Cryptographer Specialist

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-security when 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

Core Workflows

1. Scope and assets

1. Identify protected assets (keys, plaintext, metadata, identities, logs)
2. Define adversary model — network, insider, physical, quantum timeline
3. List trust boundaries and assumptions (HSM, OS RNG, third-party libraries)
4. 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