If radio waves are just non-visible light waves that are picked up by a vibrating rod, how does a radio wave get “encrypted” so that it can’t be picked up unless it’s unencrypted?
Edit: Everyone keeps commenting that the content of the message is what’s encrypted, not the radio waves itself, but that’s not what I mean. Someone answered that digital signals themselves can be modulated or disguised, which is what I meant when I asked
In: Technology
The radio wave isn’t encrypted – anyone can receive it. The *information* encoded in the radio wave is encrypted just like any kind of digital information can be encrypted.
The wave itself isn’t encrypted, the data you’re encoding in the waves is encrypted. Someone can still intercept the communication easily but without knowledge of how it was encrypted (the algorithm) and any keys used to encrypt it being in their possession, it’s just random unusable garbage to them. Easiest example of this is encrypted wifi – it’s still just broadcast out in the clear but unless someone has the network key, they can’t do anything with the data they intercept.
The content that they’re holding is encrypted.
Let’s take a basic Caesar shift. Every letter in a phrase is shifted along the alphabet by a predetermined amount. So if I start with the phrase “explain like I’m five”, I’ll get “hasodlq olnh l’p ilyh”. I transmit that over the radio waves. The receiver on the other end knows to expect a Caesar shift, so they undo it and get the original phrase.
In Networking we actually divide the entire end to end communication into seven distinct layers. Layer 1 is the physical transmission medium (i.e., radio waves in this case, ethernet cables in others, etc.). That layer is only responsible for the contents of it’s own layer, and anything else beyond it can be swapped out for anything else without any changes. The encryption would be at a much higher layer that doesn’t really care about the medium that carries it.
The medium is not encrypted; the *message* is encrypted.
The simplest way to send an encrypted message via radio waves is a [numbers station](https://en.wikipedia.org/wiki/Numbers_station) – using a radio to send a message which is meaningless gibberish to everyone except the intended recipient.
The radio wave can still be picked up. You just don’t know what it’s saying. Think of two people in the same room talking and you are listening. But they are speaking a unknown language.
*Signals* can be encrypted, not necessarily the medium carrying them.
Many radio transmissions are now digital, rather than the analog methods used since its inception. Instead of converting sound pressure directly to varying voltage, a series of pulses are transmitted that correspond to bits.
Most everything we call “wireless” today is digital, such as 4G, Wi-Fi, and Bluetooth. Those data streams can be obscured with encryption, even if the transmissions themselves are still visible to other parties. Converted directly to an audio signal without decoding, all you would hear is a series of beeps, or noise if the signal is too dense. Digital encoding is itself a form of encryption if eavesdroppers do not know what encoding scheme is used, or do not possess the proper decoding equipment.
Even with analog means, the transmitted messages can still be encrypted as described in other answers. They can also be made difficult to track or eavesdrop using methods like spread spectrum (use more than one frequency, and divide the signal among these) or frequency hopping (changing the frequency in a pattern). The intended parties decide on the system used in advance.
A lot of people here have answered this, but I also want to add another method of “encryption”. Its called have-quick. Basically two radios sync up according to a gps time signal and hop frequencies while transmitting in a predetermined pattern. Unless you know the pattern and programmed the radio with it, the most you could receive is fractions of a second of the message.
It can be picked up, and others can still see that you’re sending a signal, but they can’t figure out what it means. Imagine if someone was talking in a language you don’t understand. You can still hear that they’re talking, you just don’t know what is being said
—–BEGIN PGP MESSAGE—–
hIwD6XcolaauiZgBA/9kjkI8OcW2bBiFJpbOUoSKF9W2F/M35fDq3cLGLB5d+D/v
DV30HpRZU4VulcNVxWuEgPBxGflscDyKTcu3WPJPCql9y572uKa4YLfQgxn1A28D
PSRMQPt2zsldXXRHBYr23qzajLyMbSttnYe0V+XT1ymwz45RZhloOP5BhdO5ytJI
AW4EQUp/BfEBCbyLBz46y6kd4N2WLNsVEadgEUonaF70ULUDhq+x91oHwT8mDy9v
cE0pYMb7YBIgJ40at729eqouQc2hCrtF
=5+f0
—–END PGP MESSAGE—–
This *message* is encrypted, but the *text* is not. Its made of completely normal letters and punctuation, but the pattern of letters corresponding to a meaningful message has been scrambled.
It works the exact same way for radio, or any other transmission method.
“Encrypted” radio waves are just radio waves, so they can be picked up by anyone.
The hard part is making sense out of them. There will be some a process with a key unknown to eavesdroppers that turns them into something meaningful.
For example convert to binary, multiply by some secret number, apply modulus.
To as to how the receiver got that key in the first place, check out Shamir’s three pass protocol (example with boxes, actually done with numbers)-
1. A sends a box containing a message to B. The box is locked, but unlike the prior approach, the key stays with A.
2. B adds a second lock and sends the box back to A. The box is now locked with two locks, and neither users’ keys are transmitted.
3. A removes their own lock and re-sends the locked box back to B. The box is now locked only with B’s lock.
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