The DRAM substrate is becoming increasingly more vulnerable to Rowhammer as we move to smaller technology nodes. We introduce PROTRR, the first principled in-DRAM Target Row Refresh mitigation with formal security guarantees and low bounds on overhead. Unlike existing proposals that require changes to the memory controllers, the in-DRAM nature of PROTRR enables its seamless integration. However, this means that PROTRR must respect the synchronous nature of the DRAM protocol, which limits the number of DRAM rows that can be protected at any given time. To overcome this challenge, PROTRR proactively refreshes each row that is most likely to observe bit flips in the future. While this strategy catches the rows that are hammered the most, some others may still fly under the radar. We use this observation to construct FEINTING, a new Rowhammer attack that we formally prove to be optimal in this setting. We then configure PROTRR to be secure against FEINTING. To achieve this, PROTRR should keep track of accesses to each row, which is prohibitively expensive to implement in hardware. Instead, PROTRR uses a new frequent item counting scheme that leverages FEINTING to provide a provably optimal yet flexible trade-off between the tolerated DRAM vulnerability, the number of counters, and the number of additional refreshes. Our extensive evaluation using an ASIC implementation of PROTRR and cycle-accurate simulation shows that PROTRR can provide principled protection for current and future DRAM technologies with a negligible performance, power, and area impact. PROTRR is fully compatible with DDR4 and the new Refresh Management (RFM) extension in DDR5.

Sharing a common clock signal among the nodes is crucial for communication in synchronized networks. This work presents a heartbeat-based synchronization scheme for body-worn nodes. The principles of this coordination technique combined with a puncture-based communication method are introduced. Theoretical models of the hardware blocks are presented, outlining the impact of their specifications on the system. Moreover, we evaluate the synchronization efficiency in simulation and compare with a duty-cycled receiver topology. Improvement in power consumption of at least 26% and tight latency control are highlighted at no cost on the channel availability.

Wireless Body Area Networks (WBANs) are a fast-growing field fueled by the number of wearable devices developed for countless applications appearing on the market. To enable communication between a variety of those devices, the IEEE 802.15.6 standard was established. However, this standard has some intrinsic limitations in addressing the heterogeneity of the network nodes in terms of activity, data rates (from less than bit/s to multiple Mbit/s), energy availability, form factor, and location on, around or inside the body. To address these concerns, an alternative model is proposed that could serve as an extension of the IEEE 802.15.6 Standard. At its core is an adaptive and low-overhead synchronization scheme based on heartbeat sensing. This forms the base for a TDMA-based (Time Division Multiple Access) Media Access Control (MAC) protocol dedicated to multi-tier networks. While this effort focuses specifically on Capacitive Body-Coupled Communication (C-BCC), other physical layers can be easily incorporated as well. Based on these premises, this paper compares various random-access slot allocation approaches to accommodate the multiple data rates matching the system requirements, while incorporating a duty-cycling strategy anchored by heartbeat detection. This work proposes a novel, flexible, and robust solution, making use of heartbeat synchronization and addressing the corresponding challenges. It efficiently interconnects multiple device types over a wide range of data rates and targets a mesh of stars topology. At the cost of an increased communication latency, the proposed protocol outperforms the IEEE 802.15.4 MAC standard in terms of energy efficiency by a factor of at least 12x in a realistic scenario.