Notary: A Device for Secure Transaction Approval

Notary is a new design for a hardware wallet, a type of security token that is used to protect sensitive transactional operations like cryptocurrency transfers. Notary aims to be more secure than past hardware wallets by eliminating classes of bugs by design and by formally proving the correctness of the key operation used in its implementation. We built a physical prototype of Notary and showed that it achieves functionality similar to existing hardware wallets while avoiding many bugs that affect them.