ABAC access control for Fedd

The ​ABAC access control system, developed at Stanford and realized by a group in Trusted Information Systems that later moved to SPARTA, is a formal, flexible, scalable access control system based on formal derivation of user attributes, attested by other trusted users. We have been ​planning to integrate it into fedd for some time. We have recently implemented ABAC in a ​portable library and this implementation has been integrated into fedd. Under our associated TIED project, we have completed a similar ​integration with GENI's ​reference aggregate manager, part of their developing ​GENI API.

This page describes the use of ABAC with fedd, concentrating on using the transition tools to create initial ABAC credential stores from which to run fedd. In order to get the most from this page, you should be familiar with

• three-names and fedids
• ​The ABAC model as it is used by DETER.
  • There is a ​worked example that can be helpful here
• The existing fedd access databases

Storing Credentials

Users and servers (fedd instances) now both have credential stores to maintain. When using ABAC credentials to enforce the same kinds of access control as three-names neither users nor servers will see much change. Credentials will be managed transparently.

By default a user will maintain a credential store in a directory named .abac. Any credentials in the users abac directory will be passed as parameters when requests are made to fedd. The user can limit the credentials passed by specifying a directory with only a subset of the credentials.

Similarly, a running fedd instantiation will be configured to use a specific abac directory in which its credentials are kept. As the instance learns more credentials they are aslo stored in this directory.

Unlike a user, the fedd directory contains metadata beyond the credential lists. This directory is populated using the access_to__abac.py command for access controllers and the fedd_to_abac.py command for experiment controllers.

Operation of Experiment Controller

The experiment controller can operate in two modes, as an experiment controller dedicated to use by a single user, or as a service on behalf of multiple users. In the first case the controller acts as the same principal as the user commands. Essentially the experiment controller is a command run by the single user. In the second case a common piece of infrastructure acts as an experiment controller for many users. Because this fedd acts as a distinct principal, some additional delegation is required to make the access control reasonable.

When the experiment controller is run as a service, it acts as a separate principal for the purposes of experiment creation, and the user and the controller negotiate what principal the controller will act as when making resource allocations from access controllers. This allows a user to delegate a subset of attributes to the experiment principal and then allow the experiment controller to act as that principal. (The experiment principal may have attributes delegated by multiple principals, if needed). This extra principal is required to prevent the experiment controller from combining rights from multiple principals that did not intend it. The figure below shows this:

When a user is running an experiment controller on their own behalf, like a utility program, the situation is much simpler. Both experiment controller operations and experiment allocations are simply carried out as the user. The user's fedid is specified for both the experiment controller's ID and the experiment ID, leading to the simpler situation below:

Expressing Three-names as ABAC credentials

Three-names are really an encoding of a fairly small attribute space used by access controllers to control which fedids can perform operations and how to map authorized fedids into the local identifier space. Experiment controllers assert the attributes.

The attributes an experiment controller asserts are given in its access database in lines of the form:

fedid:xxx -> (proj1, user1)

That line asserts that this controller will assert that a user with fedid of xxx is in project proj1 and is user user1. This encodes in ABAC (using the RT0 syntax supported by ​libabac as:

ec_fedid.user_user1 <- fedid:xxx
ec_fedid.project_proj1 <- fedid:xxx

ec_fedid is the fedid of the experiment controller. The fedd_to_abac.py script converts an experiment controller's access DB to an ABAC credential store with those credentials, encoded as X.509 attribute certificates.

The access controller uses three-names to both make the access control decision (does a requester have the right to make this call) and a mapping of the fedid into the user access space. For example a line like:

(ec_fedid, proj1, user1) -> create, (DETER, faber, faber)

says that a user with a project of proj1 and a user of {{user1}} attested by the controller with fedid ec_fedid can create experiments as local user faber on the local DETER project. The ABAC credentials for the access control decision look like:

ac_fedid.project_proj1_user_user1 <- ec_fedid.project_proj1 & ec_fedid.user_user1
ac_fedid.create <- ac_fedid.project_proj1_user_user1

The first rule names the conjunction of two experiment controller attributes and the second line maps that to a local create attribute. The first attibute is used to map to local credentials.

The mapping to local credentials is accomplished by a