However, Marko Bencun argues that this defense is weak as devices may start to behave differently over time. Bencun also points out that, while most hardware wallets allow users to import their own BIP39 seed, it is still necessary to compare the public keys output by the hardware wallet with a second computation to ensure that the device is using the correct seed. This defeats the purpose of a hardware wallet as it requires storing the seed on a second device. Both parties agree that there is a need for a clearly specified full protocol that can be analyzed.