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109:) 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
572:
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.
571:
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.
503:
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
50:
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
648:
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
533:. 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.
181:
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
412:
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
499:
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
552:
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 "
851:
136:
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)
467:
359:
623:
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
649:
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
159:
521:. 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
553:
133:
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.
808:
791:
295:). 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
488:
Multiplicative scramblers lead to error multiplication during descrambling (i.e. a single-bit error at the descrambler's input will result in
213:) encryption as scrambling as well. This may well be because (traditional) mechanisms employed are based on feedback shift registers as well.
660:
enthusiasts often use them to listen in to scrambled communications at car races and some public-service transmissions. It is also common in
51:
sync pulses in television signals; televisions will not be able to display a picture from such a signal. Some modern scramblers are actually
38:
at the sender's side to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Whereas
641:
around a static point to various complex methods of changing the inversion point randomly and in real time and using multiple bands.
158:
To enable accurate timing recovery on receiver equipment without resorting to redundant line coding. It facilitates the work of a
856:
909:
712:
set. A descrambler is a device that restores the picture and sound of a scrambled channel. A descrambler must be used with a
102:, as the intent is not to render the message unintelligible, but to give the transmitted data useful engineering properties.
899:
309:
Additive scrambler/descrambler is defined by the polynomial of its LFSR (for the scrambler on the picture above, it is
585:
631:
than their earlier analog counterparts. Only these types of systems are considered secure enough for sensitive data.
87:
83:
417:. Multiplicative scrambler/descrambler is defined similarly by a polynomial (for the scrambler on the picture it is
63:
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and other adaptive circuits of the receiver (eliminating long sequences consisting of '0' or '1' only).
20:
74:) is a device that manipulates a data stream before transmitting. The manipulations are reversed by a
716:
to be able to unencrypt all of the premium & pay-per-view channels of a Cable
Television System.
291:
A sync-word is a pattern that is placed in the data stream through equal intervals (that is, in each
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framing structure, channel coding and modulation for 11/12 GHz satellite services (EN 300 421)
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79:
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373:
167:
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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
91:
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In order to assure a synchronous operation of the transmitting and receiving LFSR (that is,
661:
805:
Support for use of scrambling and
Conditional Access (CA) within digital broadcast systems
8:
894:
713:
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206:(LFSRs) due to their good statistical properties and ease of implementation in hardware.
47:
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reprocesses the signal, thus descrambling it and making it available for viewing on the
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Electronic kits for scrambling and descrambling are available from hobbyist suppliers.
589:
292:
221:
217:
59:
27:
16:
Telecommunications device used to make a signal unintelligible to unintended recipients
619:
The latest scramblers are not scramblers in the truest sense of the word, but rather
537:
401:
866:
751:
689:
645:
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Both types may fail to generate random sequences under worst-case input conditions.
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186:(also known as cross-modulation) caused by non-linearities of the receiving tract).
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140:
130:
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529:. A matching pair of records was produced, each containing the same recording of
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241:
697:
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263:(PRBS) (by modulo-two addition). Sometimes a pre-calculated PRBS stored in the
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One of those, used (among other duties) for telephone conversations between
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43:
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coder, or it can be placed after the FEC, just before the modulation or
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126:
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39:
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video signal that has been provided by a cable television company for
34:
is a device that transposes or inverts signals or otherwise encodes a
522:
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95:
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284:
173:
For energy dispersal on the carrier, reducing inter-carrier signal
46:
domain, scrambling usually refers to operations carried out in the
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368:
35:
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It was the need to synchronize the scramblers that suggested to
530:
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services, processed by a scrambler and then supplied over a
125:
An algorithm that converts an input string into a seemingly
113:, which, through a coding step, removes unwanted sequences.
667:
The term "scrambling" is sometimes incorrectly used when
385:
A multiplicative descrambler used in V.34 recommendation
664:
radios. This is an easy way to learn about scrambling.
228:, refer to encryption at the link layer as scrambling.
377:
A multiplicative scrambler used in V.34 recommendation
423:
315:
98:. A scrambler in this context has nothing to do with
588:, which ultimately led to the invention of both the
496:
equals the number of the scrambler's feedback taps).
236:
78:
at the receiving side. Scrambling is widely used in
306:is just the same device as the additive scrambler.
154:There are two main reasons why scrambling is used:
461:
353:
881:
818:
564:was used for higher-level voice communications.
