Common Criteria (ISO/IEC 15408): evaluating products against the claims they choose

Common Criteria grew out of three national evaluation schemes: the US 'Orange Book' (TCSEC), Europe's ITSEC, and Canada's CTCPEC. Their sponsors merged them in the 1990s so a vendor could be evaluated once rather than three times, and the result was adopted internationally as ISO/IEC 15408 in 1999. The evaluation methodology that labs follow is its companion, ISO/IEC 18045 (the CEM).

The defining difference from FIPS 140-3 is that Common Criteria has no single list of requirements every product must meet. It is a catalog of security functional requirements and assurance requirements, plus rules for combining them. Each evaluation picks its own set, writes it down, and the lab checks the product against that set. A firewall, a smart card chip, an HSM, and an operating system can all be 'Common Criteria certified', against completely different claims.

Five terms carry almost all of the meaning in a Common Criteria certificate.

The seven Evaluation Assurance Levels are packages of assurance requirements that get progressively more demanding about design evidence, testing, and analysis. An EAL says nothing about which security functions the product has. A product evaluated at EAL4 against a Security Target with weak claims has had weak claims checked thoroughly.

The '+' in 'EAL4+' means the package was augmented with individual assurance components from a higher level. The one that matters most for cryptographic hardware is AVA_VAN, vulnerability analysis: AVA_VAN.5 means the lab's penetration testing assumed an attacker with 'high' attack potential, the level that includes serious side-channel and fault-injection work. That's why smart card chips and HSMs are so often certified at 'EAL4+ (AVA_VAN.5)' or 'EAL5+' rather than a plain EAL.

If every vendor writes its own Security Target, two certificates for the same kind of product can be hard to compare. Protection profiles fix that by letting a community agree on one requirement set for a product type, so every conforming product makes the same baseline claims.

Different schemes lean on this to different degrees. In the US, NIAP evaluates only against NIAP-approved protection profiles and doesn't assign EALs at all; products on its list are what US national security systems are required to buy. Since 2014 the international arrangement has promoted collaborative protection profiles (cPPs), written jointly by vendors, labs, and several governments, with exact conformance so there's no room to dilute them. In Europe, EN 419221-5 is the protection profile for HSMs used by trust service providers under eIDAS (for certificate issuance, signing, and sealing), and certified HSMs typically claim it at EAL4 augmented with AVA_VAN.5. Paired with a Signature Activation Module certified against EN 419241-2, such an HSM is what makes up a remote qualified signature creation device; the ETSI & eIDAS page covers what that means legally and how the ETSI policy standards around it fit together.

Certificates are issued by national certification bodies (BSI in Germany, ANSSI in France, NIAP in the US, and others) based on evaluations by accredited labs. Recognition across borders comes from separate agreements, and each one recognizes a different range of assurance.

A serious HSM vendor usually holds both, because they answer different questions for different buyers. Payment HSMs add a third, PCI PTS HSM, run by the PCI Security Standards Council (see the EMVCo & PCI SSC page).