29 April 2003
Source: US Patent Office:
http://www.uspto.gov
This is a formerly secret encoding invention for the precursor to the National Security Agency. "William Friedman is regarded as the father of American cryptology."
http://www.nsa.gov/museum/fsw.html
United States Patent | 6,097,812 |
Friedman | August 1, 2000 |
The crytographic system automatically and continuously changes the cipher equivalents representing plaintext characters so as to prevent any periodicity in the relationship. The system has a series of juxtaposed, rotatable, connection changing mechanisms to provide a large number of alternative paths for the passage of an electric current corresponding to a message character. Further, the system has parts for the irregular and permutative displacements of the members of a set of circuit changing mechanisms to thwart cryptanalysis.
Inventors: | Friedman; William F. (Washington, DC) |
Assignee: | The United States of America as represented by the National Security (Washington, DC) |
Appl. No.: | 682096 |
Filed: | July 25, 1933 |
Current U.S. Class: | 380/26; 341/50; 341/90; 341/91; 380/52; 380/56; 380/57; 380/59; 380/287 |
Intern'l Class: | H04L 009/38; H04L 009/10; H04L 017/02; H04L 017/16 |
Field of Search: | 380/255,259,270,287,26,51,52,55,56,57,58,59,27,47 341/50,90,91 178/17 A |
1356546 | Oct., 1920 | Morehouse | 380/47. |
1522775 | Jan., 1925 | Friedman | 380/27. |
1683072 | Sep., 1928 | Hebern | 380/52. |
1912183 | May., 1933 | Dirkes et al. | 178/17. |
Primary Examiner: Gregory; Bernarr E.
FIG. 1 is a diagrammatic view of a mechanism embodying the invention,
employing one tape-transmitter;
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FIGS. 2 and 3 show diagrammatically the interacting relation of a plurality
of tape-transmitters.
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DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, which is merely diagrammatic, there are shown the following elements
all of which are well-known in the art applicable to modern cryptographs:
The numeral 1 generally designates a standard typewriter keyboard provided
with a set of keys for closing a set of contacts corresponding to the 26
letters of the alphabet; the numeral 2 generally designates a recording or
indicating device which may comprise translating devices such as the magnets
of a printing mechanism, or the translating devices may take the form of
a bank of glow lamps to indicate by illumination of superimposed lettering
the equivalents resulting from encipherment or decipherment; 3 generally
designates a set of juxtaposed, rotatable circuit changers constructed in
the form of cipher wheels or disks, mountable upon a common shaft and arranged
to rotate relative to one another and to fixed end disks, in order to provide
a large series of variable paths for the passage of electric currents
representing message characters, the exact path in each instance being determined
by the relative rotatory positions of the whole set of cipher wheels and
end disks at that instant. The essence of my invention consists in the addition
of a set of cipher-wheel stepping mechanisms, generally designated by the
numeral 4, which may be controlled by a sensing mechanism such as one or
more tape-transmitters of the usual type employed in Baudot systems of printing
telegraphy. In FIG. 1 only one such tape-transmitter is shown as at 5. In
FIG. 2 two such transmitters are shown in interaction as at 5 and 5'; and
in FIG. 3 three transmitters are shown in interaction as at 5, 5' and 5".
In cryptographs of this general character the principal reliance for
cryptographic security is placed upon keeping secret the initial conditions
as regards the relative positions and the arrangement of the cipher wheels
at the beginning of the cryptographic operations. These initial conditions
constitute the "key", and the latter usually consists of two paths. First,
the specific horizontal permutation of the cipher wheels upon the shaft,
that is, the order of the wheels from left to right or right to left between
the stationary disks must be indicated. Each cipher wheel consists of two
rings of 26 contacts, one ring on the obverse face, the other on the reverse
face; the contacts of the obverse face are connected, by insulated conductors
passing through the wheel, to those of the reverse face in an entirely random
manner. The cipher wheels bear identifying designations and are interchangeable
as regards the order in which they may be inserted into their positions upon
the shaft, and it is usual to agree upon a key which indicates that order.
