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securitycritical PriorityID: sigstore-v3-rekor-inclusion-verification-standard

Sigstore v3 Keyless OIDC Ephemeral Certificate Rekor Inclusion Verification

Production admission controllers and deployment pipelines must verify cryptographically provable transparency log (Rekor) inclusion proofs (SET/inclusion promise and Merkle audit path) for Fulcio-issued ephemeral X.509 certificates. Verification must confirm SAN OIDC claims and certificate validity windows alongside Rekor integrated time rather than relying solely on leaf certificate X.509 signature validity.

Prohibited Anti-Pattern: Accepting Fulcio ephemeral leaf certificates without validating cryptographic Rekor inclusion proofs and SCT timestamps

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---
description: Sigstore v3 Keyless OIDC Ephemeral Certificate Rekor Inclusion Verification - Production admission controllers and deployment pipelines must verify cryptographically provable transparency log (Rekor) inclusion proofs (SET/inclusion promise and Merkle audit path) for Fulcio-issued ephemeral X.509 certificates. Verification must confirm SAN OIDC claims and certificate validity windows alongside Rekor integrated time rather than relying solely on leaf certificate X.509 signature validity.
globs: src/admission/**/*.{ts,go,py}, src/security/**/*.{ts,go,py}, src/verification/**/*.{ts,go,py}, deploy/admission-controllers/**/*.{yaml,json}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/sigstore-v3-rekor-inclusion-verification-standard"
---

# Sigstore v3 Keyless OIDC Ephemeral Certificate Rekor Inclusion Verification

> **Severity**: CRITICAL | **Category**: security
> **Anti-Pattern Warning**: Accepting Fulcio ephemeral leaf certificates without validating cryptographic Rekor inclusion proofs and SCT timestamps

## System Constraints
You are a Principal Security Architect enforcing Sigstore v3 Keyless OIDC Identity Ephemeral Certificate Rekor Inclusion Verification. You ensure zero-trust artifact admission into production clusters by requiring verifiable transparency log inclusion proofs, strict SAN OIDC subject and issuer matching, and checkpoint log signature verification against official public root targets.

## Strict Guidelines
- Engineers MUST ALWAYS verify cryptographic Rekor inclusion proofs (inclusionPromise and inclusionProof against the log tree root) when validating Sigstore v3 bundles before allowing workload admission.
- Engineers MUST NOT accept X.509 certificate chains from Fulcio without verifying that the certificate's notBefore/notAfter interval envelopes the signed entry's integratedTime recorded in the Rekor transparency log.
- Code SHOULD enforce strict SAN (Subject Alternative Name) URI validation, confirming the OIDC issuer (e.g., https://token.actions.githubusercontent.com) and exact identity string (e.g., repository workflow path).
- Services MUST download and verify the TUF root of trust metadata before validating Rekor checkpoints, ensuring verification keys are trusted and unexpired.
- Components NEVER allow fallback or bypass modes where unverified signatures pass admission when transparency log endpoints are degraded or offline.

## Bad vs Good Implementations
### Sigstore Bundle Verification with Rekor Log Inclusion

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The code bypasses the transparency log requirement. Fulcio ephemeral certificates expire in 10-20 minutes; trusting them without checking Rekor log inclusion allows an attacker with a rogue or compromised intermediate CA to forge short-lived signatures without leaving a verifiable, non-repudiable audit trail.
```typescript
import { verify } from '@sigstore/verify';

// ANTI-PATTERN: Verifies signature and basic certificate validity,
// completely ignoring transparency log inclusion and identity constraints.
export async function verifyArtifact(bundle: any, artifactBytes: Buffer): Promise<boolean> {
  const leafCert = bundle.verificationMaterial.certificate;
  // Flaw: Only checks X.509 expiration, vulnerable to rogue/compromised Fulcio certs
  // without proving the certificate was publicly logged to Rekor.
  return leafCert.notBefore <= new Date() && leafCert.notAfter >= new Date();
}
```

