U.S. patent number 3,773,977 [Application Number 05/154,851] was granted by the patent office on 1973-11-20 for method of enciphered information transmission by time-interchange of information elements.
This patent grant is currently assigned to Patelhold Patentverwertungs-& Electro-Holding AG. Invention is credited to Gustav Guanella.
United States Patent |
3,773,977 |
Guanella |
November 20, 1973 |
METHOD OF ENCIPHERED INFORMATION TRANSMISSION BY TIME-INTERCHANGE
OF INFORMATION ELEMENTS
Abstract
An information signal train which may, for example, be an audio
signal, is divided into equal time intervals and temprarily stored.
Each stored element is read out in a random pattern so as to
randomly "scramble" the arrangement of the elements as compared
with their original arrangement. The "scrambling" of the elements
is continuously monitored so as to prevent more than one element
from being shifted to the same (new) time position and further to
prevent any gaps in the transmitted signal train. The process is
effectively reversed at the receiving end which is provided with a
similar random generating and deciphering means operating in
synchronism with the enciphering means at the transmitter facility.
Shifting of the element positions may be confined to a group
containing a predetermined number of elements or alternatively may
be progressively shifted to new positions without concern for
limiting shifting in time of elements to a group of a predetermined
number of elements. Additional techniques may be employed to
reverse polarity of selected elements or to randomly superimpose
other signals upon selected ones of the elements in a random
fashion.
Inventors: |
Guanella; Gustav (Zurich,
CH) |
Assignee: |
Patelhold Patentverwertungs-&
Electro-Holding AG (Glarus, CH)
|
Family
ID: |
4360828 |
Appl.
No.: |
05/154,851 |
Filed: |
June 21, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Jul 7, 1970 [CH] |
|
|
10227/70 |
|
Current U.S.
Class: |
380/36; 380/275;
380/37 |
Current CPC
Class: |
H04L
9/34 (20130101); H04K 1/06 (20130101) |
Current International
Class: |
H04K
1/06 (20060101); H04L 9/34 (20060101); H04k
001/06 (); H04l 009/00 () |
Field of
Search: |
;178/22 ;340/348
;179/1.5R,1.5S |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Birmiel; H. A.
Claims
What is claimed is:
1. A method of enciphered information transmission, in which the
plain-language signals to be transmitted are split up into elements
of equal length whose original time sequence is modified by
interchange prior to transmission and restored after transmission
by a reverse process of interchange, the elements interchanged (and
the reverse process carried out at the receiving end) through a
process of storage in an information store, characterized by the
steps at transmitting and receiving ends of: (a) generating
coinciding aperiodic cipher signals (w); (b) generating control
signals (i FIG. 2) which are derived from the cipher signals which
determine the storage position of the individual elements in the
information store; (c) storing binary pulses, each in a
multi-position store in which each position is assigned to an
information element; (d) modifying the binary pulses in an
irregular sequence by hunting pulses (h) in the sense that occupied
positions are evacuated (or empty positions are occupied) in
accordance with the state of said cipher signals at any given time,
by moving from each position which has already undergone the
aforesaid change in occupancy, i.e., has either been evacuated or
occupied, to those positions which have not yet been evacuated or
occupied, without modifying the occupancy of any position which has
already changed (e) producing control signals (i) depending on
these changes to determine the storage position of the
corresponding element in the information store, so that automatic
monitoring of the occupancy of the information store is achieved
whereby, on the one hand, control signals which are required to
avoid omissions of individual elements are ensured, and on the
other hand control signals which lead to the repetition of
individual elements, being suppressed.
2. A method as claimed in claim 1, characterized in that the
positions in the information store (NS) are initially cleared; in
that after each determination of a storage position an element is
supplied to this position; and in that the extraction of the
elements from the information store takes place in accordance with
a progressive sequence.
3. A method as claimed in claim 1, characterized in that the
elements are supplied to the storage positions in the information
stre (NS) in a progressive sequence; and in that after each
determination of a storage position, an element is extracted from
it.
4. A method as claimed in claim 1, characterized in that binary
pulses are stored in first and second independent stores in order
to determine storage positions; determining the storage positions
to which the elements are supplied by altering the binary data of
pulses in said first store and altering the state of binary pulses
in the second store to determine the storage positions from which
the elements are subsequently extracted.
5. A method as claimed in claim 1, characterized in that the
elements consist of sections of the unmodified plain-language
signal.
6. A method as claimed in claim 5, in which the plain-language
signal is converted into digital form by sampling and
analog/digital conversion of the sampling pulses, characterized in
that the elements each consist of a specific number of coded
sampling pulses of the plain-language signal.
7. A method as claimed in claim 1, in which the plain-language
signal is provided in analogue form, characterized in that the
elements consist of a specific number of amplitude-modulated pulses
which are obtained by periodic scanning of the plain-language
signal.
