`link` attestor

Emits an in-toto Link v0.3 predicate synthesized from the step's command-run, material, product, and environment attestors — for compatibility with legacy in-toto verifiers.

Name	`link`
Predicate type	`https://in-toto.io/attestation/link/v0.3`
Lifecycle	`postproduct`
Default binary?	No
Recommended trace	off — no syscall tracing needed
Auto-attaches when	Not auto-detected — attach explicitly with `-a`.

The facts in this box are generated from the cilock binary's own catalog (cilock tools list). Do not hand-edit — run npm run gen:catalog.

What it captures

This attestor does not produce its own predicate type — it produces the upstream in-toto Link predicate. The serialized JSON shape (attestation/intoto/link.Link) has these fields:

name — the cilock step name (from AttestationContext.StepName())
command — argv of the executed command, copied from the command-run attestor's cmd field
materials — list of in-toto v1 ResourceDescriptor entries (name, digest) built from the material attestor's pre-execution file digests
environment — map of environment-variable name → value, copied from the environment attestor's filtered variables
byproducts — reserved field in the upstream schema; not populated by the current Attest() implementation

Subjects are derived from the product attestor: each product path is emitted as `file:<path>` with its digest set.

When to use

Enable link when a downstream consumer expects raw in-toto Link statements rather than cilock-native predicates — for example, a legacy in-toto verifier, or interop with another supply-chain tool that already knows how to consume https://in-toto.io/attestation/link/v0.3. For new pipelines, prefer the dedicated command-run, material, product, and environment attestors directly.

Flags

Flag	Type	Default	Effect
`--attestor-link-export`	bool	`false`	Emit the Link predicate as its own standalone DSSE envelope instead of nesting it inside the cilock collection envelope.

Output shape

{
  "name": "build",
  "command": ["go", "build", "./..."],
  "materials": [
    {
      "name": "main.go",
      "digest": {"sha256": "…"}
    }
  ],
  "environment": {
    "PATH": "/usr/local/bin:/usr/bin:/bin",
    "GOOS": "linux"
  }
}

Gotchas

Requires sibling attestors. link runs at postproduct and only populates fields it can read off CompletedAttestors(). If command-run, material, product, or environment did not run, the corresponding command / materials / subjects / environment fields are simply empty — no error is raised.
Standalone vs wrapped. Without --attestor-link-export, the Link predicate is wrapped inside the cilock collection alongside the source attestors. With --attestor-link-export=true, Export() returns true and cilock emits the Link in its own DSSE envelope — useful when feeding it directly to an in-toto verifier.
Duplication. The Link data is a re-projection of command-run + material + product + environment. Enabling link does not replace those attestors; it adds a second view of the same evidence.
byproducts is not populated by this implementation even though the upstream schema defines it.

CLI example

Real in-toto Link statement v0.3 derived from material + product + command-run, with stable byte-identical canonical encoding.

cilock run --step link-emit \
  --signer-file-key-path key.pem --outfile attestation.json --workingdir . \
  --attestations link \
  -- make build 

Validated against a real build producing an in-toto Link statement. See the full real-data example at https://github.com/aflock-ai/attestor-compliance-examples/tree/main/08-link.

What it captures​

When to use​

Flags​

Output shape​

Gotchas​

CLI example​

See also​