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(11) | EP 0 378 446 A3 |
(12) | EUROPEAN PATENT APPLICATION |
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(54) | Signal encryption |
(57) Methods and apparatus for encrypting and subsequently decrypting an analog or digital
signal are disclosed. During encryption the signal waveform is transformed by a substantially
continuous non-linear complex function of frequency. The transformation is characterised
in that the time duration of a transformed impulse signal is substantially increased.
Decryption requires transformation of the encrypted signal by substantially the complex
inverse of the encryption function. The transformations may vary in time during encryption/decryption
of a signal. |