Crypto-Agile by Design: The Enterprise Playbook for Post-Quantum Cryptography Migration Across TLS, PKI, and Code Signing
Quantum computing changes the risk calculus for every enterprise that depends on cryptography—which is to say, every enterprise. Even before fault-tolerant quantum machines exist, adversaries can capture encrypted traffic and sensitive binaries today in a “harvest-now, decrypt-later” strategy, waiting for the day they can break classical public-key schemes. The path forward is not panic or wholesale replacement; it’s crypto agility: building systems that can discover, switch, and roll out new cryptographic algorithms without breaking availability, compliance, or customer experiences.
This playbook lays out how to plan and execute a post-quantum cryptography (PQC) migration across three of the most visible and risk-bearing surfaces in a modern enterprise: TLS for transport security, PKI for identities and trust, and code signing for the software supply chain. It focuses on practical design patterns, rollout strategies, and operational considerations, with an emphasis on what it takes to be crypto-agile by design—so you can adopt PQC safely, at your pace, and adapt as standards and tooling evolve.
Why Crypto Agility Matters Now
Quantum threats are asymmetric: a single breakthrough can invalidate widely deployed algorithms at once. RSA and elliptic-curve schemes (ECDSA/ECDH) are vulnerable to Shor’s algorithm on a sufficiently powerful quantum computer. While no such machine is known to exist today, the time horizon for sensitive data often exceeds a decade. If you protect health records, strategic plans, or confidential IP, their secrecy lifetime is likely long enough to be at risk. Crypto agility buys you control: the ability to respond to new standards, vulnerabilities, or vendor support changes without wholesale rewrites.
Agility also addresses non-quantum realities: deprecations (e.g., SHA-1), policy shifts (e.g., 398-day TLS certificate lifetimes), and new assurance requirements (e.g., FIPS 140-3). The same patterns that let you add ML-KEM to your TLS ciphersuite will help you retire insecure algorithms, rotate keys at scale, and run A/B deployments that prove compatibility before committing.
Standards Snapshot: What to Track and Why
The standards landscape is maturing quickly. Enterprise teams should anchor planning in efforts that have strong consensus:
- NIST PQC selections: Key encapsulation mechanism (KEM) ML-KEM (formerly CRYSTALS-Kyber) and digital signatures ML-DSA (formerly CRYSTALS-Dilithium) and SLH-DSA (formerly SPHINCS+). These are in the process of being standardized as FIPS publications and referenced across ecosystems. Falcon remains relevant for certain constrained use cases, with standardization progressing separately.
- IETF work: TLS and LAMPS working groups maintain drafts for hybrid key exchange (ECDHE + KEM), KEM-based authentication variants, and X.509 algorithm identifiers and certificate profiles for PQC. Watch for drafts on composite/hybrid certificates and for updates to OCSP/CRL profiles.
- Platform roadmaps: Browser vendors, operating systems, and large CDNs have run production experiments with hybrid TLS using ML-KEM plus X25519. Major HSM and KMS vendors are introducing PQC support paths; CSPs are adding PQC primitives to managed keys and certificate services.
- Guidance: NIST SP 800-57, 800-131A, and the NCCoE PQC Migration Project; European bodies such as ENISA and BSI have published migration advice and algorithm recommendations.
Crypto-Agile Design Principles
Abstract Cryptography Behind Stable Interfaces
Hard-coding algorithms into applications guarantees friction later. Introduce a crypto service abstraction—library or sidecar—that exposes intent (“sign”, “verify”, “key exchange”, “encrypt at rest”) and takes policy input for the algorithm suite. For microservices, standardize a client library that negotiates TLS ciphersuites and certificate validation, and source it from a central artifact repository to ensure consistent updates.
Drive Choices with Policy, Not Code
Define a global cryptographic policy with environments and exceptions. Express allowed algorithms, key sizes, certificate profiles, and deprecation dates. Enforce via:
- Build-time checks (linting of TLS and certificate configuration, CI gates for code signing choices)
- Runtime policy engines (sidecars or Envoy filters that constrain negotiated ciphers, require PQC where supported, and record downgrades)
- Change management that treats algorithm switches like feature flags
Use Managed Key Infrastructure and Tamper-Resistant Storage
PQC keys and artifacts will be larger and sometimes more CPU-intensive. Favor KMS/HSM integrations that can be upgraded. Require vendors to document plans for ML-KEM/ML-DSA support, FIPS 140-3 validations, and performance on target modules. Design fallback paths where software implementations can be used temporarily in non-FIPS environments while HSM support matures, with compensating controls.
