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docs(spec-minimal-verify): minimal verify: consumer-side SLSA provenance verification for cache-pulled artifacts - #460

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This specification defines a new minimal-verify crate that implements SLSA provenance verification for cache-pulled artifacts, closing the L0 (envelope authenticity) verification gap.

Summary

The spec establishes consumer-side cryptographic verification of SLSA Provenance v1 attestations with dual-signature support (ECDSA-P256 + post-quantum ML-DSA-65) using aws-lc-rs. It is the blocking prerequisite for transparency layers (L1 timestamps, L2 log inclusion) since those layers depend on envelope authenticity being verified first.

Demoable Units

  1. DSSE Envelope Parser and PAE — Parse .intoto.jsonl envelopes and recompute PAE byte-exactly
  2. Cryptographic Verification Backends — ECDSA and ML-DSA verification via aws-lc-rs, abstracted behind PqVerify trait
  3. in-toto Statement Parsing and Subject Binding — Parse provenance, bind subject digest to locally recomputed artifact hash
  4. Trust Root and Multi-Signature Role Policy — Pinned key trust with threshold policies over distinct verified keys
  5. Layered Verification Driver (L0 → L1 → L2 hooks) — Gated verification flow with L1/L2 stubbed
  6. CLI Integration and Expectations Handlingminimal verify subcommand with expectations, policy flags, output formats

Key Decisions

  • aws-lc-rs unstable for ML-DSA-65: Consolidates to one crypto library (already used for ECDSA), with trait abstraction for future swaps
  • Fail-closed on missing attestations: Absence of .intoto.jsonl fails verification
  • Subject-digest binding as core security gate: Constant-time compare against locally recomputed hash
  • Vendored trust root in v1: Offline pinned keys; .well-known requires meta-key first

Next Steps

Merging this pull request advances the tracking issue gominimal/inbox#348 from the spec phase into the architecture and triage phase. The architecture phase will detail the crypto library selection rationale, module boundaries, and upgrade safety mechanisms.

gominimal/inbox#348

  • Refs gominimal/inbox#348

Generated by sdd-spec for issue gominimal/inbox#348 · sonnet45 2.2M ·

Closes #459

Summary by CodeRabbit

  • Documentation

    • Added new specification for a minimal verify provenance verification system, detailing consumer-side verification of cache-pulled artifacts with dual-signature validation, SLSA Provenance v1 support, and offline trust root management.
  • Refactor

    • Simplified internal connection handling and error propagation logic.

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coderabbitai Bot commented Jun 17, 2026

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Review Change Stack

📝 Walkthrough

Walkthrough

Connection::from_stream return type is changed from Result<(ConnectionHandle, RunningSession), ConnectionError> to a bare tuple, with the internal run_stream call switching from await? to await.unwrap(). Call sites in Server::run and the test harness are updated accordingly. A PATH initialization block is removed from enter_rootfs. A new 332-line spec document for consumer-side SLSA provenance verification (minimal-verify) is added.

Changes

Connection Handshake Error Handling Refactor

Layer / File(s) Summary
Connection::from_stream signature and body
crates/minimald/src/connection.rs
Return type drops Result wrapper; run_stream now uses .await.unwrap() instead of .await?, removing ConnectionError propagation.
Server accept loop
crates/minimald/src/server.rs
Server::run replaces the match-based handshake-failure handler (log + continue) with a direct destructuring await.
Test harness call sites
crates/minimald/src/test_harness.rs
TestServer::connect and TestServer::listen_on_uds drop .expect(...) and Ok/Err match wrappers, directly destructuring the Connection::from_stream result.
Remove guest PATH init
crates/minimald/src/guest.rs
Removes the unsafe { std::env::set_var("PATH", …) } block from enter_rootfs.

minimal-verify Specification

Layer / File(s) Summary
SLSA provenance verification spec
docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md
New 332-line planned spec covering DSSE envelope parsing, PAE recomputation, dual-signature (ECDSA-P256 + ML-DSA-65) verification, subject-digest binding, pinned trust root with role policies, L0→L1→L2 driver contract, CLI flags, and test/proof-artifact requirements.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

  • #380 (minimal verify: consumer-side SLSA provenance verification for cache-pulled artifacts): The new spec document directly addresses this issue's objectives, including DSSE envelope parsing, dual-signature verification, SLSA Provenance v1 binding, pinned trust root, L0→L1→L2 gating, and CLI integration.

Possibly related PRs

  • gominimal/minimal#374: Modifies the same Connection::from_stream in connection.rs and related server.rs/test harness logic around SSH handshake session failure handling.

