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

[Claudio Martins <ctpm@xxxxxxxxxxxxxxx>]

  I think that appending a signature to a plain text command cannot be taken 
as abscuring the meaning of the communication. The signature is a hash 
function. That hash function is publicly documented, so everybody knows how 
to compute it. And the hash is a function of the plain text command and a key 
that only the command station and the satellite know what is. The fact that 
*you* don't know the key is strictly your problem. Am I violating regulations 
just because, during the course of a QSO with a ham friend of mine, I talk 
about some subject that you've never heard of and so don't understand fully? 
See what I mean? Thats why I don't suppose it violates regulations.

cheers

Claudio


On Tuesday 23 April 2002 19:19, Timothy J. Salo wrote:
> > 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.)
>

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