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"Inversion Scramble" vs. "rolling code"

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MikeSD

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Academic question: What is the difference between "inversion" scramble and "rolling code" scramble? Technical and real world difference.

I've been trying to find a description that defines the differences between "inversion" scramble and "rolling code".

I have found descriptions that say "inversion" is a less secure scramble and that "rolling code" is much more secure. And rolling code give you more codes to choose from but in tests, I don't hear much of a difference. I did a test where I recorded a simple "inversion" scramble from a radio and compared it to the same radio, using "rolling code" (actually did this with 2 different codes). The reality was, you could still kind of understand what was being said. Well, almost. I knew what I said, so for my test, I could kind of understand what was being said.

I really didn't notice how the "rolling code" scramble was any more secure. Most radios that have "rolling code" cost a bit more and say that rolling code is a much more secure communications. How so?

Anyone have a technical understanding of these types and can explain the difference?
 
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ecps92

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The Voice Inversion is basic and in it's day there were a few sources to purchase a decoder. It's basic sound is like donald duck.

Rolling Code has a Synch pulse [click] that changes the code at every synch

Samples of many audio formats are avail at
Digital Modes Samples

Academic question: What is the difference between "inversion" scramble and "rolling code" scramble? Technical and real world difference.

I've been trying to find a description that defines the differences between "inversion" scramble and "rolling code".

I have found descriptions that say "inversion" is a less secure scramble and that "rolling code" is much more secure. And rolling code give you more codes to choose from but in tests, I don't hear much of a difference. I did a test where I recorded a simple "inversion" scramble from a radio and compared it to the same radio, using "rolling code" (actually did this with 2 different codes). The reality was, you could still kind of understand what was being said. Well, almost. I knew what I said, so for my test, I could kind of understand what was being said.

I really didn't notice how the "rolling code" scramble was any more secure. Most radios that have "rolling code" cost a bit more and say that rolling code is a much more secure communications. How so?

Anyone have a technical understanding of these types and can explain the difference?
 

MikeSD

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I listened to the "rolling code" scramble audio at the site you suggested. Mine doesn't sound like that. I wonder if there are different types. I DO have the initial burst, on the rolling code, but don't have the periodic clicking. Mine basically sounds like inversion, with the initial burst.

Should all rolling code sound similar to the audio on that site? I guess I'll have to do some more testing. Perhaps I can post some audio later. I'm wondering if the rolling code is actually working on my radio. I know it scrambles and decodes but it sounds only like inversion, except it has the initial cherp.
 
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mancow

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Several different manufacturers make audio scrambling devices and they all differ a bit. I suppose yours could be a signalling packet for unit ID only and fixed inversion. There are quite a few different possibilities.
 

MikeSD

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I have fired off this question to the mfg. rep. to see if I'm doing something wrong in setup.

I have the UT-110R scrambler module, for ICOM installed in the F4161T.

Another thing I wonder about is, I have seen writing that say scramblers are illegal on GMRS/FRS and some say it's not. But there are radios that are GMRS/FRS only (and not programmable) that have scrambling built in. If they are illegal, how is it that a part 95 radio can have built in scrambling?
 
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b7spectra

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I think that the "built in scrambling" is on the FRS vs the GMRS channels. Then again, at a max of 4 watts on portable usage, in a normal enviroment, you are going to get about 2-3 miles, so, then again, who is going to care? Now, using it on the repeater side, going out at a lot more power and a lot more range, you will most likely get people who are on the repeater to complain (either because it sounds like Donald Duck on helium or they have nothing better to do). I have noticed that when on inversion, the range effectively drops, so it's not a plus there.
 

n5ims

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I have fired off this question to the mfg. rep. to see if I'm doing something wrong in setup.

I have the UT-110R scrambler module, for ICOM installed in the F4161T.

Another thing I wonder about is, I have seen writing that say scramblers are illegal on GMRS/FRS and some say it's not. But there are radios that are GMRS/FRS only (and not programmable) that have scrambling built in. If they are illegal, how is it that a part 95 radio can have built in scrambling?

The radios are not allowed to have built in scrambling that work on the GMRS frequencies (scrambling on FRS frequencies are OK from what I understand though). I believe that with this "Notice of apparent Liability for forfeiture" http://www.fcc.gov/eb/Orders/2009/DA-09-2374A1.html that the FCC sent to Uniden for including "Voice Scramble Security" on some of their GMRS radios validates that. They indicate "Section 95.183(a)(4) of the Rules prohibits GMRS operators from transmitting coded messages and messages with hidden meanings."
 