8. A method as claimed in claim 1, characterized in that each
storage position in the multi-position store (BS, FIG. 4),
corresponds with a specific position in the information store (NS);
in that the number of multi-position store positions corresponds
with the number of elements in a group; in that at the commencement
of element interchange in a group, all positions in the
multi-position store operating as occupation register have the same
occupancy, i.e., all are occupied or all are free; in that with any
modification of the occupancy of a register position by a
corresponding control signal (i), a corresponding position
(corresponding, that is to this register position), in the
information store is determined; and in that the number of the
associated register position, which number is assigned to said
hunting pulses, is formed in accordance with the rules of binary
addition, from several pulses of the cipher signal.
9. A method as claimed in claim 1, characterized in that in the
multi-position store (BR, FIG. 5) operating as occupation register,
binary pulses are stored and advanced therethrough step by step; in
that the content of the information store (NS) is likewise
displaced vis-a-vis fixed tappings; in that the first stage of the
occupation register always exhibits a first (state of) occupancy,
corresponding to the "occupied" or "unoccupied" conditions; in that
by means of hunting pulses (d), which depend at least partially
upon the cipher signal (w) individual positions of the occupation
register are converted from the said first to the said second state
of occupancy; in that the hunting pulse operation in each case
commences with the last stage of the occupation register and moves
back step by step until a stage is converted from the first to the
second occupancy; in that this change in state of a stage takes
place in such stage still exhibits a first state of occupancy and
if, furthermore, a blocking pulse (a) dependent upon the size of
the signal, does not occur; and in that with each conversion of a
register position from the first to the second occupancy, a
corresponding control signal (d) determines a position
(corresponding to this register position) in the information store
(NS).
10. A method as claimed in claim 1 characterized in that the
information store (NS) consists of several individual independent
stores operating in synchronism (M.sub.1 -M.sub.6, FIG. 7); and in
that the control signals for driving the associated individual
stores are displaced by varying amounts, through additional
registers (HR).
11. A method as claimed in claim 1, characterized in that the
information store (NS) consists of several individual stores; in
that the occupation register (BR, FIG. 7) consists of several
individual registers; in that in the hunting operation, the
individual occupation registers are successively tested as to their
binary states; and in that each new hunting pulse commences with
the particular individual register next in succession.
12. A method as claimed in claim 1, characterized in that each
individual information store and each individual occupation
register has several positions; and in that in the hunting
operation a position in each occupation register is tested and in
the ensuing hunting pulse a position in each individual occupation
register is tested (FIG. 9).
13. A method as claimed in claim 1, characterized in that with
changing directions of information transmission, recording and
extraction in and from the information store change
correspondingly, although the driving of the storage positions
remains the same.
14. A method as claimed in claim 1, characterized in that the
information elements are time-compressed prior to transmission, by
increasing the rate of store extraction, and are expanded again at
the receiving end by slowing the rate of store extraction.
15. A method as claimed in claim 1, characterized by additional
enciphering of the information elements by reversal of selected
elements in accordance with special cipher signals.
16. A method as claimed in claim 1, characterized in that the
cipher signals (w) are generated from intermediate signals (s) by
means of a cipher computer (SC, FIG. 12); in that in order to
produce these intermediate signals, programme signals (u) are
generated using programme generators (PS) which consist of shift
registers with facility for feedback of output pulses to the input
via logic switching circuits; in that several intermediate signals
are extracted from selectable shift register stages through
selector switches (FIG. 13); and said cipher computer (SC, FIG. 14)
consisting of at least two shift registers in association with
switches S.sub.1, S.sub.4), inverters (S.sub.2, S.sub.5) and
contact breakers (S.sub.3, S.sub.6) which interrupt the pulsing
signals, these switches being controlled by the intermediate
signals (s).
Description
The present invention relates to method and apparatus for
transmitting data in enciphered fashion and more particularly
relates to apparatus and method for enciphering information
transmitted, in which the plain language signals to be transmitted
are divided into elements of preferably equal time length whose
original time sequence prior to transmission is modified by
interchange and restored after transmission by a reverse process of
interchange, the elements being in part at least interchanged (and
the reverse process carried out at the receiving end) by dissimilar
time shifts through the utilization of a storage process within an
information store.
BACKGROUND OF THE INVENTION
Methods of the type referred to hereinabove and devices for
carrying them out are well known in the prior art as evidenced, for
example, in Swiss Pat. Nos. 22,742 and 232,768. However, a very
important provision in such systems employing an interchange
process, and which is fundamental to the method of the present
invention, is that there must be no repetitions and no omissions of
individual information elements (i.e., signal sections); the
interchanged sequence must contain all the elements of the sequence
forming the original plain language signal (i.e., a speech signal),
without any overlap between any two elements and without any gaps.
