Re: [Curdle] Kathleen Moriarty's Yes on draft-ietf-curdle-ssh-dh-group-exchange-05: (with COMMENT)

[Kathleen Moriarty <[e-mail]>]

Hello,

Sent from my iPhone

> On Sep 15, 2017, at 10:04 AM, Spencer Dawkins at IETF <[e-mail]> wrote:
> 
> So, Kathleen's ballot thread, but since she and I share this curiosity ...
> 
>> On Fri, Sep 15, 2017 at 6:01 AM, Loganaden Velvindron <[e-mail]> wrote:
>> On Wed, Sep 13, 2017 at 10:08 PM, Kathleen Moriarty
>> <[e-mail]> wrote:
>> > Kathleen Moriarty has entered the following ballot position for
>> > draft-ietf-curdle-ssh-dh-group-exchange-05: Yes
>> >
>> > When responding, please keep the subject line intact and reply to all
>> > email addresses included in the To and CC lines. (Feel free to cut this
>> > introductory paragraph, however.)
>> >
>> >
>> > Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
>> > for more information about IESG DISCUSS and COMMENT positions.
>> >
>> >
>> > The document, along with other ballot positions, can be found here:
>> > https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-dh-group-exchange/
>> >
>> >
>> >
>> > ----------------------------------------------------------------------
>> > COMMENT:
>> > ----------------------------------------------------------------------
>> >
>> > I do agree with Spencer, the text that is non-normative reads as if this is
>> > fully deprecating any recommendation below 2048, but then the normative text
>> > just says SHOULD.  Is there a reason this is not MUST?  I know deprecating
>> > things takes a long time.
>> 
>> Yes, it takes a long time, and also because of backward compatibility.
>> We felt that "SHOULD" was sufficient at the time.

Hmm, I'd like to push on this a bit more.  First, do you still feel it's sufficient?

Next, what's the explicit compatibility concern?  If your just waiting on a key rollover or something along those lines, it's fine for this RFC to draw a hard line.

Thanks,
Kathleen 
> 
> That doesn't surprise me (speaking only for myself).
> 
> It might be helpful to add a sentence explaining that the SHOULD is for backward compatibility. 
> 
> That changes the incentives a bit - implementers have more incentive to implement a SHOULD if it's not a MUST *yet*, but when the community stops worrying about backward compatibility, it could be, and then other implementations won't interop with yours. 
> 
> And, for extra credit, that could happen suddenly, if someone posts a clever attack on 1024-bit keys that requires minimal computing resources and includes an implementation that anyone can pick up ... so everyone else stops accepting shorter keys, like, today.
> 
> But do the right thing, of course.
> 
> Spencer