[Openid-specs-ab] Defining a Hardened (Mix-up and Cut-and-Paste Proof) OpenID Connect Profile

Hans Zandbelt hzandbelt at pingidentity.com
Tue Apr 12 19:50:14 UTC 2016

from an implementers/deployment standpoint I would argue that if the 
id_token is delivered in the front channel, I may just as well get the 
access token from there too rather than having to deal with the overhead 
of calling the token endpoint, esp. since at_hash is there to protect 

so I'd favor response_mode=form_post, response_type="id_token token" 
over hybrid

I realize that this doesn't leverage the possibility of using a client 
secret to get the access token but it doesn't really seem to matter 
security-wise at this point as the id_token was delivered without 
leveraging it as well

anything wrong with that line of reasoning?


On 4/12/16 9:23 PM, William Denniss wrote:
> Good point.
> Regarding the OP tests, the following are relevant to mitigate the
> cut-and-paste and mix-up attacks:
>  1. ID Token has nonce when requested for code flow [Basic] (OP-nonce-code)
>  2. Request with response_mode=form_post [Extra] (OP-Response-form_post)
> 1) is important for preventing cut-and-paste (the id token needs to
> contain the 'nonce')
> 2) is important for preventing mix-up as it means the redirect endpoint
> gets the id_token on the response at the server, as opposed to in the
> URI fragment.
> Unfortunately, form_post is optional for OPs, and sending the nonce on
> the code flow is optional for RPs (though fortunately to it is
> compulsory for OPs to support thanks to OP-nonce-code).
> We could add an hardened OP test for:
> – Forcing nonce to be present on the code flow
> We should definitely have RP tests for:
> – sending and validating nonce on the code flow
> – validating the c_hash, iss, aud on the hybrid flow
> How we would profile these tests I'm not sure; would they go in the
> Basic testing profile, or in a new Hardened one?  We could move
> OP-Response-form_post to the Basic profile if we wanted to be
> opinionated, or define a new profile.
> The good news is that supporting the features required to mitigate
> mix-up & cut-and-paste is not all that hard to do in Connect.
> On Tue, Apr 12, 2016 at 10:46 AM, Nick Roy <nroy at internet2.edu
> <mailto:nroy at internet2.edu>> wrote:
>     Would it be possible to check for the secure behavior in Roland's
>     test suite and either not certify non-mitigating implementations, or
>     offer a risk mitigation add-on cert for those that do the right thing?
>     Nick
>     From: Openid-specs-ab <openid-specs-ab-bounces at lists.openid.net
>     <mailto:openid-specs-ab-bounces at lists.openid.net>> on behalf of
>     William Denniss <wdenniss at google.com <mailto:wdenniss at google.com>>
>     Date: Tuesday, April 12, 2016 at 11:01 AM
>     To: "openid-specs-ab at lists.openid.net
>     <mailto:openid-specs-ab at lists.openid.net>"
>     <openid-specs-ab at lists.openid.net
>     <mailto:openid-specs-ab at lists.openid.net>>
>     Subject: [Openid-specs-ab] Defining a Hardened (Mix-up and
>     Cut-and-Paste Proof) OpenID Connect Profile
>     One item that came out of the discussions on the sidelines of IETF95
>     with folk from this WG (specifically Nat, Mike, John, Brian and
>     myself) was the need for the Connect community to respond to the
>     recently <http://arxiv.org/abs/1508.04324v2/> documented
>     <http://arxiv.org/abs/1601.01229v2/> security threats.
>     Connect is actually in a much stronger place for mitigating these
>     attacks (as noted in the papers themselves) than pure OAuth, with
>     the id_token offering a cryptographic binding of the code to the
>     issuer, audience and session identifier (nonce).
>     However, certain steps need to be followed, for example using
>     'nonce' with the code flow (which is optional to implement for
>     clients) to protect against cut-and-paste, and using the form-post
>     response type with the hybrid flow to verify that the code was
>     issued by the expected IdP, to ensure the code is exchanged at the
>     correct token endpoint (mitigating mix-up).
>     We discussed last week creating a profile of Connect that recommends
>     those practices to mitigate these classes of attack as a response to
>     the security researchers' findings. I wanted to share that
>     suggestion with the list, and continue the conversation.
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Hans Zandbelt              | Sr. Technical Architect
hzandbelt at pingidentity.com | Ping Identity

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