Re: [amsat-bb] System Security (was Question about AO-40 telemetry)

["Timothy J. Salo" <salo@xxxxxxxxxxx>]

> Date: Tue, 23 Apr 2002 09:35:35 -0400
> From: Bob Snyder <rsnyder@toontown.erial.nj.us>
> To: amsat-bb@AMSAT.Org
> Subject: Re: [amsat-bb] System Security (was Question about AO-40 telemetry)
> 	[...]
> Sec 97.211(b)
>  A telecommand station may transmit special codes intended to 
>  obscure the meaning of telecommand messages to the station in space 
>  operation.
> 
> I just had a quick peak at http://www.radio.gov.uk/, and while I find 
> the prohibition of obscuring a message, I don't see a provision similar 
> to the one the FCC grants US operators as above... Hopefully it's just 
> my lack of knowledge of the UK regs. :-)

The suggestion for protecting the command channel of amateur satellites
is a plain-text command message with an appended, cryptographically
generated signature (or message digest).  I haven't heard any reasonable
argument that a cryptographic signature obscures the meaning of
anything; it's only function is to ensure the integrity of the 
plain-text message.  (Ok, ok, I am sure that there is at least one person
out there who will argue that cryptographic signatures, like AX.25
CRCs, obscure the meaning of something, but I haven't a clue what...)

Therefore, I believe that the security mechanism summarized above
conforms to UK regulations.  Perhaps, the UK regulations were just
ahead of their time (although perhaps nobody knew it).

(I wonder what Surrey does.)

-tjs

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