That exists: look for 'trusted path'. It was a feature of compartmented mode workstation (CMW) operating systems like Trusted Solaris and lives on in the requirement to use Ctrl-Alt-Del to call up the Windows login prompt. In Trusted Solaris (TSOL) it was a dedicated area of the screen—along the bottom—where no user mode process was allowed to write; the OS displayed a special symbol there (sort of like the padlock in a web browser) when the user was interacting directly with the OS. Some CMW systems even implemented that functionality in hardware, electronically compositing windows from different physical frame buffers to the video display. Ctrl-Alt-Del is actually in hardware, too (or it used to be); the keyboard interface on the first IBM PC detected that specific key combination and toggled the reset line on the CPU (or maybe it was an interrupt; I forget). Every subsequent PC-compatible machine, to this day, has the same functionality built in to the hardware, on the A20 reset line. It's mostly vestigial today.
This is one global-scale geoengineering project I can rally get behind. It has the smallest chance of catastrophic second-order effects of any of the several methods I've heard of.
Mother's maiden name is documented to have been in use for authentication at least as far back as 1882, and even then it was known to be a weakness [1, §3].
[1] Stephen M. Bellovin. 'Frank Miller: Inventor of the One-Time Pad'. Cryptologia 35(3), pp. 203–222, 2011. DOI: 10.1080/01611194.2011.583711
It could be a 12V AC adapter. Not too common, but they do exist. Four of the myriad diodes would be connected in a bridge rectifier to convert the AC to DC. (I don't see any smoothing capacitors though....)
Depending on how creative you wanted to get, a clock might be designed to run directly on a pulsating rectified DC supply. That would give you a sort of baseband embedded clock signal at 120 Hz. Or use two half-wave rectifiers and design the whole clock based on trinary logic, +12V/0/-12V.
Realistically, since the mains connection is hidden behind the frame, it would be easy to tap off internally a connection to the 12V AC signal from the secondary of the transformer, before it gets rectified and filtered to DC.
Interestingly, the audio chipsets in modern motherboards and sound cards include an option to change the function of an audio port at the software level, a type of audio port programming sometimes referred to as ’jack retasking’. This option is available on most audio chipsets (e.g., Realtek’s audio chipsets) integrated into PC motherboards today. Jack retasking, although documented in the technical specifications, is not well-known [34]. For an in-depth technical discussion on malicious retasking of an audio jack, from the hardware to the operating system level, we refer the interested reader to the following previous work [29].
References:
Mordechai Guri and Yosef Solwicz and Andrey Daidakulov and Yuval Elovici. 'MOSQUITO: Covert Ultrasonic Transmissions between Two Air-Gapped Computers using Speaker-to-Speaker Communication'. arXiv preprint 1803.03422v1 [cs.CR], 9th March 2018.
Mordechai Guri and Yosef Solewicz and Andrey Daidakulov and Yuval Elovici. 'Speake(a)r: Turn speakers to microphones for fun and profit'. 11th USENIX Workshop on Offensive Technologies (WOOT 17). USENIX Association, 2017.
Curious how the average user could try to mitigate this threat. Perhaps if you were using speakers connected to an HDMI monitor, rather than an audio jack? Presumably then you'd have to figure out how to exploit both the audio chip on the motherboard and the HDMI device, which I presume would not by default be willing to operate as an input device.
Lightsail. You carry a laser and a lightsail. You shoot the laser at the black hole and the laser light gravitationally slingshots around the black hole, returning to you with more energy than you gave the laser. The returning laser light pushes your lightsail. The black hole needs to be moving for this to work, although it doesn't really matter what direction the black hole is moving.
It does very much matter which direction the black hole is moving; it needs to be moving toward you or you won't get any blueshifting effect, which is the entire reason the energy budget works out.
It was an experiment to test radiation effects; the In-flight Radiation Dose Distribution (IDRD) experiment:
This joint NASA/DoD experiment was designed to examine the penetration of radiation into the human cranium during spaceflight. The female skull was seated in a plastic matrix, representative of tissue, and sliced into ten layers. Hundreds of thermo-luminescent dosimeters were mounted in the skull's layers to record radiation levels at multiple depths. This experiment, which also flew on STS-28 and STS-31, was located in the shuttle's mid-deck lockers on all three flights, recording radiation levels at different orbital inclinations.
