Re: [MLS] AEAD data in messages

Richard Barnes <rlb@ipv.sx> Tue, 13 August 2019 14:22 UTC

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From: Richard Barnes <rlb@ipv.sx>
Date: Tue, 13 Aug 2019 10:21:49 -0400
Message-ID: <CAL02cgRYcwRQ==4LbBvgi8q45KaAp=rgNdnP+W2zxLRnvzg9dQ@mail.gmail.com>
To: Peter Slatala <psla=2Bmls=40google.com@dmarc.ietf.org>
Cc: Jeff Burdges <burdges@gnunet.org>, Messaging Layer Security WG <mls@ietf.org>
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Subject: Re: [MLS] AEAD data in messages
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I don't think we have a slot for this, but it seems sensible enough.
Basically you'd just be changing the API from
session.encrypt(application_data) to session.encrypt(aad,
application_data).  I'd be happy to review a PR.

--Richard

On Tue, Aug 13, 2019 at 10:20 AM Peter Slatala <psla=2Bmls=
40google.com@dmarc.ietf.org>; wrote:

>
>
> On Mon, Aug 12, 2019 at 11:24 PM Jeff Burdges <burdges@gnunet.org>; wrote:
>
>>
>>
>> > On 13 Aug 2019, at 01:15, Peter Slatala <psla=2Bmls=
>> 40google.com@dmarc.ietf.org>; wrote:
>> > I was wondering if you considered allowing additional plaintext but
>> authenticated data in MLS messages.
>>
>> It’d be outside the header encryption, making the AEAD would be the
>> header encryption?
>>
>> How would the delivery service authenticate it?
>
>  Delivery service is often TLS encrypted so client-server connection
> should be secure.
>
>
>> > Here are some use-cases for MLS that I can think of:
>> > * sending a 'sending device identifier' in case if delivery service
>> can't differentiate different user devices from each other.
>>
>> I’d hope the delivery service does not care too much to which device it
>> communicates.
>>
>> > * sending 'message type' that server can act upon. For example,
>> delivery report sent by the recipient to the sender, which also acts as an
>> ACK to the server that the message was persisted.
>>
>> > * authenticating message id (but make it visible to server to avoid
>> redelivery),
>>
>> ACKs and message ids should often be done fully encrypted, but yeah
>> making one ACK or message id notify both the delivery service and the end
>> user makes sense in some use cases.
>>
>> Jeff
>>
>>
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