bob wrote:

Okay, so if it's several hundred times per minute, that would definitely
change everything. However, if that's the case, would it not be most
likely they're employing some sort of sinewave (or sawtooth, or
stepwave) 'seed' signal into a VCO which supplies the mixer freq?

Both seems to be in use, depending on the manufacturer.

Check out those sites:

www.transcrypt.com
www.kavitsecure.com
http://www.daxonfil.com/en/index.html

It's not impossible, but it may be unlikely the mixer freq changes that
often.

It is not too unlikely - anything else would decrease the security too
much.

The more I think about it, it could be a nasty chore to straighten it
out. Harris has a system for HF that's straight analog but certainly not
easy to decipher, but their's is not straight inversion either. If
however, the mixer truly shifts about that much, it's simply not worth
the effort, unless you don't mind placing your sanity at risk...

*g*





regards - Ralph

--

Want to get in touch? http://www.radio-link.net/whereisralph.txt

Wayne Howell wrote:

The tick that started this thread is at a one second interval......

These scrambled (?) messages occur quite infrequently (perhaps 2-3 times
a day) and it is always in incoming message. The dispatcher usually
(but not always!) responds in plain talk.

The same here with some APCO25 users Often only one person
scrambles, the other not :-)

About half the time, from the context of the dispatcher's message, I can
identify which field radio the scrambled (?) speech is coming from.
And, in those cases I will have heard the same radio in clear speech and
will hear it later on also.

Same here, too.

Wayne Howell
Port Townsend, WA




regards - Ralph

--

Want to get in touch? http://www.radio-link.net/whereisralph.txt

the sync ticks give it away as hopping " rolling code voice inversion
encryption "

Rolling/Hopping Code Scrambling

This inverts the audio around a frequency which keeps changing. This
requires synchronization of the inversion frequency between sender and
receivers.

The security of this system depends on the combination of how often
the inversion frequency changes and how random the change is. The use
of random codes to specify the inversion frequency allows a high level
of control over the security.

This allows the techniques of key generation used in digital data
security to be applied, yielding immensely large number of codes, and
the added security from these changing frequently as well.

"
http://www.machine-ware.co.nz/Safehand.htm




rather than " muse " yourself into oblivion , why not just type
" rolling code voice inversion " into Google to learn why this is
the " latest and greatest " form of super secure encryption ,
even used extensively by the military.

you'd have more luck breaking into your cable box than
decoding this newer encryption product ......



k.................




On Thu, 09 Jun 2005 09:30:19 -0400, bob wrote:

Okay, so if it's several hundred times per minute, that would definitely
change everything. However, if that's the case, would it not be most
likely they're employing some sort of sinewave (or sawtooth, or
stepwave) 'seed' signal into a VCO which supplies the mixer freq?

It's not impossible, but it may be unlikely the mixer freq changes that
often. If it changes too much, then it itself starts to become a
problem, because the switching itself will begin to encroach into the
audio spectrum. The mathematical limit would be 3000 seed changes per
minute, as this would impose a 50Hz noise on the information. I suppose
part of the problem is my not ever hearing this type of signal, so I'm
only able to imagine what it sounds like. Is the system is truly an
analog mangling of the source material? Also, there was another system
out back in the 70's where they took the passband, inverted it, sliced
it up, and shifted the pieces about. It think Radio-Electronics did a
feature on it, including a project for one that broke 300Hz-3000Hz into
4 pieces, mangled them a bit and out popped your encoded audio. It was a
symmetrical system.

The more I think about it, it could be a nasty chore to straighten it
out. Harris has a system for HF that's straight analog but certainly not
easy to decipher, but their's is not straight inversion either. If
however, the mixer truly shifts about that much, it's simply not worth
the effort, unless you don't mind placing your sanity at risk...






Ralph A. Schmid, DK5RAS wrote:
bob wrote:


roward to decode." I was not suggesting it would not be labour
intense. It could turn out to be a royal pain in the a$$, however, if
it's simply inversion with a variable mixer freq, there's no real
security there.


