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b90fa8e | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 | # 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.
|