Re: [Ace] Security of the Communication Between C and RS

Hannes Tschofenig <Hannes.Tschofenig@arm.com> Tue, 18 December 2018 08:47 UTC

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From: Hannes Tschofenig <Hannes.Tschofenig@arm.com>
To: Ludwig Seitz <ludwig.seitz@ri.se>, Stefanie Gerdes <gerdes@tzi.de>, Jim Schaad <ietf@augustcellars.com>, "ace@ietf.org" <ace@ietf.org>
Thread-Topic: [Ace] Security of the Communication Between C and RS
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Subject: Re: [Ace] Security of the Communication Between C and RS
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Hi Ludwig,

A few remarks inline:

-----Original Message-----
From: Ludwig Seitz <ludwig.seitz@ri.se>
Sent: Dienstag, 18. Dezember 2018 09:27
To: Hannes Tschofenig <Hannes.Tschofenig@arm.com>om>; Stefanie Gerdes <gerdes@tzi.de>de>; Jim Schaad <ietf@augustcellars.com>om>; ace@ietf.org
Subject: Re: [Ace] Security of the Communication Between C and RS

On 15/12/2018 16:04, Hannes Tschofenig wrote:
> Hi Steffi,
>
> ~snip~
>
>> I really think you should point out that symmetric keying material
>> that the AS provides to the client is valid as long as the token.
>
> I think that's a useful recommendation. I do, however, believe that we
> are not making the same assumption for an asymmetric key bound to the
> token.
>

Ok, I'll add text to the draft that says this.

Note that this can be trouble if a client asks the AS to bind an existing symmetric pop-key to another (new) token it is requesting.
Which one of the two tokens bound to that key is now steering the expiration of the key?

[Hannes] Normally, the client would only request a symmetric PoP token from the AS and the AS would create the symmetric key and return the PoP token + the symmetric key.
Hence, in the normal case this shouldn't be happen.

>> The access information optionally can contain an expires_in field.
>> It would help to prevent security breaches under the following
>> conditions:
> 1. the keying material is valid as long as the ticket, 2. the
> expires_in field is present in the access information that AS sends to
> C, 3. the client checks the expires_in field when it gets the access
> information from the AS, and 4. the client checks if the keying
> material is still valid each time before it sends a request to RS.
>
> These checks make sense to me.
>
Are you proposing we make the expires_in field mandatory? If so, why isn't it mandatory already in OAuth (currently only RECOMMENDED)?

[Hannes] I would do the check when the field is actually there. However, it is a good question why it is not mandatory in OAuth. Let me drop a mail to the list.

Ciao
Hannes

/Ludwig


--
Ludwig Seitz, PhD
Security Lab, RISE
Phone +46(0)70-349 92 51
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