Using Digital Credentials on The World-Wide Web

While looking for references on Automated Trust Negotiation, I found this paper: M. Winslett, N. Ching, V. Jones, I. Slepchin, “Using digital credentials on the World Wide Web”, Journal of Computer Security, 1997.

The concepts and solutions proposed by this paper, more than ten years ago, have lots of similarities with more recent proposals, such as the Identity Metasystem and related specifications.

1. Access control based on properties of the requestor

“…we have been investigating the use of digital credentials, which may be thought of as on-line analogues to the paper credentials that people carry in their wallets. (…). These credentials can be issued (typically online) by the same kinds of authorities as issue paper credentials today: voter registrars, driver’s license facilities, schools, employers, hospitals, etc. The credentials can be submitted along with a request for service to prove that the client has the particular properties required by the service provider of its clients. Using modern encryption technology, digital credentials can be made unforgeable and verifiable

Winslett et. al propose this credential-based approach in opposition to the classical identity-based approach

Traditionally, it has been thought that authentication facilities provide the answer to this problem. Authentication allows a service to verify the identity of a client,(…). But knowing the identity of a client is not enough to ensure that the client is over 21 or does not live in Texas – in fact, the client’s exact identity is irrelevant in these cases, and the client might be reluctant to divulge its identity for privacy reasons.

The Identity Metasystem extends the definition of identity to incorporate these properties, renamed as claims:

In the Metasystem, digital identities consist of sets of claims made about the subject of the identity, where “claims” are pieces of information about the subject that the issuer asserts are valid. This parallels identities used in the real world. For example, the claims on a driver’s license might include the issuing state, the driver’s license number, name, address, sex, birth date, organ donor status, signature, and photograph, the types of vehicles the subject is eligible to drive, and restrictions on driving rights

In the proposal by Winslett et al., properties are transported inside unforgeable and verifiable credentials, such as X.509 certificates. In the Identity Metasystem, this role is played by security tokens, such as SAML assertions, which can be signed (unforgeable) and have cryptographic subject confirmation methods (verifiable).

2. Policies describing credentials requirements

In Winslett et. al.:

The applications running at Web servers (…) must have policies on which credentials are required for which services. (…) In addition, servers must have a means of communicating their policies to clients, so that clients can obtain and attach appropriate credentials to requests.

In the Identity Metasystem:

Format and claims negotiations between participants are conducted using WS-MetadataExchange (…) and WS-SecurityPolicy (…)

3. Client side security agent

In Winslett et. al.:

The central task of the personal security assistant (PSA) is to manage a client’s credentials in accordance with the stated policies of the client. The PSA helps the client obtain credentials, stores them locally, attaches them to service requests in accordance with the policies established by the client, determines what credentials are needed for a particular service request, and communicates as needed with the client while carrying out its assigned tasks.

In the Identity Metasystem, this role is played by the Identity Selector

The Identity Metasystem employs software on each platform that lets users choose an identity from among their portfolio of identities to use for each authentication. This software is called the Identity Selector, and is invoked each time the user needs to make a choice of identities.




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