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# 5. Access Control

The previous sections described how transport security is achieved with the OpenSplice Secure Networking Module. This section explains how access control is realized in OpenSplice and gives a short introduction to the underlying concepts.

## 5.1. Overview

The OpenSplice Access Control Module is an optional, pluggable service to the OpenSplice Secure Networking Module. It complements the Secure Networking Module by offering different types of access control modules that may be flexibly plugged in (for example, mandatory access control, role-based access control, etc.).

OpenSplice currently supports Mandatory Access Control (MAC) based on the Bell-LaPadula/Biba model. Other Access Control Modules may be available in a future release.

Access Control can be enabled in the OpenSplice secure networking configuration (see Secure Networking Configuration ). An external file containing the policy rules in XML format can be referenced.

The following section, Mandatory Access Control, introduces mandatory access control. MAC in OpenSplice explains how Mandatory access control is realized in OpenSplice.

## 5.2. Mandatory Access Control

An access control policy defines whether a user (referred to as a subject) is allowed to access an object.

The access control policy is centrally controlled when Mandatory Access Control is in force. Users (subjects) may not override the policy. For example when Mandatory Access Control is in force users may not grant access to objects that would otherwise be restricted.

Mandatory Access Control in OpenSplice ensures data confidentiality as well as data integrity: data may only be created and accessed by authorized parties. The control of information flow is based on the Bell-LaPadula model. This ensures that the information received via the network can only be retrieved on nodes that:

- are accredited for the secrecy level of this information, and
- contain applications that have a need-to-know for the information.

Additionally, care is taken to preserve data integrity (based on the Biba model) by:

- preventing data modification by unauthorized parties
- preventing unauthorized data modification by authorized parties
- maintaining internal and external consistency

The following sections give a short introduction to the Bell-LaPadula and Biba models. MAC in OpenSplice explains how mandatory access control is realized in OpenSplice.

### 5.2.1. Bell-LaPadula Confidentiality Model

The Bell-LaPadula Confidentiality model describes a set of access control rules which use clearances for subjects (the users) and classifications on objects (resources). The clearance for a user and a classification of an object define a secrecy level and a set of compartments. Secrecy levels are hierarchical and range from the least sensitive, for example “Unclassified” or “Public”, to the most sensitive, for example “Top Secret”.

Compartments are a non-hierarchical list of ID’s (strings) structuring information to enforce the ‘need-to-know’ principle.

The clearance of the subject is compared to the classification of the object in order to determine if a subject is authorized to access a certain object. The Bell-LaPadula model defines two mandatory access control rules:

- a subject at a given secrecy level may not read an object at a higher secrecy level (no read-up).
- a subject at a given secrecy level must not write to any object at a lower secrecy level (no write-down).

In the Bell-LaPadula model, users can create content only at or above their own secrecy level. For example, secret researchers can create “Secret” or “Top-Secret” files, but may not create “Public” files (no write-down). On the other hand, users can view content only at or below their own secrecy level. For example, secret researchers can view “Public” or “Secret” files, but may not view “Top-Secret” files (no read-up).

Additionally, a subject must have a ‘need-to-know’ for the object it wants to access; in other words, the set of compartments contained in the user’s clearance must be a subset of the set of compartments contained in the object’s classification.

### 5.2.2. Biba Integrity Model

The Biba Integrity Model describes a set of access control rules designed to ensure data integrity. Resources (objects) and users (subjects) are grouped into ordered levels of integrity.

The Biba model defines two mandatory access control rules:

- a subject at a given level of integrity may not read an object at a lower integrity level (no read down).
- a subject at a given level of integrity must not write to any object at a higher level of integrity (no write up).

In the Biba model, users can only create content at or below their own integrity level (no write up). On the other hand, users can only view content at or above their own integrity level (no read down).

## 5.3. Access Control in OpenSplice

In OpenSplice, access control is enforced on the network-level for inter-node communication, in other words, the communication between different nodes. One node (host) corresponds to one user. When running multiple DDS applications on one host these will all run under the same User ID.

There are two access control enforcement points:

- for inbound traffic: when reading data from the network, the following checks are carried out:
  - is the reader allowed to receive the data,
  - was the data published by a trusted node (in other words, was the sender allowed to send the data)
- for outbound traffic: when writing data to the network, the following check is carried out:
  - is the user allowed to write data to the network

Note that access control is not enforced for intra-node communication, in other words communication between DDS applications running on the same node.

### 5.3.1. Objects to be Protected

One access control policy applies to one DDS Domain. The objects to be protected by the access control policy in OpenSplice apply to DDS topics and DDS partitions.

For example, a classification can be attached to a topic. This may result in restricting access in a way that only users with a matching clearance may use this topic for publication of data or for subscription to data of this topic, respectively. The same applies to partitions which are referenced by a resource element of the access control policy.

### 5.3.2. Secure vs. Insecure

The ‘secure’ world is strictly separated from the ‘insecure’ world in OpenSplice. If a resource does not have access control information (for example a classification), then no access control will be enforced for this resource. If a user has no access control information (for example a clearance) they may only access ‘insecure’ resources (resources that do not have access control information like a classification). If a user has access control information, then they may not access ‘insecure’ resources that don’t have access control information.

### 5.3.3. User Authentication

The system authenticates the user’s identity.

OpenSplice currently supports SSL X.509 Certificate Authentication. Other authentication mechanisms (such as user ID - password authentication) may be available in a future release.

X.509 is a standard for digital certificates used by SSL. Certificates include, among other things, information about the identity of the certificate holder (in other words: the user). The user authenticates to the system presenting a certificate. The system accepts the user’s certificate if it was issued by a trusted authority. A list of trusted certificates can be defined in the secure networking configuration (see Element X509Authentication and Element TrustedCertificates.

The user’s identity is determined by a distinguished name (DN) contained in the user’s certificate. The system retrieves the corresponding user from the access control policy (each user entry in the policy defines the subject’s DN) and applies the defined access control information to this user.

## 5.4. MAC in OpenSplice

Mandatory Access Control (MAC) in Open Splice combines the Bell-LaPadula and Biba models to ensure confidentiality and data integrity. Each resource (object) has a classification which comprises a secrecy level, an integrity level and a set of compartments that this resource is intended for. Each user (subject) has a clearance which comprises a secrecy level, an integrity level and a set of compartments this user has a ‘need-to-know’ for.

In order to determine if a user is authorized to access a certain resource, in other words, if they can publish a certain topic or subscribe to a topic, the clearance of the user is compared to the classification of the resource. This process comprises the evaluation of the:

- secrecy level
  - subscribing is permitted if the resource’s secrecy level is identical or lower than the user’s secrecy level
  - publishing is permitted if the resource’s secrecy level is identical or higher than the user’s secrecy level
- integrity level
  - subscribing is permitted if the resource’s integrity level is identical or higher
  - publishing is permitted if the resource’s integrity level is identical or lower
- need to know (compartment)
  - publish/subscribe is permitted if the user’s set of compartments is a subset of the resource’s set of compartments

Access is only granted if all three parts of the user’s clearance (secrecy level, integrity level, and need-to-know) are evaluated positively against the resource’s classification.

The following section, Access Control Configuration describes access control policy configuration elements for MAC in OpenSplice.

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