Would sending audio fragments over a phone call be considered a form of cryptology?

I have been wondering if sending audio fragments over a phone call would be considered a form of cryptology.

Let's say that you own two mobile phones and say that one of your phones is on the Verizon network and the other is on the AT&T network. You have a friend who also owns two mobile phones. Say that one of his phones is on the T-Mobile network and the other is on the U.S. Cellular network.

One day, you decide to call your friend with your Verizon smart phone and he answers on his T-Mobile phone. Without hanging up on the phone call you just made, you grab your AT&T mobile phone and call your friend again and he answers on his U.S. Cellular mobile phone.

Next, you put both of your mobile phones down on a table and you then put each of them on speaker. You then tell your friend to put both of his mobile phones down on a table and to turn on the speaker on each one.

You then turn on Mute on one of your smartphones and begin speaking to your friend. Every two seconds you press the Mute button on both of your smart phones at the same time, which turns off the Mute on one phone and turns on the Mute on the other phone.

As you are speaking, your friend should hear everything you are saying because he should hear your voice coming over on one of his smart phones. When your friend speaks to you, he does the same thing you did and you should hear everything he is saying because his voice is coming over on one of your mobile phones.

Now, let's say that your phone conversation happened to be listened to/recorded by an outside source. As they are listening, or when they play back the recorded phone conversation, they should hear a phone conversation of two-second long audio fragments followed by two seconds of silence, which should make understanding your phone conversation rather difficult to comprehend.

Moreover, say that more mobile phones are used, thus creating more concurrent phone calls between two parties. On each individual phone call, there would be longer periods of silence between each two-second long audio fragment. This should make it almost impossible for an outside source listening in, or listening to the playback of any of these recorded phone calls to understand the overall phone conversation.

Would sending audio fragments over a phone call be considered a form of cryptology?

This overly complicated idea is at best a form of communication link obfuscation against eavesdroppers. It is at the transmission/network level, albeit with multiple networks and a manual and complicated way of buying some physical security.

No encryption of any strength is performed. if you want to call it steganography because it hides the transmission, fine.

Also, if someone human was actually monitoring that voice conversation, as you assume, they would sense something was fishy right away attracting attention to the owner of the mobile phone service.

Yes, it's starting to be.

You're starting along the lines of a manual version of Frequency Hopping Spread Spectrum techniques. You're using phones in this case, whereas in reality radios would be used. But the effect is the same, and is used for both civilian and military applications.

Now imagine instead of two phones (as you suggest), you had 50 or more. And imagine that you can un-mute the phones for less than 0.4 seconds. So each fragment of conversation can be on any phone for less than 0.4 seconds ($t_{ch}$). And no phone is reused for 20 seconds ($T$).These numbers are from US FCC guidelines, § 2.2 FHSS equipment. I can't speak for military specifications.

Now lastly imagine that the mute / un-mute order is pseudo random as determined by a preshared key. TCP/IP, cellular latency and propagation delays would mess up the relative packet order / phase given a short $t_{ch}$. Even if all the phone conversations could be intercepted, the assailant would only have a series of short disjoint throaty sounds that would be very difficult to re-order into a sensible conversation without knowledge of the key.

It's not nearly as effective as using multiple frequencies on a radio, and appears frivolous with phones. For teaching purposes though you can see how the principal works. Under the control of a secret key.

That's cryptography.

From § 2.2 FHSS equipment:-

$t_{ch}$ = average time of occupancy.

$T$ = period.

You're mixing up encoding with encryption, which is a common fallacy because lay people think of "code" as something obscure and (intentionally) incomprehensible. But this is really the opposite of what a code/encoding means. An encoding is a protocol for ensuring that any party who knows the protocol can recover the message. Encryption is a protocol for ensuring (among other properties) that any party who does not know a particular secret (even if they do know the protocol!) cannot recover the message.

What you have is a way of encoding information. It does not prevent anyone from recovering the message; it gives them a means for doing so.

You idea is a bit like stream ciphers, but much less efficient.

In a stream cipher, an algorithm is used to generates a stream of bits from a key, which toggles the bits in the plaintext message (assuming it's bit-encoded like MP3 or AAC) using the XOR operation. In your case, the bits are used to select communication channel (carrier).

Stream ciphers work at bit level, which maximizes encryption efficiency and security; switching channels quickly on the other hand, isn't efficient, and allows for message re-construction by any party that had harvested your communication.

What you just described in theory similar to what we used in the military with regards to frequency hopping radios (HAVE QUICK is the name of the system). Essentially, the radio would hop frequencies while transmitting and receiving amoung many different frequencies per second so each fragment is just a millisecond of audio. It relied on each radio being keyed to a set of tables and the radios being synchronized through a tone or time slice. On top of the hoping in the clear, you could layer secure crypto on top of it to prevent anyone from collecting the small millisecond fragments wtihout having the same key. FYI talking on secure radio is annoying because you have a slight delay as you can imagine for technical reasons :)