Publisher trust and revocation

Takoform defines package identity, publisher-policy data, offline signature verification, and append-only revocation verification. The machine-readable contract is profile.json.

Publisher choice, installation, support, and activation remain caller or Host decisions; an implementation consumes their exact policy and verification inputs.

Package identity

package-index.json is UTF-8 I-JSON canonicalized with RFC 8785. Its identity is sha256:<lowercase hex> over those canonical bytes. The index closes every data payload by path, media type, size, and digest. An archive is only a transport container and is not semantic package identity.

The verifier rejects duplicate object names, invalid Unicode, non-finite numbers, negative zero, unlisted files, traversal, links, devices, executable files, credentials, operator configuration, target/capacity/pricing data, and executable validation or adapter code.

Publisher policy

A publisher policy supplies exact values for:

• OIDC issuer;
• source repository;
• workflow identity; and
• protected ref.

The caller also supplies the trusted-root bytes, exact signed subject, Sigstore bundle, and previous revocation pin. The contract has no ambient trusted root, default publisher, official field, privileged repository, or verification bypass.

The bundle is verified offline against the exact subject and publisher policy. Verification requires its transparency-log inclusion evidence and fails closed when the root, signature, issuer, source, workflow, ref, subject, or log proof does not match.

The issued BundleVerification also carries three commits copied only from the verified Fulcio certificate summary:

• sourceCommit is SourceRepositoryDigest, the exact source revision built;
• workflowCommit is BuildSignerDigest, the revision of the specific build instructions responsible for signing; and
• buildConfigCommit is BuildConfigDigest, the revision of the top-level initiating build instructions.

Each value is mandatory and must already be one non-null, lowercase 40-hex Git commit digest. There is no caller-supplied fallback or normalization. A verifier validates the three fields separately and does not require them to be equal. Equality is a publisher/import policy decision: a reusable signing workflow can make the specific signing instructions a different revision from the source or calling workflow. Fulcio defines the three independent extension roles in its OID directory and maps GitHub's sha, job_workflow_sha, and workflow_sha claims to them separately in its GitHub CI issuer profile.

An operator may trust multiple publishers by installing multiple policies. Every policy traverses the same verifier and produces the same report shape.

Rotation and revocation

Publisher identity rotation is an explicit policy change. Existing package bytes and their historical policy remain immutable.

A revocation statement names an exact package digest and FormRef. The current statement and checkpoint data-format identity is trust.forms.takoform.com/v1. It is a record format consumed by implementations, not another Host API lane or a third negotiated version axis. Current statements use the exact current, versionless FormRef schema. A checkpoint entry records statementApiVersion: trust.forms.takoform.com/v1; the verifier derives its other identity fields and digest only from an already-canonical, validated statement, so the digest names the same RFC 8785 bytes that a publisher signs.

Every new current chain begins with this exact data document:

{"apiVersion":"trust.forms.takoform.com/v1","checkpointVersion":"0.0.0","entries":[],"kind":"FormPackageRevocationCheckpoint","previousCheckpointDigest":null,"sequence":0}

This is the only empty checkpoint. 0.0.0 is reserved as its checkpointVersion and is not a current statementVersion; every later checkpoint has at least one entry, uses the final statement's version, and carries the exact digest of its predecessor. Thus sequence one descends from the signed genesis rather than starting a new chain with a null predecessor.

The document alone grants nothing. The publisher signs its exact canonical bytes, and VerifyRevocationCheckpoint still requires the caller's exact publisher policy, trusted root, Sigstore signature, transparency inclusion, certificate provenance, and previous pin. Only that complete verification issues the unforgeable capability consumed by CheckNotRevoked. A verified genesis capability proves the publisher's signed current revocation set is empty and can authorize CheckNotRevoked without inventing evidence. The capability remains FormRef-profile-bound: a current checkpoint covers current versionless FormRefs, while a retained v1alpha1 checkpoint covers its retained FormRef epoch. An empty current genesis cannot answer for the legacy chain.

A current verifier persists (checkpointApiVersion, sequence, checkpointDigest, cumulativeEntriesDigest) and accepts only the next checkpoint in that same profile whose predecessor digest and complete retained prefix match the pin. Rollback, omission, fork, prefix rewrite, and cross-profile advancement fail closed. The caller stores that pin under the exact publisher policy that verified it; a pin is not cross-publisher authority.

The occupied trust.forms.takoform.com/v1alpha1 statement and checkpoint schemas remain byte-exact readable history. Those chains begin at sequence one with a null predecessor, and their historical pin JSON omits checkpointApiVersion. They cannot be continued by a current v1 checkpoint or used as an alias for the signed v1 genesis.

Security revocation blocks create, update, and activation. It does not replace package bytes or erase existing Resources: referenced bytes remain available for observe, delete, or an explicit operator evacuation path. Publication and support records remain separate owner decisions.

Use of verification results

Verification supplies caller and Host inputs; publication, Host installation, support, activation, provisioning, client support, and a commercial Offering remain separate decisions.

Host-side policy persistence and mutation ordering belong to the Host, outside this contract. Takoform provides deterministic formats and offline verification primitives.

Provider signing keys, Registry identities, provenance, and publication workflows are external trust inputs, not Takoform defaults.