Agent skill
crypto
Client-side cryptography with libsodium. Use when working on files in src/lib/crypto/.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/crypto
SKILL.md
Crypto Guidelines
All crypto happens client-side. Server NEVER sees plaintext.
Architecture
- Seed phrase (128-bit) → Ed25519 keypair (signing) → X25519 keypair (encryption)
- Vault key (random 256-bit) wrapped with user's X25519 public key
- Data encrypted with XChaCha20-Poly1305
Critical Rules
- Never log keys or sensitive data - not even in development
- Use libsodium - don't implement crypto primitives
- Async everywhere - all functions async (libsodium-wrappers)
- Constant-time comparisons -
sodium.comparefor secrets - Zeroize secrets -
sodium.memzerowhen done - Type-safe keys - use branded types (VaultKey, SigningKey)
Common Pitfalls
- Don't use
crypto.randomBytes→ usesodium.randombytes_buf - Don't concatenate key material → use proper KDFs
- Don't store keys in localStorage without encryption
- Don't forget
await sodium.readybefore operations
Testing
Use property-based tests for roundtrip verification with fast-check.
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