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crypto-misuse

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Block weak ciphers, predictable RNG, undersized keys, fast-hash password storage, nonce reuse, and non-constant-time comparison. Use when generating code that hashes, encrypts, or signs, code that compares secrets, MACs, or tokens, or config for key sizes and randomness.

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<!-- Native skill bundle for Claude Code. Generated by `secure-vibe dev regenerate`. -->
<!-- Do not edit by hand; the source of truth is skills/crypto-misuse/SKILL.md. -->

# Cryptographic Misuse

Block weak ciphers, predictable RNG, undersized keys, fast-hash password storage, nonce reuse, and non-constant-time comparison. Use when generating code that hashes, encrypts, or signs, code that compares secrets, MACs, or tokens, or config for key sizes and randomness.

## ALWAYS

- Use a maintained, widely reviewed cryptographic API — the platform's own (Node `crypto`, Java JCE, .NET `System.Security.Cryptography`, Go `crypto/*`) or a reputable third-party one (PyCA `cryptography`, `golang.org/x/crypto`, Bouncy Castle). Prefer high-level, misuse-resistant APIs over assembling low-level primitives yourself. In Python, `from Crypto…` resolves to either the abandoned `pycrypto` or its maintained fork `pycryptodome` depending on what is installed — the import line is identical, so depend on `pycryptodome` explicitly.
- Use a cryptographically secure RNG for anything security-relevant: Python `secrets.token_bytes` / `secrets.token_urlsafe`, JS `crypto.getRandomValues` / `crypto.randomBytes`, Go `crypto/rand.Read`, Java `SecureRandom`.
- Hash passwords with a password-specific KDF and a unique random salt per password. Prefer Argon2id; scrypt where appropriate; bcrypt for legacy compatibility; PBKDF2-HMAC-SHA-256 where FIPS-140 compliance is required. Take minimum parameters from the current [OWASP Password Storage Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html), then benchmark on production hardware and choose the highest cost that still meets the application's authentication latency and availability budget. The cost is meant to be raised over time as hardware gets cheaper — it is not a constant to copy once.
- Account for bcrypt's 72-byte input limit: it silently truncates, so a long passphrase and its 72-byte prefix hash identically. If bcrypt must take unbounded input, pre-hash with SHA-256 and pass the digest **base64-encoded**, never as raw bytes — a raw digest can contain a NUL byte, which truncates the input again.
- Encrypt with a vetted AEAD: AES-GCM or ChaCha20-Poly1305, or AES-GCM-SIV where nonce-misuse resistance is specifically useful and the platform ships a reviewed implementation. Absent a stated key-size requirement, AES-256-GCM or ChaCha20-Poly1305 is a safe default — AES-128-GCM is not a finding.