passnote_crypto 1.1.2

Crypto for Passnote: XChaCha20-Poly1305, Argon2id key derivation from a BIP39 passphrase, X25519/Ed25519 device identity, and SPAKE2 pairing.

passnote_crypto

Cryptographic adapters for Passnote: XChaCha20-Poly1305 encryption, Argon2id key derivation, BIP39 passphrases, SPAKE2 pairing, and the per-device identity keypair.

Implements the Cipher, Identity, and Pake ports from passnote and provides the key-derivation and mnemonic helpers installed by passnote_flutter's passnoteBuilder.

What's inside

• XChaChaPoly1305Cipher: the default Cipher, using XChaCha20-Poly1305. Frame layout is nonce (24) ‖ ciphertext ‖ tag (16), with a fresh random 192-bit nonce per message. Authentication failures surface as CipherAuthError. AesGcmCipher is available for callers who need AES.
• DeviceIdentity: the X25519 + Ed25519 device keypair behind pairing, key wrapping, and revocation, including fromRecoveryPhrase for the recovery flow.
• Spake2Pake: SPAKE2 over P-256 (RFC 9382), the exchange behind the nine-digit pairing code.
• generateMnemonic / isValidMnemonic: BIP39 passphrases at 12, 15, 18, 21, or 24 words (128 to 256 bits of entropy).
• deriveKey: BIP39 seed, then Argon2id (19 MiB, 2 passes, 1 lane), to a 32-byte key. deriveKeyPbkdf2 keeps a PBKDF2-HMAC-SHA256 pipeline for FIPS callers.
• roomTag: a one-way, truncated SHA-256 of key material used for discovery; it reveals nothing about the key or data.

Install

dependencies:
  passnote_crypto: ^1.1.2

Usage

import 'package:passnote_crypto/passnote_crypto.dart';

final words = generateMnemonic(words: 24).join(' ');
final key = await deriveKey(words, 'myapp:v1');
final cipher = XChaChaPoly1305Cipher(key);

final sealed = await cipher.encrypt([1, 2, 3]);
final opened = await cipher.decrypt(sealed); // throws CipherAuthError if tampered

Documentation

See the Passnote security model for cryptographic details and the threat model.