RayAir

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I have some Midian TVS-2's that are set up to initial sync only. If you want to know if you have rolling code or not put the radio in scramble mode and listen to the audio on a scanner. Then whistle in the radio. If the audio is warbled then you have rolling code.

Rolling code changes the inversion frequency at various speeds depending on the scrambler. Some hop inversion frequencies others sweep. Typically inversion frequencies from 2600-4000Hz are used. Fixed inversion is low security and rolling code inversion is medium security.

The highest security scramblers that permute the frequency domain would be the rolling bandsplitters with random sub-band inversion, such as the Transcrypt DES series scrambler or the late MASC encryption formerly utilized by UK police forces before they went digital.

voice_encryption_and_scrambling : Voice Encryption and Scrambling Group
 

gewecke

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The radios are not allowed to have built in scrambling that work on the GMRS frequencies (scrambling on FRS frequencies are OK from what I understand though). I believe that with this "Notice of apparent Liability for forfeiture" http://www.fcc.gov/eb/Orders/2009/DA-09-2374A1.html that the FCC sent to Uniden for including "Voice Scramble Security" on some of their GMRS radios validates that. They indicate "Section 95.183(a)(4) of the Rules prohibits GMRS operators from transmitting coded messages and messages with hidden meanings."

Not only uniden are noted for radios with this feature,but there even motorola gmrs/frs radios which include the scramble feature on both frs and gmrs channels.
I'm not aware of a NALF issued to motorola for this either,even though they still market these units. Double standards maybe?
n9zas
 

gmclam

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inversion is not scrambling

I don't consider "inversion" to be a form of scrambling. Think of eggs sunny-side up as being normal, flip them over for inversion, and scramble them for scrambling. In other words, to scramble, you really mix things up.

Speech inversion works by mixing two signals; the desired audio with a "tone" or constant frequency. When you mix you get the sums and differences of the input frequencies. For my example, consider using a tone of 4,000 cycles. If the input audio is 1,000 cycles; you will get 5,000 (sum) and 3,000 (difference) cycles at the output of the mixer. The signal is then fed through a low pass filter (let's use 4,000 cycles) and that leaves only the 3,000 cycle signal. Summary 1k in gives you 3k out.

If the audio frequency is 3,000 cycles (still mixing with 4,000 cycles), that would result in 1,000 and 7,000 cycles and filtering leaves only the 1,000.

On the receive end you perform the exact same process. They "key" is knowing the frequency that was mixed before transmission. I think you can see why it is called "inversion" (and hopefully why I don't consider it scrambling).

True scrambling (changing the order of things) in analog mode takes some work, but in a digital environment it is a breeze.
 

gewecke

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I don't consider "inversion" to be a form of scrambling. Think of eggs sunny-side up as being normal, flip them over for inversion, and scramble them for scrambling. In other words, to scramble, you really mix things up.

Speech inversion works by mixing two signals; the desired audio with a "tone" or constant frequency. When you mix you get the sums and differences of the input frequencies. For my example, consider using a tone of 4,000 cycles. If the input audio is 1,000 cycles; you will get 5,000 (sum) and 3,000 (difference) cycles at the output of the mixer. The signal is then fed through a low pass filter (let's use 4,000 cycles) and that leaves only the 3,000 cycle signal. Summary 1k in gives you 3k out.

If the audio frequency is 3,000 cycles (still mixing with 4,000 cycles), that would result in 1,000 and 7,000 cycles and filtering leaves only the 1,000.

On the receive end you perform the exact same process. They "key" is knowing the frequency that was mixed before transmission. I think you can see why it is called "inversion" (and hopefully why I don't consider it scrambling).

True scrambling (changing the order of things) in analog mode takes some work, but in a digital environment it is a breeze.

D-uh! This is already known,but in the final end it's still scrambled.:)
n9zas
 

MikeSD

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The radios are not allowed to have built in scrambling that work on the GMRS frequencies (scrambling on FRS frequencies are OK from what I understand though). I believe that with this "Notice of apparent Liability for forfeiture" http://www.fcc.gov/eb/Orders/2009/DA-09-2374A1.html that the FCC sent to Uniden for including "Voice Scramble Security" on some of their GMRS radios validates that. They indicate "Section 95.183(a)(4) of the Rules prohibits GMRS operators from transmitting coded messages and messages with hidden meanings."

