Re: [TLS] EXTERNAL: TLS 1.3 Authentication and Integrity only Cipher Suites

[Eric Rescorla <[e-mail]>]

On Thu, Feb 11, 2021 at 3:08 PM Jack Visoky <[e-mail]>
wrote:

> Hi Eric,
>
>
>
> I don’t have numbers offhand but I will say that many platforms I have
> experience with have some sort of HW support, and might include things like
> DMA. In these cases ChaCha20-Poly1305 is way behind in terms of performance
> (which is expected as I believe it was mainly targeted to software-only
> implementations).
>
>
>
> I’ll anticipate that someone might ask if GCM is not better that SHA-256
> with hardware support, and of course I will have to say it depends on the
> platform. For some cases it will be, and others it will not. Here is a link
> to some performance numbers which show SHA-256 is faster than GCM
> https://www.ti.com/lit/an/swra667/swra667.pdf?ts=1613069390182. In other
> cases GCM may not be supported on a platform but SHA256 is, of course
> that’s kind of a strawman but it could occur.
>

I doubt it covers the whole difference, but I'd note that SHA-256 is not
the right comparison point, because what you need here is HMAC, which
requires nested SHA invocations. This is especially relevant if you have to
go back and forth to the hardware each time.

-Ekr

Note I am not endorsing this platform or affiliated with it in any way,
> just want to give an example. And it really is just an example, sorry to
> repeat again but I just want to drive home the point that YMMV on things
> like this.
>
>
>
> Thanks,
>
>
>
> --Jack
>
>
>
>
>
> *From:* Eric Rescorla <[e-mail]>
> *Sent:* Thursday, February 11, 2021 2:51 PM
> *To:* Jack Visoky <[e-mail]>
> *Cc:* John Mattsson <john.mattsson=[e-mail]>;
> [e-mail]
> *Subject:* Re: [TLS] EXTERNAL: TLS 1.3 Authentication and Integrity only
> Cipher Suites
>
>
>
>
>
>
>
> On Thu, Feb 11, 2021 at 11:13 AM Jack Visoky <[e-mail]>
> wrote:
>
> Hi John, Eric,
>
>
>
> Thanks for the input. We will certainly make some changes to the draft
> regarding the inspection case. However, I can’t support removing the
> performance/latency information completely, as I have heard from those who
> have this very concern. That said, we will edit the language to make it
> clear that this is not true in all cases.
>
>
>
> Well, the draft just claims that there are latency concerns, but doesn't
> present details. If you want to make this case, it would be helpful to
> present performance numbers that show that these ciphersuites are
> substantially faster than the alternative algorithms (in particular
> ChaCha20/Poly1305) which is quite fast on many low end platforms.
>
>
>
> -Ekr
>
>
>