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Pairwise Agreement

Two institutions want to trust identities issued by one another, but there is no outside governance or policy framework for them to do so.  They negotiate a specific agreement that covers only the two of them. Each institution trusts the other to properly manage the identities that it issues.

Examples: A pairwise agreement can specify governance, security and verification policies, or specific technical methods.

Businesses might negotiate pairwise agreements with large supplier. Educational institutions may craft specific research agreements.

When to Use: Business or institutional partners want to grant one another access to confidential systems or information, but no standard contracts or umbrella organizations exist.

Advantages: Organizations can grant one another access to scarce resources and confidential information.  Highly customized for the specific situation and participants.

Disadvantages: Time consuming and complex to negotiate, expensive.  Difficult to scale.

Ability to Scale: Pairwise federations do not scale well, because each additional party will need to make a custom agreement with every other party.

Three Party Model

Three Party Model

A trusted third party provides identities to both the requester and service provider. In order to interact with one another, both must agree to trust the same identity provider.

Examples: Google, Facebook, American Express, Paypal, Amazon, iTunes App Store

 

There are two broad types of Three Party Model. If one (or both) of the parties insists on a particular identity provider, we refer to it as a Winner Take All network because other identity providers are locked out. If only technical methods are specified and the requester is free to specify any identity provider they like, we refer to it as a Bring Your Own Identity network.

When to Use: An identity provider may choose to offer a three party model when it can provide identities more efficiently than the requester or service provider can on their own.  Requesters and service providers may choose to implement a three party network for access to an existing market.

Advantages: Separates identity management from the service being provided. In cases where a shared third party is available, this model simplifies the process of exchanging trusted identities.  Malicious actors can be identified and isolated from the entire network.  Requesters can use a single identity with many service providers, and service providers can trust requesters without having to verify each one.

Disadvantages: Because participants can only interact if they have been authenticated by a single identity provider, that provider wields substantial power.  The identity provider effectively controls the requester’s ability to use services and the services’ ability to work with requesters.

For instance, a requester who loses their account with the identity provider also loses all of the services where they used that identity. If you use your Facebook to sign in to other products then you also lose those other products if your Facebook account is closed.

Ability to Scale: Very difficult to get started because a three party network is not interesting to service providers until it has users, but only attracts users if it has interesting services.  Once they are established and functioning, however, a successful three party network can grow extremely large.

 

Bring Your Own Identity

A special case of the three party model where the service provider specifies the technical methods that it will accept, but allows the requester to choose any identity service they like.  The service provider does not set details for identity verification or authentication and simply assumes that the requester has chosen one that’s good enough for their purposes. The service provider and requester agree to terms, the requester and the identity provider agree to terms, but the service provider does not make any agreement with the identity provider.

Examples: The most common Bring Your Own Identity technologies are SAML, OpenID, and email address verification.

When to Use: The service provider does not want to bear the cost of managing the requester’s identity, or wants to simplify account creation and sign-in.

Advantages: The requester can use an existing identity rather than having to create a new one for this service. If the requester chooses a good identity provider, the service gets the benefit of higher security with no additional cost.

Disadvantages: The account is only as secure as the authenticating service. The service provider depends on the user to select a trustworthy identity service.

Designing a user interface that allows the user to specify an identity provider has proved to be difficult.  Consumers don’t generally have the experience to know a good identity provider from a bad one so, in practice, they depend upon seeing a familiar brand. When OpenID was first introduced, supporting sites attempted to help by listing a large set of brands so that the user could choose a familiar one. The resulting products ended up so festooned with logos that they were likened to NASCAR cars, and ended up being more confusing than helpful.

Ability to Scale: Very high.

 

Winner Take All

“Winner Take All” Three Party Model

A special case of the three party model where the service provider wants to allow the requester to use an existing identity, but only accepts authentication from a defined set of providers. Participants sign an agreement with the identity provider, which also allows them to talk to one another.

Examples: Apple completely controls the channel between app vendors and iPhone users, deciding which applications are available and which users are allowed to use them. Spotify and Zynga games depend upon Facebook for authentication.

When to Use: The service provider wants to take part in a large, established channel, or requires a high level of assurance.

Advantages: The requester can use an existing identity, which lowers the amount of effort required to use a new service. The service provider gets access to the users of an identity network without having to manage the accounts itself. Some identity providers offer higher security than the service could practically provide on its own.

Large three-party model identity providers like Facebook, Google, and PayPal dedicate substantial resources to security.

Disadvantages: Because participants can only interact if they have been authenticated by a single identity provider, that provider wields substantial power.  The identity provider effectively controls the requester’s ability to use other company’s products. For instance, a requester who loses their account with the identity provider also loses all of the services where they used that identity. If you use your Facebook to sign in to other products then you also lose those other products if your Facebook account is closed.

Conversely, a service provider that depends on a single third party identity provider leaves themselves open to the third party deciding to change its terms.

Ability to Scale: Difficult to get started because it is only interesting to service providers when it has consumers, but only interesting to consumers if it can offer interesting services.  Once they are established and functioning, however, a successful identity provider can build  a very large network.