393:
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253:
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120:) with other sequences without removing undesirable sequences, and as a result it changes the probability of occurrence of vexatious sequences. Clearly it is not foolproof as there are input sequences that yield all-zeros, all-ones, or other undesirable periodic output sequences. A scrambler is therefore not a good substitute for a
583:
In use, the caller would play a tone into the phone, and both scrambler units would then listen to the signal and synchronize to it. This provided limited security, however, as any listener with a basic knowledge of the electronic circuitry could often produce a machine of similar-enough settings to break into the communications.
582:
records made in pairs, shipped as needed, and destroyed after use. This worked, but was enormously awkward. Just achieving synchronization of the two records proved difficult. Post-war electronics made such systems much easier to work with by creating pseudo-random noise based on a short input tone.
514:
The effective length of the random sequence of an additive scrambler is limited by the frame length, which is normally much shorter than the period of the PRBS. By adding frame numbers to the frame sync, it is possible to extend the length of the random sequence, by varying the random sequence in
61:
domain. Scrambling is accomplished by the addition of components to the original signal or the changing of some important component of the original signal in order to make extraction of the original signal difficult. Examples of the latter might include removing or changing vertical or horizontal
659:
are designed to prevent casual signal theft, not to provide any real security. Early versions of these devices simply "inverted" one important component of the TV signal, re-inverting it at the client end for display. Later devices were only slightly more complex, filtering out that component
544:. The recording was played into the telephone, and the mixed signal was sent over the wire. The noise was then subtracted out at the far end using the matching record, leaving the original voice signal intact. Eavesdroppers would hear only the noisy signal, unable to understand the voice.
192:
upon the actual transmitted data, making it more dispersed to meet maximum power spectral density requirements (because if the power is concentrated in a narrow frequency band, it can interfere with adjacent channels due to the
423:
systems. A multiplicative scrambler is recursive, and a multiplicative descrambler is non-recursive. Unlike additive scramblers, multiplicative scramblers do not need the frame synchronization, that is why they are also called
510:
Additive scramblers must be reset by the frame sync; if this fails, massive error propagation will result, as a complete frame cannot be descrambled. (Alternatively if you know what was sent, the scrambler can be
563:
had worked at Bell Labs before the war and came up with a way to break them. Later versions were sufficiently different that the German team was unable to unscramble them. Early versions were known as "
862:
147:
An analog or digital source of unpredictable (i.e., high entropy), unbiased, and usually independent (i.e., random) output bits. A "truly" random generator may be used to feed a (more practical)
478:
370:
634:
combined with encryption machines. In these systems the original signal is first converted into digital form, and then the digital data is encrypted and sent. Using modern
660:
entirely and then adding it by examining other portions of the signal. In both cases the circuitry could be easily built by any reasonably knowledgeable hobbyist. (see
170:
532:. These sets consisted of electronics that could mix two signals or alternatively "subtract" one signal back out again. The two signals were provided by a
564:
144:
selecting bits to invert), thus avoiding long sequences of bits of the same value; in this context, a randomizer is also referred to as a scrambler.
819:
802:
306:). A receiver searches for a few sync-words in adjacent frames and hence determines the place when its LFSR must be reloaded with a pre-defined
499:
Multiplicative scramblers lead to error multiplication during descrambling (i.e. a single-bit error at the descrambler's input will result in
224:) encryption as scrambling as well. This may well be because (traditional) mechanisms employed are based on feedback shift registers as well.
671:
enthusiasts often use them to listen in to scrambled communications at car races and some public-service transmissions. It is also common in
62:
sync pulses in television signals; televisions will not be able to display a picture from such a signal. Some modern scramblers are actually
49:
at the sender's side to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Whereas
652:
around a static point to various complex methods of changing the inversion point randomly and in real time and using multiple bands.
169:
To enable accurate timing recovery on receiver equipment without resorting to redundant line coding. It facilitates the work of a
17:
867:
920:
723:
set. A descrambler is a device that restores the picture and sound of a scrambled channel. A descrambler must be used with a
113:, as the intent is not to render the message unintelligible, but to give the transmitted data useful engineering properties.
910:
320:
Additive scrambler/descrambler is defined by the polynomial of its LFSR (for the scrambler on the picture above, it is
596:
642:
than their earlier analog counterparts. Only these types of systems are considered secure enough for sensitive data.
