If you came across both the ISO 27001 and the ISO 27002, you probably noticed that ISO 27002 is much more detailed, much more precise – so, what’s the purpose of ISO 27001 then?

First of all, you cannot get certified against ISO 27002 because it is not a management standard. What does a management standard mean? It means that such a standard defines how to run a system, and in case of ISO 27001, it defines the information security management system (ISMS) – therefore, certification against ISO 27001 is possible.

This management system means that information security must be planned, implemented, monitored, reviewed, and improved. It means that management has its distinct responsibilities, that objectives must be set, measured and reviewed, that internal audits must be carried out and so on. All those elements are defined in ISO 27001, but not in ISO 27002.

The controls in ISO 27002 are named the same as in Annex A of ISO 27001 – for instance, in ISO 27002 control 6.1.6 is named Contact with authorities, while in ISO 27001 it is A.6.1.6 Contact with authorities. But, the difference is in the level of detail – on average, ISO 27002 explains one control on one whole page, while ISO 27001 dedicates only one sentence to each control.

Finally, the difference is that ISO 27002 does not make a distinction between controls applicable to a particular organization, and those which are not. On the other hand, ISO 27001 prescribes a risk assessment to be performed in order to identify for each control whether it is required to decrease the risks, and if it is, to which extent it should be applied.

The question is: why is it that those two standards exist separately, why haven’t they been merged, bringing together the positive sides of both standards? The answer is usability – if it was a single standard, it would be too complex and too large for practical use.

Every standard from the ISO 27000 series is designed with a certain focus – if you want to build the foundations of information security in your organization, and devise its framework, you should use ISO 27001; if you want to implement controls, you should use ISO 27002, if you want to carry out risk assessment and risk treatment, you should use ISO 27005 etc.

To conclude, one could say that without the details provided in ISO 27002, controls defined in Annex A of ISO 27001 could not be implemented; however, without the management framework from ISO 27001, ISO 27002 would remain just an isolated effort of a few information security enthusiasts, with no acceptance from the top management and therefore with no real impact on the organization.