When to Use
- Select and justify cryptographic primitives (AEAD, signatures, KEMs, hashes, KDFs)
- Design key lifecycle — generation, storage, rotation, escrow policy, destruction, dual control
- Architect PKI and TLS — internal CAs, cert profiles, mTLS, pinning, stapling, cipher policies
- Review protocols — handshakes, transcript binding, downgrade resistance, session keys
- Analyze authenticated encryption misuse — nonces, IVs, associated data, key separation
- Compare password hashing (Argon2, bcrypt, scrypt) vs KDFs (HKDF, PBKDF2) for the use case
- Plan post-quantum awareness — hybrid schemes, inventory, migration sequencing (architecture level)
- Frame formal properties — secrecy, authentication, forward secrecy, agreement (ProVerif/Tamarin concepts)
- Specify implementation requirements — constant-time, zeroization, entropy, crypto agility
- Produce crypto design reviews and threat-informed recommendations with explicit assumptions
When NOT to Use
- General OWASP web/API pentest or app-layer vuln triage without crypto design →
information-security-engineer,web-pentester,penetration-tester - Broad secure-coding review across stacks (injection, authz, headers) without primitive/protocol focus → use secure-coding skills in the agent catalog (e.g.
code-securitywhen installed) - Deploy SIEM, IdP, EDR, or corp guardrails without cryptographic design →
information-security-engineer - Solidity/EVM smart contract audit or DeFi on-chain triage →
evm-solidity-defi-triage-agent(agent skill) or protocol-specific audit skills - Blockchain address tracing, clustering, or compliance screening → blockint / on-chain investigation skills
- Legal export control, sanctions, or jurisdiction classification →
commercial-counsel(legal boundaries only; not legal advice) - Implement a full production crypto library from scratch without peer review, standards alignment, and test vectors
- ML adversarial robustness on models →
ai-adversarial-robustness-engineer - Assurance cases and DO-178C-style software assurance without crypto-specific claims →
software-assurance-formal-methods-specialist
Related skills
| Need | Skill |
|---|---|
| KMS/TLS deployment, secrets stores, corp encryption ops | information-security-engineer |
| Secure coding and vulnerability patterns (general) | code-security (agent catalog, when available) |
| Constant-time implementation review | constant-time-analysis, constant-time-testing (agent catalog) |
| Protocol sequence diagrams from specs/code | crypto-protocol-diagram (agent catalog) |
| Mermaid → ProVerif model translation | mermaid-to-proverif (agent catalog) |
| Secret zeroization audit in C/C++/Rust | zeroize-audit (agent catalog) |
| Contract/export and commercial legal boundaries | commercial-counsel |
| Formal assurance cases, GSN, DO-178C context | software-assurance-formal-methods-specialist |
| CI/CD and supply-chain crypto in pipelines | devsecops |
| Cloud KMS, cert managers, private CA in cloud | cloud-security-engineer |
Core Workflows
1. Scope and assets
- Identify protected assets (keys, plaintext, metadata, identities, logs)
- Define adversary model — network, insider, physical, quantum timeline
- List trust boundaries and assumptions (HSM, OS RNG, third-party libraries)
- Record compliance or policy constraints (FIPS, regional, customer crypto profiles)
See references/cryptographer_specialist_scope.md.
2. Primitive and algorithm selection
Map security goals to approved primitive families; document tradeoffs and deprecation status.
See references/primitives_and_algorithm_selection.md.
3. Key management, PKI, and TLS
Design key hierarchy, rotation, escrow exceptions, and certificate/TLS profiles.
See references/key_management_pki_and_tls.md.
4. Protocol design and security properties
Specify messages, key derivation, binding, and the properties each layer must achieve.
See references/protocol_design_and_properties.md.
5. Implementation pitfalls and side channels
Translate design into developer requirements: AEAD usage, timing, memory, RNG, error handling.
See references/implementation_pitfalls_and_side_channels.md.
6. Formal methods, agility, and governance
Align with verification artifacts, algorithm sunset, and review gates for crypto changes.
See references/formal_methods_agility_governance.md.
Outputs
- Crypto design note — goals, primitives, key sizes, lifetimes, assumptions, open risks
- Protocol review — message flow, derived keys, downgrade and replay analysis
- TLS/PKI profile — versions, cipher suites, cert fields, rotation, monitoring
- Implementation checklist — nonce rules, constant-time surfaces, zeroization, test vectors
- Migration plan — deprecated algorithms, PQ hybrid options, inventory and phases
- Formal-methods brief — intended properties, model scope, tool fit (when applicable)
Principles
- Prefer well-vetted libraries and standards (RFCs, NIST, CFRG) over custom constructions
- Never roll your own block cipher, hash, or protocol; compose proven building blocks
- Separate confidentiality, integrity, and identity keys; document nonce uniqueness rules
- Treat password hashing and key derivation as different problems with different parameters
- Plan crypto agility before algorithms break; monitor deprecations (SHA-1, RSA-1024, TLS 1.0/1.1)
- Escalate legal/export questions to counsel; do not provide export classification advice
When to load references
- Scope and boundaries →
references/cryptographer_specialist_scope.md - Algorithms and primitives →
references/primitives_and_algorithm_selection.md - Keys, PKI, TLS →
references/key_management_pki_and_tls.md - Protocols and properties →
references/protocol_design_and_properties.md - Implementation and side channels →
references/implementation_pitfalls_and_side_channels.md - Formal methods and governance →
references/formal_methods_agility_governance.md