A lot of radios have this ability. I have a Kenwood (TK3131), that is part 95 certified, works on GMRS and FRS, and has scramble. The scramble feature works on all the GMRS frequencies it uses 462.550, to 462.725. And on the FRS channels it will even transmit at 1Watt. And, there is another interesting smoking gun with the TK3131. It doesn't even use the higher FRS ONLY frequencies, for simplex. It only uses the GMRS/FRS frequencies, and uses a higher 1W output, which tends to suggest that the targeted market is the GMRS market, yet it has scramble.

How is it that these GMRS radios, have built in scramble, if they are not allowed? I have read somewhere that inversion scramble is tolerated but not encrypted. I think this might be a vague area since it would be very clear to the FCC that these radios violate that rule, if that rule in fact, forbids scramble on GMRS radios.

Keep in mind too that the FCC rules don't actually say no scrambling. They say "no coded or hidden meaning", which is subjective. Basic inversion scramble can be easily undone. In fact, you can almost make it out, without decoding, which is why I started this thread. I was wondering if my rolling scramble was actually more secure.

Is "basic inversion" really any tougher to decode than say someone speaking in a foreign language. Must all communications be in English, to avoid coming afoul of this rule? I hear non-english all the time. It's just as "coded" as "inversion scramble" to me. ;) The FCC should lighten up on this a bit and have "no hidden or coded" messages to mean heavy encrypted transmissions. Just my opinion.
 
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SkipSanders

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MikeSD - How is it that these GMRS radios, have built in scramble, if they are not allowed? I have read somewhere that inversion scramble is tolerated but not encrypted. I think this might be a vague area since it would be very clear to the FCC that these radios violate that rule, if that rule in fact, forbids scramble on GMRS radios.

The FCC is lazy. They don't actually CHECK type acceptance applications, they accept the word of the approved testing labs. You will find some radios with 'Part 95A' Type acceptance in their grants for modulation types which are not allowed on GMRS, too. The lab submitted it that way, the FCC rubber stamped it. You, however, are still required to obey the rules that say you can't DO it.

Keep in mind too that the FCC rules don't actually say no scrambling. They say "no coded or hidden meaning", which is subjective. Basic inversion scramble can be easily undone. In fact, you can almost make it out, without decoding, which is why I started this thread. I was wondering if my rolling scramble was actually more secure.

Shocking as this seems to be to you, we don't get to define the terms. The FCC does, and has stated (in notices of violation) that yes, 'no coded or hidden meaning' means 'NO SCRAMBLING'.

Several manufacturers have recieved violation notices, and orders to cease selling radios in violation, selling stuff which will not use scrambling on GMRS frequencies, only FRS. More probably would have/will, except (see above) the FCC is lazy, undermanned, underfunded, etc, and is very slow to react to anything not desperately important, like, say, illegal FM Broadcast Band transmitters, or transmitting on police systems illegally.
 
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MikeSD

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Shocking as this seems to be to you, we don't get to define the terms. The FCC does, and has stated (in notices of violation) that yes, 'no coded or hidden meaning' means 'NO SCRAMBLING'.

According to you. But the FCC hasn't defined it that way. If they have, provide the link to that definition. If they meant "no scrambling" that's what they should use in their wording. Like I said, this is vague. All "vague" wording is decided in court... should they choose to prosecute. And providing certification on equipment they "should have known was in violation" is defacto approval, in law.

It might also be argued, in law, that there is no "hidden meaning" since the decription key is sent (or widely known) along with the transmission. Or to put it another way, the means is readily available for the FCC or anyone else, to understand what was sent. Anyone who receives the transmission, can get the "meaning". I don't believe that you can send any transmission, using inversion scramble, or even rolling code, that can't be recorded and decyphered later. The FCC or authorities can decyper anything sent, that is using these types of common scramble. Nothing is "hidden" except for briefly. .
 