Operational Observability and a Cryptographic Bill of Materials (CBOM)
Inventory is prerequisite to migration. Build a CBOM that maps:
- Where and how TLS is used (ports, clients, ciphersuites, protocol versions, session resumption)
- All X.509 certificates in use (issuers, algorithms, expirations, intermediates, revocation status)
- Code signing mechanisms per platform (signing toolchains, timestamping, notarization)
- Third-party dependencies that terminate TLS or verify signatures
Feed the CBOM from automated scans: certificate transparency logs, TLS handshake fingerprinting (e.g., JA3/JA4), endpoint management data, and repository searches for crypto APIs. Update continuously, not annually.
The Enterprise Playbook: A Phased Roadmap
Phase 1: Inventory, Risk, and Objectives
- Classify data by secrecy lifetime and exposure. Identify systems with long confidentiality requirements (healthcare, legal, R&D) and prioritize their channels.
- Catalog TLS endpoints (inbound and outbound), mutual TLS usage, and devices that cannot easily update.
- Map PKI landscape: internal CAs, external CAs, RA processes, OCSP/CRL infrastructure, and certificate automation.
- Document code signing coverage: platforms (Windows, macOS, Linux, Android, iOS), firmware, containers, and the build systems that produce them.
- Establish success criteria: e.g., hybrid TLS in all public-facing sites by date X, dual-signed binaries by date Y, PQ-capable internal PKI by date Z.
Phase 2: Architecture and Patterns
- Adopt policy-driven crypto libraries across services, with default TLS 1.3 and ALPN-aware configurations.
- Design a parallel PQ-capable PKI hierarchy in staging: separate roots and intermediates to avoid risk to production chains; plan for dual hierarchies and cross-signing where permitted.
- Define certificate profiles with algorithm identifiers for ML-DSA or SLH-DSA, key usage, and extension policies. Pre-agree on name constraints and validity periods.
- Select code signing strategies: dual signatures (classical + PQC) where platform supports multi-signing; where not, adopt parallel distribution channels or POC pilots until platform support lands.
Phase 3: Interoperability Lab and Pilots
- Build a testbed with browsers, OS versions, mobile clients, proxies, WAFs, and middleboxes that reflect your production path.
- Stand up PQC-capable TLS on test endpoints using hybrid key exchange (e.g., X25519 + ML-KEM). Validate handshake sizes, fragmentation, and observability.
- Issue PQC test certificates from staging CA; test chain building, OCSP, CRLs, and RPs that parse new OIDs.
- Run pilot code signing with PQ signatures and timestamping; test validation on target platforms and packaging systems.
Phase 4: PKI Parallelization
- Deploy a parallel PQ-capable PKI alongside classical hierarchies. Keep production roots offline; issue limited-scope intermediates for controlled pilots.
- Introduce ACME/EST/CMP automation to request, renew, and rotate both classical and PQC certificates. Instrument for failures and pathologic retries.
- Stand up status services for PQC chains; ensure OCSP stapling works with larger responses and that caches are sized appropriately.
Phase 5: Controlled Rollout and SRE Readiness
- Traffic-shape PQ endpoints behind front doors/CDNs to smaller audiences. Record error rates, handshake metrics, and performance deltas. Set guardrails to auto-roll back on regressions.
- Enable hybrid TLS on internal services first; migrate mutual TLS clusters where client control is strongest.
- Dual-sign code artifacts and publish in parallel with classical signatures. Monitor support lines for validation issues; maintain explicit fallback guidance.
Phase 6: Legacy Decommission
- Retire disallowed ciphers and protocols in waves. For endpoints that cannot be updated, isolate and front them with policy-enforcing proxies.
- Shorten certificate lifetimes to accelerate fleet turnover and minimize long-tail risk.
- Update procurement controls so new vendors meet PQC and crypto agility requirements by default.
TLS Migration, In Depth
Protocol Baseline and Cleanups
Make TLS 1.3 the baseline. Remove TLS 1.0/1.1; evaluate remaining 1.2 dependencies and plan retirement. Normalize minimum cipher suites to ECDHE with AEAD (e.g., AES-GCM or ChaCha20-Poly1305). For HTTP/3, ensure QUIC stacks can handle larger handshake messages.
