Question about an old scrambler phone [telecom]

(moderator please change my email address so spammers can't use it.)

I've got an odd sort of a question for your group.

When I was a kid, my friend's dad had a phone in his house that he told me was a "scrambler". It was a regular telephone, mounted on a metal base, with an AC cord for the base. The base had just two vacuum tubes in it, and a couple of transformers. It didn't look like much, but my friend said his dad used it to make scrambled phone calls to his reserve unit.

Has anyone ever seen anything like that? I never knew if he was yanking my chain or not.

Ernie Donlin

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Reply to
Ernest Donlin
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One of the simplest forms of a 'scrambler' simply frequency-inverted the audio input. basically, use the audio to AM modulate a circa 4kHz 'carrier', and send only the the _lower_ sideband over the wires..

Conveniently, you can 'unscramble' the signal by doing exactly the same thing to the 'scrambled' signal.

Necessary components are: 1) an oscillator, 2) a modulator, 3) a low-pass filter. That's two tubes, and an inductor with a couple of capacitors, plus a multi-tap (filament and B+) power transformer to run it all.

Sounds _real_ close to what your friend's dad had. >

Now, to answer the _actual_ question you asked: "No, I've never actually

*seen* one of them myself." I only know "of" such devices, having read about, seen schematics in books, etc.
Reply to
Robert Bonomi

When the Bell System introduced overseas communications via radio, they included frequency shifting as a privacy measure. It was more designed to prevent inadvertent evesdropping as opposed to stringent security. They said a person with excellent hearing and skill could listen the discern the conversation, and of course constructing a descrambler would not be hard to do.

It's written up in the Bell Labs history.

Reply to
Lisa or Jeff

Thanks, that's nice to know. I didn't think my friend would go to all that trouble to put a box and tubes, etc. on the bottom of a phone, but it still seemed so simple a circuit that I couldn't quite believe it would work.

Now, I'm curious: is that kind of scrambling still possible? It seems like it would be a neat way to keep the kids from picking up the phone when I want to gab with the wife. I'm not going to build one, but I wonder if there's anything I can buy online?

Thanks for helping.

Reply to
Ernest Donlin

I'm somewhat amused that anybody would consider their conversations with their reserve unit sensitive enough to require speech scrambling.

More recently, speech inversion has been used in some analog cordless phones, various radio systems, and in central office remote line testing equipment to allow line monitoring while maintaining some level of privacy. The Harris DATU from the 90's is one example, and I'm sure there are others.

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"AUDIO MONITOR - The subscriber line may be monitored for up to 10 minutes, after which time the DATU disconnects from the No-Test trunk. Audio Monitor may be used on either busy or idle lines. Traffic on a busy line will be audible but unintelligible. The Audio Monitor Mode may be exited before the end of the 10 minute period by selecting an appropriate test function."

Reply to
Chris Hoaglin / Primary Rate

A long time standard feature in telephone service is the ability of the operator to break into ongoing calls to announce an emergency call. (Now they charge a steep fee to do that). Before doing so, they listen in to ensure the line is actually 'busy talking' and not merely off hook or our of order. (Verifying a busy line is a fee now, too.)

Some time ago Bell Labs Record reported on a device that would allow operators to confirm the line was in use with a conversation without the operator being able to listen to the conversation. The device would scramble the conversation so the operator would hear something.

To me, this seemed like overkill. Bell operators worked under strict quotas and supervision and they wouldn't have time to sit there and listen in to a conversation, especially with a subscriber on the line waiting for a result. Plus, I dare say the vast majority of telephone conversations are rather boring.

Anyway, I have no idea if this device was ever rolled out, or if so, how widely it was used.

Reply to
Lisa or Jeff

Faugh! talk about overkill! A simple voltmeter across the pair will give a 'good' indicator of conversation on the line. And, with an ESS you could do it purely in _software_ -- the 'mean' level of the signal, the extreme values, and a variance-type number (e.g. std deviation), should provide an extremely reliable indicator. Most of the 'development cost' would lie in developing the 'norms' against which data from a specific test was compared. It would be trivial to hook this to an IVR system that could report, w/o -any- human intervention: 1) line is 'on hook' 2) line is 'off hook', and appears to be actively in use 3) line is 'off hook', but appears to be not in active use

with a little _hardware_ support -- instrumentation to measure things on the analog tail loop itself, rather than just looking at data in the switch, one can add: 4) trouble on the line, apparent short 5) possible trouble on the line, line break or no instruments connected.

Getting result 5 does require some fairly sophisticated test gear, but 4 is trivial.

I'd guesstimate the _total_ development cost of the analyzer for results 1-3 at 'low 5 figures' with the preponderance of that going for gathering the data for the 'norms' used in setting the reference check-points. since it's a pure software function, the 'cost of deployment', once developed, is essentially zero for each location.

Reply to
Robert Bonomi

There are "anti-eavesdropping devices" you can get which tell you whether another phone on your line is off hook; I believe they're nothing more than a zener diode bridged across the pair.

Detecting activity is harder, because some lines are "noisy" enough that, with a phone off hook but left idle, a sound meter would show a higher volume than two people talking quietly on a better line. I've seen causes for this ranging from old wiring in an old house to squirrels eating the insulation off the drop wires (and wondered why the phone company wouldn't let us cure that by substituting an armored cable).

Reply to
John David Galt

From: John David Galt

Squirel guards are common on aerial cables in much of Oklahoma and surrounding states. I don't think there was much problem on drops.

