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

Hannes Tschofenig <Hannes.Tschofenig@arm.com> Tue, 18 December 2018 15:26 UTC

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From: Hannes Tschofenig <Hannes.Tschofenig@arm.com>
To: Stefanie Gerdes <gerdes@tzi.de>, Ludwig Seitz <ludwig.seitz@ri.se>, 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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Date: Tue, 18 Dec 2018 15:26:00 +0000
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Subject: Re: [Ace] Security of the Communication Between C and RS
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Hi Steffi,

> In OAuth, the expires_in field is usually used to inform the client how long the access token is valid. If the client uses the access token in a request after the token expired, the RS will reject the request, which usually is not a big problem for the client.

> In ACE, AS provides the client with keying material for the RS, which is a completely different situation. If the client does not know how long the keying material is valid, it may use outdated keying material to communicate with RS. The expires_in field can be used to inform the client how long the keying material for RS is valid, if the keying material is valid as long as the access token.

> The main reason to change keying material from time to time is to avoid that it is compromised. I therefore think that it is necessary for the security of the solution that C knows how long the keying material is supposed to be valid.

If a client uses either an old key or an old token then the request will fail. I don't see much difference here between OAuth and ACE.

Adding a note to recommend the use of the expires_in field appears still useful to me.

Ciao
Hannes

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