With a periodic period of interchange, as used, for example, in the
methods disclosed in the aforesaid patent specifications, the
compliance with this condition is something which can be achieved
of course without difficulty, by appropriate adjustments. This kind
of periodically recurring interchange process, however, is
unsatisfactory from the cryptological point of view since the
periodicity as well as the cipher may be easily detected and
reconstructed by unauthorized third parties who may receive the
message. Consequently, it has also been proposed in the prior art
(for example, see Swiss Pat. No. 220,056) that the interchanges be
controlled by correspondingly prepared punched tapes. However,
handling of tapes of this time introduces many attendant problems,
along which are the necessity of a tape of great length, the need
for synchronism between transmitting and receiving ends at the time
of start-up and halting of the punched tapes, as well as the fact
that the tapes are relatively fragile and are incapab e of being
used over and over again.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is to overcome these drawbacks.
In accordance with the invention, this is achieved in that the
transmitting and receiving ends are provided with coinciding
aperiodic cipher signals which are produced by cipher signal
generators and supplied to ancillary devices whereby special
control signals are derived from the cipher signals which are
utilized to determine the storage positions of the individual
elements in the information store; in that additional devices each
containing an additional storage means serve as an occupation
register in which binary pulses are stored, each of which is
assigned to an information element; in that by means of hunting
pulses (h) which depend in part at least upon the cipher signals,
the (state of) occupancy occupany of individual positions in the
occupation register is modified in an irregular sequence in the
sense that occupied positions are evacuated (or empty positions are
occupied;) in that, when a hunting pulse tests a register position
which has already undergone the aforesaid change in occupany, i.e.,
has either been evacuated (or occupied,) the hunting operation is
continued for register positions which have not yet been changed in
this manner, without further modification of the occupancy of any
register position which is already changed; and in that, with any
change in occupany, a control signal (i) is produced which
determines the storage position of the corresponding element in the
information store, so that automatic monitoring of the occupancy of
the information as stored is achieved, whereby on the one hand,
control signals which are required to avoid omissions of individual
elements is insured, and on the other hand, control signals which
lead to repetition of individual elements are suppressed.
In one embodiment of the present invention, first and second stores
are provided which are capable of storing a predetermined number of
elements of equal time length. One of said stores is filled while
the other is emptied and the process is then reversed whereby the
store being emptied is emptied in such a manner as to interchange
the positioning of the stored elements in an aperiodic fashion with
monitoring means continuously monitoring the interchange operations
so as to prevent the occurrence of overlapping or gaps in the
interchanged signal train. The process is reversed at the receiving
end.
In another embodiment of the present invention, a single store is
provided in which continuous interchange of the signal elements is
performed.
It is therefore a primary object of the present invention to
provide a novel apparatus and method for enciphering a signal
transmission by aperiodic interchange of the time position of the
signal elements and monitoring the interchanged operation so as to
prevent the occurrence of overlapping of elements or the occurrence
of gaps within the transmitted signal train.
Another object of the present invention is to provide a novel
apparatus and method as described herein wherein the deciphering of
the enciphered signal train occurs by a technique reverse from that
set forth in the previous object.
BRIEF DESCRIPTION OF THE FIGURES
These as well as other objects of the present invention will become
apparent when reading the ensuing description and drawings in
which:
FIG. 1 is the block diagram illustrating the fundamental principles
of the invention;
FIG. 2a illustrates information signal wave forms showing the
manner in which the wave form is broken down into individual
elements and further illustrating the interchange and reversal of
the individual signal elements;
FIG. 2b symbolically represents the interchange of signal elements
at the transmitting end and the reverse operation at the receiving
end;
FIG. 3a symbolically represents the principle of interchange of
signal elements within equilength groups ("leapfrogging
window");
FIG. 3b schematically depicts another interchange principle which
avoids closed groups ("sliding window");
FIG. 4 illustrates an example of a device for implementing the
method of the invention, which device employs the group interchange
technique;
FIG. 5 is an examply of another variant embodiment of the invention
with continuous interchange of signal elements;
FIG. 6 schematically represents the mode of operation of the device
shown in FIG. 5;
FIG. 7 is a further example of the invention employing an
information store consisting of several individual magnetomotor
stores;
FIGS. 8a and 8b schematically represent the mode of operation of
the device of FIG. 7;
FIG. 9 illustrates an example of the invention employing individual
stores for the information store and separate occupation register
for the individual information stores;
FIG. 10 is a schematic illustration of the principle of time
compression of the interchanged signal elements, prior to
transmission;
FIG. 11 shows the block diagram of a device for additional
concealment signals which are added to the interchanged information
signals;
FIG. 12 illustrates the block diagram of a cipher signal generator
employed in performing the method of the present invention;
FIG. 13 is a detailed illustration of a portion of the cipher
signal generator of FIG. 12; and
FIG. 14 is a block diagram of the cipher computer employed in the
cipher signal generator.
