trezor-firmware/src/apps/common/cache.py

from trezor.crypto import random, hashlib, hmac
from apps.common.storage import get_device_id


memory = {}
_seed = None
_passphrase = None
_state_salt = None


def get_state(salt: bytes=None, passphrase: str=None):
    global _passphrase, _state_salt
    if salt is None:
        # generate a random salt if not provided and not already cached
        if _state_salt is None:
            _state_salt = random.bytes(32)
    else:
        # otherwise copy provided salt to cached salt
        _state_salt = salt

    # state = HMAC(passphrase, salt || device_id)
    if passphrase is None:
        key = _passphrase if _passphrase is not None else ''
    else:
        key = passphrase
    msg = _state_salt + get_device_id().encode()
    state = hmac.new(key.encode(), msg, hashlib.sha256).digest()

    return _state_salt + state


def get_seed():
    global _seed
    return _seed


def set_seed(seed, passphrase):
    global _seed, _passphrase
    _seed, _passphrase = seed, _passphrase


def clear():
    global _seed, _passphrase
    global _state_salt
    _seed, _passphrase = None, None
    _state_salt = None