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. The first voice scramblers were invented at Bell Labs in the period just before WWII. One of those, used for (among many others) phone conversations between Winston Churchill and Franklin Roosevelt was intercepted and 'unscrambled' by the Germans. At least one German engineer had worked at Bell Labs before the War. Later versions were sufficiently different that the German team was unable to unscramble them.
One notion, actually put into (secret) production use, was to add noise at the sending end, and subtract the same noise at the receiving end. The 'noise' was provided on large shellac phonograph records which made in pairs, shipped around as needed, and destroyed after use. This worked, but was enormously awkward. Synchronization alone was a trial. This suggested to James 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.
Note: The first scramblers, and many commercial ones as late as the end of the 20th century, used a simple algorithm (or scrambling mechanism). These do not provide much security against a determined knowledgeable attacker, and provide communicationsprivacy that is inadequate for classified traffic. More recent designs are much better, and some are approved by the US Government for secure traffic. Most of these digitize the analog signals (ie, the voice at either end) and encrypt the digital data stream, reversing the process at the destination. These can be as secure as the underlying cryptography and the security of the distribution mechanism for the keys needed. It should also be noted that the "scramblers" used in cable television are designed to prevent casual signal theft - not to provide any real security.
Scrambler State The special value of 1 for Packet Length is reserved to transfer the scrambler state from the transmitter to the receiver for the optional set-reset scrambler.
This is a free-running scrambler that is not affected by the patterns in the user data, and therefore minimizes the possibility that a malicious user could present data to the network that mimics an undesirable data pattern.
SDL Scrambler Synchronization As described in the previous section, the special value of 1 for Packet Length is reserved to transfer the scrambler state from the transmitter to the receiver.
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.
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