DETAILED DESCRIPTION OF THE FIGURES
Referring initially to FIG. 1, there is shown therein a block
diagram of an enciphering system in which at the transmitting end
(Index I) and receiving end (Index 2) the cipher signal generators
SG.sub.1 and SG.sub.2 produce the aperiodic cipher signals w. These
signals are supplied to the additional devices ZE.sub.1 and
ZE.sub.2 , respectively, and are processed thereby in such a manner
that at the outputs of these devices control signals i are
produced, which signals satisfy the special conditions in terms of
repetition and omission in the ensuing process of element
interchange. The breakdown of the plain language signal x.sub.1
into equilength (timewise) elements and the interchange of these
elements in accordance with the control signal i, take place in the
cipher modulator SM.sub.1 where the enciphered signal z.sub.1 is
produced. In order to restore the plain language signal x.sub.2 at
the receiving end from the receive signal z.sub.2 and by a reversal
in the process of interchange of the elements, the cipher
demodulator SM.sub.2 is provided.
The plain language signal x may, in accordance with FIG. 2a,
consist of a periodic train of oscillations, of the type, for
example, occurring in a speech signal. This signal is divided into
the sections or elements (i.e., time intervals) s.sub.1, s.sub.2, .
. . , of uniform length throughout and which generally have no
fixed relationship to the periodicity of the signal. These elements
are stored for dissimilar times, for time-interchange purposes, so
that a new signal z is produced. In order to make it more difficult
for unauthorized persons to carry out the reverse process of
interchange, it is also advisable to reverse the polarity of
selected ones of the individual elements. Thus, for example, the
element s.sub.5 .sub.' has been produced by reversing the polarity
of element s.sub.5. If the plain language signal is already
available in digital form or is otherwise placed in this form by an
analog-to-digital conversion, then the "elements" naturally consist
of a specific number of bits, the number being the same in each
element.
The interchange of signal elements at the transmitting end and the
reverse procedure of interchange at the receiving end, taking also
into account the individual cases of reversal of polarity which
lead to the production of the s' type elements are symbolically
illustrated in FIG. 2b wherein the elements s.sub.1 -s.sub.7 are
interchanged in time so as to form the signal z.sub.1. This signal
is received as z.sub.2 by the receiving end and is processed in
such a manner as to rearrange the individual elements to return the
elements to their original arrangement, as shown symbolically by
the signal arrangement x.sub.2.
As shown in FIG. 3a, the interchange can take place within
individual groups of elements of length F or can, for that matter,
take place progressively, avoiding closed groups, as shown in FIG.
3b. The displacement of each individual element from its original
position, is in each case restricted to the cross-hatched area
which, in the case of FIG. 3a, leapfrogs ("leapfrogging window"
technique) from group to group, or as in the case of FIG. 3b,
shifts from element to element ("sliding window" technique).
A device SM for producing time-interchange between the elements of
a plain language signal x.sub.1, as well as an additional device ZE
for producing the control signals i for this interchange function,
are shown in FIG. 4. These control signals must be derived from the
aperiodic cipher signal w of the cipher signal generator SG, in
such a way that in the interchange operation, no repetitions and
omissions occur. Each element of the plain language signal x.sub.1
will be assumed for example, to consist of a train of k analogue
pulses (scanned values), which have been obtained by periodic
scanning of the original signals. A group of, for example, six
elements for six k scanned values of the plain laungauge signal is
then supplied via the double-throw switch W.sub.2 to the analogue
shift store NS.sub.2 which is comprised of six k cells. The
transfer through the register during the introduction of these
scanned values is effected by pulsing signals e.sub.o which are
applied through switch W.sub.3. At the same time, the elements of
the previous group already stored in NS.sub.1 (which is
substantially identical in design and operation to NS.sub.2), are
extracted in the modified sequence through the output switch
W.sub.4. The double-throw switches W.sub.0 and W.sub.1 are so
designed that a control pulse i.sub.2, for example, with W.sub.1 in
the solid line position illustrated in FIG. 4, causes k individual
pulses of the pulsing signal e.sub.oo to be supplied to those
storage cells Z.sub.2 .sub.' of the register NS.sub.1 which are
assigned to pulse i.sub.2. These k individual pulses thus form a
pulse train (pulsing signal) j.sub.2 .sub.' which brings about the
extraction of the k scanned values of the second element, from the
store.
In a similar fashion, the other elements are extracted in a
sequence which is determined by the control signal i. During the
extraction operation, gaps and repetitions must be avoided.
In order to fulfill the above requirements the device ZE is
provided with an occupation store BS. The six cells of this store
are initially filled by the pulse e.sub.6, with the commencement of
each sixth element group, and is subsequently individually emptied
by the hunting pulses h. The hunting pulses are produced from the
cipher signals y.sub.1, y.sub.2, y.sub.3 of the cipher signal
generator SG, with the aid of code converter CW which produces an
appropriate (single) output pulse dependent upon the state of the
three input pulses which it receives from binary adder AD. Since
the three binary outputs from signal generator SG is capable of
producing a combination of eight possible output pulses h.sub.1 . .
