Re: [Curdle] Which curves are MUST and SHOULD ?

Simo Sorce <simo@redhat.com> Tue, 05 January 2021 01:55 UTC

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From: Simo Sorce <simo@redhat.com>
To: "Mark D. Baushke" <mdb=40juniper.net@dmarc.ietf.org>, Hubert Kario <hkario@redhat.com>
Cc: curdle@ietf.org
Date: Mon, 04 Jan 2021 20:55:25 -0500
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Subject: Re: [Curdle] Which curves are MUST and SHOULD ?
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Votes inline.

On Mon, 2021-01-04 at 12:21 -0800, Mark D. Baushke wrote:
> Hubert Kario <hkario@redhat.com> writes:
> 
> > On Thursday, 17 December 2020 20:35:24 CET, Mark D. Baushke wrote:
> > > Ron Frederick <ronf@timeheart.net> writes:
> > > 
> > > > On Dec 15, 2020, at 8:09 AM, Salz, Rich <rsalz@akamai.com> wrote:
> > > > > >   I’m not comfortable with algorithms going from REQUIRED to
> > > > > > SHOULD NOT without some kind of transitional period. My
> > > > > > suggestion would be to ease into this with SHOULD NOT for
> > > > > > now. If you want to discuss BCP in this draft, perhaps that
> > > > > > can be a separate section.
> > > > > 
> > > > > We've done it before, MD5, short RSA/DH keys, etc.
> > > > > 
> > > > > We shouldn't pretend that crypto-breaking advances haven't happened.
> > > > > 
> > > > > Admins can make trade-offs anyway.
> > > 
> > > I am under the impression that the audience here is the maintainers of
> > > SSHv2 software rather than the administrators that manage the sites
> > > using it.
> > 
> > it's both
> 
> Fair enough.
> 
> Two kinds of stakeholders: a) "implementors" and b) "users" should mean
> more responses for the question.
> 
> Okay. In the original RFC4253 specification both
> 
>     diffie-hellman-group1-sha1 
> and
>     diffie-hellman-group14-sha1
> 
> were REQUIRED key exchanges.
> 
> The group1 parameters in RFC4253 point to the 1024-bit MODP Second
> Oakley Group given in RFC2409 section 6.2 and RFC2412 section E.2.
> 
> There are two issues with diffie-hellman-group1-sha1: 1) recent
> estimages are that it has roughly 80 bits of security strength, and 2)
> it uses SHA1 for hashing which is considered weak.
> 
> If we choose "MUST NOT" for this key exchange, then we are going from
> "MUST" to "MUST NOT" which could be a hardship for low-end devices
> unable to run calculations to generate a shared secret using a larger
> MODP group if support is completely removed.
> 
> If we choose "SHOULD NOT", then it is hoped that most implementors would
> default to not configuring this option by default, but may provide it
> for enviornments that need it.
> 
> If we choose "MAY", then it is not certain if implementors or users will
> do much of anything different and this potentially insecure key exchange
> may continue to be used even when it may be a hazard to those that
> desire a more secure by default system.
> 
> Are you an SSH impelmentor or user or both?
> 
>   Implementor
>   User
>   Both

I am Both, but I lean on the Implementor side.

> I would like to get a straw vote for the six *sha1* related key
> exchanges. I am proposing that the rsa1024-sha1-* kex be a MUST NOT and
> that all of the others be a SHOULD NOT.
> 
> 1. For diffie-hellman-group1-sha1 what is your vote?
> 
>   MUST          -- current for RFC4253
>   SHOULD
>   MAY
>   SHOULD NOT    -- proposed in the -13 draft
>   MUST NOT

SHOULD NOT

> 2. For diffie-hellman-group14-sha1 what is your vote?
> 
>   MUST          -- current for RFC4253
>   SHOULD
>   MAY           -- proposed in the -13 draft
>   SHOULD NOT
>   MUST NOT

MAY

> 3. For diffie-hellman-group-exchange-sha1 what is your vote?
> 
>   MUST
>   SHOULD
>   MAY           -- current for RFC4419    
>   SHOULD NOT    -- proposed in the -13 draft
>   MUST NOT

SHOULD NOT

> 4. For rsa1024-sha1 what is your vote?
> 
>   MUST
>   SHOULD
>   MAY           -- current for RFC4432
>   SHOULD NOT
>   MUST NOT      -- proposed in the -13 draft

MUST NOT

> 5. For gss-gex-sha1-* what is your vote?
> 
>   MUST
>   SHOULD        -- current for RFC4462
>   MAY
>   SHOULD NOT    -- proposed in the -13 draft
>   MUST NOT  

SHOULD NOT

> 6. For gss-group1-sha1-* what is your vote?
> 
>   MUST
>   SHOULD        -- current for RFC4462
>   MAY
>   SHOULD NOT    -- proposed in the -13 draft
>   MUST NOT  

MAY

The reason why I voted MAY in the last is that the draft to implement
gssapi with sha2 has been published only recently, so in order to
interoperate with older client I think we still need a MAY, but I would
not be upset if the group chooses SHOULD NOT. (GEX is less used and
less critical, so I am ok with SHOULD NOT there)

HTH,
Simo.

> You may direct your votes to the list or to the chairs and me.
> 
> 	Be safe, stay healthy,
> 	-- Mark
> 
> _______________________________________________
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> Curdle@ietf.org
> https://www.ietf.org/mailman/listinfo/curdle

-- 
Simo Sorce
RHEL Crypto Team
Red Hat, Inc