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CQ Amateur Radio

Encryption and Enigma Machines

In my March column, we spoke about comput-

er security. I assume that, since then, you’ve

taken care of those three items I mentioned. If

you haven’t, just keep in mind that you’re a sitting

duck, and it’s not a matter of IF, but WHEN, your

security will be compromised. I mean, if Target,

Home Depot and eBay can’t keep hackers at bay,

what makes you think you’re safe?

Anyway, the long cold winter is over, and now

that we’re in May, let’s continue along that gener-

al line and talk about encryption and amateur

radio. Observant readers will notice this column,

which has appeared in even months for over a

decade now, has been changed to appear in odd

months. My editor tells me that “odd” is not a state-

ment about me, but I’m not so sure.

But back to encryption and amateur radio: Make

no mistake and have no doubt, encryption over the

air is legal under Part 97. Don’t believe me? Read

my column in the August 2006 issue of CQ for all

the details, but the bottom line is this: Part

97.113(a)(4) prohibits “messages in codes or

ciphers intended to obscure the meaning thereof,”

and here the key words are “intended to obscure

the meaning.” If you use encryption on the amateur

bands for a different intent, such as to command a

satellite or comply with privacy regulations, then

you are within the law to do so. Oh sure, you need

to keep the encryption keys on file and available

for the FCC to examine, along with some other

record keeping, but I’ll say it again: Encryption on

the amateur bands is legal, as long as your intent

is not to obscure the meaning of the message.

But that’s only peripheral to my column this

month, which is more about encryption as a sci-

ence than as a philosophy. I’ve written about

encryption software twice in the past; see the side-

bar for details and an idea for getting some mod-

ern software.

Decoding an Enigma

Now let’s look at the exact opposite of modern:

German Enigma machines. In case you don’t

remember World War II, Enigma machines were

used by Germany (and others) to encrypt mes-

sages. A top-secret project in the U.K. broke the

Enigma codes during the war, resulting in sub-

stantial assistance to the allies’ efforts. The story

of the work at Bletchley Park is a fascinating one,

and was only disclosed in the 1970s1.

A basic Enigma machine (Photo A) used a key-

board of electrical switches to enter letters of a

message. The electrical signal passed through a

system of rotors and switchboard-like plugs, to

light a lamp that illuminated the encrypted letter

that was to substitute for the typed letter. Each key

press caused the rotors to revolve and illuminate

a different letter. This made the Enigma a very

powerful system for its day.

In fact, the system is still considered secure, and

Enigma machines are, according to one source,

still used today by some developing countries for

their encryption needs. Although it is estimated

that about 22,000 of these were produced, buying

one today will cost somewhere in the low six-fig-

ure range, according to the Enigma Museum


Tom Perera, W1TP (Photo B), is the guy with

the Enigma machines you see every year out in

the flea market at the Dayton Hamvention®

(spaces 2551-2555). If you read this beforehand,

be sure to say 3Hi ́ to him and have a look at the

machines he has on display. They look old and

simple on the outside, but inside they are works

of art, a testament to fine assembly techniques.

The dexterity needed even for my Heathkit SB-

102 HF transceiver pales in comparison.

You can buy an exact replica of an Enigma

from Klaus Kopacz <

replica/>, which supposedly cannot be differentiated from an original. But don’t expect such a thing to cost much less than half the price of an original. I can’t speak for your sit-

uation, but spending the equivalent of a new Mercedes-Benz

on what some may consider a non-essential item isn’t in my

budget, at least not this year.

Which brings us to Marc Tessier and James Sanderson

from S & T Geotronics <>. They

ran a successful Kickstarter <>

campaign to fund the development of an Enigma machine

replica, based on an Arduino Mega2560 clone. For under

$1000, you can buy a fully-assembled 4-rotor Enigma repli-

ca, in a wooden case 2 as long as you can accept having

LED displays serving as code rotors (Photo C). In fact, if

you¶re a build-it kind of person, you can get a full kit with a

software plugboard (Photo D) for only $300, or a set of bare

boards for under $50. Compare that to the cost for an origi-

nal Enigma machine.

How it Works

It comes to mind that after studying Enigma machines for

some weeks, I’m possibly using some terms that are unfa-

miliar 2 rotor, plugboard, and so on. Let me briefly explain

how this encryption machine works 2 it’s a little complicat-

ed, so if anyone finds an error, it is absolutely my own; please

let me know. Just in case I need to do this correctly some

day, of course.

