Version: 1, Published: 2025-02-11

Impacted Documents

  • CPP_HCD_V1.0e

References

CPP:

  • A.4.3. FCS_COP.1/CMAC Cryptographic Operation (for cipher-based message authentication)

  • D.5.2. FPT_KYP_EXT Extended: Secure Boot

  • I.10. Security Functional Requirements Dependencies Analysis

Issue Description

HCD cPP v1.0e includes FCS_CKM.1/SKG (symmetric key generation) as a dependency of FCS_COP.1/CMAC. When the CMAC’s symmetric key is implemented in the Root of Trust statically it is unnecessary to claim FCS_CKM.1/SKG.

ASE_REQ.1-9 mentions as follows:

A justification that a dependency is not met should address either:

  • why the dependency is not necessary or useful, in which case no further information is required; or

  • That the dependency has been addressed by the operational environment of the TOE, in which case the justification should describe how the security objectives for the operational environment address this dependency.

By modifying cPP, eliminate FCS_CKM.1/SKG from the FCS_COP.1/CMAC dependency under certain conditions.

Resolution

  • Eliminate FCS_CKM.1/SKG from the FCS_COP.1/CMAC dependency under certain conditions

  • Update SFR Dependencies Analysis

CPP_HCD_V1.0e

  • Modify FCS_COP.1/CMAC’s Application Note:

FCS_COP.1/CMAC

Application Note:

If one or more HMAC algorithms are selected, the ST author selects “HMAC” in the second selection and “ISO/IEC 9797-2:2011, Section 7 ‘MAC Algorithm 2’”in the third selection. For the assignment, the key size [k] falls into a range between L1 and L2 (defined in ISO/IEC 10118 for the appropriate hash function). For example, for SHA-256, L1 = 512 and L2 = 256 where L2 ≤ k ≤ L1 for HMAC, and the size is either 128, 192, or 256 bits for CMAC.

For the assignment, the key size will fall into a range between 128 and 256.

When CMAC is used in FPT_SBT_EXT.1, the dependency on FCS_CKM.1/SKG, FCS_CKM_EXT.4 can be removed for the symmetric key used for message authentication. This is because in other standards (*) that specify security requirements for cryptographic modules, public verification key or keyed message authentication key is allowed to be placed in the module code and is not CSP. Such a key can be considered as not needing to rely on the requirements for key generation and key destruction.

(*) ISO/IEC 19790 "Security requirements for cryptographic modules" 7.5 Software Firmware Security

  • Modify I.10. Security Functional Requirements Dependencies Analysis:

SFR

Dependencies

Rationale Statement

FCS_COP.1/CMAC

FCS_CKM.1/SKG, FCS_COP.1/Hash, FCS_CKM_EXT.4

FCS_CKM.1/SKG included, FCS_COP.1/Hash included, FCS_CKM_EXT.4 included

When FCS_COP.1/CMAC is applied to keys used in FPT_SBT_EXT.1, the key-based message authentication key is not CSP, so dependencies on FCS_CKM.1/SKG and FCS_CKM_EXT.4 can be removed.

Tracking

Issue #27