[security] Nonrepudiation, and Trusting OpenID Providers

[Shearer, Charles Dylan]

Ben,

I use "nonrepudiation" according to its meaning: starting from the
reasonable assumption that a user has not compromised his/her own
secret/token (e.g., password, smart card), you can prove that it is very,
very probable that a given message was sent/signed by the user.

I'm not interested in any "legal" concept of nonrepudiation.  I am
interested in the inferences that a security technology allows the parties
involve to make.  For example, if I were the manager of a group of people
who access a sensitive system using, I would want the authentication system
to allow me to be very sure of who sent each message to the system.  Then I
could reasonably enforce this policy: "Protect your credentials, because I
will assume that messages signed by your private key are from you and will
revoke your privileges if I think you have behaved inappropriately."

Charles (Dylan)


On 12/9/09 8:24 AM, "Ben Laurie" <benl at google.com> wrote:

> On Tue, Dec 8, 2009 at 12:55 AM, David Recordon <recordond at gmail.com> wrote:
>> Hey Dylan,
>> Yes, this is correct but Google could also start sending email as me
>> or even fill in forgotten password pages and then login as me. :)
>> 
>> This is one thing which is known to be a challenge to see OpenID scale
>> into higher levels of assurance.  The ultimate answer for these sorts
>> of use cases is not only the user trusting their provider, but the
>> relying party having some form of trust in the provider as well.
> 
> That's only one ultimate answer. Another is for the user to sign stuff.
> 
> BTW, I wish people would not use nonrepudiation in this way - you can
> always repudiate a digital signature. Nonrepudiation is a legal term -
> it means that the law doesn't _care_ if you repudiate it.
> 
> 
>> 
>> --David
>> 
>> On Mon, Dec 7, 2009 at 4:47 PM, Shearer, Charles Dylan <cdsheare at nps.edu>
>> wrote:
>>> I have some concerns about OpenID, and I would like to see what those
>>> involved think about them.
>>> 
>>> It seems to me that, regardless of how OpenID is deployed, it is always
>>> possible for an OpenID provider itself to authenticate with a relying party
>>> as any user by forging a request to authenticate using the user¹s
>>> identifier.  This is because a relying party cannot tell the difference
>>> between a user attempting to log in using his or her identifier, and the
>>> user¹s OpenID provider spoofing that user to gain access to whatever
>>> services the relying party provides to that user.  This seems to require
>>> that both users and relying parties put a lot of trust in OpenID providers:
>>> for example, if I used my OpenID identifier for online banking and email, my
>>> OpenID provider could easily access my email and bank account.
>>> 
>>> Additionally, even if we assume that OpenID providers will not log into
>>> users¹ accounts, I still cannot see how OpenID could provide nonrepudiation
>>> regarding messages sent to a relying party by an authenticated user: for
>>> example, if I authenticate with my bank using my OpenID identifier and then
>>> use the bank¹s ³bill pay² service to pay a bill, there¹s no way the bank can
>>> prove that I ordered that payment because it is possible that someone
>>> working for my OpenID provider logged in as me and ordered it.
>>> 
>>> Does anyone disagree with my analysis?
>>> 
>>> Dylan
>>> _______________________________________________
>>> security mailing list
>>> security at lists.openid.net
>>> http://lists.openid.net/mailman/listinfo/openid-security
>>> 
>>> 
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