Re: [saag] Section 2.9: was Re: AD review of draft-iab-crypto-alg-agility-06

[Viktor Dukhovni <[e-mail]>]

On Thu, Sep 03, 2015 at 04:08:59PM -0400, Russ Housley wrote:

> > It can be a sentence or two, just enough to not give the impression
> > that weak crypto is preferred with OS.
> 
> The words in my current edit buffer are:
> 
>    Despite the guidance in Section 2.4, opportunistic security [RFC7435]
>    also deserves consideration, especially at the time a protocol
>    implementation is deployed and configured.  Using algorithms that are
>    weak against advanced attackers but sufficient against others is one
>    way to make pervasive surveillance significantly more difficult.  As
>    a result, algorithms that would not be acceptable in many negotiated
>    situations are acceptable for opportunistic security when legacy
>    systems are in use for unauthenticated encrypted sessions as
>    discussed in Section 3 of [RFC7435] as long as their use does not
>    facilitate downgrade attacks.  Similarly, weaker algorithms and
>    shorter key sizes are also acceptable for opportunistic security with
>    the same constraints.  That said, the use of strong algorithms is
>    always preferable.
> 
> Would it help to change "As a result" to "As a result, when communicating
> parties do not have strong algorithms in common"?

You're heading in the right direction, but I think this is a sentence
or so too late.  The sentence that starts with "Using algorithms
that are weak ..." is troublesome.  How about:

    Using the strongest available encryption (even if not strong
    enough for mandatory security) is one way ...

And then perhaps still make the additional change you're proposing.

-- 
	Viktor.