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Imagine two people want to practice the procedure for sending and receiving messages over amateur radio that are encrypted using a one-time pad. Here’s what doing this for real would look like:

  1. Person A converts the message text to numeric values;
  2. Person A uses modular addition to add these numbers to the random numbers of a key known to both people (thereby encrypting the message);
  3. Person A transmits these encrypted numbers openly over the radio;
  4. Person B receives and records these encrypted numbers;
  5. Person B uses modular subtraction to subtract the encrypted numbers from the key numbers to generate the message numbers;
  6. Person B converts the message numbers to the message text.

Obviously, they aren’t allowed to send encrypted messages over amateur radio. But suppose they just want to practice accurately transmitting and receiving strings of numbers. Could they legally practice transmitting and receiving random numbers which do not encode any message over amateur radio? Note that from the perspective of a third party listening in, this practice would be indistinguishable from them actually exchanging encrypted messages.

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  • $\begingroup$ What if you were to transmit the pad itself along with the message? $\endgroup$ Sep 27, 2023 at 21:25
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    $\begingroup$ That’s one way to do it. But I was wondering if it would be legal for Person A to transmit say 50 truly random numbers (not encoding any message) which Person B would just try to accurately record. The idea being the two could later compare to see how accurate they were. $\endgroup$
    – Bryan
    Sep 27, 2023 at 21:42
  • $\begingroup$ I'd also point out the technical aspect of the hypothetical (forbidden) application of that practice: In 2023, it's hard to imagine that someone has access to a transmitter, but not the technological means to automatedly transmit in a digital mode – which is by far more efficient in terms of transmit power needed for any given robustness/data rate/reach than doing it by hand. It's a cute idea to practice that, but the times of number stations serving any realistic use case are over, I'd say. Their non-ham use case is restricted to "oh, we need 90 years of backwards-compatibility" today. $\endgroup$ Sep 28, 2023 at 13:24

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The following might serve to practice sending and receiving random numbers without falling foul of any encryption laws:

ISBN 0833030477 p1 10079 32533 ...

This is the well-known book:

The RAND Corporation, A Million Random Digits with 100,000 Normal Deviates, The Free Press, NY, 1955. ISBN 0-8330-3047-7

So you are simply quoting from a well-known book, and you've said what it is. The original just happens to contain random digits.

enter image description here

Obviously you could use pretty much any sequence at OEIS. Or from a trigonometry table.

Quoting from a printed book with an ISBN seems very clearly not encrypted, in a way lawyers can easily understand.

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    $\begingroup$ Another idea: transmit a block of text backwards (end to beginning). Encryption & decryption not needed. $\endgroup$
    – glen_geek
    Sep 29, 2023 at 14:37
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First, telegraphy practice is acknowledged as an approved activity in Part 97, so cool on that front.

My interpretation of the rules is that groups of otherwise nonsensical characters is allowed, but that encrypted messages are not.

If the messages are encoded with a published method, then the messages are not encrypted, they are merely encoded. Base64 is one such encoding method, and you can feel free to publish your own as well.

If transmitting via voice, it’s still OK to transmit/exchange nonsensical groups of letters and numbers under the same rules above regarding encoding versus encryption.

and if they’re just random without decoding to a particular message, that’s OK too!

This kind of practice via voice is frequently done using the NTS system of Telegram-style messages where the messages are somewhat sensical but fictional.

Anyway, your use case is quite unusual but doesn’t seem to be out-of-bounds in my opinion. as long as you’re polite and courteous to those who ask what’s going on, I suspect you’ll find no problem at all.

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  • $\begingroup$ I could see this falling under telegraphy practice if the numbers are being sent via CW. But the numbers could also just be transmitted by voice (e.g., the Cuban HM01 numbers station does this), that wouldn’t count as telegraphy practice, would it? I tend to agree that transmitting random numbers that do not encode a message should be allowed. Still, what would happen if someone accuses you of sending encrypted messages? $\endgroup$
    – Bryan
    Sep 27, 2023 at 22:20
  • $\begingroup$ “what would happen if someone accuses you of sending encrypted messages“ in practice, little to nothing. I’ll also amend my answer shortly regarding non-CW modes $\endgroup$
    – webmarc
    Sep 28, 2023 at 0:14
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You’re off the hook if you can prove that it is not an encrypted message. So take the numbers 10 through 99, write a short program to scramble the order, and transmit the resulting sequence of digit pairs. The receiver just needs to verify that every pair of digits was received, and only once. To the “information police,” show them the details of what you did. (I assume you’re in the U.S. The laws in a few other countries truly are draconian.)

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  • $\begingroup$ 1) a negative cannot be proven, it’s not possible to “prove that it is not an encrypted message“; 2) when it comes to accusations, the burden of proof lies with the accuser (at least in the jurisdiction in question here). $\endgroup$
    – webmarc
    Oct 27, 2023 at 12:54
  • $\begingroup$ Fair enough. So in this case you can only demonstrate that the system is <i>probably</i> benign. $\endgroup$
    – mcpublic
    Oct 28, 2023 at 18:30

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