Here’s a compact, practical design for a **smart‑difference scanner** that produces tiny, verifiable binary deltas and plugs cleanly into a release/provenance workflow—explained from the ground up.

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# What this thing does (in plain words)

It compares two software artifacts (containers, packages, binaries), computes the *smallest safe update* between them, and emits both:

* a **delta** (what to apply),
* and **proof** (why it’s safe and who built it).

You get faster rollouts, smaller downloads, and auditable provenance—plus a built‑in rollback that’s just as verifiable.

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# Core idea

1. **Content‑defined chunking (CDC)**
   Split files into variable‑size chunks using Rabin/CDC, so similar regions line up even if bytes shift. Build a **Merkle DAG** over the chunks.
2. **Deterministic delta ops**
   Delta = ordered ops: `COPY <chunk-id>` or `ADD <chunk-bytes>`. No “magic heuristics”; same inputs → same delta.
3. **Function‑level diffs (executables only)**
   For ELF/PE, disassemble and compare by symbol/function to highlight *semantic* changes (added/removed/modified functions), but still ship chunk‑level ops for patching.
4. **Verification & attestation**
   Every delta links to attestations (SLSA/DSSE/cosign/Rekor) so a verifier can check builder identity, materials, and inclusion proofs **offline**.

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# Supported inputs

* **Blobs**: OCI layers, .deb/.rpm payloads, zip/jar/war
* **Binaries**: ELF/PE segments (per‑section CDC first, then optional symbol compare)

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# Artifacts the scanner emits

**`delta-manifest.json` (deterministic):**

* `base_digest`, `target_digest`, `artifact_type`
* `changed_chunks[]` (ids, byte ranges)
* `ops[]` (COPY/ADD sequence)
* `functions_changed` (added/removed/modified counts; top symbols)
* `materials_delta` (new/removed deps & digests)
* `attestations[]` (DSSE/cosign refs, Rekor log pointers or embedded CT tile)
* `score_inputs` (pre‑computed metrics to keep scoring reproducible)

The actual **delta payload** is a compact binary: header + op stream + ADD byte blobs.

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# How verification works (offline‑first)

* **Content addressability**: chunk ids are hashes; COPY ops verify by recomputing.
* **Attestations**: DSSE/cosign bundle includes builder identity and `materials[]` digests. Rekor inclusion proof (or embedded tile fragment) lets verifiers reassemble the transparency chain without the Internet.
* **Policy**: if SLSA predicate present and policy threshold met → “green”; else fall back to vendor signature + content checks and mark **provenance gaps**.

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# Risk scoring (explainable)

Compute a single `delta_risk` from:

* `provenance_completeness` (SLSA level, DSSE validity, Rekor inclusion)
* `delta_entropy` (how many new bytes vs copies; unexpected high entropy is riskier)
* `new_deps_count` (materials delta)
* `signed_attestation_validity` (key/trust chain freshness)
* `function_change_impact` (count/criticality of changed symbols)

Expose the **breakdown** directly in UI so reviewers see *why* the score is what it is.

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# Rollback that’s actually safe

* Rollback is just “apply delta going to previous artifact” **plus** a **signed rollback attestation** anchored in the transparency log.
* Verifier refuses rollbacks without matching provenance or if the computed rollback delta doesn’t reproduce the earlier artifact’s digest.

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# Minimal internal data structures (sketch)

```txt
Chunk {
  id: sha256(bytes),
  size: u32,
  merkle: sha256(left||right)
}

DeltaOp = COPY {chunk_id} | ADD {len, bytes}

DeltaManifest {
  base_digest, target_digest, artifact_type,
  ops[], changed_chunks[],
  functions_changed: {added[], removed[], modified[]},
  materials_delta: {added[], removed[]},
  attestations: {dsse_bundle_ref, rekor_inclusion[]},
  score_inputs: {provenance, entropy, deps, attestation_validity, fn_impact}
}
```

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# Pipeline (end‑to‑end)

1. **Ingest** base & target → normalize (strip nondeterministic metadata; preserve signatures).
2. **CDC pass** → chunk map → Merkle DAGs.
3. **Delta construction** (greedy minimal ADDs, prefer COPY of identical chunk ids).
4. **(Executables)** symbol table → lightweight disassembly → function map diff.
5. **Attestation linkage** → attach DSSE bundle refs + Rekor proofs.
6. **Scoring** → deterministic `delta_risk` + breakdown.
7. **Emit** `delta.manifest` + `delta.bin`.

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# UI: what reviewers see

* **Top changed functions** (name, section, size delta, call‑fanout hint)
* **Provenance panel** (SLSA level, DSSE signer, Rekor entry—click to open)
* **Delta anatomy** (COPY/ADD ratio, entropy, bytes added)
* **Dependencies delta** (new/removed materials with digests)
* **“Apply” / “Rollback”** buttons gated by policy & attestation validity

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# How this fits your Stella Ops stack (drop‑in plan)

* **Module**: add `DeltaScanner` service under Evidence/Attestor boundary.
* **Air‑gap**: store DSSE bundles and Rekor tile fragments alongside artifacts in EvidenceLocker.
* **SBOM/VEX**: on delta, also diff SBOM nodes and attach a *delta‑SBOM* for impacted components; feed VEX evaluation to **AdvisoryAI** for surfaced risk notes.
* **Release gates**: block promotion if `delta_risk > threshold` or `provenance_completeness < policy`.
* **CLI**: `stella delta create|verify|apply|rollback --base A --target B --policy policy.yaml`.

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# Implementation notes (concise)

* **CDC**: Rabin fingerprinting window 48–64B; average chunk 4–16 KiB; rolling mask yields boundaries.
* **Hashing**: BLAKE3 for speed; SHA‑256 for interop (store both if needed).
* **Disassembly**: Capstone/llvm‑objdump (ELF/PE), symbol map fallback if stripped.
* **Determinism**: fix chunk params, hash orderings, and traversal; sort tables prior to emit.
* **Security**: validate all COPY targets exist in base; cap ADD size; verify DSSE before score.

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# Deliverables you can ship quickly

* `delta-scanner` lib (CDC + DAG + ops)
* `delta-verify` (attestations, Rekor proof check offline)
* `delta-score` (pure function over `delta-manifest`)
* UI panels: Delta, Provenance, Risk (reuse Stella’s style system)
* CI job: create delta + attach DSSE + upload to EvidenceLocker

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# Test matrix (essentials)

* Small edit in large file (ADD minimal)
* Repacked zip with same payload (COPY dominates)
* Stripped vs non‑stripped ELF (function compare graceful)
* Added dependency layer in OCI (materials_delta flagged)
* Missing SLSA but valid vendor sig (gap recorded, lower score)
* Rollback with/without signed rollback attestation (accept/deny)

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If you want, I can generate:

* a ready‑to‑commit **Go/.NET** reference implementation skeleton,
* a **policy.yaml** template with thresholds,
* and **UI wireframes** (ASCII + Mermaid) for the three panels.