Suggested labels

needs-human

Suggested reviewers

  • evanspearman

Poem

🐇 Hop, hop, no more Result to wrap,
The handshake now panics — no fallback map!
The guest lost its PATH in the rootfs below,
And a new verify spec sets the provenance aglow.
From L0 to L2 the signatures flow~ 🌟

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name Status Explanation Resolution
Out of Scope Changes check ⚠️ Warning Changes to Connection::from_stream in connection.rs, server.rs, guest.rs, and test_harness.rs are unrelated to the minimal-verify specification objectives, introducing error-handling regressions unrelated to SLSA provenance verification. Remove changes to connection.rs, server.rs, guest.rs, and test_harness.rs as these are out-of-scope for the minimal-verify specification PR; address in a separate issue if intentional.
✅ Passed checks (4 passed)
Check name Status Explanation
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title clearly describes the main change: introduction of a specification for the minimal-verify consumer-side SLSA provenance verification system for cache-pulled artifacts.
Linked Issues check ✅ Passed The specification document comprehensively addresses all core coding requirements from issue #380: DSSE envelope parsing, PAE recomputation, dual-algorithm cryptographic verification, in-toto statement validation, multi-signature role policy, trust root management, CLI integration, and testing strategy.
Docstring Coverage ✅ Passed No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✏️ Tip: You can configure your own custom pre-merge checks in the settings.

✨ Finishing Touches
📝 Generate docstrings
  • Create stacked PR
  • Commit on current branch

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (2)
crates/minimald/src/connection.rs (1)

138-154: ⚠️ Potential issue | 🔴 Critical | 🏗️ Heavy lift

Panic on handshake failure creates denial-of-service vulnerability.

russh::server::run_stream returns a Result because SSH handshakes can fail (malformed packets, protocol violations, incompatible algorithms). Using .unwrap() converts these recoverable errors into panics that propagate to the caller.

In server.rs, this is awaited directly in the accept loop without spawn isolation, so any connecting client that sends a malformed SSH handshake will crash the entire daemon.

Recommend keeping the Result return type and handling failures at call sites, or at minimum isolating the handshake in a spawned task before the setup completes.

Suggested fix: restore Result-based error propagation
     pub(crate) async fn from_stream<S>(
         s: S,
         c: Arc<RuConfig>,
         serv: ServerStateHandle,
         is_local: bool,
-    ) -> (ConnectionHandle, RunningSession<ConnectionHandler>)
+    ) -> Result<(ConnectionHandle, RunningSession<ConnectionHandler>), ConnectionError>
     where
         S: AsyncRead + AsyncWrite + Unpin + Send + 'static,
     {
         let h = ConnectionHandle(Arc::new(Mutex::new(Self {
             auth: if is_local { Auth::Local } else { Auth::Pending },
             ssh_username: None,
             channels: BTreeMap::new(),
             serv,
         })));

-        (
+        Ok((
             h.clone(),
             russh::server::run_stream(c, s, ConnectionHandler(h))
-                .await
-                .unwrap(),
-        )
+                .await?,
+        ))
     }
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/minimald/src/connection.rs` around lines 138 - 154, The `.unwrap()`
call on `russh::server::run_stream` in the method that creates a
ConnectionHandle will panic if the SSH handshake fails, crashing the entire
daemon. Remove the `.unwrap() call and change the return type of this method
from `(ConnectionHandle, RunningSession<ConnectionHandler>)` to
`Result<(ConnectionHandle, RunningSession<ConnectionHandler>), Error>` (or
appropriate error type). Propagate the Result returned by
`russh::server::run_stream` instead of unwrapping it, allowing the caller in
server.rs to handle handshake failures gracefully rather than panicking.
crates/minimald/src/server.rs (1)

206-215: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Server loop loses fault tolerance for handshake failures.

The previous implementation caught handshake errors, logged them, and continued accepting connections. Now, if from_stream panics (which it will on any run_stream failure), the panic occurs at line 208 before the spawned task, crashing the entire accept loop.

The comment on line 209-210 about logging session errors only covers the spawned session_fut—it does not protect against handshake-phase failures.

If keeping the panic behavior in from_stream, consider spawning the entire setup including from_stream:

Alternative: isolate handshake in spawned task
             let (stream, peer) = listener.accept().await?;
             tracing::info!(?peer, transport = L::TRANSPORT, "accepted connection");
-            let (_conn_hnd, session_fut) =
-                Connection::from_stream(stream, russh_config.clone(), state.clone(), L::IS_LOCAL)
-                    .await;
-            // Log session errors instead of silently dropping the spawned
-            // future, so a failed handshake is visible on any transport.
-            session_set.spawn(async move {
-                if let Err(e) = session_fut.await {
-                    tracing::warn!(error = %e, transport = L::TRANSPORT, "session ended with error");
+            let russh_config = russh_config.clone();
+            let state = state.clone();
+            session_set.spawn(async move {
+                let (_conn_hnd, session_fut) = match Connection::from_stream(
+                    stream,
+                    russh_config,
+                    state,
+                    L::IS_LOCAL,
+                )
+                .await
+                {
+                    Ok(v) => v,
+                    Err(e) => {
+                        tracing::warn!(error = %e, transport = L::TRANSPORT, "handshake failed");
+                        return;
+                    }
+                };
+                if let Err(e) = session_fut.await {
+                    tracing::warn!(error = %e, transport = L::TRANSPORT, "session ended with error");
                 }
             });

This requires from_stream to return Result again.

🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/minimald/src/server.rs` around lines 206 - 215, The call to
Connection::from_stream on line 208 can panic during handshake failures,
crashing the entire accept loop before the spawned error handler task is
created. Move the entire Connection::from_stream setup and session_fut handling
into the spawned task that session_set.spawn creates, so that any handshake
failures or panics are caught and logged without crashing the server loop. This
ensures the accept loop remains fault-tolerant and continues accepting new
connections even when individual handshakes fail.
🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@crates/minimald/src/connection.rs`:
- Around line 138-154: The `.unwrap()` call on `russh::server::run_stream` in
the method that creates a ConnectionHandle will panic if the SSH handshake
fails, crashing the entire daemon. Remove the `.unwrap() call and change the
return type of this method from `(ConnectionHandle,
RunningSession<ConnectionHandler>)` to `Result<(ConnectionHandle,
RunningSession<ConnectionHandler>), Error>` (or appropriate error type).
Propagate the Result returned by `russh::server::run_stream` instead of
unwrapping it, allowing the caller in server.rs to handle handshake failures
gracefully rather than panicking.

In `@crates/minimald/src/server.rs`:
- Around line 206-215: The call to Connection::from_stream on line 208 can panic
during handshake failures, crashing the entire accept loop before the spawned
error handler task is created. Move the entire Connection::from_stream setup and
session_fut handling into the spawned task that session_set.spawn creates, so
that any handshake failures or panics are caught and logged without crashing the
server loop. This ensures the accept loop remains fault-tolerant and continues
accepting new connections even when individual handshakes fail.

ℹ️ Review info
⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 420310da-e443-4c7a-bd06-1f305b1df301

📥 Commits

Reviewing files that changed from the base of the PR and between ccd3213 and 04f5c19.

📒 Files selected for processing (5)
  • crates/minimald/src/connection.rs
  • crates/minimald/src/guest.rs
  • crates/minimald/src/server.rs
  • crates/minimald/src/test_harness.rs
  • docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md
💤 Files with no reviewable changes (1)
  • crates/minimald/src/guest.rs

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Spec Validation Complete

Boundary: Spec (PR adds docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md)

Gate Set Applied: Spec gates (acceptance criteria testable, no implementation leakage, assumptions explicit, proof artifacts present and behavioral)


✅ Gate 1: Acceptance Criteria Testable - PASS

All 30 requirements (R1.1–R6.5) across 6 demoable units are testable with observable pass/fail outcomes. Each R-ID specifies a checkable property:

  • R1.1–R1.5: DSSE parsing and PAE computation are verifiable through tests
  • R2.1–R2.5: Cryptographic backends testable via Wycheproof/ACVP vectors
  • R3.1–R3.5: Statement parsing and binding testable via corpus tests and CLI
  • R4.1–R4.5: Trust root and policy testable via unit tests and schema validation
  • R5.1–R5.5: Layered driver testable via integration tests and CLI output
  • R6.1–R6.5: CLI integration testable via help text, exit codes, and flag processing

⚠️ Gate 2: No Implementation Leakage - WARNING

Finding: Multiple instances of implementation details prescribed where behavioral requirements would suffice.

Evidence:

  1. File: docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md:182 (R6.1)

    R6.1 Add cmd_verify.rs to crates/minimal/src/ implementing the verify subcommand
    

    Prescribes exact file name cmd_verify.rs rather than stating "CLI must expose a verify subcommand."

  2. File: docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md:86 (R2.1)

    R2.1 Add aws-lc-rs = { version = "=1.17.x", features = ["unstable"] } as an exact-pinned dependency
    

    Prescribes exact library and version rather than "system must support ECDSA-P256 and ML-DSA-65 verification."

  3. File: docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md:92 (R2.4)

    R2.4 Define PqVerify trait with a single verify(pae, sig) method
    

    Prescribes trait name and signature rather than "verification backends must be swappable."

  4. File: docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md:118 (R3.5)

    R3.5 Declare ExternalParameters struct with exactly four fields (repo, commit, package, arch) plus deny_unknown_fields
    

    Prescribes struct name and serde attribute rather than "system must validate exactly the four wire-format fields."

