1 make intelligible; "Can you unscramble the message?" [ant: scramble]
2 become or cause to become undone by separating the fibers or threads of; "the sweater unravelled" [syn: unravel, unknot, untangle, unpick] [ant: ravel, ravel]
- Rhymes: -æmbəl
In telecommunications, a scrambler is a device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Whereas encryption usually refers to operations carried out in the digital domain, scrambling usually refers to operations carried out in the analog 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 sync pulses in television signals; televisions will not be able to display a picture from such a signal. Some modern scramblers are actually encryption devices, the name remaining due to the similarities in use, as opposed to internal operation.
NoiseThe first voice scramblers were invented at Bell Labs in the period just before World War II. These sets consisted of electronics that could mix two signals, or alternately "subtract" one signal back out again. The two signals were provided by telephones for one, and a record player for the other. Sets of matching pairs of records were produced containing recordings of noise, which would then be played into the telephone and the mixed signal sent over the wires. The noise would then be subtracted back 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 inside.
One of those, used (among other duties) for telephone conversations between Winston Churchill and Franklin D. Roosevelt was intercepted and 'unscrambled' by the Germans. At least one German engineer 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.
The 'noise' was provided on large shellac phonograph 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. 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.
CryptographicIt was the need to synchronize the scramblers that suggested to James H. Ellis the idea for non-secret encryption which ultimately led to the invention of both the RSA encryption algorithm and Diffie-Hellman key exchange well before either was reinvented publicly by Rivest, Shamir, and Adleman, or by Diffie and Hellman.
The latest scramblers are not scramblers in the truest sense of the word, but rather digitizers 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 public-key systems, these "scramblers" are much more secure than their earlier analog counterparts. Only these types of systems are considered secure enough for sensitive data.
Voice inversion scrambling can be as simple as inverting the frequency bands around a static point to various complex methods of changing the inversion point randomly and in real time and using multiple bands.
The "scramblers" used in cable television 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 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 Television encryption
Electronic kits for scrambling and descrambling are available from hobbyist suppliers. Scanner enthusiasts often use them to listen in to scrambled communications at car races and some public service transmissions. It is also common in FRS radios. This is an easy way to learn about scrambling. Scramble mode makes your voice sound like "Donald Duck", yet it is often possible to understand the general idea of the conversation.
The term "scrambling" is sometimes incorrectly used when jamming is meant.
unscramble in German: Scrambler
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