A Response to Going Analog, by M.G.

Selectric Typewriter Security Issues

Back in the 1970s IBM was required by at least one of its customers to make some options available for Selectric typewriters because they discovered the Selectric design was susceptible to electronic eavesdropping that could determine what the typewriter was printing. As it turns out, mid-’70s electronics were capable of detecting not only the unique electronic signature of individual typewriter motors but also measuring the load incurred by that motor during character selection from the main power feed outside the building. So, it’s possible that even using a mechanical electric typewriter for written communications may not be as secure as we think.

Typebar typewriters, both electric and manual, do produce a typeface “signature”; so actually does a Selectric typing element– the “ball”. However, it’s trivial to change elements. Were someone to use a Selectric for secure communications I’d suggest, depending on the level of security required, one typing element be reserved and used only for that purpose. The elements are metal-coated plastic and will burn, although there will be some metal remaining, assuming it is not melted.

Regarding Selectric-type ribbons, you have pointed out that the correctable film ribbon can be very easily read; so can the correction tape. Even the fabric ribbons can be read, although it’s much more work than the film ribbon. As an FYI, typewriters of all types will leave impressions on the platen (the rubber roller the paper goes around), with typebar machines, especially manuals, leaving the strongest impression. I do not know how long those impressions remain readable, but I know some impressions can be readable in limited form for a day.

Smart Electric Meters

Given the proliferation of smart electric meters for residences and businesses, it is entirely possible that those meters have the capability to more closely monitor activities inside a home or business and report their findings across the electric grid to entities unknown. For example, it is entirely possible for monitoring electronics to determine the brand and model of home appliances and some activities associated with use of those appliances. Refrigerator manufacturers now use LED lighting for interior lighting, which requires the 120 volt AC the compressor runs on to be stepped down and converted to (usually) 12-18 volts DC.

To accomplish this requires a stepdown transformer equipped with at least one diode; energizing the induction coils in the transformer (by opening the door which turns on the light) causes a brief interference pattern, a.k.a. “unique electronic noise”, to be generated, which can be detected. That doesn’t sound like much until one realizes it can be used to determine if a house is occupied. Similar electronic noise is generated by the closing or opening of a standard single pole light switch. So even if the light activated is not visible outside the structure, it is still possible to determine if a structure is occupied.

Given the proclivity of NSA and others to monitor U.S. citizens, it’s probable that a dictionary of electronic signatures exists. You may be tumbling your brass cartridge cases inside a closet in the basement at 2 AM, but it’s possible someone can determine what you’re doing. Also as an FYI, flat screen TVs have constantly variable power draws, depending on what is being displayed; bright pictures with lots of detail will draw more watts than a dark picture with little detail.

Eliminating Electronic Noise Signatures

I suspect but do not know for certain that interjecting a UPS (Uninterrupted Power Supply) between the power source and the appliance will eliminate the unique noise signatures from the building’s wiring. It should be noted that a true UPS constantly operates the load that is plugged into it from a battery and has an internal charging system to keep the battery charged. There are “failover power supplies” that do not supply power from a battery until input power has failed; these devices supply building power to the load as long as building power is present and very rapidly switch to battery if building power ceases. I suspect they will simply pass through whatever unique noise signatures may be generated by the load.

Capabilities of Smart Electric Meters

I do not know what capabilities current smart electric meters have or what’s being developed for them. But even disassembly and inspection may be of questionable value since integrated circuits do not display on the exterior what their internal functions are. The same is true of EPROMs (electronically programmable read-only modules), although were several EPROMS to be discovered inside a smart meter it would raise a very large list of questions.

I’ve provided an explanation of why this is an issue on Selectric typewriters and Selectric-similar printing equipment, but it’s technical (and boring) enough to put just about everyone to sleep. Suffice it to say, if one is sufficiently under investigation by entities capable of monitoring the electrical signature inside a residence or business, which can be done from a neighborhood transformer or power line in the next block (even without using a smart meter), the difficulties increase greatly. The hazard with smart meters, as I see it, is that they may offer an exceedingly easy way to establish widespread spying on households.

Technical Explanation

Back in the 1970s a Certain Government Agency required IBM to make some options available for Selectric typewriters because they discovered the Selectric design was susceptible to electronic eavesdropping that could determine what the typewriter was printing. As it turns out, mid-’70s electronics were capable of detecting not only the unique electronic signature of individual typewriter motors but also measuring the load incurred by that motor during character selection, from the main power feed outside the building.