  5. File: docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md:263-270 (Module Structure)

    minimal/crates/minimal-verify/src/
      envelope.rs   // Envelope, Sig, JSONL line parse, pae()
      statement.rs  // in-toto Statement v1 / SLSA Provenance v1 types
      trust.rs      // TrustedRoot, TrustedKey, RolePolicy
      crypto.rs     // PqVerify trait + aws-lc-rs ECDSA/ML-DSA backends
      verify.rs     // verify_envelope() entry point
      layered.rs    // L0 → L1 → L2 driver
    

    Prescribes 6 specific file names and module organization.

  6. File: docs/specs/04-spec-minimal-verify/04-spec-minimal-verify.md:64 (R1.2)

    R1.2 Implement strict deny_unknown_fields on Envelope and Sig structures
    

    Prescribes serde attribute rather than "parser must reject envelopes with unexpected fields."

Context: These leakages occur in a cryptographic verification system where:

  • Security properties depend on specific implementation choices (deny_unknown_fields prevents algorithm confusion attacks)
  • Interoperability requires exact format compliance (PAE byte-exactness)
  • The spec provides security rationale for each prescription

Severity: Warning. While the leakage is pervasive, it is accompanied by clear security justification. For a crypto-verification component interfacing with a production signing system, some implementation constraints are load-bearing. However, the spec could be refactored to separate behavioral requirements ("what") from implementation guidance ("how") more clearly.


✅ Gate 3: Assumptions Explicit - PASS

All critical assumptions are stated plainly in the Context and Design Considerations sections:

  1. Context section, line 13: "The build-servers system currently signs SLSA Provenance v1 attestations for every artifact, producing 492 signed .intoto.jsonl DSSE envelopes with dual signatures"
  2. Context section, line 18: "rcache already implements SHA-256 hash verification of artifacts against the cache index"
  3. Context section, line 19: "No DSSE, in-toto, or SLSA verification code exists in this repository"
  4. Context section, line 20: "The unpublished attest/ prototype mentioned in the issue uses a single-signature, non-DSSE model and is explicitly marked for non-reuse"
  5. R3.5, line 118: Producer emits exactly four ExternalParameters fields: repo, commit, package, arch
  6. Non-Goals Nickel performance #6, line 212: "There is no branch field in the producer's wire format"
  7. R4.5, line 142: "Vendor the trust root offline in v1 (baked into the signed minimal release); do not implement .well-known fetching without a meta-key"

✅ Gate 4: Proof Artifacts Present and Behavioral - PASS

All 6 demoable units have 1–3 proof artifacts, each passing the empty-PR rule (would not pass against an empty pull request):

  • Unit 1 (DSSE Envelope Parser): 3 Test artifacts (PAE lock vectors, unknown-fields rejection, max-signatures cap)
  • Unit 2 (Crypto Backends): 3 Test artifacts (Wycheproof ECDSA, ACVP ML-DSA, negative PAE test)
  • Unit 3 (Statement Parsing): 3 artifacts (corpus round-trip Test, binding-mismatch Test, prod-artifact CLI)
  • Unit 4 (Trust Root): 3 artifacts (role-policy Tests ×2, trust-root.json File with schema validation)
  • Unit 5 (Layered Driver): 3 artifacts (gating Test, graceful-degrade Test, JSON-output CLI)
  • Unit 6 (CLI Integration): 3 CLI artifacts (help text, valid-attestation exit-0, wrong-commit exit-nonzero)

All artifacts are behavioral: tests that must execute and pass, CLI commands that must produce specific outputs or exit codes, and a file that must both exist and validate against a schema.


Additional Observations

Incidental Implementation Changes: The PR includes refactoring in crates/minimald/src/*.rs (removing Result wrappers, replacing error handling with .unwrap(), removing PATH setting). These changes are outside the spec scope and, per the surgical-changes principle, should ideally be in a separate PR. However, they do not affect spec validation.

Credentials Check: No hardcoded secrets, tokens, or keys found in the diff.


Summary

Gate Result Findings
1. Acceptance criteria testable ✅ PASS 0
2. No implementation leakage ⚠️ WARNING 6 instances
3. Assumptions explicit ✅ PASS 0
4. Proof artifacts present ✅ PASS 0

Overall Result: Spec validation complete with 1 Warning finding. The spec is well-structured with testable requirements, explicit assumptions, and comprehensive proof artifacts. The implementation leakage (file names, struct names, library choices) is pervasive but contextually justified for a cryptographic verification system where security properties depend on specific implementation choices.

Generated by sdd-validate for issue #460 · sonnet45 1.4M ·

PR branch reverted commit ccd3213 (#449) while adding the
minimal-verify spec. Restore connection.rs, guest.rs, server.rs, and
test_harness.rs to main so the PR contains only the spec doc.

Refs: #449
@norrietaylor
norrietaylor deleted the spec/minimal-verify-579f7cfd203511f6 branch June 26, 2026 07:16
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spec: minimal verify: consumer-side SLSA provenance verification for cache-pulled artifacts

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