# Capability: crypto-noble-defaults

## ADDED Requirements

### AEAD façade

- REQ-NOBLE-010: Exports `aeadEncrypt(algo: AeadAlgorithm, key: Uint8Array, plaintext: Uint8Array, options: AeadEncryptOptions, opts?: { engine?: AeadEngine }): Uint8Array`.
- REQ-NOBLE-011: Exports `aeadDecrypt(algo: AeadAlgorithm, key: Uint8Array, ciphertext: Uint8Array, options: AeadDecryptOptions, opts?: { engine?: AeadEngine }): Uint8Array`.
- REQ-NOBLE-012: `AeadEncryptOptions = { nonce: Uint8Array; aad?: Uint8Array }`. `AeadDecryptOptions` is the same shape.
- REQ-NOBLE-013: Default engine is noble: `@noble/ciphers` AES-256-GCM and ChaCha20-Poly1305; `@noble/ciphers` XChaCha20-Poly1305.
- REQ-NOBLE-014: Key must be 32 bytes; throws `CryptoError("CRYPTO.KEY.INVALID_LENGTH")` otherwise.
- REQ-NOBLE-015: Nonce must be 12 bytes for AES-256-GCM and ChaCha20-Poly1305, 24 bytes for XChaCha20-Poly1305; throws `CryptoError("CRYPTO.AEAD.INVALID_NONCE")` otherwise.
- REQ-NOBLE-016: Exports `AEAD_KEY_LENGTH = 32`, `AEAD_NONCE_LENGTH = 12`, `AEAD_XCHACHA_NONCE_LENGTH = 24`.

### Sign façade

- REQ-NOBLE-020: Exports `ed25519` namespace: `{ generateKeypair(opts?), sign(secretKey, message), verify(publicKey, signature, message) }`.
- REQ-NOBLE-021: Exports `ecdsaP256` namespace: same shape as `ed25519`.
- REQ-NOBLE-022: All functions accept `{ engine?: SignEngine }` as a trailing options arg.
- REQ-NOBLE-023: Noble defaults: `@noble/curves` ed25519 and P-256.
- REQ-NOBLE-024: `verify` always returns `boolean`, never throws on a bad signature.
- REQ-NOBLE-025: `ecdsaP256.generateKeypair` retries until `noble.utils.isValidSecretKey(secretKey)` is true.

### Agree façade

- REQ-NOBLE-030: Exports `x25519` namespace: `{ generateKeypair(opts?), agree(mySecret, theirPublic) }`.
- REQ-NOBLE-031: Accepts `{ engine?: AgreeEngine }`.
- REQ-NOBLE-032: Noble default: `@noble/curves` x25519.

### Sealed-box façade

- REQ-NOBLE-040: Exports `sealedBox` namespace: `{ seal(recipientPublic, plaintext, opts?), open(recipientSecret, recipientPublic, ciphertext, opts?) }`.
- REQ-NOBLE-041: Noble default: X25519 key agreement + XChaCha20-Poly1305 encryption (crypto_box_seal semantics).

### Auth-box façade

- REQ-NOBLE-050: Exports `authBox` namespace: `{ seal(senderSecret, recipientPublic, plaintext, nonce, opts?), open(senderPublic, recipientSecret, ciphertext, nonce, opts?) }`.
- REQ-NOBLE-051: Noble default: X25519 key agreement + XChaCha20-Poly1305 (crypto_box semantics).

### Constants

- REQ-NOBLE-060: Exports `ED25519_SECRET_KEY_LENGTH = 32`, `ED25519_PUBLIC_KEY_LENGTH = 32`, `ED25519_SIGNATURE_LENGTH = 64`, `X25519_KEY_LENGTH = 32`, `ECDSA_P256_SIGNATURE_LENGTH = 64`.