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Proc-Type: 2001,MIC-CLEAR
Originator-Name: keymaster@town.hall.org
Originator-Key-Asymmetric:
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 pKb9/DClgTKIm08lCfoilvi9Wl4SODbR1+1waHhiGmeZO8OdgLUCAwEAAQ==
MIC-Info: RSA-MD5,RSA,
 L6xeNj2+1366e0wOq/IS8amzqRTJoG+82TW6UZQBLoRXG3qyM3OX1w0BOmE5F2JF
 MaZnuiaCkOYZHSsCadGasw==


PATN  Patent Bibliographic Information
WKU     Patent Number:				05375168
SRC     Series Code:				7
APN     Application Number:			7687516
APT     Application Type:			1
ART     Art Unit:				222
APD     Application Filing Date:		19911017
TTL     Title of Invention:			Method for scrambling and unscrambling a video signal
ISD     Issue Date:				19941220
NCL     Number of Claims:			4
ECL     Exemplary Claim Number:			1
EXP     Primary Examiner:			Barron, Jr.; Gilberto
NDR     Number of Drawings Sheets:		2
NFG     Number of Figures:			4

INVT  Inventor Information
NAM     Inventor Name:				Kudelski; Andre
CTY     Inventor City:				Crissier
CNT     Inventor Country:			CHX

ASSG  Assignee Information
NAM     Assignee Name:				Kudelski S.A. Fabrique D'Enregistreurs Nagra
CNT     Assignee Country:			CHX
COD     Assignee Type Code:			03

PRIR  Foreign Priority
CNT     Priority Country:			CHX
APD     Priority Application Date:		19900221
APN     Priority Application Number:		563/90-7

CLAS  Classification
OCL     Original U.S. Classification:			380 14
XCL     Cross Reference Classification:			380 10
EDF     International Classification Edition Field:	5
ICL     International Classification:			H04N  7167
FSC     Field of Search Class:				380
FSS     Field of Search Subclass:			14;10;20

UREF  U.S. Patent Reference
PNO     Patent Number:					4405942
ISD     Issue Date:					19830900
NAM     Patentee Name:					Block et al.
OCL     Original U.S. Classification:			380 14

UREF  U.S. Patent Reference
PNO     Patent Number:					4673975
ISD     Issue Date:					19870600
NAM     Patentee Name:					Inaba et al.
OCL     Original U.S. Classification:			380 14

UREF  U.S. Patent Reference
PNO     Patent Number:					4796299
ISD     Issue Date:					19890100
NAM     Patentee Name:					Hamilton
OCL     Original U.S. Classification:			380 14

FREF  Foreign Reference
PNO     Patent Number:				0260886
ISD     Issue Date:				19880300
CNT     Foreign Reference Country Code:		EPX

FREF  Foreign Reference
PNO     Patent Number:				0309984
ISD     Issue Date:				19890400
CNT     Foreign Reference Country Code:		EPX

FREF  Foreign Reference
PNO     Patent Number:				0325509
ISD     Issue Date:				19890700
CNT     Foreign Reference Country Code:		EPX

FREF  Foreign Reference
PNO     Patent Number:				0224965
ISD     Issue Date:				19841200
CNT     Foreign Reference Country Code:		JPX
OCL     Original U.S. Classification:		380 14

FREF  Foreign Reference
PNO     Patent Number:				1590579
ISD     Issue Date:				19810600
CNT     Foreign Reference Country Code:		GBX
OCL     Original U.S. Classification:		380 14

OREF  Other Reference

International Journal of Electronics, vol. 59, No. 4, Oct. 1985, Londres,
GB), V. Zacharopoulos et al.: "An analogue scrambling scheme for
television signals", pp. 501-509.

LREP  Legal Information
FRM     Legal Firm:				Davis, Bujold & Streck

PCTA  PCT Information
PCN     PCT Number:				PCT/CH91/00042
PD1     PCT 371 Date:				19911017
PD2     PCT 102(e) Date:			19911017
PD3     PCT Filing Date:			19910221
PCP     PCT Publication Number:			WO91/13517
PCD     PCT Publication Date:			19910905

ABST  Abstract

     A scrambling method wherein each image line (23-309) of a frame having been
produced in unscrambled form before being scrambled, is given the
pseudorandomly determined address (B) of the memory line in the storage
memory (8) in which said image line is to be stored on reception; and
wherein the moment (or the running order) for broadcasting said image line
is determined so that on reception, the image line causes, because it is
stored in the memory line to which it was addressed, the image line
previously stored at the same address to be output to the television set
at the right moment (or in the right order) so that an unscrambled picture
is reconstructed.

