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Author Topic: Encryption over long haul RF link  (Read 19515 times)

Posts: 85

« Reply #15 on: March 28, 2010, 06:25:26 AM »

Hi John,

You (and others here) seem to be confusing _encryption_ for what should really be _message validation_.  Encryption is used when you do not want the contents of a message to be readable to others.  You really don't care about that in a control situation.  What you do care about is that the control message you received came from your control transmitter and no one else. The message itself can be unencrypted as long as there is a way to validate its source.  This is usually done by attaching an ever-changing validation code to each message.  
Validation is legal on the hams bands.

Glenn AC7ZN

Posts: 3202


« Reply #16 on: March 28, 2010, 07:34:22 AM »

The following citations from 47 CFR Part 97 deal with 'codes' or 'ciphers':

97.113 Prohibited transmissions.
(4) Music using a phone emission except
as specifically provided elsewhere
in this section; communications intended
to facilitate a criminal act;
messages in codes or ciphers intended
to obscure the meaning thereof
, except
as otherwise provided herein; obscene
or indecent words or language; or false
or deceptive messages, signals or identification;

97.211 Space telecommand station.
(b) A telecommand station may
transmit special codes intended to obscure
the meaning of telecommand
messages to the station in space operation.

97.215 Telecommand of model craft.

An amateur station transmitting signals
to control a model craft may be
operated as follows:
(b) The control signals are not considered
codes or ciphers intended to obscure
the meaning of the communication.

97.217 Telemetry.
Telemetry transmitted by an amateur
station on or within 50 km of the
Earth’s surface is not considered to be
codes or ciphers intended to obscure
the meaning of communications.


Within the narrow parameters defined above, a control
link for a terrestrial station might be acceptable. 
HOWEVER, using codes or ciphers (you may note that
the term 'encryption' does not appear in Part 97) to
obscure the data/message is NEVER allowed.

Posts: 85

« Reply #17 on: March 28, 2010, 11:49:39 AM »

It seems because I used the word 'code' in my post, it is considered a violation by some.  But 'code' as used by the FCC is clearly intended to convey the idea that someone is using a code to keep the actual message private.

Here, an authentication number or code does not encrypt a message in any sense as the message is still sent in the open.  It falls into the same category as all error correction and message verification codes including byte counts, message serial numbers, CRC's, error correction codes, and even sending something is used just like these other methods to verify the integrity of a message sent in the clear.  It has no intrinsic information beyond verifying the message was sent from the correct transmitter. The complete message itself is decipherable by anyone.

We could split hairs about whether or not a verify message such as this can be considered a coded message as well, but I hope everyone realizes that is not the intent of the FCC regulation, which is to assure the amateur service is not used for private, business or spy activity.

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