Frequency or time domain speech scrambling technique and system which does not require any frame synchronization

Claim 1

Apparatus, responsive to an audio frequency analog input signal applied thereto, for generating a scrambled audio frequency analog signal for transmission, said apparatus comprising: input interface means, responsive to said analog input signal, for sampling said analog input signal at a predetermined rate, and generating digital data signals representative of said samples; input switching buffer means, responsive to said digital data signals, for grouping said digital data signals into successive digital data frames (Xr) each representing a predetermined number (N) of samples, where X r (q); r=0,1,2 . . . ; q=0, 1, . . . N-1; input memory means, responsive to signals indicative of said digital data frames, for storing indicia of a predetermined number (2L) of successive digital data frames; filter means, responsive to said stored data frame indicia, and signals indicative of a predetermined filter function h(-Nr'+q), to calculate a time domain digital vector U rR , where ##EQU19## the elements of said vector being indicative of the corresponding frequency (k) component value of the corresponding sample; Fourier transform means, responsive to signals indicative of said digital vector [U rR (q), 0≦q≦N-1] T , for generating a frequency domain digital vector [Y rR (k), k=0, 1 . . . N-1] T where {Y rR (k), k=0, 1, . . . n-1}=DFT {U rR ((q-rR)) moduloN , q=0, 1, . . . N-1}, where DFT represents the Discrete Fourier Transform operator; permutator means, responsive to signals indicative of said frequency domain digital vector Y rR (k), k=0, 1 . . . N-1, and signals indicative of a predetermined N by N cryptographic matrix M, for generating a scrambled frequency domain digital vector Y r '=MY r inverse Fourier Transform means, responsive to signals indicative of said scrambled frequency domain digital vector Y r '(k), k=0, 1 . . . N-1, for generating a scrambled time domain digital vector [y rR (q), q=0, 1 . . . N-1] T where {y.sub.rR (q), q=0, 1, . . . N-1}=IDFT{Y'.sub.rR (k), k=0, 1 . . . N-1}, where IDFT is the inverse Discrete Fourier transform operator; interpolation means, responsive to signals indicative of said scrambled time domain vector [Y rR (q), q=0, 1 . . . N-1,] T and signals indicative of a predetermined interpolation function f(q), for generating an interpolated scrambled digital signal X' rR (n), where: ##EQU20## where Z is the greatest integer less than q/R; and output buffer means, responsive to signals indicative of said interpolated digital signal X rR '(n), for generating a scrambled audio frequency analog signal corresponding to said interpolated vector X rR '(q) for transmission.