Appendix 3.B Departures from MS-DTYP
KACS uses the binary formats MS-DTYP specifies, so a descriptor authored by a Windows domain controller and replicated through Samba is evaluated without translation. PCDS specifies those formats normatively.
Evaluator behaviour is a separate question. Given the same token, descriptor and desired mask, KACS generally reaches the same decision MS-DTYP describes — which is what makes policy authored in an AD environment behave predictably here — but it departs deliberately in the following places.
| Area | Departure | Why |
|---|---|---|
Conditional ACE @Local. | Resolved from an AccessCheck parameter rather than a token field | The context is per-call and varies between checks. |
| Virtual groups in expressions | Member_of({S-1-3-4}) returns true for the owner | Keeps the SID matcher and the expression evaluator semantically consistent. |
| INT64/UINT64 promotion | Relational operators promote between the two | Without promotion, UINT64 claims cannot be used in conditions at all. |
Member_of filtering | Filtered by ACE polarity, so deny-only groups do not satisfy allow-ACE conditions | Consistent with deny-only group semantics everywhere else. |
Exists scope | Extended to all four attribute namespaces | No reason to restrict existence tests to Local and Resource. |
| ACE mask mapping | ACE masks are mapped through GenericMapping at evaluation time | Required for GENERIC_ALL in central access policy recovery ACEs (§3.8.8). |
MAXIMUM_ALLOWED | First-writer-wins for targeted and maximum-allowed requests | Eliminates disagreement between "what can I do?" and "can I do this?" on a non-canonically ordered DACL. |
| Zero desired mask | Succeeds rather than returning access denied | "Asked for nothing, got nothing" is a valid answer. |
| Alarm ACEs | Repurposed for continuous per-operation auditing (§3.8.9) | Reserved but never implemented in the reference model. |
| Multiple scoped policy ACEs | Several permitted per SACL | AND semantics make composition safe. |
| Mandatory policy mutability | mandatory_policy is immutable on the token (§3.2.2) | A mutable policy reduces MIC to advisory. |
| Impersonation integrity ceiling | Enforced unconditionally; SeImpersonatePrivilege does not bypass it (§3.5.2) | MIC is a real boundary precisely because the mandatory policy is immutable. |
| Impersonation origin check | Dropped | Eliminates hidden impersonation paths. |
| PIP determination | Kernel-only, from the binary signature, with no parent input (§3.3.2) | One input, one answer, no ambiguity. |
| Object type list validation | Duplicate GUIDs and level gaps rejected (§3.8.5) | Prevents node lookup returning the wrong node and propagation becoming undefined. |
| Composite equality | Element-wise ordered comparison | Never over-grants. |
3.B.1 Features handled elsewhere #
Several capabilities relevant to a complete security posture are not KACS's, and are named here so their absence is not mistaken for a gap. Kerberos and NTLM authentication, S4U, and credential storage and protection belong to authd, as do Resource-Based Constrained Delegation and Authentication Policies and Silos through the KDC. Active Directory replication is Samba's. Group Policy distribution goes through the registry and roles. Network share permissions belong to the Samba SMB layer. An Encrypting File System is a future service.