The option involved adding a 3 1/2 pound flywheel to the Selectric motor and some simple electronics that would randomly shut off electric current to the motor for a random number of seconds, during which the momentum of the flywheel would enable the typewriter to continue functioning until the electronics restored electrical power to the motor.

Identifying Motors and Characters Typed

Because of the Selectric’s design, and that of its electronic descendants, the I/O Printer (Input/Output, a cast iron frame electronically controlled Selectric-like machine usually found embedded in mainframe operator consoles, and which was developed into the standalone Mag(netic) Card, Memory Typewriter and Selectric Composer business machines), it was, and is, possible to do the following:

  1. Through the electronic noise generated by a particular motor, it is possible to identify individual motors, even in a large group of motors;
  2. Because the typing element (the type ball in Selectric/Mag Media machines operates with or against spring pressure to select characters that changes the load on the motor and the duration of the load (or lack of load), this can be used to identify the character being typed.

Tilt Rows

The typing element has four tilt rows (tilt 0,1,2,3, with Tilt 0 being the “home” tilt row at the top of the four circumferential rows of characters (“z” is the home character, in both upper- and lowercase), and controlled by the Tilt Ring to which the spherical typing element is attached), five positive rotate columns against spring pressure and five negative rotate columns with spring pressure, with one zero rotate column (the “home” column). There are an equal number of tilt columns and rotate rows in both lower case and upper case. Case change is accomplished by rotating the ball 180 degrees against spring tension.

Selectric, Selectric I, and Selectric II machines, along with the Mag Media line, used 88 character typing elements, 44 in each lower case and symbols and upper case and symbols. (If the cycle shaft is released to cycle – one-half revolution – without any latches pulled to select a character, a hyphen will print because the hyphen is located in the Tilt 3 Positive Rotate 5 position; this unique phenomenon is used to trouble shoot cycle shaft and shaft latching problems) Selectric III machines, Electronic Selectric Typewriters (called the “E-tron”) and later Selectric Composers used a 96 character element.

Whiffletree and Electronic Nature of the Machines

In both Mag Media and Selectric machines, there is a group of levers and latches– the “Whiffletree” mechanical linkage copied from earlier mechanical adding machines and calculators, with five latches controlling five pivoting links, or levers. Depending on which latches were selected, two of the latches control the tilt mechanism, the other three control the rotation (the Selectric does this mechanically with rods and links from the key-operated bails located under the keyboard; Mag Media machines use electronic solenoids controlled either by magnetic reed switches under the keyboard or electronic signals from magnetic storage (magnetic cards or, initially, 8-inch magnetic disks) or electronic impulses from a computer, as in the case of mainframe-connected I/O machines.

Typing on Mag Media or I/O machines appears to operate just like a mechanical Selectric, but there is no direct mechanical connection between the keys on the keyboard and the printing mechanism; it is passed through, and entirely controlled, by the internal or connected electronics.

As the Selectric is used, or the Mag Media or I/O machine prints, one or more of the five latches is selected (pulled), which also releases the cycle shaft that has three double cams with lobes oriented 180 degrees from each other, and the shaft rotates 180 degrees with each activation. These cams operate the bail mechanism, which pulls down the unselected Wiffletree latches, placing a load on the motor.

Load Variations

That load varies with character selection because each character on the typing element is either zero spring pressure or against spring pressure for positive tilt/positive rotate characters or with spring pressure in the case of negative rotate characters (a shift to upper case is a positive 180 degree rotation, at which point the tilt and rotate functions select upper case characters in exactly the same manner as lower case characters; in Selectric-based machines a cycle shaft release during which a character is not selected will print a hyphen in lower case or an underscore in upper case).

Trivia On Common Functional Issues

Just as added trivia, the Selectric mechanism can operate at 17-19 characters per second in continuous mode and 19-23 characters/second in bursts. The less tilt and rotate called for, the faster it will print, and speed is dependent upon proper adjustment and lubrication. When they were in use, however, it was not uncommon to see Mag Media and I/O printers suffer complete neglect for as long as 2-3 years and continue to function nearly at optimum speed. The most common failure was stretch of the very thin steel tapes that actuated the typing element tilt and rotate mechanisms in the print carrier, maladjustment/wear of the Whiffletree mechanism, or failure of the flat spring cycle clutch on the cycle shaft.

