Common Criteria

The Common Criteria for Information Technology Security Evaluation (referred to as Common Criteria or CC) is an international standard (ISO/IEC 15408) for computer security certification. It is currently in version 3.1 revision 5.

Common Criteria is a framework in which computer system users can ''specify'' their security ''functional'' and ''assurance'' requirements (SFRs and SARs respectively) in a Security Target (ST), and may be taken from Protection Profiles (PPs). Vendors can then ''implement '' or make claims about the security attributes of their products, and testing laboratories can ''evaluate'' the products to determine if they actually meet the claims. In other words, Common Criteria provides assurance that the process of specification, implementation and evaluation of a computer security product has been conducted in a rigorous and standard and repeatable manner at a level that is commensurate with the target environment for use. Common Criteria maintains a list of certified products, including operating systems, access control systems, databases, and key management systems.

Key concepts

Common Criteria evaluations are performed on computer security products and systems.

* Target of Evaluation (TOE) – the product or system that is the subject of the evaluation. The evaluation serves to validate claims made about the target. To be of practical use, the evaluation must verify the target's security features. This is done through the following:
** Protection Profile (PP) – a document, typically created by a user or user community, which identifies security requirements for a class of security devices (for example, smart cards used to provide digital signatures, or network firewalls) relevant to that user for a particular purpose. Product vendors can choose to implement products that comply with one or more PPs, and have their products evaluated against those PPs. In such a case, a PP may serve as a template for the product's ST (Security Target, as defined below), or the authors of the ST will at least ensure that all requirements in relevant PPs also appear in the target's ST document. Customers looking for particular types of products can focus on those certified against the PP that meets their requirements.
** Security Target (ST) – the document that identifies the security ''properties'' of the target of evaluation. The ST may claim conformance with one or more PPs. The TOE is evaluated against the SFRs (Security Functional Requirements. Again, see below) established in its ST, no more and no less. This allows vendors to tailor the evaluation to accurately match the intended capabilities of their product. This means that a network firewall does not have to meet the same functional requirements as a database management system, and that different firewalls may in fact be evaluated against completely different lists of requirements. The ST is usually published so that potential customers may determine the specific security features that have been certified by the evaluation.
** Security Functional Requirements (SFRs) – specify individual security functions which may be provided by a product. The Common Criteria presents a standard catalogue of such functions. For example, a SFR may state how a user acting a particular role might be authenticated. The list of SFRs can vary from one evaluation to the next, even if two targets are the same type of product. Although Common Criteria does not prescribe any SFRs to be included in an ST, it identifies dependencies where the correct operation of one function (such as the ability to limit access according to roles) is dependent on another (such as the ability to identify individual roles).

The evaluation process also tries to establish the level of confidence that may be placed in the product's security features through quality assurance processes:

* Security Assurance Requirements (SARs) – descriptions of the measures taken during development and evaluation of the product to assure compliance with the claimed security functionality. For example, an evaluation may require that all source code is kept in a change management system, or that full functional testing is performed. The Common Criteria provides a catalogue of these, and the requirements may vary from one evaluation to the next. The requirements for particular targets or types of products are documented in the ST and PP, respectively.
* Evaluation Assurance Level (EAL) – the numerical rating describing the depth and rigor of an evaluation. Each EAL corresponds to a package of security assurance requirements (SARs, see above) which covers the complete development of a product, with a given level of strictness. Common Criteria lists seven levels, with EAL 1 being the most basic (and therefore cheapest to implement and evaluate) and EAL 7 being the most stringent (and most expensive). Normally, an ST or PP author will not select assurance requirements individually but choose one of these packages, possibly 'augmenting' requirements in a few areas with requirements from a higher level. Higher EALs ''do not'' necessarily imply "better security", they only mean that the claimed security assurance of the TOE has been more extensively verified.

So far, most PPs and most evaluated STs/certified products have been for IT components (e.g., firewalls, operating systems, smart cards).
Common Criteria certification is sometimes specified for IT procurement. Other standards containing, e.g., interoperation, system management, user training, supplement CC and other product standards. Examples include the ISO/IEC 27002 and the German IT baseline protection.

Details of cryptographic implementation within the TOE are outside the scope of the CC. Instead, national standards, like FIPS 140-2, give the specifications for cryptographic modules, and various standards specify the cryptographic algorithms in use.

More recently, PP authors are including cryptographic requirements for CC evaluations that would typically be covered by FIPS 140-2 evaluations, broadening the bounds of the CC through scheme-specific interpretations.

Some national evaluation schemes are phasing out EAL-based evaluations and only accept products for evaluation that claim strict conformance with an approved PP. The United States currently only allows PP-based evaluations. Canada is in the process of phasing out EAL-based evaluations.

History

CC originated out of three standards:

* ITSEC – The European standard, developed in the early 1990s by France, Germany, the Netherlands and the UK. It too was a unification of earlier work, such as the two UK approaches (the CESG UK Evaluation Scheme aimed at the defence/intelligence market and the DTI Green Book aimed at commercial use), and was adopted by some other countries, e.g. Australia.
* CTCPEC – The Canadian standard followed from the US DoD standard, but avoided several problems and was used jointly by evaluators from both the U.S. and Canada. The CTCPEC standard was first published in May 1993.
* TCSEC – The United States Department of Defense DoD 5200.28 Std, called the Orange Book and parts of the Rainbow Series. The Orange Book originated from Computer Security work including the Anderson Report, done by the National Security Agency and the National Bureau of Standards (the NBS eventually became NIST) in the late 1970s and early 1980s. The central thesis of the Orange Book follows from the work done by Dave Bell and Len LaPadula for a set of protection mechanisms.

CC was produced by unifying these pre-existing standards, predominantly so that companies selling computer products for the government market (mainly for Defence or Intelligence use) would only need to have them evaluated against one set of standards. The CC was developed by the governments of Canada, France, Germany, the Netherlands, the UK, and the U.S.

Testing organizations

All testing laboratories must comply with ISO/IEC 17025, and certification bodies will normally be approved against ISO/IEC 17065.

The compliance with ISO/IEC 17025 is typically demonstrated to a National approval authority:
* In Canada, the Standards Council of Canada (SCC) under Program for the Accreditation of Laboratories (PALCAN) accredits Common Criteria Evaluation Facilities (CCEF)
* In France, the (COFRAC) accredits Common Criteria evaluation facilities, commonly called (CESTI). Evaluations are done according to norms and standards specified by the Agence nationale de la sécurité des systèmes d'information

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