98:
94:
428:. Multiplicative scrambler/descrambler is defined similarly by a polynomial (for the scrambler on the picture it is
74:
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271:
185:
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236:
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181:
and other adaptive circuits of the receiver (eliminating long sequences consisting of '0' or '1' only).
31:
85:) is a device that manipulates a data stream before transmitting. The manipulations are reversed by a
727:
to be able to unencrypt all of the premium & pay-per-view channels of a Cable
Television System.
302:
A sync-word is a pattern that is placed in the data stream through equal intervals (that is, in each
840:
framing structure, channel coding and modulation for 11/12 GHz satellite services (EN 300 421)
154:
90:
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691:
635:
384:
178:
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devices, the name remaining due to the similarities in use, as opposed to internal operation.
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It is common for physical layer standards bodies to refer to lower-layer (physical layer and
102:
285:
In order to assure a synchronous operation of the transmitting and receiving LFSR (that is,
672:
816:
Support for use of scrambling and
Conditional Access (CA) within digital broadcast systems
8:
905:
724:
568:
217:(LFSRs) due to their good statistical properties and ease of implementation in hardware.
58:
719:
reprocesses the signal, thus descrambling it and making it available for viewing on the
667:
Electronic kits for scrambling and descrambling are available from hobbyist suppliers.
600:
303:
232:
228:
70:
38:
27:
Telecommunications device used to make a signal unintelligible to unintended recipients
630:
The latest scramblers are not scramblers in the truest sense of the word, but rather
548:
412:
877:
762:
700:
656:
620:
496:
Both types may fail to generate random sequences under worst-case input conditions.
275:
197:(also known as cross-modulation) caused by non-linearities of the receiving tract).
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151:
141:
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767:
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540:. A matching pair of records was produced, each containing the same recording of
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252:
708:
624:
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274:(PRBS) (by modulo-two addition). Sometimes a pre-calculated PRBS stored in the
202:
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One of those, used (among other duties) for telephone conversations between
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coder, or it can be placed after the FEC, just before the modulation or
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video signal that has been provided by a cable television company for
45:
is a device that transposes or inverts signals or otherwise encodes a
533:
525:
121:
106:
849:
639:
560:
295:
184:
For energy dispersal on the carrier, reducing inter-carrier signal
57:
domain, scrambling usually refers to operations carried out in the
772:
572:
556:
379:
46:
591:
It was the need to synchronize the scramblers that suggested to
541:
711:
services, processed by a scrambler and then supplied over a
136:
An algorithm that converts an input string into a seemingly
124:, which, through a coding step, removes unwanted sequences.
678:
The term "scrambling" is sometimes incorrectly used when
396:
A multiplicative descrambler used in V.34 recommendation
675:
radios. This is an easy way to learn about scrambling.
239:, refer to encryption at the link layer as scrambling.
388:
A multiplicative scrambler used in V.34 recommendation
434:
326:
109:. A scrambler in this context has nothing to do with
599:, which ultimately led to the invention of both the
507:
equals the number of the scrambler's feedback taps).
247:
89:
at the receiving side. Scrambling is widely used in
317:is just the same device as the additive scrambler.
165:There are two main reasons why scrambling is used:
472:
364:
892:
829:
575:was used for higher-level voice communications.
270:) transform the input data stream by applying a
101:modems. A scrambler can be placed just before a
53:usually refers to operations carried out in the
820:European Telecommunications Standards Institute
803:European Telecommunications Standards Institute
116:A scrambler replaces sequences (referred to as
607:well before either was reinvented publicly by
380:Multiplicative (self-synchronizing) scramblers
648:scrambling can be as simple as inverting the
278:is used, but more often it is generated by a
188:. It eliminates the dependence of a signal's
703:context is the act of taking a scrambled or
524:The first voice scramblers were invented at
256:An additive scrambler (descrambler) used in
487:
140:output string of the same length (e.g., by
132:A scrambler (or randomizer) can be either:
127:
578:The noise was provided on large shellac
391:
383:
251:
715:and delivered to the household where a
555:was intercepted and unscrambled by the
411:of the input signal by the scrambler's
407:) are called so because they perform a
201:Scramblers are essential components of
14:
893:
242:
799:Specifications for Data Broadcasting
492:Scramblers have certain drawbacks:
213:. They are usually defined based on
638:, these "scramblers" are much more
24:
25:
937:
515:accordance with the frame number.
