US5101432A — Signal encryption

Claim 1

Independent Claim 103 words

A method of transferring information comprising: encrypting the information by passing it through a first network having a programmable impulse response; said network impulse response being determined by a set of network constants; said constants being provided by an encryption key consisting of a first set of pseudo random numbers; decrypting the encrypted information by passing it through a second network similar to said first network which has as network constants a decryption key consisting of a second set of pseudo random numbers which produce an impulse response for the second network which is complementary to the impulse response of the first network.

Claim 2

Independent Claim 103 words

A method of transferring information comprising: encrypting the information by passing it through a first network having a programmable impulse response; said network impulse response being determined by a set of network constants; said constants being provided by an encryption key consisting of a first set of pseudo random numbers; decrypting the encrypted information by passing it through a second network similar to said first network which has as network constants a decryption key consisting of a second set of pseudo random numbers which produce an impulse response for the second network which is complementary to the impulse response of the first network.

Claim 3

Independent Claim 115 words

A method of secure signal transmission comprising: encrypting the signal by passing it through a first network having a programmable impulse response; said network impulse being determined by a set of network constants; said constants being provided by an encryption key consisting of a first set of pseudo random numbers; passing the encrypted signal through a transmission medium; decrypting the signal received from the transmission means by passing it through a second network similar to said first network which has as network constants a decryption key consisting of a second set of pseudo random numbers which produce an impulse response for the second network which is complementary to the impulse response of the first network.

Claim 4

Independent Claim 115 words

A method of secure signal transmission comprising: encrypting the signal by passing it through a first network having a programmable impulse response; said network impulse being determined by a set of network constants; said constants being provided by an encryption key consisting of a first set of pseudo random numbers; passing the encrypted signal through a transmission medium; decrypting the signal received from the transmission means by passing it through a second network similar to said first network which has as network constants a decryption key consisting of a second set of pseudo random numbers which produce an impulse response for the second network which is complementary to the impulse response of the first network.

Claim 5

Dependent Claim 14 words

A method according to claim 2 wherein the transmission medium is a communications channel.

Claim 6

Dependent Claim 14 words

A method according to claim 2 wherein the transmission medium is a data bus.

Claim 7

Dependent Claim 13 words

A method according to claim 2 wherein the signal is a digital signal.

Claim 8

Dependent Claim 13 words

A method according to claim 2 wherein the signal is an analog signal.

Claim 9

Dependent Claim 14 words

A method according to claim 6 wherein the analog signal is a voice signal.

Claim 10

Dependent Claim 26 words

A method according to claim 2 wherein the network constants are selected to produce constant amplitude response, with a non-linear phase response over the transmission bandwidth.

Claim 11

Dependent Claim 24 words

A method according to claim 2 wherein said network constants are chosen to produce phase response and non-linear amplitude response over the transmission bandwidth.

Claim 12

Dependent Claim 70 words

A method according to claim 2 wherein the pseudo random numbers making up said first set are changed during encryption of a signal and the pseudo random numbers making up said second set are changed during decryption of the encrypted signal such that the impulse response determined by the changed numbers for the second network is complementary to the impulse response determined by the changed numbers for the first network.

Claim 13

Dependent Claim 62 words

A method according to claim 10 wherein there are two available sets of pseudo random numbers for each of the first and second networks; those at the second network being complementary to those at the second network being complementary to those at the first network; and the numbers used at each network are synchronously cycled between complementary pairs during encryption and decryption.

Claim 14

Dependent Claim 35 words

A method according to claim 11 wherein the two number sets for the first network and the two number sets for the second network produce impulse responses for their respective networks which are Hilbert pairs.

Claim 15

Dependent Claim 78 words

A method according to claim 2 wherein the second set of pseudo random numbers is derived from the first set by: obtaining the complex Fourier transform of the impulse response for the first network produced by the first set of numbers; deriving the complex inverse of said Fourier transform; and truncating the number of terms in the inverted Fourier transform to the number of members in the first set of numbers to produce said second set of numbers.

Claim 16

Dependent Claim 92 words

Apparatus for encrypting a signal comprising: a network having a programmable impulse response; said network having an input to which the signal is applied and an output which delivers the encrypted signal; said network impulse response being determined by a set of constants selected to produce a complex aperiodic impulse response; first storage means for storing at least one encryption key consisting of set of pseudo random numbers; each number corresponding to a network constant; and first loading means for loading the network constants with a key from said first storage means.

Claim 17

Dependent Claim 92 words

Apparatus for encrypting a signal comprising: a network having a programmable impulse response; said network having an input to which the signal is applied and an output which delivers the encrypted signal; said network impulse response being determined by a set of constants selected to produce a complex aperiodic impulse response; first storage means for storing at least one encryption key consisting of set of pseudo random numbers; each number corresponding to a network constant; and first loading means for loading the network constants with a key from said first storage means.

Claim 18

Dependent Claim 34 words

Apparatus according to claim 14 wherein said network is a finite impulse response (FIR) digital filter of the Rabiner and Gold type and the network constants are the h values of the FIR filter.

