The US Federal Government requires that its agencies protect sensitive, but unclassified information using cryptographic modules that have been validated to Federal Information Processing (FIPS) Standard 140-2 “Security Requirements for Cryptographic Modules.“
This standard replaced its predecessor, FIPS 140-1. In this context, the term “validated” means tested by accredited testing organizations to demonstrate that the module itself provides a specific level of security assurance.
To fully understand what FIPS 140-2 validation of a particular security product, it is important to understand the contextual meaning of “module” as defined by the standard:
Cryptographic module: the set of hardware, software, and/or firmware that implements approved security functions (including cryptographic algorithms and key generation) and is contained within the cryptographic boundary._
In the field of information security, the concept of a security boundary is of vital importance. Security is assurance (to a specific level) is only offered within a specific, defined boundary. In other words, if a certain HSM has FIPS 140-2 validation it can be trusted to perform its cryptographic functions securely within the limits of the defined level of security. However, it is still possible to implement an HSM in an insecure manner making the FIPS 140-2 validation misleading to a layman who does not understand the limitations of the validation. The Overview section of the standard even contains the following caveat:
Similarly, the use of a validated cryptographic module in a computer or telecommunications system is not sufficient to ensure the security of the overall system.
Discussions regarding FIPS 140-2 typically involve a determination of what level of security is appropriate. The FIPS 140-2 Standard defines four different levels:
Security Level 1 – This is the lowest level of security. While only approved security functions or algorithms may be used there are no specific physical security requirements. This security level allows the cryptographic module to be implemented in software. The standard reads, “Security Level 1 allows the software and firmware components of a cryptographic module to be executed on a general purpose computing system using an unevaluated operating system.”
Security Level 2 – Requires tamper-evidence as a physical security measure. This is typically implemented by using special coatings or seals of physical boundary of the security module. In addition, the operating system must meet the specified Common Criteria Protection Profiles listed in the Standard’s Annex B. As a result of these requirements the security module must take on a specific form factor and is listed as a specific product on the list maintained by NIST. Security Level 2 also requires role-based authentication.
Security Level 3 – Attempts to thwart an attacker from obtaining the plaintext secrets (called “critical security parameters” by the standard) by securely wiping the memory when the module is tampered with. Level 3 requires that the plaintext secrets moved in or out of the cryptographic module use a trusted path to protect their integrity and confidentiality.
Security Level 4–This is the highest and most rigorous level of security and is suitable for operation in physically unprotected environments. The goal at this security level is to detect and thwart all manner of physical access attempts, including manipulations of voltage or temperature, destroying the secrets if necessary.
The four different levels of security allow the data owner to determine the level of security that is warranted based on the data’s classification and the threat model. Additional security comes at an increasing cost. Since it is expensive for the device manufacturers to obtain FIPS 140-2 validation for each product, this expense is baked into the cost of the unit.