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SkipSanders

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Lots of text, but feel free to read the official FCC notice to Midland where they rejected your claim that 'coded/hidden' doesn't apply to inversion scrambling, and fined Midland, along with ordering them to stop selling.

http://www.fcc.gov/eb/Orders/2009/DA-09-1390A1.html

From that:

2. Section 95.183(a)(4) of the Rules prohibits GMRS operators from
transmitting coded messages and messages with hidden meanings. The
Enforcement Bureau's Spectrum Enforcement Division ("Division")
received information indicating that Midland was marketing GMRS
transmitters that have a voice scrambling feature. After its receipt
of this information, the Division began an investigation. In pursuance
of the investigation, the Division conducted internet research on
February 24, 2009, on the website Midland Radio - Midland Radio | Home. During the
internet research, Division personnel observed that Midland was
offering for sale the following GMRS transmitter models described as
having a "Voice Privacy Scramble" feature: GXT900VP4 and GXT950VP4.

7. Midland's arguments are unconvincing. It was not justified in its
assumption that the Commission decided not to require the removal from
the market of GMRS devices with voice scrambling. In 2007, the
Commission staff publicly interpreted its rules to advise that voice
scrambling constitutes coded messaging and, therefore, is not allowed
for GMRS devices
. Additionally, in 2004 the former Public Safety and
Critical Infrastructure Division of the Wireless Telecommunications
Bureau granted Garmin International, Inc. ("Garmin") a waiver of
Section 95.183(a)(4) of the Rules to permit the manufacture and
marketing of GMRS devices capable of transmitting and receiving Global
Position System (GPS) location information. In the absence of a
waiver, the transmission of GPS location information over the radios
marketed by Garmin would have been prohibited by Section 95.183(a)(4)
of the Rules. Although Midland's voice scrambling technology differs
from Garmin's technology, it has an analogous effect - the
transmission of messages that are undecipherable to many GMRS users.
In both circumstances, the undecipherable messages are coded messages
within the meaning of Section 95.183(a)(4) of the Rules.
 

MikeSD

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Well, since this is a purely academic discussion, I will point out that nothing posted there counters what I said. I said the FCC rules are vague, not enforced uniformly, and defacto approval of such devices.

Further, when I read this text, Midland's case makes more sense than the FCC.

Finally, as I said, "vagueness" is decided in court. If Midland just chose to give up, that's a business case. That text is merely a one-time, specific ruling, on one incident. They even point out that Garmin uses "coded transmissions" and that is acceptable.

So, until and unless someone takes this through the courts OR the FCC makes the vague law unvague, it's still just a topic for discussion.

My bottomline is if the FCC approves a piece of equipment and that equipment is used precisely, as it was approved for use, I don't see a violation.
 
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MikeSD

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Another thing to wonder about, but almost pointless to ask is, why should the FCC even care. There are a vast number of legitimate reasons for wanting to use scramble for private citizens and even businesses and almost no reason to disallow it. But the proposed rule changes seems to indicate this will continue.

If this has anything to do with eliminating the potential use in crime, that's a ridiculous reason, since criminals wouldn't give a rip. But honest citizens, have potentially unlimited legitimate reasons for needing to use scramble. But if you ask the FCC you'd probably get an answer that doesn't even make logical sense.
 
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gmclam

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D-uh! This is already known,but in the final end it's still scrambled.
It is not scrambled.

If something is white and you want to call it black, blue or whatever, you may do so. Like they say, a rose by any other name is still a rose.

To put this into different words; scrambling changes the "order" of the elements of something. Speech inversion does not change the order, it simply inverts the audio spectrum (content) of the transmission.

The above would also explain why this technology is "allowed" in some radios. Does the FCC wording actually state "scrambling" or use some other term? Speech inversion is VERY SIMPLE to undo. Scrambling usually is not.
 

MikeSD

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The above would also explain why this technology is "allowed" in some radios. Does the FCC wording actually state "scrambling" or use some other term? Speech inversion is VERY SIMPLE to undo. Scrambling usually is not.

The rules do NOT use "scrambling". They say "coded" or "hidden meaning". I agree with you on this.

In my view, this isn't hidden or coded. It's easy to convert it back to original clear speech. It can be recorded by the FCC or anyone with the desire, and everything can be recovered, with very little effort. Further, the manufacturers who get this type certification disclose and give all the details of the inversion process and the FCC is fully aware of it.

The other interesting part of this new "interpretation" is this supposedly "pertinent" part.
"[a] station operator must not communicate ... coded messages or
messages with hidden meanings."
This applies to an "operator" NOT the manufacturer. So I don't see how the manufacturer could even be held liable, for this. To me a "pertinent" part would be quoting the rule that says "no manufacturer may provide scrambling in a GMRS/FRS radio", however no such rule exists and the FCC routinely certifies such radios.
 
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