Re: [EAT] Scope, Goals & Background for RATS
Denis <denis.ietf@free.fr> Tue, 18 September 2018 10:41 UTC
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From: Denis <denis.ietf@free.fr>
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Subject: Re: [EAT] Scope, Goals & Background for RATS
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Hi Henk, I browsed through the document and I am a bit puzzled. I was expecting some words about the attestation certificates that FIDO is using, but I found none. In FIDO, the concept of an attestation certificate is that a batch of devices from the same model have the same attestation private key and thus the same certificate. In this WG, such a restriction should not necessarily be made and when the certificate is different for each device model the question is how we should name it. Let me attempt a proposal: "shared attestation certificates" to designate attestation certificates that are specific to a batch of devices from the same model (like in FIDO), "individual attestation certificates" to designate attestation certificates that are specific to each device. The introduction section states: Authentication presumes some protection: e.g., that there is not an illicit copy of the private key available to anyone other than the intended subject. This is insufficient, it also assumes that a legitimate client does not perform all the cryptographic computations that another client needs: preventing the export of private keys does not prevent a client to use a private key for the benefits of another client. The background section states: Generally speaking, attestation is applied before data is exchanged to avoid disclosure to insufficiently trusted environments. I don't believe so. There is the need to demonstrate that a data exchange really originates from a secure device, acting as a client, and that that device has some well known properties. In the terminology section, I would expect to find a definition for an attestation certificate. I read the definition of an "Attestation Evidence" in the terminology section several times and I have difficulties to understand it. I wonder if such a concept really exists. In particular, within this definition, the text states: Attestation Evidence veracity may be augmented by Claimant signatures over portions of the Attestation Evidence. I don't believe so. If I am assuming the use of Attestation Certificates, there is an attestation private key associated to the public that is in it. The authentication exchange performed by a client should be counter-signed by the attestation private key corresponding to the public key placed within the Attestation Certificate. In the background section, the concept of a remote attestation is the following: /Remote Attestation/ is where the Attester conveys Attestation Evidence to a Verifier that compares it with Reference Values (in order for it to be considered, for example, healthy). A Relying Party (or the Verifier acting as a Relying Party) appraises the verification result to assess device trustworthiness and to manage security risk. Since I could not grasp the concept of Attestation Evidence, I couldn't grasp the concept of a Remote Attestation which is based on it. The goal is not simply to "assess device trustworthiness" but to make sure that some data exchange is really coming from a device that has specific properties. Such properties are going beyond the protection, the non-export and the non-import of private keys. I could not understand either the value of local attestations. IMO, the WG should only focus on remote attestations. Finally, the following invitation was raised: Naturally, we are also very interested in feedback about the illustrated difference between explicit attestation and implicit attestation. The current definition for Explicit Attestation is: /Explicit Attestation/ is where the Attestation Claims/Evidence is conveyed authentically (e.g. signed) by the Attester to the Verifier where a root-of-trust enumerates the Attestation Claims/Evidence associated with an execution environment. I would rephrase it in the following way: /Direct Attestation/ is when a verifier can be confident that some data originating from a client originates in practice from a secure device that has specific *functional and security* properties. The current definition for Explicit Attestation is: /Implicit Attestation/ is where the Attester conveys evidence of the availability of an authenticating credential that allows the Verifier to infer the Attestation Claims/Evidence associated with an execution environment. The Verifier knows that the availability of the authenticating credential is bound to certain Attestation Claims/Evidence. Inferred knowledge may further be conveyed as Attestation Evidence by a Trusted Third Party via a credential certificate or other out-of-band method. It is quite hard to understand the concept since three sentences are being used. Let me attempt to define a different but, maybe, close concept: /Inferred Attestation/is when a Trusted Third Party (TTP) testifies to a verifier that some data originating from a client originated in practice from a secure device that has specific functional and security properties. Denis > Hi all, > > we pushed an initial document to the RATS github in order to focus the > discussion about remote attestation procedures a bit. > >> https://github.com/ietf-rats/charter/blob/master/ietf-rats-charter.md > > We included a background section to better highlight the meaning of > the term "attestation" in general. Hence, there is a trade-off between > clarity and conciseness, which is one of the things we would like to > get feedback about. > > Naturally, we are also very interested in feedback about the > illustrated difference between explicit attestation and implicit > attestation. > > Viele Grüße, > > Henk > > > > > > _______________________________________________ > EAT mailing list > EAT@ietf.org > https://www.ietf.org/mailman/listinfo/eat
- [EAT] Scope, Goals & Background for RATS Henk Birkholz
- Re: [EAT] Scope, Goals & Background for RATS Denis
- Re: [EAT] [Rats] Scope, Goals & Background for RA… Fuchs, Andreas
- Re: [EAT] Scope, Goals & Background for RATS Henk Birkholz
- Re: [EAT] Scope, Goals & Background for RATS Denis
- Re: [EAT] Scope, Goals & Background for RATS Carsten Bormann
- Re: [EAT] Scope, Goals & Background for RATS Michael Richardson
- Re: [EAT] Scope, Goals & Background for RATS Michael Richardson
- Re: [EAT] Scope, Goals & Background for RATS Eric Voit (evoit)
- Re: [EAT] Scope, Goals & Background for RATS Carsten Bormann
- Re: [EAT] Scope, Goals & Background for RATS Melinda Shore
- Re: [EAT] Scope, Goals & Background for RATS Smith, Ned
- Re: [EAT] Scope, Goals & Background for RATS Laurence Lundblade
- [EAT] Implicit vs Explicit Attestation (was Re: S… Laurence Lundblade
- Re: [EAT] Scope, Goals & Background for RATS Diego R. Lopez
- [EAT] Terminology definitions (was Re: Scope, Goa… Laurence Lundblade
- Re: [EAT] Terminology definitions (was Re: Scope,… Henk Birkholz
- Re: [EAT] Implicit vs Explicit Attestation (was R… Henk Birkholz
- Re: [EAT] Scope, Goals & Background for RATS Henk Birkholz
- Re: [EAT] [Rats] Terminology definitions (was Re:… Smith, Ned
- Re: [EAT] Scope, Goals & Background for RATS Laurence Lundblade
- Re: [EAT] Scope, Goals & Background for RATS Henk Birkholz
- Re: [EAT] Scope, Goals & Background for RATS Diego R. Lopez
- Re: [EAT] Implicit vs Explicit Attestation (was R… Laurence Lundblade
- Re: [EAT] [Rats] Implicit vs Explicit Attestation… Fuchs, Andreas
- Re: [EAT] Implicit vs Explicit Attestation (was R… Henk Birkholz
- Re: [EAT] [Rats] Implicit vs Explicit Attestation… Laurence Lundblade
- Re: [EAT] [Rats] Implicit vs Explicit Attestation… Wheeler, David M
- Re: [EAT] Implicit vs Explicit Attestation (was R… Laurence Lundblade
- Re: [EAT] [Rats] Implicit vs Explicit Attestation… Smith, Ned
- [EAT] Naming (was Re: Scope, Goals & Background f… Laurence Lundblade
- [EAT] EAT additions to Charter (was Re: Scope, Go… Laurence Lundblade
- Re: [EAT] EAT additions to Charter (was Re: Scope… Suresh Marisetty
- Re: [EAT] Naming (was Re: Scope, Goals & Backgrou… Diego R. Lopez
- Re: [EAT] EAT additions to Charter (was Re: Scope… Carl Wallace
- Re: [EAT] Naming (was Re: Scope, Goals & Backgrou… Laurence Lundblade