Using smartcards to enable probabilistic transactions on an untrusted device

A non-transitory tangible computer-readable storage medium storing program instructions that are executed by a processor to perform operations comprising:

• issuing, via an interface between a smart card and a user's device, a first random string to the user's device, the first random string being based in part on a first cryptographic key;
• locking a cryptographic module on the smart card;
• receiving an authorization code and a value to be added from the user's device, the authorization code including a message authentication code being based in part on a second cryptographic key;
• authenticating the message authentication code using the first cryptographic key and a serial number associated with the smart card;
• adding the value to the cryptographic module;
• and
• unlocking the cryptographic module.

A method, comprising:

• issuing, from a smart card comprising a processor, a first random string to a user's device via an interface coupled to the processor, the first random string being based in part on a first cryptographic key stored in a memory of the smart card;
• using the processor for locking a cryptographic module on the smart card;
• receiving, by the processor via the interface, an authorization code and a value to be added from the user's device, the authorization code including a message authentication code being based in part on a second cryptographic key;
• authenticating, by the processor, the message authentication code using the first cryptographic key and a serial number stored on the memory;
• and
• adding, by the processor, the value to the cryptographic module.