## Overview ##

After a response goal has been generated, goal modelling continues until one or more countermeasure requirements have been defined and associated with their parent goals. Following this, a countermeasure can be defined. Defining a countermeasure also has the effect of satisfying a response goal and resolving any obstacles associated with the underlying risk’s threat or vulnerability.

Countermeasures target a risk’s threat, vulnerability, or both. Countermeasures also have a level of effectiveness. This effectiveness level determines how much the countermeasure reduces the likelihood of the associated threat, or severity of the associated vulnerability.

Countermeasures are associated with roles, who may be responsible for developing, maintaining or using the countermeasure. Consequently, countermeasures are also associated with tasks and, when defining a countermeasure, it is also necessary to indicate how much the countermeasure helps or hinders the properties of associated tasks.

Adding, updating, and deleting a countermeasure



Generating countermeasure assets and security patterns

By right clicking on a countermeasure in the Countermeasures window, an associated asset can be generated. If defined, this will retain the same security properties associated with the countermeasure. The asset will be situated in whatever environments the countermeasure was situated in. In the asset model, a << safeguard >> association is added between the countermeasure asset and any assets threatened or exposed by the risk the countermeasure helps mitigate.

Assets can be generated directly based on the countermeasure properties, or on the basis of a pre-existing template asset. It is also possible to situate security patterns based on a countermeasure, rather than an asset. To do this, select Situate Pattern from the speed menu, select the security patten, followed by the countermeasure environments to situate the pattern assets in.

Security Patterns can be imported into the tool by using the Import/Import Security Patterns option, and selecting the XML based patterns catalogue to import. An example catalogue file, schumacher.xml, which incorporates a number of patterns from the Security Patterns text book by Schumacher et al is included in the cairis/sql directory.

Associating countermeasures with pre-existing patterns

By right clicking on a countermeasure in the Countermeasures window, you can also associate a countermeasure with a pre-existing security pattern by selecting the ‘Associate with situated Countermeasure Pattern’ option. However, a list of possible security patterns to choose from will only be displayed if the components of the security pattern are present in ALL of the environments the countermeasure is situated for.

Weaking the effectiveness of countermeasures

Countermeasures mitigate risks by targetting its risk elements, i.e. its threats or vulnerabilities. However, when one or more assets are generated from these countermeasures, several factors may weaken the effect of the countermeasure.

First, situating assets may cause you to look at the environments where the assets are situated in a different light. Changing properties of assets, or existing threats or vulnerabilities could increase the potency of the risk, thereby weakening the effect of the countermeasure.

Existing threats or vulnerabilities can also explicitly weaken countermeasures. If a countermeasure asset is associated with a threat or vulnerability then, when either artifact is created or modified, CAIRIS allows users to override the effectiveness of the related countermeasure. The detail associated with the risk scores in the Risk Dialog box will indicate cases where countermeasures have been weakened by threats and/or vulnerabilities.

Mitigating weakening effects

If a countermeasure is weakened, the weakness by removed by generating a new countermeasure which targets the weakening threat or vulnerability. If this is carried out, the detail associated with the risk score in the Risk Dialog box will indicate cases where, although the effectiveness score for the countermeasure holds, this is by virtue of a countermeasure targetting the weakening threat or vulnerability.

Countermeasures cannot, however, be simply defined on the fly. They arise as the result of rational risk analysis, so risks need to be defined based on the weakening threats or vulnerabilities.