473:{\displaystyle 1+z^{-18}+z^{-23}}
365:{\displaystyle 1+z^{-14}+z^{-15}}
248:Additive (synchronous) scramblers
861: This article incorporates
856:
586:
874:General Services Administration
852:Earth Station Standard IESS-308
215:linear-feedback shift registers
808:
791:
571:). An unrelated device called
280:linear-feedback shift register
266:(they are also referred to as
13:
1:
830:External links and references
784:
685:
272:pseudo-random binary sequence
921:Telecommunications equipment
503:errors at its output, where
7:
730:
605:Diffie–Hellman key exchange
10:
942:
911:Applications of randomness
689:
528:in the period just before
32:Scrambler (disambiguation)
29:
655:The "scramblers" used in
603:encryption algorithm and
401:Multiplicative scramblers
205:system standards besides
519:
488:Comparison of scramblers
692:Cable television piracy
171:timing recovery circuit
155:random number generator
81:(also referred to as a
926:Television terminology
916:Satellite broadcasting
869:Federal Standard 1037C
863:public domain material
559:. At least one German
474:
397:
389:
366:
260:
179:automatic gain control
128:Purposes of scrambling
18:Scrambler (randomizer)
882: (in support of
662:Television encryption
597:non-secret encryption
553:Franklin D. Roosevelt
475:
421:linear time-invariant
395:
387:
367:
255:
846:ITU-T recommendation
569:AT&T Corporation
484:of the descrambler.
432:
419:. They are discrete
324:
315:additive descrambler
157:, which extends the
30:For other uses, see
725:cable converter box
480:), which is also a
264:Additive scramblers
243:Types of scramblers
227:Some standards for
118:whitening sequences
97:communications and
709:premium television
636:public-key systems
470:
426:self-synchronizing
398:
390:
362:
261:
229:digital television
207:interleaved coding
71:telecommunications
39:telecommunications
549:Winston Churchill
482:transfer function
413:transfer function
16:(Redirected from
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887:
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876:. Archived from
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763:Secure telephone
701:cable television
657:cable television
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768:Satellite modem
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650:frequency bands
646:Voice inversion
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403:(also known as
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195:intermodulation
142:pseudo-randomly
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822:(ETSI), 1996.
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595:the idea for
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587:Cryptographic
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538:record player
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901:Cryptography
878:the original
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797:EN 301 192,
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758:Secure voice
753:One-time pad
743:Cryptography
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530:World War II
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186:interference
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117:
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82:
78:
68:
42:
36:
884:MIL-STD-188
717:set-top box
291:descrambler
268:synchronous
159:random seed
95:radio relay
87:descrambler
906:Line codes
895:Categories
785:References
721:television
697:Descramble
690:See also:
686:Descramble
682:is meant.
632:digitizers
580:phonograph
372:) and its
231:, such as
222:link layer
211:modulation
173:(see also
111:encrypting
83:randomizer
64:encryption
51:encryption
814:ETR 289,
705:encrypted
534:telephone
526:Bell Labs
463:−
447:−
355:−
339:−
296:sync-word
287:scrambler
122:line code
107:line code
91:satellite
79:scrambler
75:recording
43:scrambler
850:Intelsat
731:See also
619:, or by
567:" (from
561:engineer
282:(LFSR).
773:SIGSALY
738:Ciphony
680:jamming
669:Scanner
625:Hellman
617:Adleman
573:SIGSALY
557:Germans
417:Z-space
55:digital
47:message
640:secure
621:Diffie
615:, and
613:Shamir
609:Rivest
536:and a
233:DVB-CA
177:), an
161:value.
138:random
59:analog
865:from
542:noise
520:Noise
304:frame
293:), a
844:V.34
623:and
551:and
313:The
289:and
235:and
209:and
99:PSTN
77:, a
73:and
41:, a
838:DVB
699:in
673:FRS
664:.)
601:RSA
565:A-3
415:in
258:DVB
237:MPE
103:FEC
69:In
37:In
897::
886:).
872:.
818:,
801:,
627:.
611:,
466:23
450:18
376:.
358:15
342:14
310:.
93:,
505:w
501:w
459:z
455:+
443:z
439:+
436:1
351:z
347:+
335:z
331:+
328:1
34:.
20:)
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