The problem may be that the tick usually has nothing to do with the
number of frequency changes. The inversion frequency may change
several hundred times per minute, and the tick is just used to keep in
sync.



regards - Ralph

Even back in high school the cable boxes were never a significant
problem... ;-)



I will concur that a high rate rolling code inversion could be a
complete pain in the keester, but I also maintain it would not be as
secure as an asymmetrical digital system with an exception, that being
key changes at a significant rate. If the rate of key changes equal the
information rate, then you're flummoxed. If it's much less, then you
have a good chance of figuring it out. Speech itself is simply the
concatenation of known allophones that can only be serialized in limited
and well known sequences, so the number of possibilities of inverted
speech is limited. Digital encryption allows the absolute obscurity of
the source information. Please don't read into this that cracking analog
systems is a 'walk in the park' so to speak, but they are not nearly as
secure as a digital system. I initially assumed the source signal was
simple inverted speech with a key change once or twice a second; that
would be easily deciphered. It would seem this is not at all the case
with respect to the communiques being discussed.

That said, there are some valuable cribs to be found in utility
communications; call signs, phrases such as 10-4, roger, etc, are dead
giveaways to someone on the right track, if indeed they are attacking
something with a significantly lower rate of frequency shifts.


B.



krackula wrote:
the sync ticks give it away as hopping " rolling code voice inversion
encryption "

Rolling/Hopping Code Scrambling

This inverts the audio around a frequency which keeps changing. This
requires synchronization of the inversion frequency between sender and
receivers.

The security of this system depends on the combination of how often
the inversion frequency changes and how random the change is. The use
of random codes to specify the inversion frequency allows a high level
of control over the security.

This allows the techniques of key generation used in digital data
security to be applied, yielding immensely large number of codes, and
the added security from these changing frequently as well.

"
http://www.machine-ware.co.nz/Safehand.htm




rather than " muse " yourself into oblivion , why not just type
" rolling code voice inversion " into Google to learn why this is
the " latest and greatest " form of super secure encryption ,
even used extensively by the military.

you'd have more luck breaking into your cable box than
decoding this newer encryption product ......



k.................




On Thu, 09 Jun 2005 09:30:19 -0400, bob wrote:


Okay, so if it's several hundred times per minute, that would definitely
change everything. However, if that's the case, would it not be most
likely they're employing some sort of sinewave (or sawtooth, or
stepwave) 'seed' signal into a VCO which supplies the mixer freq?

It's not impossible, but it may be unlikely the mixer freq changes that
often. If it changes too much, then it itself starts to become a
problem, because the switching itself will begin to encroach into the
audio spectrum. The mathematical limit would be 3000 seed changes per
minute, as this would impose a 50Hz noise on the information. I suppose
part of the problem is my not ever hearing this type of signal, so I'm
only able to imagine what it sounds like. Is the system is truly an
analog mangling of the source material? Also, there was another system
out back in the 70's where they took the passband, inverted it, sliced
it up, and shifted the pieces about. It think Radio-Electronics did a
feature on it, including a project for one that broke 300Hz-3000Hz into
4 pieces, mangled them a bit and out popped your encoded audio. It was a
symmetrical system.

The more I think about it, it could be a nasty chore to straighten it
out. Harris has a system for HF that's straight analog but certainly not
easy to decipher, but their's is not straight inversion either. If
however, the mixer truly shifts about that much, it's simply not worth
the effort, unless you don't mind placing your sanity at risk...






Ralph A. Schmid, DK5RAS wrote:

bob wrote:



roward to decode." I was not suggesting it would not be labour
intense. It could turn out to be a royal pain in the a$$, however, if
it's simply inversion with a variable mixer freq, there's no real
security there.


The problem may be that the tick usually has nothing to do with the
number of frequency changes. The inversion frequency may change
several hundred times per minute, and the tick is just used to keep in
sync.



regards - Ralph