Key Exchange: Hybrid Now, Pure PQC Later
The most pragmatic near-term move is hybrid key exchange: combine classical ECDHE (X25519 or P-256) with ML-KEM. This yields confidentiality if either primitive remains unbroken and preserves compatibility with clients that only understand classical ECDHE. Cloud providers and CDNs have shown production viability with minimal latency regression, though packet sizes increase.
Implementation tips:
- Prefer ephemeral KEM keys per handshake to maintain forward secrecy properties.
- Monitor ClientHello and ServerHello extensions to ensure negotiation cannot be silently downgraded; log when hybrid is not negotiated and why.
- Beware MTU fragmentation: Kyber768 adds roughly a couple of kilobytes to the handshake; ensure path MTU discovery and TCP settings minimize retransmits.
Authentication: Certificates and Signatures
TLS server authentication depends on X.509 signatures. There are three options:
- Classical certificates with hybrid key exchange only: easiest to deploy today; protects confidentiality against quantum adversaries but leaves authentication on classical signatures.
- Dual chains: operate classical and PQC certificate chains in parallel. Servers present a chain based on client capabilities or in a multi-certificate handshake where supported. This avoids unstandardized “composite” signatures and leverages existing validation logic.
- PQC certificates: use ML-DSA or SLH-DSA keys and signatures end-to-end. Requires clients to parse new OIDs and accept larger signatures. Best suited for controlled internal environments first.
Practical reality: start with hybrid KEM plus classical certs on the public edge, while moving to PQC certs inside service meshes and data centers where you control clients and libraries. As PKI and browser ecosystems finalize PQC path building, you can expand outward.
Middleboxes and “The Path”
Firewalls, TLS inspectors, DLP boxes, and traffic analyzers may fail on larger handshake messages, unknown signature OIDs, or fragmented records. Your interoperability lab should mirror this path. Include CDN edges, bot managers, and API gateways. Pre-announce maintenance windows, and pilot geographies or tenants to reduce the blast radius. Ensure observability tools decode and display PQC identifiers so operations teams don’t interpret them as anomalies.
Performance and Tuning
Measure rather than assume. Key exchange with ML-KEM is fast on modern CPUs, but signatures like ML-DSA have larger sizes, and SLH-DSA signatures can be tens of kilobytes depending on parameters. Use:
- HTTP/2 or HTTP/3 connection reuse to amortize handshakes
- Session tickets/resumption while avoiding resumption across policy boundaries
- TCP initial congestion window tuning where handshake sizes stress slow-start
- Edge termination with hybrid KEM and careful multiplexing to backend connections that use PQC in mTLS
Client Compatibility Matrix
Maintain a living matrix of client stacks and their PQ characteristics: browser versions, mobile OS releases, JVMs, Python/Go/Node TLS libraries, and embedded SDKs. For each, record support for hybrid KEM, PQC certs, and any flags required. Use analytics to map client populations to capabilities to guide cutovers.
PKI Evolution for Post-Quantum
Hierarchies and Certificate Profiles
Build a PQC-capable CA hierarchy in parallel to your classical one. Keep roots offline, with distinct names and policies. For leaf and intermediate certificates, define profiles that include:
- Algorithm identifiers and parameters for ML-DSA or SLH-DSA
- Appropriate Extended Key Usage (serverAuth, clientAuth, codeSigning) per use case
- Name constraints and path length limits to contain risk
- Shorter validity periods to accelerate turnover and improve agility
Ensure RA workflows and certificate management platforms support the new OIDs end-to-end, including CSR parsing, approval, issuance, and revocation.
Cross-Signing and Dual Hierarchies
Where external trust is required (public TLS, partner integrations), you may need cross-signing or dual chains to bridge classical and PQC worlds. Options include:
- Cross-sign classical intermediates with a PQ root and PQ intermediates with a classical root, yielding alternate validation paths. Use carefully; it can be complex to reason about trust paths and revocation.
- Operate two parallel hierarchies and choose the chain at issuance time or during TLS negotiation, based on peer capability signaling.
Keep path building simple. Resist composite certificate constructions until tooling and standards settle. Document how revocation propagates across dual hierarchies to avoid stale trust.
Lifecycle Automation
Automation is where crypto agility pays dividends. Use ACME for web servers and APIs; EST or CMP for devices and internal mTLS identities. Your automation should:
- Request both classical and PQC certificates where appropriate
- Monitor issuance times and failure reasons; fall back intelligently but visibly
- Rotate keys on policy, not just certificate renewals, to reduce key age
Revocation and Status
OCSP responders and CRLs must cope with larger signatures. Ensure caches, bandwidth, and stapling logic are tuned. Validate that relying parties recognize PQC algorithm OIDs in OCSP responses. For privacy and performance, favor stapling and OCSP multi-responder architectures at scale.
Audit and Compliance
Update CP/CPS documents to incorporate PQC algorithms, issuance practices, and incident response. Extend audit controls to verify key ceremony procedures for PQ keys and to ensure PQC issuance and revocation events are logged and immutable. Align with FIPS 140-3 validated modules as your HSM/KMS vendors add PQC.
Code Signing and the Software Supply Chain
Platform-Specific Realities
- Windows Authenticode: Supports multiple signatures on a PE file and on catalog files. Begin dual-signing with ECDSA and a PQ signature when platform and tooling allow. Use RFC 3161 timestamping to preserve trust across algorithm deprecations. Track EV Code Signing policies and smartcard/USB token support for PQ keys.
- Apple notarization: The notarization service validates signatures and scans binaries. Monitor Apple developer updates for PQC acceptance timelines. In the interim, maintain classical signatures while preparing PQ signing in the build pipeline.
- Android APK signing: APK Signature Scheme v2/v3 supports multiple signers. Test dual signatures and verify Play Store and device validators accept expanded manifests and signature blocks.
- Java JAR signing: Multiple signers are allowed; define jar signer policies that include both classical and PQ cert chains where tooling supports it.
Containers and DevOps Toolchains
Container and artifact signing is rapidly modernizing:
- Sigstore/cosign: Public good infrastructure (Fulcio for issuing, Rekor for transparency) supports experimentation and rapid iteration. Work toward PQ signatures once supported; in the meantime, gain agility by decoupling keys from developers and centralizing policy.
- Notary v2 and OCI artifacts: Ensure registries and admission controllers accept larger signatures and can enforce per-repository policy on algorithms used.
- TUF/Uptane for secure updates: Plan PQ signatures in metadata, recognizing that large signatures may require metadata chunking and bandwidth considerations for edge devices.
Build Pipeline Changes
Make the build system algorithm-aware:
- Centralize signing operations in dedicated services with HSM/KMS backing; do not distribute keys across CI workers.
- Expose a policy service that selects the signature suite by artifact type and target platform.
- Record signature events and publish to transparency logs; include algorithm identifiers in SBOM/attestations so downstream consumers can enforce policies.
Time-Stamping and Long-Term Validation
Time stamps anchor trust when algorithms are deprecated. Operate or rely on TSA services that can produce PQC-signed responses once available. For existing classical TSAs, plan for a migration path that preserves the chain of evidence: artifact signature time-stamped, then a later notary counter-signature attesting to the time stamp while both algorithms are still trusted.
Developer Enablement
Developers need a paved road. Provide SDKs and CLI tools with sane defaults, templates for signing workflows, and guardrails in CI that prevent non-compliant signatures from shipping. Offer test environments that simulate verifier behavior for both classical and PQC validation to catch issues early.
Edge and IoT Considerations
Secure Boot and Firmware Updates
Devices rely on secure boot chains anchored in signatures burned into ROM or eFuses. PQ migration here requires careful sequencing:
- Introduce dual-verify bootloaders that accept both classical and PQ signatures for a transition period.
- Stage bootloader updates first, then firmware images signed with PQ algorithms. Maintain rollback protections and audit trails.
- Account for signature size increases; ensure flash layout and update transport protocols can carry larger metadata.
Constrained Devices and Networks
ML-DSA signatures and especially SLH-DSA can be large for constrained links. Consider:
- Hybrid TLS with classical authentication to keep handshake sizes manageable during early phases, moving to PQ auth once firmware and networks are proven.
- Compression at the transport or application layer for update packages to offset larger metadata.
- Batching or delta updates to reduce transfer frequency.
Update Orchestration at Scale
For fleets in the millions, orchestrate by cohorts, not all at once. Maintain per-cohort telemetry on verification failures, download errors, and boot success. Embed a kill switch that can temporarily accept legacy signatures if a PQ-related regression appears, with strict time bounds and alerting.
Real-World Migration Scenarios
Global Bank: Hybrid TLS on Trading Gateways
A bank prioritizes confidentiality for trading APIs. It deploys hybrid TLS (X25519 + ML-KEM) on gateway terminators fronted by a CDN. Client analytics show 92% of API clients negotiate hybrid on day one; those that don’t are older libraries on partners’ systems. The bank keeps classical certs while requiring partners to upgrade within six months. Operational data shows a 2–3% handshake size increase affecting only the highest latency geographies, mitigated by initial window tuning. Internally, mTLS between microservices moves to PQC certificates signed by a new offline PQ root. Observability pipelines tag connections by negotiated KEM and signature OIDs, enabling precise tracking and incident response.
