| # UBDA V1.2-alpha — Architectural Reference | |
| ## 1. Core principles | |
| * **Hardware boundary of authority** — a software behavioral engine may adjust | |
| dynamic trust metrics, but no software component possesses the authority or | |
| cryptographic material to derive keys or release protected data | |
| independently. | |
| * **Capability-scoped execution** — protected keys are ephemeral and bound | |
| strictly to the target resource, permitted operation, classification level, | |
| TTL, and non-replayable nonce defined in a signed Data Access Capability | |
| (DAC). | |
| * **Metadata & payload uniformity** — at rest, both file payloads and | |
| structural metadata are treated as cryptographically indistinguishable from | |
| noise (an at-rest design goal this prototype does not itself implement). | |
| ## 2. Dynamic trust-state matrix | |
| ``` | |
| ┌─────────────────────────┐ | |
| │ T-1: COMPROMISED │ | |
| └────────────▲────────────┘ | |
| │ Hardware Reset / Reset to T0 | |
| ┌─────────────────────────────────────┴─────────────────────────────────────┐ | |
| │ │ | |
| ┌──┴──┐ Device Auth ┌─────┐ BTE Assertion ┌─────┐ Step-Up Auth ┌─────┐ Out-of-Band ┌─────┐ | |
| │ T0 ├─────────────►│ T1 ├───────────────►│ T2 ├──────────────►│ T3 ├───────────►│ T4 │ | |
| └─────┘ └─────┘ └─────┘ └─────┘ └─────┘ | |
| Cold Public / Personal Sensitive Critical | |
| Boot System Data (D1) Records Master | |
| Shell (D0) (D2) Keys (D3) | |
| ``` | |
| | Trust State | Name | Minimum Gatekeeper Requirement | Accessible Data Classification | | |
| | --- | --- | --- | --- | | |
| | `T-1` | Compromised | Hard anomaly / system intrusion interrupt | None — active keys revoked, state frozen | | |
| | `T0` | Unauthenticated | Cold boot / sealed state | None — all payload & metadata encrypted | | |
| | `T1` | Device Authenticated | Hardware-backed passkey / attestation | `D0` — OS shell, public binaries, non-sensitive configs | | |
| | `T2` | Behavioral Continuity | Validated telemetry (`T1` + BTE assertion) | `D1` — standard personal files, documents | | |
| | `T3` | High Assurance | Hardware biometric / local PIN (`T2` + step-up) | `D2` — financial, medical, private records | | |
| | `T4` | Critical Elevation | Hardware HSM / out-of-band token (`T3` + elevation) | `D3` — root signing keys, master vault seeds | | |
| ## 3. System architecture & component isolation | |
| ``` | |
| ┌───────────────────────────┐ | |
| │ USER INTERACTION │ | |
| └─────────────┬─────────────┘ | |
| │ | |
| ▼ | |
| UNTRUSTED SOFTWARE DOMAIN │ | |
| ┌───────────────────────────────────────┼───────────────────────────────────────────┐ | |
| │ ▼ │ | |
| │ ┌────────────────────┐ │ | |
| │ │ BEHAVIOURAL TRUST │ ── Processes Telemetry Vectors │ | |
| │ │ ENGINE (BTE) │ (No direct key access) │ | |
| │ └──────────┬─────────┘ │ | |
| │ │ Policy Assertion │ | |
| │ ▼ │ | |
| │ ┌────────────────────┐ │ | |
| │ │ REFERENCE MONITOR │ ── Requests capability │ | |
| │ │ & POLICY ENGINE │ and evaluates operations │ | |
| │ └──────────┬─────────┘ │ | |
| └───────────────────────────────────────┼───────────────────────────────────────────┘ | |
| Authorization | |
| Request | |
| HARDWARE / TEE TRUST DOMAIN │ | |
| ┌───────────────────────────────────────┼───────────────────────────────────────────┐ | |
| │ ▼ │ | |
| │ ┌────────────────────┐ │ | |
| │ │ KEY AUTHORITY │ ── Validates Trust State & │ | |
| │ │ (Hardware / TEE) │ Signs Canonical DAC │ | |
| │ └──────────┬─────────┘ │ | |
| │ │ Signed DAC │ | |
| │ ▼ │ | |
| │ ┌────────────────────┐ │ | |
| │ │ KEY BROKER │ ── Checks Signatures, Anti- │ | |
| │ │ (Execution Boundary)│ Replay, & Derives Ephemeral │ | |
| │ └──────────┬─────────┘ Session Key ($K_{eph}$) │ | |
| └───────────────────────────────────────┼───────────────────────────────────────────┘ | |
| Ephemeral Key | |
| │ | |
| ▼ | |
| ┌──────────────────────┐ | |
| │ PLAINTEXT EXECUTION │ | |
| │ (RAM Ephemeral) │ | |
| └──────────────────────┘ | |
| ``` | |
| ## 4. Where the code maps to the diagram | |
| | Diagram component | Source file | | |
| | --- | --- | | |
| | Behavioural Trust Engine | `src/bte_interface.rs` | | |
| | Reference Monitor / trust-state transitions | `src/state_machine.rs` | | |
| | Key Authority (hardware/TEE) | `src/hardware_authorizer.rs` | | |
| | Key Broker (execution boundary, anti-replay) | `src/key_broker.rs`, `src/replay_store.rs` | | |
| | Shared types (DAC, telemetry, trust/classification enums) | `src/types.rs` | | |
| ## 5. Known simplifications in this prototype | |
| * `MockHardwareAuthorizer` runs in the same process as everything else — a | |
| real implementation would put the `KeyAuthority` behind a TEE/HSM boundary | |
| with no shared address space. | |
| * The "demo master root secret" is a fixed byte array for reproducibility in | |
| tests/demos; a real system would provision this from hardware-backed key | |
| storage and never expose it to software. | |
| * At-rest payload/metadata encryption (Invariant 3) is described but not | |
| implemented here — this prototype focuses on the trust-state machine and | |
| capability lifecycle. | |