A covert signal is still beneficial even if the signal is secure. The existence of the signal is valuable metadata.

For a contrived example, imagine I'm in a warzone:

- Secure = Enemies can't read my messages. Good. But they can still triangulate my position.

- Covert = Enemies don't know I exist

Another example: in some regimes merely using Tor is illegal, or say in the US using it is enough to justify a search warrant for probable cause, with no evidence of any actual wrongdoing. The EU Chat Control lobby is also trying very hard to criminalize encryption. The simple act of trying to communicate privately is taken as indicative of criminal wrongdoing in the modern world. Being able to communicate without adversarial parties knowing you're communicating is a boon.

> in the US using it is enough to justify a search warrant for probable cause, with no evidence of any actual wrongdoing

Source:

+1. As another example see https://en.wikipedia.org/wiki/Numbers_station -- people can't decipher the messages, but they strongly suspect something spy-y is going on. If they couldn't even detect it, there would be no suspicion.

Also hi StevenWaterman, I recognize you from previous comments! I think this is the first time that's happened to me on HN

Also even if they know you are transmitting, it may still be beneficial to prevent them from knowing how much you are transmitting.

Imagine the enemy detects some of your transmission, even knowing it's encrypted, they can still look at the data rate (or estimate order of it):

- 5 bps = probably a random transmitter, maybe audio spy device, maybe remote detonated weapon

- 5 Mbps = probably a feed from military hardware or personnel

Similar inferences can be made about volume, if they can identify distinct transmissions. Etc. If tricks like these can make the enemy confuse 5 Mbps TX for a 5 bps one, it has obvious tactical utility.

Unless they have "the right equipment". Then you are right back at the same situation.

Nobody has "the right equipment" everywhere all at once, especially not with operators (human or otherwise) set to monitor it all the time.

In the real world, obscurity is the cornerstone of security.

If you know it exists and becomes popular, in the right situation you will make sure to have it. The dynamics don't change with this.

A lot of spy movies or police procedural movies show someone coming with a magic detector for hidden spying cameras or microphones that is used to sweep a room and remove all offending devices.

The device presented in the parent article would be undetectable by any classic detectors.

However, if such a method would ever become widely used in reality, it would not be difficult to make detectors for it. So it could have a window of opportunity, between the first development of spying devices based on it and the development of countermeasures.

DSSS is sort of both security and obscurity at the same time. The very act of spreading your spectrum out via a secret key also has the effect of reducing the amplitude of your transmission, ideally below the noise floor. A receiver on the other side wouldn't see anything except noise unless they had the same key.

The same is true for any other method of spread spectrum modulation, e.g. for FHSS (frequency-hopping spread spectrum) or for ultra-wideband pulses.

The detection of weak signals requires long integration times, which remove from the output any spread spectrum signal present in the input, unless you know and apply before the integration the correct scrambling or frequency-hopping sequence.

Secure channels can still be jammed. Undetectability is a fundamentally different goal than secrecy.

Unless your adversary is scanning for RF emissions, which is getting more and more common.

I am sure you could encrypt the warmth message somehow.