Re: [Webpush] Major change to encryption

Hi Martin,

Thanks for the update and the proposal!

I've reviewed these today, and have minor some points of feedback. I'll
deliberately avoid the topics of interoperability and upgrade cost here.

First of all, this indeed vastly improves layering between the drafts. I
very much like how webpush-encryption is now built on top of encryption-
encoding as opposed to being some sort of fork.

>> A push message MUST include a zero length keyid parameter in the
>> content coding header. This allows implementations to ignore the first
>> 21 octets of a push message.

I don't think this is right. The `salt` and the `rs` must still be known,
and those are included in the header.

>> A push service is not required to support more than 4096 octets of
>> payload body (see Section 7.2 of [I-D.ietf-webpush-protocol]), which
>> equates to at most 4059 octets of cleartext.

I think this forgot about the padding --

  4096 - 16 (auth) - 2 (padding length) - 21 (header w/o keyid) = 4,057

May also want to s/cleartext/plaintext/ for consistency with encryption-
encoding.

>> An Application Server MUST include exactly one aes128gcm content
>> coding, and at most one entry in the Crypto-Key field. This allows the
>> keyid parameter to be omitted.

This means the draft is incompatible with VAPID again. It must have at
most one Crypto-Key entry that has a `dh` value.

I haven't yet been able to validate the examples in the draft, but it
sounds like you're changing these anyway per jr's feedback (+1 to that).

Thanks,
Peter

On Mon, Oct 31, 2016 at 11:19 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> On 1 November 2016 at 10:07, jr conlin <jconlin@mozilla.com> wrote:
> > One small comment, then? Can we change the transmitted Content-Encoding
> > type to match the new Content-type of "aes128gcm" instead of the long
> > abandoned "aesgcm128"? (See point #4)
>
> Ouch, that's going to hurt.  I'll have to redo the examples :*(  40
> minutes until the deadline, go!
>
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