Steel tape stretch caused an out-of-time condition which led to, first, the element “locking in” one column off or the tilt ring “locking in” one row short, and was obvious because it printed the wrong character. This condition usually led to breaking of the tape(s) once it persisted for longer than a few days. Since they were left on, frequently either all day (Mag Media) or 24X7 (I/O) neglected Mag Media machines usually wore out the bronze center bearing that supports both the cycle shaft (the one with the cams) and the operational shaft that performs carriage return and backspace (Selectrics only, Mag Media carrier movement was controlled by a lead screw and pawl) or shift (all models). When the bearing wore sufficiently, it allowed the cycle shaft to “float” usually resulting in character mis-selection, followed by broken tapes.

The Burroughs Corporation modified Selectrics with their proprietary electronics to convert them into I/O printers; since Selectrics were aluminum-framed and used much lighter internal components, they did not hold up well in 24X7 usage unless they were scrupulously maintained.

A Poor Man’s Crypto Machine

I haven’t heard it in decades, but way back a few suggested the Selectric could be used as a “poor man’s crypto machine” by either deliberately maladjusting the typing element lock-in, or using a different and unique element. This is a non-starter because cryptographic security is dependent upon a massive degree of randomness in the relationship between the character selected and the character displayed. Changing the element would result in the same, incorrect, character being printed each time the same character was selected, posing not much of a challenge to any cogent third grader.

In WWII the German Enigma was mechanically defeated by the British with a machine that solved Enigma messages with a brute force attack, once the options had been reduced substantially, primarily because the Enigma period– the number of characters between a selected character being encoded with the same code character wasn’t long enough. I forget the exact length of the Enigma period, but I seem to recall it was something greater than 100 trillion characters.

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  1. As far as smart meters go, FIRE is more of a realistic threat. I see nothing else that is of any concern. The only way I see to counter the very real and documented fire concern is to not have it mounted on the house but maybe on a pole several feet away.

  2. Huh! it’s funny you mentioned crypto, while in the Army years ago as a radio teletype operator we used electric teletype machines and a crypto machine. this machine was re-keyed every day. But I learned recently on a Bletchley park movie, that one way they they broke the codes, was the standard used in training radio operators to giving thier call signs and greetings. in the clear was the same on the pre-emble of any encrypted message. Well something struck me recently that standard operating proceedure for U.S. Army radio teletype operators was using 5 line feeds, 2 carriage returns and 5 spaces to start a fresh message. Thus clearing any possible messages left on the receiving stations page printer. We knew there was the chance that our codes were broken within 23 hours so they were all changed every 24 hours. Well I used to tell my guys to change that habitual start up just to keep the decoders guessing. our message format was standard 16 line format. so the format of a message can be guessed at too, by the crypto annalist. It kind of makes you wonder will we ever learn, that habitual practices can always cause quicker decryption by the enemy.

  3. A Response to Going Analog, by M.G. is of great interest to, I suspect, those few of us who are interested in arcane Security trivia.

    Theodore Kaczynski, the Unabomber, used two manual typewriters which helped to positively identify him when law enforcement closed in.

    The article doesn’t mention it, but the I.B.M Selectric Magnetic Tape Composer used toroidal cores as memory. These devices retain their state even when the machine is turned off, thus making it possible to read whatever was recently typed, even if no mag tape is present.

    As for using an Uninterrupted Power Supply, it might be more secure to simply use a battery with an inverter to power an electric typewriter. This would eliminate any concerns about Smart Electric Meters.

    Everybody is aware that computer memory is easy to read by anyone who gets a hold of it. But nowadays, many devices have memory. Lately there have been several cases where printer memory has been used to convict law breakers. We all leave a larger footprint than we might imagine.

  4. Thanks for this enlightening and thorough information about the Selectric, which was always my favorite typewriter. And you’re right; I didn’t understand a good part of it.

  5. When I was with a District Attorney’s office we caught a lawyer who was forging real estate papers by running a search warrant and seizing the single strike ribbons from his Selectric typewriters. Every word of the forgery was there, as well as documents showing an intent to influence a Federal investigation.

  6. Then there’s the tried and true method of hand encryption, that can change at a moment’s notice as directed. Bottom line, never do the same thing twice, change it up. Never travel the same routes, use alternate methods. When in doubt, change it again. Avoid predictable patterns at all cost. Communication, travel, operations orders, it all needs flexibility.

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