Summary
ROM 2.1.2 introduces several entropy-source related changes:
- Support for entropy_src single-bit mode
- CONF.THRESHOLD_SCOPE = false
- repcnts health test disabled
- Updated adaptive proportion threshold handling for single-bit mode
Taken together, these changes appear to modify the operational entropy-source configuration and health-test behavior rather than only fixing implementation defects.
Concern
From an ESV/FIPS perspective, health-test configuration is part of the operational behavior of the entropy source.
As a result, ROM 2.1.2 appears to introduce a validation-relevant behavioral change relative to ROM 2.1.1 despite being released as a minor ROM update.
In particular:
- Health-test scope changed
- Repetition-count test configuration changed
- Entropy-source operating mode became configurable
- Adaptive proportion threshold derivation changed
THRESHOLD_SCOPE Change
The change of CONF.THRESHOLD_SCOPE is particularly notable because it modifies an already established health-test configuration rather than introducing an entirely new feature.
According to the associated discussion, the rationale for setting THRESHOLD_SCOPE to false is that health tests should be triggered on individual RNG lanes rather than on the aggregated multi-bit source.
However, this also changes the semantics of the health tests and therefore the operational entropy-source behavior. As a result, systems operating in the traditional multi-bit mode may no longer observe the same health-test behavior as previous ROM releases.
The concern is not the introduction of single-bit mode itself. The concern is that single-bit-mode related changes become part of the default health-test configuration even when operating in multi-bit mode. This makes it difficult to view ROM 2.1.1 and ROM 2.1.2 as behaviorally equivalent from an entropy validation perspective.
Proposed Compatibility Approach
Since ROM 2.1.2 already introduces a configurable single-bit mode, it may be beneficial to tie the health-test configuration to the selected entropy operating mode.
Single-bit mode
- RNG_BIT_ENABLE = 1
- THRESHOLD_SCOPE = false
- Current ROM 2.1.2 behavior
Multi-bit mode
- RNG_BIT_ENABLE = 0
- Legacy health-test configuration
- repcnts enabled
- Previous THRESHOLD_SCOPE behavior
This would provide a compatibility path for deployments that were characterized or validated against the pre-2.1.2 entropy-source behavior while preserving the new single-bit mode support.
It would also make the behavioral change explicit and allow integrators to intentionally select either the legacy or updated entropy-source configuration.
Summary
ROM 2.1.2 introduces several entropy-source related changes:
Taken together, these changes appear to modify the operational entropy-source configuration and health-test behavior rather than only fixing implementation defects.
Concern
From an ESV/FIPS perspective, health-test configuration is part of the operational behavior of the entropy source.
As a result, ROM 2.1.2 appears to introduce a validation-relevant behavioral change relative to ROM 2.1.1 despite being released as a minor ROM update.
In particular:
THRESHOLD_SCOPE Change
The change of CONF.THRESHOLD_SCOPE is particularly notable because it modifies an already established health-test configuration rather than introducing an entirely new feature.
According to the associated discussion, the rationale for setting THRESHOLD_SCOPE to false is that health tests should be triggered on individual RNG lanes rather than on the aggregated multi-bit source.
However, this also changes the semantics of the health tests and therefore the operational entropy-source behavior. As a result, systems operating in the traditional multi-bit mode may no longer observe the same health-test behavior as previous ROM releases.
The concern is not the introduction of single-bit mode itself. The concern is that single-bit-mode related changes become part of the default health-test configuration even when operating in multi-bit mode. This makes it difficult to view ROM 2.1.1 and ROM 2.1.2 as behaviorally equivalent from an entropy validation perspective.
Proposed Compatibility Approach
Since ROM 2.1.2 already introduces a configurable single-bit mode, it may be beneficial to tie the health-test configuration to the selected entropy operating mode.
Single-bit mode
Multi-bit mode
This would provide a compatibility path for deployments that were characterized or validated against the pre-2.1.2 entropy-source behavior while preserving the new single-bit mode support.
It would also make the behavioral change explicit and allow integrators to intentionally select either the legacy or updated entropy-source configuration.