For example, in a cryptograph constructed for five cipher wheels, the key
4-1-3-2-5 may mean that cipher wheel number 4 is placed in the first position
next to the left stationary disk, cipher wheel number 1, in the second position,
and so on. The cipher wheels may be inserted on the shaft in a right side
up or up side down position. Since the wirings within the respective wheels
are different, it is obvious that each of the 10.times.8.times.6.times.4.times.2
or 3840 different permutations of the five wheels is available. Each such
permutation will produce different cipher results from every other permutation
because the complete path through the whole set of wheels is established
by the juxtaposition of five separate paths, one in each wheel. The sequence
or arrangement of the individual cipher wheels upon the shaft will hereafter
be called the permutative key. The second part of the key is the specific
alignment of identifying marks on the peripheries of the cipher wheels after
they have been inserted on the shaft according to the permutative key. The
periphery of each wheel bears a series of 26 identifying characters corresponding
to the 26 stopping positions of the wheel as it is displaced by rotation
on the shaft. The initial rotatory positions of the five cipher wheels relative
to one another and to the stationary end disks, as designated by the horizontal
sequence of the identifying characters on their peripheries as aligned on
a "bench mark" on the end disks, will hereinafter be called the rotatory
key. In cryptographs of the type under consideration the permutative key
remains fixed, as a rule, throughout the encipherment of a message or a series
of messages; the initial rotatory key usually changes from message to message.
Now in all cryptographs based upon the use of rotatable cipher wheels of
the type referred to above, and arranged as indicated, means are embodied
within the cryptograph for automatically changing the rotatory positions
of the cipher wheels during the course of enciphering or deciphering a message;
these means are always of such a nature as to make these changes of a definite
and predetermined character. For example, in Hebern, U.S. Pat. No. 1,683,072,
the fixed character of the successive rotatory movements of the cipher wheels
is explained in quite a detailed manner, and the same is true as regards
similar cryptographs produced abroad. The progression of the cipher wheels
in these cases is similar to that of indicating meters or counting mechanisms,
which are basically regular or periodic in their motion. This regularity
or periodicity of motion produces predictable relationships between the
plain-text characters and the cipher characters for any given initial rotatory
key. Thus, should the cryptograph and cipher messages fall into the hands
of unauthorized parties, the latter can place themselves in a position to
decipher the messages largely as a result of the predetermined nature of
the successive rotatory displacements of the cipher wheels, even though the
initial keys may not be known.
The basic feature of my invention is the elimination of this predictable
factor and the provision of a mechanism for displacing the cipher wheels
in an entirely irregular, aperiodic manner. This is accomplished by means
of the wheel-stepping mechanisms shown as at 4, and operated in the present
embodiment by individual magnets which are controlled by the single tape
transmitter 5 of FIG. 1, or by two or more tape transmitters as shown in
FIGS. 2 and 3. In this description I show a cryptograph with a set of five
rotatable cipher wheels and a transmitter using a plural unit code based
upon the permutations of two elements through five positions, but it is obvious
that the invention is applicable to a cryptograph using a fewer or a greater
number of cipher wheels and a plural-unit code of a different type than the
well-known Baudot five-unit code.
Tape transmitter 5 in FIG. 1 is of the type well known in printing telegraphy,
but only one of the usual two bus bars is connected to current source in
this case. The transmitter is operated by a tape bearing a series of perforations
permuted in accordance with the Baudot code. The perforations in the tape
control the action of the five contact members 6-10, which, in turn, through
the circuit including power source 33, and conductors 21 to 32, inclusive
control the action of the five magnets, 11, 12, 13, 14, 15, as a set of elements
operable in a permutative manner, as will be shown subsequently.
The magnets 11 to 15, with their associated stepping mechanisms, which may
be of the ratchet and pawl type, control, permutatively, the displacement,
in step-wise manner, of the individual cipher wheels 16 to 20, and thus
continuously vary, in an irregular, aperiodic manner, the rotatory positions
of the five cipher wheels in encipherment or decipherment. It is assumed
naturally that correspondents must be equipped with a similar cryptographs
and similar cipher wheels, wired identically, and that the correspondents
are provided with identical key tapes for controlling the movements of the
cipher wheels. The exact initial permutative and rotatory key and the initial
point of action of the key tape must also be the same between correspondents,
and can be predetermined by agreement.
