(19)
(11) EP 0 378 446 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
27.05.1992 Bulletin 1992/22

(43) Date of publication A2:
18.07.1990 Bulletin 1990/29

(21) Application number: 90300407.5

(22) Date of filing: 15.01.1990
(51) International Patent Classification (IPC)5H04K 1/00
(84) Designated Contracting States:
AT BE CH DE DK ES FR GB GR IT LI LU NL SE

(30) Priority: 13.01.1989 NZ 227621

(71) Applicant: Webb, Joseph Alfred
Christchurch (NZ)

(72) Inventor:
  • Webb, Joseph Alfred
    Christchurch (NZ)

(74) Representative: Robinson, Nigel Alexander Julian et al
D. Young & Co., 21 New Fetter Lane
London EC4A 1DA
London EC4A 1DA (GB)


(56) References cited: : 
   
       


    (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.







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