Rifaat & Hannes,
Hereafter are my comments:
The introduction states :
Recipients of such tokens are then able to verify the binding of
the token to the key pair thatthe client has demonstrated
that it holds via the DPoP header, thereby providing some
assurance that the client presenting the token also possesses the
private key.
In other words, the legitimate presenter of the token is
constrained to be the sender that holds and can prove possession of the
private part of the key pair.
The client presenting the token *does not necessarily possess the
private key*. The client presenting the token has been able to use
the results of some cryptographic functions using the private part of
the key pair.
These results may be communicated by one client to another client, if
the two clients agree to collaborate. This statement will be added later on.
Proposed rewording:
Recipients of such tokens are then able to verify the binding of
the token to the key pair thatthe client has demonstrated
that it holds via the DPoP header, thereby providing some
assurance that the client presenting the token *either *also possesses
the private key *or* has been able to use the result of
cryptographic computations from another client that possesses the
private key.
In other words, the presenter of the token can prove that it has
been able to use the results of cryptographic computations performed
by using the private part of the key pair.
The objectives states
The primary aim of DPoP is to prevent unauthorized or
illegitimate parties from using leaked or stolen access tokens,
by binding a token to a public key upon issuance and requiring
that the client proves possession of the corresponding
private key when using the token.
DPoP does not prevent unauthorized or illegitimate parties from using
access tokens, as soon as two clients agree to collaborate.
Proposed rewording:
The primary aim of DPoP is to bind a token to a public key upon
issuance and requiring that the client proves possession
of the corresponding private key when using the token.This does
not demonstrate that the client presenting the token is
necessarily the legitimate client. In the case of
non-collaborating clients, DPoP prevents unauthorized or illegitimate
parties
from using leaked or stolen access tokens. In the case of
collaborating clients, the security of DPoP is ineffective
(see section 11.X).
Section 11 is about "Security Considerations" and addresses the
following topics:
11.1.DPoP Proof Replay
11.2.DPoP Proof Pre-Generation
11.3.DPoP Nonce Downgrade
11.4.Untrusted Code in the Client Context
11.5.Signed JWT Swapping
11.6.Signature Algorithms
11.7.Message Integrity
11.8.Access Token and Public Key Binding
11.9.Authorization Code and Public Key Binding
The case of collaborative clients should be addressed within section 11.
Text proposal.
11.X. Collaborative clients
DPoP demonstrates that the client presenting the token has
been able to use the results of some cryptographic functions
using the private part of the key pair.
If a client agrees to collaborate with another client, the security of
DPoP is no longer effective.When two clients agree to collaborate,
these results of the cryptographic computations performed by one client
may be communicated to another client.
Even if the private key used for DPoP is stored in such a way that it
cannot be exported, e.g., in a hardware or software security module,
the client can perform all the cryptographic computations needed by the
other client to create DPoP proofs.
The client can easily create new DPoP proofs as long as the other client
is online.
Note: There exist other techniques able to limit, in some cases, the use
of a token transmitted voluntarily by a legitimate client
to an illegitimate client.
Denis
All,
As discussed during the IETF meeting in *Vienna* last week, this is a
*WG Last Call *for the *DPoP* document:
https://datatracker.ietf.org/doc/draft-ietf-oauth-dpop/
Please, provide your feedback on the mailing list by April 11th.
Regards,
Rifaat & Hannes
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