algorithm-selection

A reference for choosing cryptographic algorithms, which protect data and communications, including rules for avoiding broken or outdated choices and preparing for future quantum attacks.

In plain words
What is it for?
Use it when selecting, reviewing, or configuring cryptographic algorithms, cipher suites, protocol versions, key exchange, and key management.
Why use it?
It reduces the risk of using insecure encryption, hashing, signatures, key exchange, or protocol settings.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/redhatproductsecurity/prodsec-skills/algorithm-selection
Any agent
npx skills add RedHatProductSecurity/prodsec-skills --skill algorithm-selection
Clone the repo
git clone --depth 1 https://github.com/RedHatProductSecurity/prodsec-skills

Made for: Claude Code, Codex.

Per session 49 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,471 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00049 $0.01471
Opus 5 $0.00024 $0.00736
Sonnet 5 $0.00010 $0.00294
Haiku 4.5 $0.00005 $0.00147

Measured 2d ago against content hash 977779389134, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

algorithm-selection scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

module/skills/algorithm-selection/SKILL.md · 139 lines

How it starts

The opening of the file, as written. The whole thing — 139 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Cryptographic Algorithm Selection and Post-Quantum Readiness

Reference for which cryptographic algorithms to use, which to avoid, and how to prepare for post-quantum cryptography.

Banned (Insecure) Algorithms

NEVER use these algorithms. They are cryptographically broken.

Type Banned
Hash MD2, MD4, MD5, SHA-0
Symmetric RC2, RC4, Blowfish, DES, 3DES
Key Exchange Static RSA, Anonymous Diffie-Hellman

Deprecated (Legacy/Weak) Algorithms

Avoid in new designs. Prioritize migration away from these.

Type Deprecated Issue
Hash SHA-1 Collision attacks demonstrated
Symmetric AES-CBC, AES-ECB Unauthenticated; ECB leaks patterns
Signature RSA with PKCS#1 v1.5 padding Padding oracle attacks
Key Exchange DHE with weak/common primes Vulnerable to precomputation attacks

Recommended and Post-Quantum Ready Algorithms

Symmetric Encryption

  • Standard: AES-GCM (AEAD), ChaCha20-Poly1305
  • PQC requirement: prefer AES-256 keys -- resistant to Grover's algorithm
  • Avoid: custom crypto or unauthenticated modes

Key Exchange (KEM)

  • Standard: ECDHE (X25519 or secp256r1)
  • Hybrid key exchange (classical + PQC) when supported:
    • Preferred: X25519MLKEM768 (X25519 + ML-KEM-768)
    • Alternative: SecP256r1MLKEM768 (P-256 + ML-KEM-768)
    • High assurance: SecP384r1MLKEM1024 (P-384 + ML-KEM-1024)
  • Pure PQC: ML-KEM-768 (baseline) or ML-KEM-1024. Avoid ML-KEM-512 unless explicitly risk-accepted.
  • Use vendor-documented identifiers (RFC 9242/9370). Remove legacy/draft "Hybrid-Kyber" groups and hardcoded OIDs.

Signatures and Certificates

  • Standard: ECDSA (P-256)
  • PQC migration: continue using ECDSA (P-256) for mTLS and code signing until hardware-backed (HSM/TPM) ML-DSA is available.
  • Hardware requirement: do not enable PQC ML-DSA signatures with software-only keys. Require HSM/TPM storage.

Protocol Versions

Read the full file on GitHub · 139 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 139 lines · 49 tokens per session scan A 977779389134

Subscribe to this mod's changes

algorithm-selection is a skill published in the GitHub repository RedHatProductSecurity/prodsec-skills (52 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 49 tokens to every session and 1,471 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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