[unwind]

Today (but perhaps slightly less in 2016, not sure) you could easily imagine a microcontroller (or FPGA) with a microphone that bugs you, but encodes that audio (using steganography) onto a canned audio file of elevator music, and then sends the result over the network "in the open".

To a casual observer snooping the relevant network, it would probably (as here) look as elevator music, but to the intended recipient who can decode the steganography, it would be a covert listening device.

[koolba]

Even better than a canned audio file would be machine generated music. Otherwise you could detect that the “same” song is being transmitted with slightly different bits.

Or you could have an extremely long audio file so the repeat situation doesn’t occur.

[jalbertoni]

There's a very simple way around this. Grab any encoding that uses a dictionary, like, I think zip does. Sent tiny zip files with an excerpt of a .wav file or something that needs to be compressed.

The decompressed data is always the same, but the data in the dictionary used is where you store your sneaky bits.

Sure, that's still mildly suspicious. But way less than the actual music data changing all the time.

[eru]

You could also hide the bits in eg timing of package transmission or omiting an expected package every once in a while, it'll just look like udp dropped a package.

You can use a channel with lots of noise, because you can use error correcting codes to to restore the intended message.

(To elaborate with an example: sometimes a package might already drop randomly, or timings might be slightly delayed anyway.)

[srcreigh]

I always wondered why in mr robot a few scenes involve ripping a CD with some jpgs.

[mlyle]

If you have a legacy music system and encode it over the network, the data will vary— time bases wont line up, there will be noise, etc, even if it repeats.

[counttheforks]

Elevator music tends to loop.

[matt_heimer]

Yeah, that's the problem. If the song is known either because its a previously published song or because it repeats then the bits should be the same every time the song is played. If you are adding extra data with steganography then you don't want it easy to detect because someone could make a steganography detector by testing if the same song's data seems to vary for no reason.

I guess you could also build an auto-auto-tune or auto-remix solution so the songs always have justifiable variation without needing fully generated music.

[twojacobtwo]

I know next to nothing about steganography, beyond the general concept, so please excuse my ignorance if I'm way off base, but couldn't you design the encoding system such that you could encode the same amount of data within the time frame of each loop, with only some portion of the new data containing real data (audio recording)?

-edited because it didn't make sense before

[viciousvoxel]

Yes

[sublinear]

> to the intended recipient who can decode the steganography

Not just decode, but also decrypt.

You'd probably want to encrypt not just for the secrecy, but so that the noise introduced by the steganography doesn't seem so suspicious.

[ajsnigrutin]

This would work if the elevator music was a never-repeating stream. With most elevator music, it's a few minutes of a "song" playing on repeat 24/7, so if you recorded a few repetitions of the "song", you'd probably see also repeated packets on the network.

If the music was repeating but the stream was different all the time, then steganography could be the reason :)

[rhacker]

I haven't actually heard elevator music as much as people say it exists.

In fact I don't think I've every been on an elevator that had music.

[bigiain]

Pretty sure I've never heard Brian Eno playing in an airport either.

[rerdavies]

Tragedy.

Google sez: Music for Airports was installed at the Marine Air Terminal of New York's LaGuardia Airport for a brief period during the 1980s.

Elevator music may no longer be a thing, but apparently, airport music still is:

https://www.youtube.com/watch?v=Km0h6Ix3Zcs

[sublinear]

I think it's a trope from the second half of the 20th century (mostly the 3rd quarter).

[eru]

The modern equivalent is probably mall music?

[eru]

Encryption is in another layer.

Basically, you'd use steganography to hide that you send a message. And that message would be encrypted. You can use almost any standard encryption scheme, as long as you remove headers etc. Any ciphertext of a crypto-system worth its salt will be indistinguishable from random noise without the key.

[forgotusername6]

You don't even have to change the audio data. Just alter the packet pace slightly to encode the data. That way a cold trace like OP's is useless.

[rhd]

Sounds like a great CTF challenge, will have to explore

[rurban]

Sonos, a not so well known CIA front, did it much simpler. They hide their covert up-traffic by claiming to compress their streams to their speakers.

[lostlogin]

Install Unifi gear and watch the chaos unfold in that CIA operation.

Weirdly, my Sonos/Unifi issues are gone at the moment, but wow is it painful when you hit it.