A technique of message-passing using shared memory of an RF tag involves storing a message in the shared memory while a security processor of the RF tag is in a sleep mode, the security processor being constructed and arranged to access the shared memory when the security processor is in a wakened mode. The technique further involves transitioning the security processor from the sleep mode to the wakened mode, and processing the message from the shared memory using the security processor after the security processor has transitioned from the sleep mode to the wakened mode. If the security processor is awakened only as needed (rather than remain in the wakened mode), lifetime of a battery which powers the security processor can be maximized.