Gevulot is a technological device used in the Oubliette, a former panopticon prison, now walking city on the surface of Mars in the Jean-Le-Flambeur universe created by Hannu Rajaniemi. Gevulot is a modulator of human interaction in the Oubliette. It allows for an adjustable degree of privacy between the citizens of the Oubliette. The Gevulot covers the Oubliette citizen and can be controlled by his / her mind. It modulates how much of private information is revealed to the environment or a conversation partner. Citizens of the Oubliette can enter so called "Gevulot contracts" which for instance ensure that a conversion remains totally private and will not be recorded by the Oubliette's exomemory system, which consists of ubiquitous nanosensors and records every event in the Oubliette. Gevulot in the maximum privacy mode blurs out the image of the person hiding behind it totally and replaces it with a placeholder not even revealing the face, name or other credentials.
Only in so called Agoras, special public places, the Gevulot is neutralized and prevents all citizens from hiding behind their Gevulot. Gevulot technology is based on very advanced cryptography but Jean Le Flambeur managed to hack into Gevulot by using a Sobornost pirate gogol engine.