. h.sub.8, and only six are actually required to empty the BS
register, feed back of the pulses h.sub.7, h.sub.8 to binary adder
AD is provided for. Adder AD is capable of performing a binary
addition of three units to bring about a change in the hunting
pulses h.sub.1 -- h.sub.6 which hunting pulses will be
automatically changed each time a pulse h.sub.7 or h.sub.8 is
generated. The emptying of a cell in register BS results in the
generation of a corresponding control pulse i. However, if this
cell has already been emptied, then an output pulse k is produced
which once again results in a binary addition operation in AD to
cause another change in the hunting pulse h, until a cell in BS
which is still occupied is encountered and emptied. This procedure
is repeated with each pulse e.sub.1 of the pulsing signal, each
such pulse corresponding to a stored element. Thus, in this
fashion, the result is achieved in that each of the control pulses
i.sub.n occurs only once and that none is omitted. This insures the
desired unbroken and unrepeated extraction of all elements from
register NS.sub.1.
After this emptying operation, a change pulse e'.sub.6 reverses the
state of switches W.sub.1 through W.sub.4. At that time, the shift
store NS.sub.1 is filled with elements of the plain language signal
while the elements of the store NS.sub.2 which has previously been
filled, are extracted in a changed sequence. The interchange
between the information elements thus takes place in group fashion
in accordance with the "leapfrogging window" principle of FIG. 3a.
The pulse output w.sub.4 and device VM of FIG. 4 are employed as an
additional enciphering device, as will be described in greater
detail hereinbelow.
A device for the continuous interchange of signal elements in
accordance with the "sliding window" principle of FIG. 3b is shown
in FIG. 5. By way of information store NS once again an analog
shift store can be used or for that matter some other known delay
system with several supply or extraction points may be employed.
For example, it is possible to employ magnetic tape recording with
moving audio signal carriers. The supply of the elements r.sub.1,
r.sub.2 . . . of the plain language signal x.sub.1 is controlled by
the switches U.sub.1, U.sub.2, . . . in accordance with the
actuation by control signals d.sub.1, d.sub.2, . . . , whose
sequence must again satisfy special conditions in order to avoid
repetitions and omissions. To insure that these conditions are
complied with, the occupation register BR is provided in
association with hunting switches S.sub.1, S.sub.2, . . . . The
information register contains the monitored cells indicated in
cross-hatched fashion while the additional cells are designed as
unmonitored shift cells in order to reduce the complexity of the
system. The cell content is shifted in rhythm with the pulsing
signal e.sub.1 which corresponds with the pulsed rate of the
individual signal elements. The still empty left-hand end of the
register can be occupied cell by cell by the pulses d.sub.5,
d.sub.4, . . . and the occupancy is checked by the monitoring
signals b.sub.4. If the last cell P.sub.17 in the register is still
empty, the absent occupation pulse b.sub.1 has the result that from
the periodic pulse train c.sub.1 an individual pulse d.sub.1 is
extracted and supplied to this cell so that the latter two are
filled. If the cell is already occupied, the individual pulse is
supplied as a pulse c.sub.2 to the hunting switch S.sub.2. This
switch is once again controlled by any occupation pulse b.sub.2
which arrives and also by the blocking pulse a.sub.2 which occurs
with a probability of A.sub.2. It is only the simultaneous absence
of a.sub.2 and b.sub.2 that the storage cell P.sub.13 is filled by
a pulse d.sub.2. Otherwise, a transmission pulse c.sub.3 is
supplied to the hunting switch S.sub.3 so that monitoring is
repeated. Any transmission pulse c.sub.5 coming from the switch
S.sub.4, finally, if necessary, fills the initially always empty
first cell P.sub.1 of the register. Thus, the function of the
hunting switch obeys the following logic relationships, where the
bar in each case indicates the negation condition:
d.sub.n = a.sub.n b.sub.n c.sub.n (1) c.sub.n.sub.+ 1 = (1 -
a.sub.n b.sub.n) (2) ub.n
Since the possibly still empty last cell is filled in all cases and
because at any rate the first cell can be occupied when all the
other monitored cells have already been occupied, it is ensured
that in each case one of the cross-hatched, monitored cells is
filled and that thus a corresponding position pulse d.sub.n is
supplied to the associated contact breaker U.sub.n. Thus, in the
store two, one of the cross-hatched cells is occupied by a single
element and a first cell (right) will ultimately always be
occupied. Of course, there is still no guaranty that in the
interchange process there is a like probability of occurrence of
all the shifts, something which would be desirable in order to make
the reverse process of interchange as difficult as possible for
anyone trying to break the cipher. In order to achieve the best
results, statistical considerations must be employed. The
probabilities of the signals a, b, c and d are indicated by A, B,
C, D respectively and the probability of the negation condition a =
1-a and by A = 1-A. Thus, we have
D.sub.n = A.sub.n B.sub.n C.sub.n (3) C.sub.n.sub.+ 1 = (1 -
A.sub.n B.sub.n) (4) ub.n
It is desirable that in each case the next element in the plain
language signal should be supplied to each of the available
cross-hatched positions with the same probability, i.e., the
condition:
D.sub.n = 1/N (N = sign number of elements per group) (5)
should s apply. This makes the probability of the occupation which
is already taken place:
B.sub.n = 1 - n/N (6)
and the probability of occupation of the position which is still
free:
B.sub.n = n/N (7)
and from this we obtain:
C.sub.n = C.sub.n.sub.-1 - D.sub.n.sub.-1 = N - n + 1/N (8) A.sub.n
= N/n(N - n + 1) (9)
For the optimum probability of the blocking pulses a, we thus
obtain the following, for N=5:
A.sub.1 = 0
A.sub.2 = 3/8 = 0.375
A.sub.3 = 4/9 = 0.444
A.sub.4 = 3/8 = 0.375
A.sub.5 = 0
In order to obtain blocking signals a.sub.2, a.sub.3, a.sub.4 whose
probabilities correspond as closely as possible to these values,
this from the cipher signals y.sub.1, y.sub.2, . . . y.sub.10 which
occur with a uniform probability distribution of 50 percent, the
cipher signal converter marked SW can be used and is made up of the
logic gates L.sub.o (logic "OR") and L.sub.u (logic "AND") as is
shown in FIG. 5. Precise adherence to these probability values is
of course generally not necessary and thus simpler circuits can be
employed to produce the desired blocking signals.
