Over-the-Air Programming (OTAP) is an essential capability when operating a large low-power wireless deployment such as wireless sensors or swarm robots. OTAP needs to be carefully crafted for these use cases to take into account the limited communication bandwidth, the unreliability and the large latency associated with the low-power wireless nature of the network, as well as the constrained nature of the microcontrollers that are being updated. This paper introduces RobOTAP, an OTAP solution specifically targeted at robotic swarms, available as an open-source implementation. RobOTAP is designed to be minimalistic, with the OTAP module and bootloader having flash footprints below 1 kB / 4 kB, respectively. It is designed to be fast: we show a full update for an 18 kB image in less than 2.3 s. Finally, RobOTAP is secure: we compare on both the nRF52840 and the nRF5340 the performance when using ARM CryptoCell-310 hardware acceleration, a software implementation of the same security routines, or no security at all.