Claim 19

Dependent Claim 105 words

Apparatus according to claim 15 wherein said network is a finite impulse response (FIR) digital filter comprising a digital delay line into which samples of the signal to be encrypted are successively read, a digital memory which holds said set of network constants having cell blocks which each store one constant for each element of said delay line, means for multiplying each sample value stored in each element of the delay line with a corresponding network constant held in said memory, and means for summing each individual product output from the multiplying means, the contents of the summing means forming the output of said network.

Claim 20

Dependent Claim 23 words

Apparatus according to claim 16 wherein the network has an input stage an analog-to-digital converter and as an output stage a digital-to-analog converter.

Claim 21

Dependent Claim 23 words

Apparatus according to claim 16 wherein the network has an input stage a serial-to-parallel converter and as an output stage a parallel-to-serial converter.

Claim 22

Dependent Claim 15 words

Apparatus according to claim 16 wherein the network has an input stage an analog-to-digital converter.

Claim 23

Dependent Claim 15 words

Apparatus according to claim 16 wherein the network has an output stage a digital-to-analog converter.

Claim 24

Dependent Claim 30 words

Apparatus according to claim 14 wherein at least one encryption key is selected such that the network has constant amplitude response; with a non-linear phase response over the signal bandwidth.

Claim 25

Dependent Claim 29 words

Apparatus according to claim 14 wherein at least one encryption key is selected such that the network has constant phase response and non-linear amplitude response over the signal bandwidth.

Claim 26

Dependent Claim 44 words

Apparatus according to claim 14 including a controller for said first loading means wherein said first storage means store more than one encryption key and said controller causes said first loading means to load more than one encryption key during encryption of a signal.

Claim 27

Dependent Claim 12 words

Apparatus according to claim 14 wherein said network is an all-pass network.

Claim 28

Dependent Claim 25 words

Apparatus according to claim 14 wherein said network is a band-pass network having a bandwidth derived from the bandwidth of the signal to be encrypted.

Claim 29

Dependent Claim 108 words

Apparatus for decrypting a signal encrypted using the apparatus of claim 14 comprising: a network having a programmable impulse response; said network having an input to which the encrypted signal is applied and an output which delivers the decrypted signal; said network impulse response being determined by a set of constants; second storage means for storing at least one decryption key consisting of a set of pseudo random numbers; each number corresponding to a network constant and selected to provide an impulse response complementary to that used to encrypt the signal; and second loading means for loading the network constants with a key from said second storage means.

Claim 30

Dependent Claim 34 words

Apparatus according to claim 26 wherein said network is a finite impulse response (FIR) digital filter of the Rabiner and Gold type and the network constants are the h values of the FIR filter.

Claim 31

Dependent Claim 105 words

Apparatus according to claim 27 wherein said network is a finite impulse response (FIR) digital filter comprising a digital delay line into which samples of the signal to be encrypted are successively read, a digital memory which holds said set of network constants having cell blocks which each store one constant for each element of said delay line, means for multiplying each sample value stored in each element of the delay line with a corresponding network constant held in said memory, sand means for summing each individual product output from the multiplying means, the contents of the summing means forming the output of said network.

Claim 32

Dependent Claim 24 words

Apparatus according to claim 28 wherein the network has as an input stage an analog-to-digital converter and as an output stage a digital-to-analog converter.

Claim 33

Dependent Claim 24 words

Apparatus according to claim 28 wherein the network has as an input stage a serial-to-parallel converter and as an output stage a parallel-to-serial converter.

Claim 34

Dependent Claim 16 words

Apparatus according to claim 28 wherein the network has as an input stage an analog-to-digital converter.

Claim 35

Dependent Claim 16 words

Apparatus according to claim 28 wherein the network has as an output stage a digital-to-analog converter.

Claim 36

Dependent Claim 28 words

Apparatus according to claim 26 wherein the decryption key is selected such that the network has constant amplitude response, with a non-linear phase response over the signal bandwidth.

Claim 37

Dependent Claim 27 words

Apparatus according to claim 26 wherein said encryption key is selected such that the network has constant phase response and non-linear amplitude response over the signal bandwidth.

Claim 38

Dependent Claim 56 words

Apparatus according to claim 26 including a controller for said second loading means wherein said second storage means store more than one decryption key and said controller causes said second loading means to load more than one decryption key during encryption of a signal time-wise synchronously with changes of encryption key during encryption of the signals.

Claim 39

Dependent Claim 12 words

Apparatus according to claim 26 wherein said network is an all-pass network.

Claim 40

Dependent Claim 26 words

Apparatus according to claim 26 wherein said network is a band-pass network having a bandwidth derived from the desired bandwidth of the signal to be encrypted.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1995-03-31	1995-09-30	1996-03-31	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1999-03-31	1999-09-30	2000-03-31	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2003-03-31	2003-09-30	2004-03-31	$7700.00	Window Closed / Lapsed

Signal encryption

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