[Milsurplus] Cipher Challenge!

[mikea]

On Wed, Nov 07, 2007 at 10:15:53AM -0500, Ray Fantini wrote:
> For well over twenty years the amateur satellite community has used a common algorithm to encrypt all 9.6 Kbps digital satellite traffic, the call letters of the originating station and of the satellite are transmitted in the clear but all other text is encrypted. not for any clandestine reason but to avoid having long strings of ones or zeros. the software and the encoding algorithm are all public knowledge and can be downloaded from many sites. I have done quite a bit of satellite operating and have never heard any complaints about using encryption. Everything that I  work with in digital television and radio has to be encrypted, not just to avoid long strings of similar states but also for forward error correction and I would speculate that anyone involved with modern digital communications beyond 1.2 Kbps is going to be using some form of encoding or what the outside observer would consider encrypted data. I have not worked with the DSTAR format yet but with its AMBE encoding scheme and Forward error correction is impossible to decode with out the proper software, so dose this mean ICOM is braking the law? And with  the ARRL promoting this format as the future of Ham radio are they law breakers too? 
> Ray Fantini KA3EKH

No, neither the satcom folks nor the DSTAR users are breaking the law,
because the algorithms have been provided to -- *and* accepted by --
the FCC, and because DSTAR falls in with AMTOR, PACTOR, GTOR, Clover,
and other accepted digital codes.

Also, there's an explicit authorization in Part 97 for the satcom
folks to encrypt the command packets that control things on their
birds, so that only the authorized operators can control "their"
satellites.

It's the hams who decide they're going to encode or encipher their 
comms without providing 
o	algorithms and keys (for ciphers), or 
o	codebooks, superencipherment tables and keys (for codes) 
to Uncle Charlie,
or who use other than the approved SS methods, that can wind up in a
big heap'o'trouble.

97.113 is very explicit on that subject: 

:    ' 97.113 Prohibited transmissions.
:      (a) No amateur station shall trans-
:    mit:
:    
:      (1) Communications specifically pro-
:    hibited elsewhere in this part;
:    
:    [snip]
:    
:      (4)
:    [snip]
:    messages in codes or ciphers intended
:    to obscure the meaning thereof, except
:    as otherwise provided herein; 


So it would be A Bad Idea, for instance. if I and another ham were to
decide to encode our communications using the WW II training codebook
found at <http://mikea.ath.cx> to encrypt our communications, unless
we get permission first -- which may or may not be forthcoming. The
same holds true if we decide to use Hydrographic Office Pub. 80, two
codebooks for use in merchant ship communications, even though that
publication is intended and approved for certain non- amateur-radio
communications, and is published by the U. S. government.

It would be at least as bad an idea if someone else and I decided to 
use a different shift register tap pattern, size, etc., than those 
set out in 97.311 for DSSS, or a different FH scheme from that set out
in the same place, because at that point reading our signals requires 
cryptanalysis, rather than running the signal through an RX set up to
read signals compliant with 97.311.

An idea that occurs repeatedly in Part 97 is that encoding is not to 
be used to obscure the meaning of a transmission, except for control 
of a space station. 

But you all know this already. 

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin