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diff --git a/paper/ihsm_paper.tex b/paper/ihsm_paper.tex index de94ea2..024ca1f 100644 --- a/paper/ihsm_paper.tex +++ b/paper/ihsm_paper.tex @@ -771,8 +771,27 @@ tamper status to the static monitoring circuit at least once every $T_\text{tx} $\SI{100}{\kilo\baud}$, a transmission of a one-byte message in standard UART framing would take $\SI{100}{\micro\second}$ and yield an $\SI{1}{\percent}$ duty cycle. If we assume an optical or RF transmitter that requires $\SI{10}{\milli\ampere}$ of active current, this yields an average operating current of -$\SI{100}{\micro\ampere}$. Reserving another $\SI{100}{\micro\ampere}$ for the monitoring circuit itself we arrive at an -energy consumption of $\SI{1.7}{\ampere\hour}$ per year. +$\SI{100}{\micro\ampere}$. This value is comparable to a reasonable estimation of the current consumption of the +monitoring cirucit itself. In our prototype we used ST Microelectronics STM32 Series ARM Cortex-M microcontrollers. To +get an estimate on the current consumption of an energy-optimized design we will refer to the datasheet of the +\texttt{STM32L486JG}\footnote{\url{https://www.st.com/resource/en/datasheet/stm32l486jg.pdf}}, a representative member +of ST's \texttt{STM32L4} low-power sub-family that provides hardware acceleration for AES256. A good target for an +implementation of a secure cryptographic channel on this device would be the noise protocol framework~\cite{perrin2018}. +While the initial handshake for key establishment uses elliptic-curve cryptography and may take several hundred +milliseconds~\cite{tschofenig2015}, the following payload data transfer messages require only symmetric cryptographic +primitives. The \texttt{STM32L486JG} datasheet lists the microcontroller's typical operating current at around +$\SI{8}{\milli\ampere}$ at $\SI{48}{\mega\hertz}$ clock speed, and lists a sleep current of less than +$\SI{1}{\micro\ampere}$ in low-power standby mode with RTC enabled. The AES peripheral is listed with less than +$\SI{2}{\micro\ampere\per\mega\hertz}$ typical current consumption. A typical high-$g$ accelerometer for an IHSM +application would be ST Microelectronics' \texttt{H3LIS331DL}. Its +datasheet\footnote{\url{https://www.st.com/resource/en/datasheet/h3lis331dl.pdf}} lists a typical current consumption +between $\SI{10}{\micro\ampere}$ in low-power mode with output sampling rate up to $\SI{10}{\hertz}$ and +$\SI{300}{\micro\ampere}$ in normal operating mode with output sampling rate up to $\SI{1}{\kilo\hertz}$. Given the low +amount of data (hundreds of bytes per second) that has to be processed in our application, if we assume a duty cycle of +$\SI{1}{\percent}$ of active data processing vs.\ sleep mode at the given clock speed we arrive at a total estimated +current consumption of our microcontroller of less than $\SI{100}{\micro\ampere}$. Thus, reserving +$\SI{100}{\micro\ampere}$ for the monitoring circuit on top of the $\SI{100}{\micro\ampere}$ for the transceiver circuit +we arrive at an energy consumption of $\SI{1.7}{\ampere\hour}$ per year. This annual energy consumption is close to the capacity of a single CR123A lithium primary cell. Thus, by either using several such cells or by optimizing power consumption several years of battery life could easily be reached. In our |