Expiring software key for unlocking a mode on a device

1. A system comprising an apparatus programmed to provide a plurality of modes, and a security token, wherein the security token comprises:

a communication interface, including a communication transceiver;

a circuit having encoded thereon an immutable hardware key; and

a tangible, nonvolatile memory, the nonvolatile memory having stored thereon a mutable software key, the mutable software key including a cryptographic key and an expiry for the cryptographic key;

and wherein the apparatus comprises:

a processor and a memory;

a communication interface; and

instructions encoded within the processor to:

provide the plurality of modes, including a restricted mode;

detect the security token via the communication interface;

cryptographically verify the immutable hardware key of the security token; and

activate the restricted mode after verifying that the mutable software key is valid and unexpired;

and wherein the system further comprises a therapeutic subsystem to administer a therapeutic treatment to a patient, wherein the restricted mode comprises a therapy administration mode.

2. The system of claim 1 , wherein the system is a dialysis machine.

3. The system of claim 1 , wherein cryptographically verifying the immutable hardware key comprises verifying that the immutable hardware key has not expired.

4. The system of claim 1 , wherein verifying that the mutable software key is valid and unexpired comprises extracting the expiry from the mutable software key.

5. The system of claim 1 , wherein verifying that the mutable software key is valid and unexpired comprises cryptographically validating the mutable software key.

6. The system of claim 5 , wherein cryptographically validating the mutable software key comprises validating the mutable software key via the immutable hardware key.