The operation of the interchange system of FIG. 5 will be explained
in somewhat more detail, making reference to FIG. 6. As shown in
FIG. 6, the reference KS refers to the plain language signal,
G.sub.r the group (of information elements in the plain language
signal), VS the interchanged signal, SpGr the storage group (in the
information store), INr, the internal number (of the storage
position within a group), FNr the serial (of the information store
positions). The elements of the plain language signal (KS) are
sequentially numbered (right-hand margin) and are also ordered in
groups of four elements each. Element 4 passes via a switch U.sub.4
(FIG. 5) to the store and is there recorded at position 17 on the
moving data carrier NS. Element 5 of the plain language signal
passes, after four pulses of the pulsing signal, via switch U.sub.1
to the data carrier which has in the meantime advanced four steps;
i.e., it is not recorded at position 5 on the data carrier, which
position was originally disposed at this location, but at position
(5+4) = 9. The position fixed in relation to the apparatus is, in
each case, marked by a square (with the element number) and the
coordinate relating to the data carrier by a circle (with the
element number). Similarly, element 9 is recorded at position 17
(of the apparatus) and at position 25 (of the data carrier) and so
on. These elements, which in each case appear at the first position
in a group, exhibit neither repetitions nor omissions after
recording, for the reasons explained earlier. In a similar manner,
the elements which are in each case located at the second position
in a group, are recorded. For example, element No. 2 of the plain
language signal is once again supplied by a switch U.sub.1 to the
data carrier which is now, however, moved by one step so that the
element arrives at position 6 on the data carrier instead of
position 5. Element 6 of the plain language signal, which is
supplied via a switch U.sub.2 would, if the carrier were at a
standstill, arrive at position 9 thereof. However, it receives an
additional shift of (1+4)=5 steps because the carrier has moved by
five steps at the time of recording, and so on. From an examination
of the positions of recording (marked by circles) thus determined,
of all the elements on the data carrier, it can be seen that at no
point have two elements been recorded on top of one another. In
other words, in the illustration, there is no point at which two
circles are superimposed upon one another. Finally, at the bottom
edge, the data carrier is illustrated, this time showing the
elements with their original numbering. Beneath it, the occupation
register, which controls recording, has been schematically
illustrated together with the extracted signals d.sub.1, d.sub.2, .
. . d.sub.5.
Instead of one continuously moving carrier, as shown in FIG. 5, it
is also possible to work with several circulating carriers which,
for example, may take the form of magnetic tape wheels or magnetic
drums M.sub.1, . . . M.sub.6 which are driven through a common
shaft as shown in FIG. 7. In order to select the eligible storage
positions, once again an occupational register BR with associated
hunting switches S.sub.1, . . . S.sub.4 can be used. The control
pulses consequently produced would primarily be suitable for
producing an effective recording upon the continuously moving data
carrier. The rotating data carriers are assigned a data carrier of
this kind in such a way that on M.sub.1 the four elements of a
first group of the moving carrier are stored, on M.sub.2 the four
elements of the second group, and so forth. The supply to the
storage wheel memory devices must be progressively switched so that
said relationship is maintained. To this end, the additional shift
register HR.sub.1 is provided, through which the position pulses d
are transmitted. The first four position pulses can be relayed
directly in the form of corresponding control pulses i. The next
group of four position pulses must, however, be moved one step to
the left in HR.sub.1 so that a recording, which, for example, by
way of U.sub.4 would take place in group 5 of the tape which has
meanwhile been moved, now takes place through store M.sub.5 which
corresponds to this group. Similarly, the next four position
pulses, which thus correspond to the third group of the plain
language signal, must be shifted two places to the left HR.sub.1
and so on. Signal extraction from the source M.sub.1, . . .