SaaS Provider: Code Signing and Container Supply Chain
A SaaS vendor dual-signs all binaries and container images. It centralizes signing in a dedicated service backed by an HSM cluster, exposes a policy API to build pipelines, and publishes attestations to a transparency log. Kubernetes admission controllers enforce that workloads are signed with approved suites and reject artifacts without dual signatures in canary namespaces. The vendor pilots PQ signatures in an early access channel for macOS and Windows agents, monitoring support tickets and verification telemetry. It coordinates with timestamping authorities for longer-term validation and includes algorithm identifiers in customer-facing SBOMs to support downstream verification.
Industrial Manufacturer: PQC for IIoT Devices
An industrial firm ships controllers with a multi-stage bootloader. It first updates the bootloader to accept ML-DSA, then rolls out firmware images with dual signatures. Field gateways terminate hybrid TLS for telemetry and command channels, while edge devices continue with classical auth until the fleet reaches 80% upgraded. The update pipeline uses TUF with expanded metadata buckets to accommodate larger signatures. Factory provisioning adds PQC enrollment with EST, and the internal PKI operates parallel hierarchies for device and server identities. Downtime decreases because update failures are detected cohort-by-cohort with automated backoff and rollback policies.
Governance, People, and Budgets
Roles and Accountability
- Crypto Steering Committee: Security architecture, PKI, platform engineering, and SRE leads with authority to set policy and accept risk.
- Service Owners: Accountable for adopting standard client/server libraries and meeting rollout deadlines.
- PKI Team: Owns CA operations, CP/CPS updates, and status infrastructure.
- Build Engineering: Owns signing services, developer tooling, and CI enforcement.
- Vendor Management: Embeds crypto agility requirements in contracts and SLAs.
Training and Readiness
Provide hands-on labs: how to read certificate profiles with PQ OIDs, interpret TLS traces with hybrid KEM, and debug signature verification. Write runbooks for incident responders: detecting downgrades, triaging handshake failures, and executing a crypto kill switch change. Include post-quantum topics in secure coding training to avoid developers inventing ad-hoc hybrid schemes.
Procurement and Budgeting
Budget for:
- PKI upgrades (offline roots, HSMs/KMS enhancements, automation tooling)
- Performance headroom and network costs from larger handshakes and signatures
- Test and staging infrastructure mirroring production middleboxes and clients
- Training and external assessments (e.g., NCCoE engagement)
Common Pitfalls and How to Avoid Them
- Hard-coding cipher suites: Use policy controls and negotiable client libraries.
- Assuming middlebox transparency: Test end-to-end; many devices mishandle large cert chains.
- Skipping status services: Larger OCSP responses and new OIDs can break caches; instrument and rehearse failover.
- Ignoring developer experience: Without paved roads, teams will diverge and introduce risk.
- All-at-once cutovers: Prefer phased, observable rollouts with rapid rollback paths.
- Over-reliance on composite certificates: Until standards and ecosystem support are stable, dual chains are safer.
- Neglecting long-term validation: Plan time-stamping and archival strategies early for signed artifacts.
Practitioner Play Cards
TLS Edge Quick Wins
- Enforce TLS 1.3 baseline and remove weak ciphers
- Enable hybrid KEM on edge/CDN for a low-risk audience
- Instrument handshake negotiation and log capabilities
- Set guardrails to auto-rollback on error spikes
PKI “Day Two” Must-Haves
- Parallel PQC hierarchy in staging with documented profiles
- OCSP/CRL services tested with PQ signatures and larger payloads
- ACME/EST integrated with issuance policy for both classical and PQC
- CP/CPS updated and audited
Code Signing Guardrails
- Centralized signing service with HSM/KMS; no developer-held keys
- Dual-sign where platform allows; timestamp every artifact
- Publish attestations and include algorithms in SBOMs
- Admission control enforcing signature policies
Testing, Telemetry, and Incident Response
Performance and Interoperability Testing
Create synthetic tests that exercise full TLS handshakes with hybrid KEM across realistic latencies. Capture:
- Handshake completion rates and time-to-first-byte deltas
- Packet retransmissions and fragmentation incidents
- CPU utilization during peak load windows
For code signing, test verification across supported OS versions in virtual device farms. Include negative tests: corrupted signatures, wrong OIDs, and clock skews affecting time stamps.