259:) transform the input data stream by applying a
90:modems. A scrambler can be placed just before a
42:usually refers to operations carried out in the
809:European Telecommunications Standards Institute
792:European Telecommunications Standards Institute
105:A scrambler replaces sequences (referred to as
596:well before either was reinvented publicly by
369:Multiplicative (self-synchronizing) scramblers
637:scrambling can be as simple as inverting the
267:is used, but more often it is generated by a
177:. It eliminates the dependence of a signal's
692:context is the act of taking a scrambled or
513:The first voice scramblers were invented at
245:An additive scrambler (descrambler) used in
476:
129:output string of the same length (e.g., by
121:A scrambler (or randomizer) can be either:
116:
567:The noise was provided on large shellac
380:
372:
240:
704:and delivered to the household where a
544:was intercepted and unscrambled by the
400:of the input signal by the scrambler's
396:) are called so because they perform a
190:Scramblers are essential components of
882:
231:
788:Specifications for Data Broadcasting
481:Scramblers have certain drawbacks:
202:. They are usually defined based on
627:, these "scramblers" are much more
13:
14:
926:
504:accordance with the frame number.
462:{\displaystyle 1+z^{-18}+z^{-23}}
354:{\displaystyle 1+z^{-14}+z^{-15}}
237:Additive (synchronous) scramblers
850: This article incorporates
845:
575:
863:General Services Administration
841:Earth Station Standard IESS-308
204:linear-feedback shift registers
797:
780:
560:). An unrelated device called
269:linear-feedback shift register
255:(they are also referred to as
1:
819:External links and references
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674:
261:pseudo-random binary sequence
910:Telecommunications equipment
492:errors at its output, where
7:
719:
594:Diffie–Hellman key exchange
10:
931:
900:Applications of randomness
678:
517:in the period just before
21:Scrambler (disambiguation)
18:
644:The "scramblers" used in
592:encryption algorithm and
390:Multiplicative scramblers
194:system standards besides
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477:Comparison of scramblers
681:Cable television piracy
160:timing recovery circuit
144:random number generator
70:(also referred to as a
915:Television terminology
905:Satellite broadcasting
858:Federal Standard 1037C
852:public domain material
548:. At least one German
463:
386:
378:
355:
249:
168:automatic gain control
117:Purposes of scrambling
871: (in support of
651:Television encryption
586:non-secret encryption
542:Franklin D. Roosevelt
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410:linear time-invariant
384:
376:
356:
244:
835:ITU-T recommendation
558:AT&T Corporation
473:of the descrambler.
421:
408:. They are discrete
313:
304:additive descrambler
146:, which extends the
19:For other uses, see
714:cable converter box
469:), which is also a
253:Additive scramblers
232:Types of scramblers
216:Some standards for
107:whitening sequences
86:communications and
698:premium television
625:public-key systems
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415:self-synchronizing
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218:digital television
196:interleaved coding
60:telecommunications
28:telecommunications
538:Winston Churchill
471:transfer function
402:transfer function
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865:. Archived from
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752:Secure telephone
690:cable television
646:cable television
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767:Voice inversion
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639:frequency bands
635:Voice inversion
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392:(also known as
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184:intermodulation
131:pseudo-randomly
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869:on 2022-01-22.
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288:must be used.
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811:(ETSI), 1996.
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584:the idea for
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527:record player
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890:Cryptography
867:the original
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786:EN 301 192,
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747:Secure voice
742:One-time pad
732:Cryptography
685:
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519:World War II
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175:interference
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31:
25:
873:MIL-STD-188
706:set-top box
280:descrambler
257:synchronous
148:random seed
84:radio relay
76:descrambler
895:Line codes
884:Categories
774:References
710:television
686:Descramble
679:See also:
675:Descramble
671:is meant.
621:digitizers
569:phonograph
361:) and its
220:, such as
211:link layer
200:modulation
162:(see also
100:encrypting
72:randomizer
53:encryption
40:encryption
803:ETR 289,
694:encrypted
523:telephone
515:Bell Labs
452:−
436:−
344:−
328:−
285:sync-word
276:scrambler
111:line code
96:line code
80:satellite
68:scrambler
64:recording
32:scrambler
839:Intelsat
720:See also
608:, or by
556:" (from
550:engineer
271:(LFSR).
762:SIGSALY
727:Ciphony
669:jamming
658:Scanner
614:Hellman
606:Adleman
562:SIGSALY
546:Germans
406:Z-space
44:digital
36:message
629:secure
610:Diffie
604:, and
602:Shamir
598:Rivest
525:and a
222:DVB-CA
166:), an
150:value.
127:random
48:analog
854:from
531:noise
509:Noise
293:frame
282:), a
833:V.34
612:and
540:and
302:The
278:and
224:and
198:and
88:PSTN
66:, a
62:and
30:, a
827:DVB
688:in
662:FRS
653:.)
590:RSA
554:A-3
404:in
247:DVB
226:MPE
92:FEC
58:In
26:In
886::
875:).
861:.
807:,
790:,
616:.
600:,
455:23
439:18
365:.
347:15
331:14
299:.
82:,
494:w
490:w
448:z
444:+
432:z
428:+
425:1
340:z
336:+
324:z
320:+
317:1
23:.
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