M.sub.6, on the other hand, is controlled by extraction pulses
k.sub.1, . . . k.sub.6 from the register HR.sub.2 through which
circulates a single control pulse so that if the control pulses
k.sub.1, k.sub.2, . . . Extraction shifts from store to store and
takes place at the same locations on the rotating data carriers, as
would correspond to scanning of a continuously transfer data
carrier in fixed relationship to the equipment.
The effect of this type of recording can best be appreciated from
FIG. 8a. The references to this figure correspond to those of FIG.
6 except that in the case of VS (interchanged signals) the
designation SpGr (store group) has been replaced by Sp (store),
since we are now dealing with individual stores. The recording
control program, i.e., the sequence of the control pulses d, is, in
this case, the same as in the arrangements of FIGS. 5 and 6.
Because of the aforesaid additional shifts, however, the recording
positions (marked by squares) which are fixed in relation to the
equipment, i.e., the numbers of the individual rotating stores
appear at the shifted locations indicated by the arrowhead lines.
For example, element 5 of the plain language signal is routed not
by way of switch U.sub.1 but instead by way of switch U.sub.2, and
is stored in M.sub.2 (See FIG. 7). Similarly, in FIG. 8a, the
recording position (in a fixed relationship to the equipment) of
the plain language element 6 has an additional left-hand
displacement (marked by the square). The storage positions of the
rotating data carriers occur in this illustration in the oblique
zones as drawn in, for example, for store M.sub.6. The first
occasion of occupation is, in each case, marked by the circled
number of the original element, while the corresponding continuing
occupancy is simply marked by circles. Thus, it will readily be
seen how the last position in store 6 is finally occupied by the
plain language element. The shift register HR for insuring the
additional shifts is drawn in at the bottom edge.
The extraction of the stored elements from the register is
illustrated in FIG. 8b where the occupancies of the stored
positions are once again indicated by the encircled numbers and
then by dots. Since recording commenced with plain language element
No. 1, in the first extraction cycle individual storage positions
still remain unoccupied. Extraction takes place successively from
store M.sub.1, M.sub.2, and so forth. It is in each case indicated
by cross-hatching of the first group position corresponding to the
read-out head. The movement of the storage positions beneath the
read-out head is indicated by the horizontal arrows. The
progressive extraction times correspond to the numbering at the
right-hand margin, and it can be seen from this that the extracted
elements appear in the same interchanged sequence as in FIG. 6.
Another interchange device for several data carriers M.sub.1, . . .
M.sub.6, is illustrated in FIG. 9. Here, separate occupation
registers BR.sub.1, . . . BR.sub.6 are provided for the individual
stores, whose outputs are returned to their inputs via the
respective switches W.sub.11, . . . W.sub.16, thus indicating the
maintenance of the occupation condition over several cycles. An
auxiliary register HR is occupied by 3 circulating pulses which in
each case bring about the closure of 3 associated switches, e.g.
W.sub.22, W.sub.23, W.sub.24. With polarity change in a storage
cell at HR, an appropriate output signal appears, in this case it
is k.sub.6, which on the one hand initiates sampling of the hunting
switches S, with a corresponding starting point (in this case at
S.sub.1), and on the other hand, via the corresponding switch U,
brings about the emp-tying of an individual store (in the present
case M.sub.6). The three neighboring occupancies in HR are ensured
by using the polarity change pulse k.sub.6 to drive individual
stages, polarity reversal taking place in VO. With the indicated
position of pulses in the register HR and the switches W.sub.22,
W.sub.23, W.sub.24 set accordingly, the switches S.sub.2, S.sub.3,
S.sub.4 are supplied with random pulses P.sub.2, P.sub.3, P.sub.4
of probability P. When triggered by the starting pulse k.sub.6,
therefore, a train of hunting pulses is propagated via the switches
S.sub.1, S.sub.2, S.sub.3, . . . in a manner similar to that
indicated in FIG. 5, until a still empty cell of one of the
registers BR is occupied. The position pulse d.sub.n which produces
this occupancy at the same time brings about the storage of a
plain-language signal element in a corresponding section of the
individual store M.sub.n. Instead of the relay (indicated in FIG.
7), of the succeeding position pulses by a second register
HR.sub.1, what happens this time is that the occupation monitoring
function is advanced by virtue of the fact that through the
shifting of the pulses through the register HR, both the control of
the switches S.sub.n and the function of the occupation register
BR, experience a cyclic displacement by one step. This also applies
to the switches U.sub.n and the stores M.sub.n, with the result
that with each group change, i.e., with each pulse e.sub.4 of the
pulsing signal, the same change is produced in the store input as
would occur with a continuous store of the kind described in FIG.
5. This also applies to the emptying of the individual stores by
the control pulses k.sub.n. The occupation register (e.g., BR.sub.6
in FIG. 9) assigned to the emptied store, is emptied at the same
time by interrupting the feedback through the agency of the
feedback switch (e.g., W.sub.16).