There are three (and in some versions, four) rotors, which

are mechanical click-wheels that have all 26 letters (and no

‘space’ character) inscribed on the outside of a ring (which

can be rotated relative to the rotor itself, for yet another layer

of encryption). There are a few versions of rotors, but they

all are hard-wired to convert one letter into another (such as

“E” when “A” is typed).

At the start of a message, the rotors are set to a code of 3

(or 4) letters. When a key is pressed to enter a letter of the

message, all three rotors perform their own scrambling action

and the signal then goes into a “reflector,” which sends it back

through the rotors to scramble the message ever further. This

electric circuit finally causes a light to light up and display the

encrypted version of the original letter. After each key press,

the rotors move into a new (but predictable) pattern that

changes the 3 (or 4) letter encryption code.

This complex set of actions made the output indecipher-

able without another Enigma machine. If you did have one,

and you knew the correct 3- or 4-digit starting code, the

process was reversed (because of the action of the reflec-

tor) and you could decrypt the message.

The plugboard is an old-phone-switchboard-like set of

phono jacks (their German equivalent, actually) at the front

of the machine. Just to further complicate the process, the

operator could use the plugboard and some jumper wires to

swap pairs of letters, for example swapping A and H, both

before and after the electricity passed through the rotors,

greatly increasing the cryptographic strength of the Enigma

machine. In photos A and B, you can see the plugboard at

the front of the machine.

In its time, it was nearly a nearly unbreakable code. As I

mentioned before, it’s still pretty secure, but not nearly as

secure as something modern computers might use, like 256-

bit AES. It did have some flaws, though: For example, a let-

ter would never be encoded to itself, a cryptographic error

surely exploited by the codebreakers at Bletchley Park. But

what really broke the enigma code was German operator mis-

takes, sloppy procedures, and relying on the machines to be

unbreakable for too long a time. The allied effort was kept so

secret that the Germans and their allies never had a clue their

codes had been broken: In fact, the

Russians weren't told until well after the

war was over.

The point is, we can get an Enigma

machine as an electronic kit for under

$500, with a plugboard, if we really want

to encrypt our amateur radio messages.

Of course, the Enigma machine is cum-

bersome to use (to put it mildly). Just

remember to keep a record of the orig-

inal message, and the 3- or 4-digit start-

ing code, and you should be OK as long

as your intent is not to obscure the


Modern operating procedures would

generally use a computer for our encryption needs, but of course we should think about it,

using encryption only as absolutely necessary, and even then

using relatively weak encryption since privacy (for example)

does not demand extreme security.

If you want to learn about encryption, the Enigma machine

is fairly well-documented and simple enough to understand

in concept. It uses a “letter-substitution” cipher, albeit a very

complex one, but if you study the rotor designs, you’ll quick-

ly come to understand the system so it really can be useful

as a learning tool. In fact, the Little Orphan Annie secret

decoder ring 2made famous in the movie, A Christmas Story

2 used a similar (but single-rotor) scheme. If you were to

change the setting of the inner ring of the decoder ring with

every letter you input, you would have the exact (albeit sim-

plified) equivalent of an Enigma machine.

Building an Enigma replica is possibly far cooler, since it

confers a very high level of bragging rights. I’m referring to

the electronic version, of course. If you want to play with one,

but haven’t the time or finances to buy or build a modern repli-

ca, a Google search of “Enigma machine emulator” will bring

up several hits, such as the one from Louise Dade at

<>. If you are looking for

something to decrypt, try this: UOCIB SHYJF BWXJP HSKIH

THDUP. This was encoded on a 3-rotor Army machine, using

the reflector version (Umkehrwalze) B, rotor types

(Walzenlage)I, II and III, ring settings (Ringstellung) AAA and

rotor setting (Grundstellung) IRZ, with no plugboard jumpers,

set for 5-character groups. Movie fans will get the decoded

reference right away.

Oh, and while you’re decoding the message, watch what

happens to the rotor settings as you type. Be sure the start-

ing settings are exactly correct: Any error will absolutely make

the decryption fail.

I’m sure I’ll hear from several of you, possibly quite angri-

ly, concerning my comments about encryption’s legality. I

welcome any and all comments, but please, keep it civil. Even

with a little vitriol, hearing from a reader is always the high-

light of my day. – 73, Don, N2IRZ

Don Rotolo

May 1, 2015

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