BSUM  Brief Summary

     The present invention relates to a method for scrambling and unscrambling a
video signal comprising steps of, at an emitting site, scrambling the
sequences of the video signal in accordance with a predetermined
scrambling function which can be different for each sequence, emitting
each sequence of such scrambled video signal, then, at a receiving site,
unscrambling said sequences of emitted video signal.

     The main application of the present invention is in pay-television (pay-TV)
systems in which it is essential to scramble the video emission and
unscramble or decode the program at the subscriber's location by means of
a suitable decoder possessed by a subscriber who is authorized to view the
emitted program.

     Some methods for scrambling and a corresponding unscrambling are well known
and, in such methods, it is aimed to make the emitted image and/or sound
incomprehensible or their vision and/or audio uncomfortable.

     A method for scrambling consisting of permuting a constant predetermined
number of lines of the video frame (or video image) in accordance with a
predetermined permuting function is well known. In this case, the
unscrambling consists in carrying out the reverse function from the
function used during the emission to permute such predetermined number of
image lines. As it is not technically easy to thus permute a great number
of image lines, the limit is now about 32 permuted image lines.

     This well known scrambling method, sometimes called the fixed block
inversion method, has a drawback which consists of requiring, at the
receiving site, a memory of great size because it is necessary to have,
just after sending to the TV set a sequence of 32 lines, several next
memorized lines for being capable to send immediately the next image to
the TV set. This method is relatively simple to carry out, at an emitting
site, but there are problems of security, reliability and the cost at the
reception site because of the great number of decoders. On the other hand,
this method is not reliable enough relative to some kinds of pirated
viewing. In fact, it is possible to recover the permutation order, even if
this order frequently varies during the emitting phase.

     It can be seen in the example mentioned above that the unscrambling
function is almost the same as the scrambling function since both
functions have the same nature and are the reciprocal. Further, this
function is simple to pirate because it is unconnected with other
parameters or informations.

     The present invention avoids the above drawbacks.

     For this purpose, the method according to the invention is characterised in
that, at the transmitting site, a first video sequence is scrambled in
accordance with a first scrambling function and another video signal
sequence is scrambled in accordance with another scrambling function and,
at the receiving site, said other video signal sequence which is scrambled
in accordance with said other scrambling function is stored in place of
said first video signal sequence which is scrambled in accordance with
said first scrambling function, replacing it, and, during this
replacement, said other video signal sequence is stored in a scrambled
manner in accordance with an actual scrambling function which is equal to
a predetermined combination of the first scrambling function and the other
scrambling function.

     According to an embodiment of the invention, each scrambling function
consists in emitting a group of lines of the video image in an order
different than a normal order which corresponds to the intelligible image,
providing at the receiving site a storage memory comprising a
predetermined number of memory lines, each memory line being able to store
one received image line, the storage of the one received image line
causing the sending of a said previously stored line in this memory line
to the TV set, indicating for each emitted image line the address in the
memory line in which this emitted image line has to be stored, and
determining the emitting time of this image line in such a way that it
replaces in the memory a previous image line just at the time when this
previous image line has to be sent to the TV set in the normal order of
the image lines for generating the intelligible image.

     According to an embodiment of the invention, at the emitting site, the
scrambling method consists of: allocating to each image line of at least
one intelligibly produced image field before its scrambling, the
pseudo-random address of the memory line of the storage memory in which
this image line will be stored at the receiving site; and determining the
emitting time (or emitting order) of this image line to cause, at the
receiving site, in response to storage of this image line in the memory
line corresponding to its address, the sending of the image line which was
previously stored at the same address to the TV set in a sequence of video
lines in the normal order for generating the intelligible (or clear)
image.

     According to an embodiment of the invention, at the transmitting site, the
method of scrambling further comprises: permanently maintaining a
correspondence table between, on the one hand, the identification number
of each image line of at least one frame or field of the intelligibly
produced emission before it is scrambled and, on the other hand, its
storage address in the storage memory at the receiving site; eventually
eliminating from this table said image lines when they are finally sent to
the TV set; arranging a number of stacks equal to the number of memory
lines of the storage memory used at the receiving site, each stack
corresponding to one memory line; successively stacking in each stack the
identification number of each image line which will be addressed to the
memory line corresponding to that stack during the reception of one or
several frames or fields, beginning this procedure with the last line of
the field(s) and stacking until the first line of the first frame or
field; then, when all the stacks for the field(s) are stacked, carrying
out an unstacking of each stack beginning with the bottom of the stack and
determining, for each image line thus extracted from the stack by said
unstacking, its emitting time (or its emitting order), this emitting time
corresponding to the time at which the image line, which is in the same
stack just above the image line which has just been unstacked, has to be
sent to the TV set for generating the intelligible or clear image.