Telemetry You Need
- Negotiated TLS parameters (protocol, KEM, signature scheme) tagged to service and client segments
- Certificate chain sizes and validation paths observed in production
- OCSP response sizes, cache hit rates, and error codes
- Build pipeline signature success/failure reasons by artifact type
Incident Response Patterns
Define a crypto kill switch: a policy change that can disable or prefer certain algorithms globally within minutes. Couple it with:
- Pre-approved change windows and on-call rotations including PKI team
- Mass certificate replacement runbooks with rate limits and canarying
- Clear partner/customer communication templates for algorithm or certificate changes
Security Guarantees and Trade-offs
Hybrid key exchange provides confidentiality if either the classical or the PQ KEM stays secure, but it does not upgrade authentication unless certificates also carry PQ signatures. Pure PQC authentication offers stronger quantum resilience yet may reduce compatibility and increase handshake size. SLH-DSA offers hard-to-quantumize security assumptions with larger signatures; ML-DSA is compact and fast with strong confidence from cryptanalysis. Choose per use case and revisit as cryptanalysis and implementation experience evolve.
Forward secrecy remains achievable with KEMs by using ephemeral keying material. Avoid static KEM keys in TLS; keep ephemeral behaviors consistent with your PFS policies. Beware of implementation pitfalls like parameter confusion or truncation attacks in hybrid constructions; rely on well-reviewed libraries and protocol drafts rather than homegrown hybrids.
Data, Logs, and Retention Implications
Larger certificates, OCSP responses, and signature blocks can stress log pipelines and storage. Ensure:
- Log schemas accept new algorithm identifiers and larger values
- Sampling and retention policies remain compliant while accommodating size growth
- Compression strategies in data lakes reduce cost without losing forensic fidelity
For packet captures used in forensics, consider controlled environments where hybrid KEM is mandated earlier to reduce harvest-now risk. Update DLP and IDS rules to recognize PQC ciphers and avoid false positives.
Vendor and Ecosystem Management
Most enterprises depend on intermediaries: CDNs, WAFs, API gateways, SASE stacks, MDMs, and managed PKI. Bake PQC and crypto agility clauses into contracts:
- Roadmaps for hybrid TLS and PQC certificate support
- Service-level targets for issuance, revocation, and status services at larger payloads
- Transparency on algorithm identifiers in telemetry and audit exports
- FIPS 140-3 validations and timelines for PQC-enabled modules
For open-source dependencies (OpenSSL, BoringSSL, NSS, wolfSSL, mbedTLS), track PQC branches and versioning. Contribute test cases from your interoperability lab back to the community where possible.
Economics and Capacity Planning
PQC introduces modest CPU overhead for KEMs and more pronounced bandwidth/storage overhead for signatures and certificate chains, depending on parameters. Model:
- Edge CPU headroom under peak handshakes, with hybrid versus classical baselines
- Bandwidth effects on initial connections, especially in mobile geographies
- Storage and memory usage for certificate caches, OCSP caches, and artifact repositories
- Build times and signing throughput for large monorepos and frequent release trains
Quantify costs ahead of budget cycles. Mitigate with connection reuse, caching, and selective parameter choices aligned with your risk posture.
Advanced Topics and Future-Proofing
Toward KEM-Authenticated TLS
Research and drafts explore KEM-based authentication models that may bring performance benefits and different trust semantics. Keep these in view but avoid blocking near-term gains waiting for them; hybrid KEM plus classical/PQ signatures yields strong protection today.
Algorithm Versioning and Sunsetting
Design a lifecycle for algorithms: introduce, prefer, require, and deprecate states. Expose these as feature flags and configuration in your policy service. Maintain a deprecation calendar aligned with vendor and standards timelines, and track dependencies that cannot meet dates to escalate remediation or isolation plans.
Attestation and Transparency
Beyond code signing, artifact and certificate transparency logs provide independent verification and ecosystem accountability. Participate in transparency ecosystems for certificates and software artifacts; publish sufficient metadata for customers and auditors to verify PQ adoption without revealing sensitive internals.
Quantum-Safe Beyond TLS and Signing
While this playbook focuses on TLS, PKI, and code signing, extend crypto agility to data at rest and in messaging systems. For key wrapping and envelope encryption, plan for PQ KEM-based key establishment in KMS and secret distribution workflows. For encrypted databases and backups with long retention, prioritize early adoption of PQ-safe key management to mitigate harvest-now risk.