The devices in the indicated examples are suitable without further
explanation for performing the reverse process of interchange of
the signal elements at the receiving end, the ciphered signals
z.sub.2 being supplied via the leads indicated and the
reverse-interchanged signals x.sub.2 being extracted at the points
shown. The functions of supply and extraction of the elements to
and from the stores are simply exchanged. With magnetic storage,
erasing will conveniently be carried out directly by the new
recording. However, an additional erasing function can be provided
which comes into operation directly after signal extraction.
The storage methods referred to here are intended purely as
examples:
Other known methods can be employed however, such as, for example,
storage in the form of electrical charges of capacitive data
carriers, electronic storage of the kind known for example from
radar work, ultrasonic delay, piezoelectric storage, magnetic wire,
film or core storage and so on.
Depending upon the storage method, the time of compression of the
individual storage elements or of the scanned values contained in
an element is possible. The individual elements s*.sub.1, s*.sub.2,
. . . of the cipher signal of FIG. 10 are produced. This achieves
the result that the linear distortions of the transmission channel
do not produce any unwanted cross-talk between the positionally
displaced elements. At the receiving end, by element expansion and
reverse interchange, plain-language signals are recovered and the
time-dispersion of the transmission channel has no undesired
effects in this context. Compression is achieved by the use of
pulsing signals e.sub.oo of somewhat higher frequency than the
signals e.sub.o (See FIG. 4), i.e., by extracting the individual
elements from the stores at a slightly faster rate. Similarly,
element expansion at the receiving end is achieved by somewhat
slower extraction from the stores.
It can be seen from FIG. 2a that reverse interchange is simplified
for unauthorized monitors, by the particular amplitude values at
the ends of the elements, i.e., such a monitor can in each case
pick out elements whose end amplitudes match one another. This
possibility is made more difficult by reversing the polarity of
individual elements (s'.sub.5 in FIG. 2a), so that additional edge
amplitudes are produced which increase the already large number of
possible solutions. Polarity reversal is effected quite simply
using the device controlled by additional cipher pulses, e.g., the
(sign-modulated) switch VM of FIG. 4, which is operated by the
cipher signal y.sub.4.
One highly effective measure to render the detection of associated
elements more difficult consists in the addition of specific
concealment signals at the transmitting end, which signals, with
undistorted transmission, can be subtracted again at the receiving
end. These concealment signals may conveniently be obtained from
special cipher signals using a digital-analogue converter, possibly
coupled with shaping by special filters. This kind of device, with
the digital-analogue converter D/A and the filter BP, is shown in
FIG. 11. Besides this concealment signal condition DM and the
position modulator LM, once again a sign modulator VM is
indicated.
The cipher generator SG used to produce the cipher pulses, can, as
FIG. 12 shows, consist of a program signal generator PG, a cipher
selector SE and a cipher computer SC. The programme signals u are
generated in the programme signal generator in accordance with a
specific logic law, e.g., using a shift register, whose output
pulses, taken from two points, are fed back via a modulo-2 logic
system and the switch S.sub.o shown in FIG. 13 to the input.
Synchronization with transmitted programme pulses g is made
possible by initial injection of this pulse train through the
switch S.sub.o until the fedback pulses coincide completely with
the new incoming pulses. This condition is detected by the
correlator KO which then automatically switches S.sub.o to the
feedback position for further operation on its own.
In the cipher selector SE, in addition to the permanently wired and
possibly exchangeable line matrix MA, an additional switching of
the extracting signals s.sub.1, s.sub.2, . . . s.sub.6 using the
decade switches SW, is provided for. These intermediate signals are
thus dependent in an unambiguous way upon the switch positions.
They serve to control the actual cipher computer SC. This, as FIG.
14 shows, can consist of the two registers R.sub.1, R.sub.2 in
association with the switches S.sub.1, . . . S.sub.6 which are
controlled by the intermediate signals s.sub.1, . . , s.sub.6. The
registers have periodic feedback via switches s.sub.1 and S.sub.4.
The after effect of pulses injected earlier disappears in the
course of time thanks to partial interruption of the feedback
function. A change in signal in the feedback channel is brought
about by product formation between the fedback signals and the
intermediate signals s.sub.2, s.sub.5 in S.sub.2, S.sub.5. Finally,
the pulsing signals e.sub.o for the registers are periodically
interrupted by the switches S.sub.3, S.sub.6 so that the
circulating pulse trains have no specific period.
It can therefore be seen from the foregoing description that the
present invention provides the method for interchanging signal
elements of a transmitted message in a non-uniform manner wherein
the transposed signal elements are introduced into new time slots
wherein the monitoring technique employed assures the fact that
there is no overlapping of signal elements nor are any gaps
provided.
Although in the foregoing preferred embodiments of this novel
invention have been described, many modifications will now become
apparent to those skilled in the art and it is therefore preferred
that this invention be limited not by the foregoing description but
only by the appending claims.
* * * * *