DRWD  Drawing Description

     The present invention will be more fully understood with reference to the
following description of an embodiment and to the accompanying drawings in
which:

     FIG. 1 shows the storage mode in a buffer of a decoder according to the
invention;

     FIG. 2 shows a means for carrying out the scrambling method according to
the invention;

     FIG. 3 shows a block diagram of a device for carrying out the invention;
and

     FIG. 4 shows a portion of the device for carrying out the invention.

DETD  Detail Description

     A digital image (frame or field) line conventionally includes a great
number, for example, 256 or 512, of digital samples but only eight samples
"a, b, c, d, e, f, g, h" are shown in the drawings for purposes of
simplification.

     Referring to FIG. 1, an addressing and storage mode of the scrambled image
lines received at the subscriber's decoder is illustrated. A storage
memory (or buffer) 8 conventionally called a buffer, including 32 memory
lines with each memory line being capable of storing the digital
information of one full image line, can be seen.

     According to the method of the invention, an emitted line Z is sent to the
buffer 8 and replaces a previously stored line X in the same memory line n
of the buffer 8. The storage of the image line Z in the memory line n of
the buffer 8 causes the previously stored image line X to be output and
sent to the TV set, possibly after reconditioning or canceling a rotation.
Accordingly, the image line emission order depends on the address n of
each of the stored lines since each line Z will be emitted only when it
replaces a previously stored line X in the buffer memory line
corresponding to the Z line address, and only at the time when the
previously stored line X is to be sent to the TV set.

     It can be seen that the order for emitting the lines (line emission order)
is not merely and arbitrarily permuted, but the permutation order is the
result of a combination with each image line address in the buffer
situated at the receiving site. Thus, the scrambling function by image
line permutation is a relative function and not an absolute function.

     According to an embodiment of the invention and with reference to FIG. 2,
the scrambling method consists of:

 a) permanently maintaining a correspondence table between, on the one hand,
  the identification number L of each image line of at least one frame or
  field of the intelligibly produced emission before it is scrambled and, on
  the other hand, its storage address B in the storage memory (or buffer) 8
  at the receiving site;

 b) eliminating from this table the image lines when they are finally sent
  to the TV set to be able to constitute a next table;

 c) providing a number B (in this example 32) of stacks P (e.g. P1 to P32)
  equal to the number B of memory lines of the storage memory (or buffer) 8
  used at the receiving site and giving a reference to each stack which is
  identical to the memory line which corresponds thereto;

 d) successively stacking in each stack P the identification number (309,
  308, 307, 306, 305, . . . ) of each image line that will be addressed
  during the receiving phase to the line of buffer 8 corresponding to this
  stack, beginning with the last line (in this example line 309) and
  stacking until the first line is stacked (in this example, the first line
  is line 23--in a video field, the active lines are conventionally
  designated by indexes 23 to 309);

 e) then, when all of the stacks are thus constituted for the frame(s) or
  field(s), carrying out an unstacking of each stack (from P1 to P32) by
  beginning with the bottom of the stack (e.g., for the first stack P1, the
  extraction begins with 308 then 306, etc . . . ) and determining for each
  image line whose identification number is thus extracted from a stack by
  said unstacking (e.g., for the line 308) its emitting time, that time
  being the time which corresponds to the time where the image line in the
  same stack just above the image line which is unstacked must be sent to
  the TV set to constitute the intelligible image (in this example, for line
  308 the emission time of this line must be the instant when the line 306
  is to be sent to the TV set to form the intelligible image;

 f) hence, all the image lines of the field(s) to be emitted can be arranged
  in a memory of great size in accordance with the time where each one will
  be emitted, and when all the lines of the field(s) are so arranged, it is
  sufficient to emit the image lines in accordance with their own
  arrangement in this memory.

