1. A computer-readable medium whose contents cause a computing system to: receive a request from a client to perform a transaction; and in response to receiving the request: identify a user requesting the transaction; identify a key corresponding to the user's authenticating device; generate a secret for the transaction, the secret being good for committing the transaction; create a bundle of transaction data for the transaction, the bundle comprising the secret, the bundle comprising a indication that the secret is not to be displayed on the client's screen; encrypt the bundle of transaction data using the identified key; and transmit the encrypted bundle of transaction data to the client.