#### Production Standard (Correct)
> **Standard**: Uses the official Sigstore verification engine configured to require cryptographic Rekor inclusion proofs (`tlogInclusionVerification: true`) and validates OIDC identity assertions (SAN URI and Issuer), ensuring artifacts cannot enter production unless logged to the public Merkle tree within the certificate's validity envelope.
```typescript
import { sigstore } from 'sigstore';

interface PolicyConstraints {
  expectedIssuer: string;
  expectedSanIdentity: string;
}

// PRODUCTION FIX: Enforces full bundle verification including Rekor tlog inclusion proof,
// checkpoint signature against trusted root, and exact OIDC SAN identity matching.
export async function verifyArtifactIngress(
  bundle: sigstore.SerializedBundle,
  artifactBuffer: Buffer,
  policy: PolicyConstraints
): Promise<void> {
  await sigstore.verify(bundle, artifactBuffer, {
    tlogInclusionVerification: true, // Forces inclusion proof verification against Rekor Merkle tree
    certificateIssuer: policy.expectedIssuer,
    certificateIdentityURI: policy.expectedSanIdentity,
    // Ensure verification does not silently fall back to offline caches
    retry: { retries: 2 }
  });
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Sigstore Policy Verifier MCP
Validates Sigstore v3 bundles, Rekor inclusion proofs, and TUF root chains for artifact verification workflows.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Cosign Security Tooling
Official container signing, verification, and transparency log query CLI tool for Sigstore ecosystems.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Sigstore v3 Keyless OIDC Ephemeral Certificate Rekor Inclusion Verification

Sigstore v3 Keyless OIDC Ephemeral Certificate Rekor Inclusion Verification defines an industrial-grade behavioral standard for security engineering. Production admission controllers and deployment pipelines must verify cryptographically provable transparency log (Rekor) inclusion proofs (SET/inclusion promise and Merkle audit path) for Fulcio-issued ephemeral X.509 certificates. Verification must confirm SAN OIDC claims and certificate validity windows alongside Rekor integrated time rather than relying solely on leaf certificate X.509 signature validity. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Accepting Fulcio ephemeral leaf certificates without validating cryptographic Rekor inclusion proofs and SCT timestamps Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftAccepting Fulcio ephemeral leaf certificates without validating cryptographic Rekor inclusion proofs and SCT timestampsCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS verify cryptographic Rekor inclusion proofs (inclusionPromise and inclusionProof against the log tree root) when validating Sigstore v3 bundles before allowing workload admission.

Engineers MUST ALWAYS verify cryptographic Rekor inclusion proofs (inclusionPromise and inclusionProof against the log tree root) when validating Sigstore v3 bundles before allowing workload admission.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST NOT accept X.509 certificate chains from Fulcio without verifying that the certificate's notBefore/notAfter interval envelopes the signed entry's integratedTime recorded in the Rekor transparency log.

Engineers MUST NOT accept X.509 certificate chains from Fulcio without verifying that the certificate's notBefore/notAfter interval envelopes the signed entry's integratedTime recorded in the Rekor transparency log.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Code SHOULD enforce strict SAN (Subject Alternative Name) URI validation, confirming the OIDC issuer (e.g., https

Code SHOULD enforce strict SAN (Subject Alternative Name) URI validation, confirming the OIDC issuer (e.g., https://token.actions.githubusercontent.com) and exact identity string (e.g., repository workflow path).

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Services MUST download and verify the TUF root of trust metadata before validating Rekor checkpoints, ensuring verification keys are trusted and unexpired.

Services MUST download and verify the TUF root of trust metadata before validating Rekor checkpoints, ensuring verification keys are trusted and unexpired.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Components NEVER allow fallback or bypass modes where unverified signatures pass admission when transparency log endpoints are degraded or offline.

Components NEVER allow fallback or bypass modes where unverified signatures pass admission when transparency log endpoints are degraded or offline.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Sigstore v3 Keyless OIDC Ephemeral Certificate Rekor Inclusion Verification critical for AI coding assistants?

Production admission controllers and deployment pipelines must verify cryptographically provable transparency log (Rekor) inclusion proofs (SET/inclusion promise and Merkle audit path) for Fulcio-issued ephemeral X.509 certificates. Verification must confirm SAN OIDC claims and certificate validity windows alongside Rekor integrated time rather than relying solely on leaf certificate X.509 signature validity. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Accepting Fulcio ephemeral leaf certificates without validating cryptographic Rekor inclusion proofs and SCT timestamps) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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