The working arrangement may be such that on the back stroke of any key of
the keyboard, a contact 34, controlled by a universal bar on the keyboard
is closed, and the circuit from power source 35, for operating the tape
step-forward magnet 36, is closed. The next character on the tape is brought
into play, the cipher-wheel magnets, 11 to 15, are operated and the cipher
wheels are set to a new position for the encipherment (or decipherment) of
the next character of the message.
The enciphering-deciphering circuits will now be set forth in detail. Let
us assume that the cryptograph is to encipher a message. A switch control
mechanism 65, carrying a series of 52 movable contact members similar to
the four shown at 37, 37', 38 and 38', all mounted on the same base, is set
to "enciphering". This brings contact member 37 against contact 40, contact
member 38' against contact 42, contact member 38 against contact 44, and
contact member 36' against contact 45. Suppose key "A" on the keyboard is
depressed. A current from power source 46 flows along conductors 47, 48,
through closed contact 49, conductor 41, contact member 37', contact 42,
to 51, which is one of the contacts on the contacts on the left-end fixed
disk; the current then continues along a zigzag path through the cipher wheels,
emerging at 52, which is one of the contacts on the right-end fixed disk,
thence along conductor 53, contact 44, contact member 38, conductor 43, through
lamp or indicator "Y", conductor 54, back to the other pole of power source
46. Lamp or indicator "Y" is energized and the cipher equivalent of "A" is
"Y", for the particular setting of the cipher wheels shown in the figure.
For a different setting of the cipher wheels, depression of "A" would yield
some other letter. If the cipher wheels are displaced each time key "A" is
depressed, the successive cipher equivalents will be casually different,
and will vary in a completely aperiodic manner so long as the displacements
of the cipher wheels are aperiodic, as would be the case in my invention
with a key tape consisting of a random sequence of Baudot perforations. The
arrangement at the keyboard is such that on the release of any key a universal
bar closes the circuit for operating the tape stepping mechanism as explained
above, thus causing the particular Baudot character then at the key-tape
transmitter to actuate the five magnets 11 to 15, and thus set up a new rotatory
arrangement of the cipher wheels 16 to 20.
Let us now reverse the operation and decipher. In this case the control device
65 for bringing the cryptograph to the deciphering condition is set so as
to bring contact member 37 against contact 55, contact member 37' against
contact 56, contact member 38 against contact 57, and contact member 38'
against contact 58. The cipher wheels 16-20 are assumed to be at exactly
the same rotatory position they were in when "A" was enciphered and produced
cipher "Y". Now depress key "Y" on the keyboard. A current from power source
46 flows along conductors 47, 59, closed contact 60 at "Y", conductor 61,
contact member 38', contact 58, conductor 62, contact 44, conductor 53, contact
52, thence through the cipher wheels, emerging at contact 51, thence along
conductor 50, contact 42, conductor 63, contact 55, contact member 37, conductor
39, thence through through lamp or indicator "A", conductors 64, 54 back
to the other pole of power source 46. Thus lamp or indicator "A" is actuated
and cipher "Y" reproduces plain text "A".
The reciprocal relationship between all the plain text and cipher letters
is accomplished in the same way; only four of the 52 contact members shown
at 37, 37', 38 and 38' are indicated in the drawing, but they are all mounted
upon one base and are moved into their enciphering or deciphering position
by the single control 65 which moves them as a set to the right or to the
left for enciphering or deciphering, respectively. All 26 upper right-hand
contacts on this movable plate, similar to those at 40 and 44, are wired
to the 26 contacts on the right-end fixed disk; all 26 lower right-hand contacts
of the movable plate, similar to those at 42 and 45, are wired to the 26
contacts on the left-end fixed disk. This arrangement for effecting reciprocity
in enciphering and deciphering is, however, not a part of my invention. This
method and others for accomplishing the same purpose are known in cryptographs
of this type.
The effect of various keying arrangements with the cryptograph of my invention
will now be shown and will be taken up individually.
