Secure controllers for replaceable print apparatus components

Circuitry for association with a replaceable print apparatus component, the circuitry comprising a serial data bus interface that is to interface with a serial data bus of a host apparatus, wherein the circuitry comprises a memory storing a cryptographic key, wherein the circuitry is to perform secure communication by one or both of (i) generating authenticated cryptographic responses to the host apparatus using the cryptographic key and (ii) validating authenticated messages from the host apparatus using the cryptographic key, wherein the circuitry is to:

• in response to a first command received from the host apparatus via the serial data bus, the first command being associated with a cryptographic operation, execute the cryptographic operation in a default-power state, wherein the cryptographic operation comprises at least one of:
• computing a session key, generating a session key identifier, generating a message authentication code, or determining a response to a cryptographic challenge, wherein the circuitry is to consume power within a first range during execution of the cryptographic operation, wherein the circuitry is to maintain the power consumption of the circuitry within the first range during the execution of the cryptographic operation by one or both of smoothing the power consumption and jamming the power consumption;
• and
• in response to a second command received from the host apparatus via the serial data bus specifying a dwell time, the second command being associated with a non-cryptographic operation comprising performing a physical measurement of the replaceable print apparatus component, enter a low-power state associated with the non-cryptographic operation for executing the non-cryptographic operation and consume power within a second range in the low-power state for a first duration based on the dwell time, wherein the second range is below the first range, and maintain the power consumption within the second range by regulating a supply current drawn by the circuitry during the first duration, wherein an upper limit of the second range is less than a lower limit of the first range.

A replaceable print apparatus component comprising:

• a serial bus interface to communicate with a host over a serial bus;
• and
• logic, wherein the logic comprises a memory storing a cryptographic key, wherein the logic is to perform secure communication by one or both of (i) generating authenticated cryptographic responses to the host using the cryptographic key and (ii) validating authenticated messages from the host using the cryptographic key,
• wherein the logic, in response to a command sent by the host over the serial bus to an address associated with the logic, is to:
• depending on a type of the command sent to the address associated with the logic, selectively transition to either a first power mode or a second power mode for executing an operation associated with the received command, wherein the operation comprises at least one of:
• computing a session key, generating a session key identifier, generating a message authentication code, or determining a response to a cryptographic challenge when in the first power mode, wherein the command specifies a dwell time when associated with the second power mode, wherein the second power mode is associated with a non-cryptographic operation comprising performing a physical measurement of the replaceable print apparatus component, wherein the logic is to consume power within a first range during the first power mode, wherein the logic is to maintain the power consumption of the logic within the first range during the first power mode by one or both of smoothing the power consumption and jamming the power consumption and consume power within a second range in the second power mode for a first duration based on the dwell time, the second range being below the first range, and maintain the power consumption within the second range by regulating a supply current drawn by the logic during the first duration, wherein an upper limit of the second range is less than a lower limit of the first range.