I had squirrels eat the insulation off the TV cable in my attic until it failed and Cox had to rewire the eintire house. It certainly got very noisy before it failed completely.

Not the only things wrong with squirrels in your attic.

Wes Leatherock snipped-for-privacy@yahoo.com snipped-for-privacy@aol.com

Reply to
Wes Leatherock

It's possible, but it would be more effective just for you and the wife to learn French or even pig latin.

The Germans very quickly learned to decrypt voice inversion systems during the war, by ear. They called it "Krenkelcan" encryption because the English word "Telephone" sounds like "Krenkelcan" when inverted.

--scott

Reply to
Scott Dorsey

I've been around the block a few times, and I'm not likely to learn another language at my age. My wife isn't going to do that, either. I need a way to scramble our calls, so let's just stick to that.

Well, rootie-toot-toot for them! I don't think that's going to hold water in this day and age - kids today can't even spell "translate", and the only special language the younger generation seems to know is foul language.

Now to get back on the track: is there a phone I can buy that has a built in scrambler? I really don't care if it's an "inverter" type or if it's the same kind that the President uses: I just want to be able to talk to my wife without worrying about who's snooping. I haven't got the President's budget, mind you, but we're not out to hide any nuclear secrets from the reds, either.

Ernie

Reply to
Ernest Donlin

I don't have time to investigate any of these, but simply Googling "telephone scrambler builtin" (without the quotes) finds some 30,400+ hits. Picking one at random on the first page of hits:

and there's a lot of interesting products. Seems most such devices are external and not explicitly builtin to phones. Couldn't find the pricing for many of the products, but a portable telephone voice scrambler is listed at US$299. All the products seem to be only for landlines.

Browsing another site of "spy stuff" was most interesting but I didn't see any phone scramblers there. Their UV LED flashlights really got my attention, though. :-)

But, I wonder: am I misremembering the fact that cellphone transmissions are already scrambled for security?

***** Moderator's Note *****

Cell phones aren't "scrambled": they just use transmission methods that ordinary receivers can't pick up. CDMA is a form of spread-spectrum, TDMA is "Slotted Aloha", etc.

It's Security Through Obscurity, but anyone with a cellular maintenance terminal can listen in to any call within range.

Bill Horne Moderator

Reply to
Thad Floryan

Sharper image _might_ havee something.

Also check with Mike Sandman.

A quick google search on 'telephone scrambler' suggests that such are available. The low end looks to be circa $500/pair, just for the black box. Complete phones, about $1,800/pair.

Ramsey Electronics has a box in _kit_ form, at about $50 each end.

Reply to
Robert Bonomi

.........

Whoa.... all GSM air traffic is highly encrypted - you cannot get much more "scrambled" than that!

Reply to
David Clayton

You call it "highly encrypted". I call it "probably better than no encryption at all". GSM has been cracked a while back. Your security under GSM is usually that nobody cares to hear your calls. If they do care, it's certainly doable. Sample cite (from 2009!):

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Reply to
Ron

Yes/no/sorta. As I recall, there are three encryption schemes, the weakest is the voice & the strongest is the call authentication/billing scheme. [Gee, guess where the carrier's interest REALLY is..]

BUT, given that Big Brother has access to the switch/MTSO, it does not make much difference. Look up the IEEE Spectrum article on the Greek wiretapoping scandal.

Reply to
David Lesher

Beg to differ. At least on GSM the audio is -not- transmitted as standard digital sampling of an audio stream. there's a bunch of comprression _and_ encryption employed. the encryption doesn't 'mean much', because there's enough information sent over-the-air to allow someone with sufficiently sophisticated monitoring gear to decrypt.

Reply to
Robert Bonomi

You can text, right? If so just use one time pads to encrypt/decrypt. Problem solved.

Reply to
T

Yeah, there isn't one out there that hasn't been cracked. Even DECT isn't so secure anymore.

Reply to
T

How difficult would it be to get real quality end-to-end encryption on a cell phone (possibly with no hardware changes)? Does anyone offer this? It seems like it would be a popular app, although most people wouldn't be able to tell if it was really working. Are there any legal problems (suppose, for the moment, the call is USA to USA), other than perhaps the phone needs to be "jailbroken" to make this work?

Establish a cell-to-cell call (in the clear, at least as far as the CO is concerned). Both parties agree to go to secure mode, fire up their app (need compatible apps, obviously), and press a button to start encrypted mode. They have a pre-shared key to use already stored in the app for each correspondent, probably along with phone numbers for that person that have the software available.

The apps on both ends sync up, then start encrypting the (digital) voice channel, perhaps with AES-256 or something stronger. TLA agencies get annoyed that their CO-based wiretaps are seeing encrypted data.

I think modern cell phones have the CPU horsepower to do the encryption in real time, possibly with degraded voice quality.

***** Moderator's Note *****

The problem is that the TLA's you alluded to won't allow any of the changes to the cellular systems which would be needed to make it work. Unless you can construct a device that will produce encrypted speech AND TRANSMIT IT AS AUDIO, you'll need to have access to the "data" side of the phone, and the ability to relay the data from the cell tower to the other encryption node at the distant end of the call. I think it's too big a change with too little demand.

Of course, "3G" and "4G" data capabilities will make _some_ kind of encryption possible, but you'd have to set it up with external computers at each end.

Bill Horne Moderator

Reply to
Gordon Burditt

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