     An example of device for carrying out this scrambling method, with
referenced to FIG. 2, is shown schematically in FIG. 3. In this figure, a
microprocessor (.mu.P) 14, a RAM 16 and a ROM 15 are shown. The ROM 16
includes a logic processing program for carrying out the logic steps
executed in the microprocessor 14, which correspond to the method
described above with reference to FIG. 2. The RAM 16 stores variable data
during execution of the program. Such a disposition is conventional. This
device outputs, via a dual port RAM 17, the series 18 of the image line
identification numbers (in the present example the series 23, 28, 305, . .
. 29) corresponding to the series of image lines as they have to be
successively emitted so as to restitute at the receiving site a clear
image in a decoder simultaneously receiving a corresponding unscrambling
code.

     FIG. 4 shows an embodiment of the remaining portion of the device for
carrying out the method of the invention. In this portion, an entry path
S1 inputs the intelligible image to the emitting station. This image is
digitalized through an A/D converter 10 and is stored in successive lines
(e.g. the field lines 23-309) in a buffer 11. During this storing, another
identical buffer 12, in which has been stored a previous field, is read
with a reading order of the lines (23-309) determined according to the
scrambling method of the present invention (with the device of FIG. 3),
and each extracted line passes through a D/A converter 13 and is then
transmitted, this transmission $2 being scrambled as the lines are not
output in natural order (which is lines Nos. 23, 24, . . . , 309).

     Three buffers can be used in place of the two buffers 11 and 12 in order to
have time during the transition from one buffer to another.

CLMS  Claims
STM     Claim Statement:			I claim:
NUM     Claim Number:				1.

     1. In a method of scrambling and unscrambling a video signal, comprising
emitting a scrambled video sequence at a transmitting site, receiving the
scrambled video sequence in a storage memory at a receiving site and
unscrambling the received video sequence, wherein the scrambling comprises
successively emitting a group of image lines of the video signal in an
order different from a normal order of the image lines which corresponds
to an intelligible image,

 the improvement wherein the storage memory at the receiving site comprises
  a predetermined number of memory lines each having an address, each memory
  line is able to store one received image line and, in response to the
  storage therein of a new image line, simultaneously outputs the image line
  previously stored therein, and

 the scrambling method at the transmitting side comprises

 determining for each emitted image line an address of the receiving site
  memory to which the image line is to be sent and stored in an order which
  is scrambled in relation to the normal order for generating an
  intelligible image; and

 determining at least one of the emitting time and the emitting sequence of
  each image line so that when each image line is sent to the address of the
  storage memory at the receiving site, the previous image line stored
  therein is output in a sequence of image lines in the normal order for
  generating the intelligible image.
NUM     Claim Number:				2.

     2. The method of claim 1, further comprising the steps of:

 associating with each image line of a group of image lines making up an
  intelligible picture an identification number (23 to 309), each image line
  being stored in a memory line of the storage memory at the receiving site
  with a pseudo-random address, and the scrambling method further comprises:

 maintaining a correspondence table between the identification number of
  each image line of a group before scrambling and each image line's storage
  address in the storage memory at the receiving site;

 arranging a number of stacks (P1 to P32) equal to the number of memory
  lines of the storage memory at the receiving site, each stack
  corresponding to a memory line of the storage memory;

 successively stacking in each stack the identification number of each image
  line which will be addressed to the corresponding memory line of the
  storage memory at the receiving site, beginning by stacking the last line
  (309) and ending by stacking the first line (23) of each group of image
  lines;

 then, when all of the image lines of a group have been stacked, carrying
  out unstacking of each stack sequentially from the bottom to the top of
  each stack, and determining for each image line whose identification
  number is thus extracted from each stack one of the emission time and
  emission order in which the image line must be emitted from the
  transmitting site, said one of the emission time and the emission order
  for each image line corresponding to the time when the image line, whose
  identification number is stacked just above that which is being unstacked,
  is to be sent from the storage memory at the receiving site in said
  sequence of image lines in the normal order for generating the
  intelligible image.
NUM     Claim Number:				3.

     3. The method of claim 2, further comprising the step of storing, once said
one of the emission time and the emission order is determined for each
group of image lines and prior to emission thereof, the image lines in a
memory at the transmission site in an order corresponding to said one of
the emission time and the emission order.
NUM     Claim Number:				4.

     4. The method of claim 1 further comprising the steps of storing, for each
group of lines and prior to emission thereof, successive image lines in a
transmission memory located at the transmission site, and then reading the
image lines stored in said transmission memory in a reading order
corresponding to one of the emitting time and the emitting sequence.
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