establish static method

RatchetSession establish({ required List<int> root, required bool thisNodeIsLow, required Cipher cipherFactory(List<int> key), })

Establishes a session from root. thisNodeIsLow must be true on the side whose node id sorts first, so the two sides pick opposite send / receive chains.

Implementation

static RatchetSession establish({
  required List<int> root,
  required bool thisNodeIsLow,
  required Cipher Function(List<int> key) cipherFactory,
}) {
  final low =
      hkdfSha256(root, const [], _ascii('passnote-ratchet-chain-low'), 32);
  final high =
      hkdfSha256(root, const [], _ascii('passnote-ratchet-chain-high'), 32);
  return RatchetSession._(
    _Chain(thisNodeIsLow ? low : high),
    _Chain(thisNodeIsLow ? high : low),
    cipherFactory,
  );
}