gss-group15-sha512-* MAY > gss-group16-sha512-* SHOULD > gss-group17-sha512-* MAY > gss-group18-sha512-* MAY > gss-nistp256-sha256-* SHOULD > gss-nistp384-sha384-* MAY > gss-nistp521-sha512-* MAY The condition is that the reader understands that "SHOULD" for these methods applies only if you implement any GSS-API key exchange methods at all. In other words, the whole category of GSS-API needs to be "MAY", but within the category the above SHOULDs are appropriate as long as the decision is made to implement any of the GSS-API key exchange methods in the first place. I agree with these: > rsa1024-sha1 MUST NOT > rsa2048-sha256 MAY In summary - my main complaint is that "diffie-hellman-group16-sha512" is too expensive to be a MUST. If that leaves no key exchange method that is a "MUST", I'm fine with it. If there needs to be a method that's a "MUST", I vote for either "curve25519-sha256" or "diffie-hellman-group14-sha256" as meeting security requirements while being the most widely compatible. Now that I've found RFC 8268, I'm also fine if we can't get consensus on this draft, though it would be a nice to have. denis On Sun, Jul 12, 2020 at 4:38 AM Mark D. Baushke <mdb@juniper.net> wrote: > Hi denis, > > denis bider <denisbider.ietf@gmail.com> writes: > > > Hey everyone, > > > > I notice the following draft has not moved forward: > > > > https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-kex-sha2/ > > > > This seems to be an important draft which would standardize the > > current use of key exchange algorithms in SSH. However, it looks like > > no changes have been made in 2.5 years? > > Correct. > > > Did I miss some event where this draft morphed into something else so > > that I'm not seeing the right information about progress? > > I have not progressed the draft, mostly due to private email received > over two years ago... > > A number of people told me to not move it forward until after all of the > RFCs for draft-ietf-curdle-ssh-curves (now RFC 8731) and > draft-ietf-curdle-gss-keyex-sha2 (now RFC 8732) were adopted. Also, many > people were unhappy with the characterizations of the existing > algorithms and my scoring of MUST, SHOULD, and MAY > > In addition, there was a general dislike for the references of the NSA > documents provided or the CNSA document reference. > > > Otherwise, what seems to be the current obstacle with making progress > > on this? > > I think that work on the document is desirable. Does anyone wish to be a > co-author with me? > > I would like to see more opinions on the list about which algorithms are > to be 'SHOULD NOT' and which are to be 'MUST' ... in general, I would > like to see this document as a KEX refernce that may be updated every > few years as we learn more about which KEX algorithms are best to use. > > My opinion for Section 5 as I write this email today is: > > Key Exchange Method Name Reference Implement > ------------------------------------ ---------- ---------- > curve25519-sha256 RFC8731 SHOULD > curve448-sha512 RFC8731 MAY > diffie-hellman-group-exchange-sha1 RFC4419 SHOULD NOT > diffie-hellman-group-exchange-sha256 RFC4419 MAY > diffie-hellman-group1-sha1 RFC4253 SHOULD NOT > diffie-hellman-group14-sha1 RFC4253 SHOULD NOT > diffie-hellman-group14-sha256 RFC8268 SHOULD > diffie-hellman-group15-sha256 RFC8268 MAY > diffie-hellman-group16-sha512 RFC8268 MUST > diffie-hellman-group17-sha512 RFC8268 MAY > diffie-hellman-group18-sha512 RFC8268 MAY > ecdh-sha2-* RFC5656 MAY > ecdh-sha2-nistp256 RFC5656 SHOULD > ecdh-sha2-nistp384 RFC5656 SHOULD > ecmqv-sha2 RFC5656 MAY > ext-info-c RFC8308 SHOULD > ext-info-s RFC8308 SHOULD > gss-* RFC4462 MAY > gss-curve25519-sha256-* RFC8732 SHOULD > gss-curve448-sha512-* RFC8732 MAY > gss-gex-sha1-* RFC4462 SHOULD NOT > gss-group1-sha1-* RFC4462 SHOULD NOT > gss-group14-sha256-* RFC8732 SHOULD > gss-group15-sha512-* RFC8732 MAY > gss-group16-sha512-* RFC8732 SHOULD > gss-group17-sha512-* RFC8732 MAY > gss-group18-sha512-* RFC8732 MAY > gss-nistp256-sha256-* RFC8732 SHOULD > gss-nistp384-sha384-* RFC8732 MAY > gss-nistp521-sha512-* RFC8732 MAY > rsa1024-sha1 RFC4432 MUST NOT > rsa2048-sha256 RFC4432 MAY > > The above list of KEX algorithms comes from the IANA ssh-parameters list > URL: > > https://www.iana.org/assignments/ssh-parameters/ssh-parameters.xhtml#ssh-parameters-16 > > Please let me know if I have missed any of the KEX algorithms in the > list. > > Of these, I am not sure if rsa2048-sha256 has support for a 'MAY' or if > its lack of use would drive it to a 'SHOULD NOT' in the table. > > To be honest, I am really not sure which KEX algorithms should be listed > as Mandatory To Implement (MTI) for key exchanges going forward. > > Which diffie-hellman FFC group should be listed as MTI? group14-sha256 > or group16-sha512? (I tentatively selected this one). Is that wise? > Should any FFC Diffie-Hellman group size be MTI? > > I would like to hear if others on this list believe that > curve25519-sha256 should be a MUST or a SHOULD. > > I also do not know if the expired draft-ietf-curdle-ssh-kex-sha2 > document should bother to give opinions on any of the KEX options other > than those being deprecated or thrust into MTI. Opinions please? > > It seems clear to me that removing the *-sha1* KEX algorithms is a good > idea. I would love to move diffie-hellman-group14-sha1, but I honestly > suspect that some hardware is deployed for which it is the only KEX > algorithm that may still need to be supported... which is the only > reason it is a 'SHOULD' on my list instead of a 'SHOULD NOT' ... > > Be safe, stay healthy, > -- Mark >
- [Curdle] State of draft-ietf-curdle-ssh-kex-sha2? denis bider
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Salz, Rich
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Salz, Rich
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… denis bider
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Mark D. Baushke
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… denis bider
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Ron Frederick
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… denis bider
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Loganaden Velvindron
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Mark D. Baushke
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Salz, Rich
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Ron Frederick
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Mark D. Baushke
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… Mark D. Baushke
- Re: [Curdle] State of draft-ietf-curdle-ssh-kex-s… denis bider