First, let us assume that the permutative key of cipher wheels and the key
tape remain the same for a series of messages. The key tape may be started
at the same initial point for all messages or at different initial points
for different messages. Assuming the former case, diversity of cipher resultants
for identical plain-text messages may be brought about by different initial
rotatory positions of the five cipher wheels. For example, a message beginning
"Proceed at once", enciphered with the initial rotatory key "White", will
yield a different cipher text from that enciphered with the initial rotatory
key "Write". Thus, since there are available, with a set of five cipher wheels,
26.sup.5 different initial rotatory keys, the potentialities of the cryptograph
in this respect are apparent.
Now assume that the key tape is in the form of a continuous ring and can
be started at different initial points. A message enciphered with the same
initial rotatory key can be enciphered in as many different forms as there
are characters on the key tape; if it is 10,000 units in length, 10,000 versions
of the same message can be produced by staring each message at a different
initial point on the tape.
It goes without saying that by using many different tapes, and changing the
permutative key of the cipher wheels on the shaft, the cryptograph will afford
an almost limitless diversity of cryptographic results.
All the foregoing variations are entirely aperiodic in character, so that
no cyclic phenomena such as are used in the analysis of the usual types of
automatic cryptographs are available for solving messages produced by the
cryptograph of my invention.
FIG. 2 shows two tape-transmitters, 5 and 5', jointly controlling the magnets
11 to 15, which are identical with similarly designated magnets of FIG. 1.
In this arrangement two different cipher-key tapes in the form of continuous
rings govern the operation of the tape transmitters. The tape passing through
transmitter 5 brings the set of contact members 6, 7, 8, 9, and 10 against
bus bar 66 or bus bar 67 in a permutative manner; similarly, the tape passing
through transmitter 5' brings the set of contact members 6', 7', 8', 9',
and 10' against bus bar 66' or bus bar 67' in a permutative manner. The circuits
are such that only when homologous contact members are in contact with opposite
bus bars will current flow from power source 33 through the magnet controlled
by this pair of homologous contact members. The tape stepping magnets 36
and 36' are controlled by a contact operated by the universal bar of the
keyboard.
The object of such an arrangement with two interacting tape transmitters
is to provide a very long resultant, or secondary cipher key by the interaction
of two relatively short, primary keys. For example, suppose a circular tape
containing 1000 characters is passed through tape transmitter 5, and another
circular tape containing 999 characters is passed through tape transmitter
5'. If the two tapes are started at given initial points and are moved forward
synchronously by single steps, then these same initial points will not again
present themselves simultaneously to the contact pins until a total of 999,000
steps have been made. Thus, two key tapes of 1000 and 999 characters produce
a resultant key of 999,000 characters.
Going one step further, three or more tape transmitters may be caused to
interact to produce still longer resultant keys. For example, three tapes
1001, 1000, and 999 characters in length will produce by interaction a resultant
key of 999,999,000 characters. FIG. 3 shows how three cipher-key tape
transmitters would be interconnected to bring this about. Transmitters 5
and 5' interact to control relays 11', 12', 13', 14' and 15'. The armatures
6", 7", 8", 9", and 10", of the latter relays act in the same manner as do
the contact members 6 to 10 and 6' to 10' of the tape transmitters 5 and
5', respectively. The interaction of the armatures 6" to 10" with the contact
members 6'" to 10'" of the third transmitter 5", controls the operation of
magnets 11 to 15, which serve the function indicated by identically numbered
magnets of FIGS. 1 and 2. The tape-stepping magnets 36, 36' and 36" are all
in the same circuit controlled by the universal bar of the keyboard, so that
all three tapes are moved synchronously.
By an extension of this manner of interconnecting tape transmitters and relays,
it is possible to have a set of four, five, or more tape transmitters all
interacting to control collectively the magnets of the cipher-wheel stepping
mechanisms.
It is one of the notable features of my invention that while employing all
the permutations of the Baudot code, 32 in number, as keying characters,
the final cryptogram is composed of only the usual 26 letters of the ordinary
alphabet. The six extra permutations (those other than the ones representing
the 26 letters of the alphabet), which, in systems using the Baudot code
as a basis for a cipher key, cause much difficulty, either in their elimination
by automatic means, or if the latter is not possible, in their representation
in written characters having standard equivalents in the Morse code, have
been automatically eliminated from the cryptograms, since all the Baudot
permutations have been excluded from direct interaction with the message
characters in my system.