Secret telephony

• US 3,967,067 A
• Filed: 09/24/1941
• Issued: 06/29/1976
• Est. Priority Date: 09/24/1941
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Potter, Ralph K.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US02/412,056
• Time in Patent Office: 12,697 Days
• Field of Search: 179/1.5, 179/1.5 R, 179/1 SA
• US Class Current: 380/41
• CPC Class Codes: H04K 1/02 by adding a second signal to make the desired signal unintelligible

Abstract

1. In a system of secret transmission of speech, means to subdivide speech waves constituting a message into a plurality of narrow frequency bands, means to integrate the energy in each band, means individual to said bands to subdivide the integrated energy from each band on a time basis to produce impulses with intervening spaces, and means to variably control said last-mentioned subdividing means individually in accordance with a key unrelated to the message.

Claims

1. In a system of secret transmission of speech, means to subdivide speech waves constituting a message into a plurality of narrow frequency bands, means to integrate the energy in each band, means individual to said bands to subdivide the integrated energy from each band on a time basis to produce impulses with intervening spaces, and means to variably control said last-mentioned subdividing means individually in accordance with a key unrelated to the message.

2. The method of secret transmission of speech comprising simultaneously deriving from each of a plurality of frequency regions of speech waves a current which varies in accordance with the variations of energy content in the corresponding frequency region of the speech, interrupting said current to break the current up into impulses of varying length and spacing, variably modifying the length and spacing of said impulses in accordance with a secret key, transmitting said impulses, and receiving and modifying the transmitted impulses in accordance with a duplicate key to restore said currents to recognizable form.

3. The method of secret transmission of speech comprising analyzing speech message waves into a plurality of speech-defining waves representing syllabic rates of energy variation in each of a plurality of different frequency regions of the speech waves, translating said speechdefining waves into marking impulses and spaces, reconstructing marking and spacing signals therefrom varying in length and spacing in accordance with a prearranged scheme unrelated to the message, transmitting said marking and spacing signals, reconstructing speechdefining waves from the transmitted marking and spacing signals by supplying impulses in accordance with the same prearranged scheme, and reconstructing understandable speech from the reconstructed speech-defining waves.

4. In secret telephony, means to derive from the speech to be sent a plurality of relatively low frequency speech-defining signals, means to translate each of said signals into marking and spacing signs, and means to render the transmission of said signs secret comprising means to combine them with a random key composed of marking and spacing signs occurring in fortuitous order.

5. In secret telephony, means to derive from the speech to be sent a plurality of relatively low frequency speech-defining signals of varying amplitude, means to produce from each such signal marking signs corresponding in length to the duration of signal current above a certain amplitude and spacing signs corresponding in length to the duration of absence of signal current above said certain amplitude, and means to render transmission of said signs secret comprising means to combine with them a random key composed of marking and spacing signs occurring in fortuitous order.

6. In secret telephony, means to derive from the speech to be sent a plurality of relatively low frequency speech-defining signals of varying amplitude, means to commutate said signals at irregular instants depending upon their amplitude to produce marking and spacing signs of varying length, and means to commutate said marking and spacing signs at irregular instants in accordance with a key.

7. In secret telephony, a multiplex transmission path, means to send through the separate channels thereof simultaneously marking and spacing signals indicative of the frequency-energy distribution of distinct frequency regions of the speech spectrum, means comprising a key for each channel and means for combining the individual keys with the respective marking and spacing signals of the different channels to render transmission of said signals secret.

8. A system according to claim 7 including at the opposite end of said path a key for each channel which is a duplicate of the respective key at the sending end, means to combine said keys at said opposite end with the secretly sent signals to restore said signals to recognizable form, and means to reconstruct speech from the restored signals.

9. In secret telephony, means to derive from the speech to be sent a plurality of speech-defining signals each indicative of the energy variations with time of a different frequency region of the speech, means to translate each such signal above a certain amplitude into a mark and each such signal below said certain amplitude into a space, an individual key for each signal, consisting of marks and spaces of random occurrence, and means to combine each key with the marks and spaces obtained from an individual one of said signals, to render transmission of the latter marks and spaces secret.

10. In secret telephony, means to derive from the speech to be sent a plurality of speech-defining signals each indicative of the energy variations with time of a different frequency region of the speech, a separate telegraphic relay operated by each such signal, each relay having an armature for opening and closing contacts, a coding mechanism having contacts adapted to be opened and closed in random manner, and transmitting means under the joint control of said relay controlled contacts and the contacts of said coding mechanism.

11. In secret telephony, a speech input, analyzing filters for subdividing the speech band into narrow portions in separate channels, means to integrate the energy passed through each filter, a relay operated by the integrated energy in each channel, tape controlled coding mechanism having circuit controllers equal in number to said relays and sending means jointly controlled by each of said relays and the circuit controllers of said coding mechanism.

12. In secret telephony, means to subdivide the speech frequency band into narrow subbands in separate channels, means to integrate the energy in each channel, means to translate the integrated energy in each channel into signals comprising fixed amplitude current impulses with intervening spaces, telegraph coding mechanism, and transmitting means jointly controlled by said signals and said coding mechanism.

13. A multichannel multiplex transmission system for transmitting marking and spacing signals between a transmitting station and a receiving station over respective channels, telegraphic relays for transmitting said signals, telegraphic relays for receiving said signals, means at the transmitting station to analyze speech waves into low frequency speech-defining currents in a plurality of separate circuits, means to actuate said transmitting relays by said respective speech-defining currents, a speech synthesizer at said receiving station including means generating waves covering the speech frequency range and means to reproduce speech from said waves under control of speech-defining currents, means controlled by said receiving relays for reproducing the speech-defining currents corresponding to those which actuate said transmitting relays, and means to control said speech synthesizer from the reproduced speech-defining currents.

14. A system according to claim 13 including a mechanical coding mechanism at the transmitting station for modifying the action of said transmitting relays to render unauthorized reception of the signals difficult and a cooperating decoding mechanism at the receiving station for modifying the action of the receiving relays in complementary manner to restore the signals.

15. In a secret telephone system, means at a transmitting station to analyze speech waves into a number of low frequency currents in separate circuits, such currents having gradually varying amplitude, means to translate such currents into marking and spacing signals, means to transmit said signals to a distant receiving station, means at the latter station comprising thermoresponsive resistances to translate said marking and spacing signals into currents of gradually varying amplitudes, and means to reconstruct speech waves under control of said last-mentioned currents.

16. In secret telephony, means at a transmitting station to analyze speech waves into relatively low frequency speech-defining currents simultaneously existing in a plurality of circuits, circuit control means responsive to said currents, coding mechanism comprising a punched tape and automatic stepping means therefor, contacts controlled by said tape in permutations and combinations occurring in random manner, transmitting means under the joint control of said coding mechanism and curcuit control means, for transmitting coded signals to a distant receiving station, receiving means thereat, means at said latter station including a decoded mechanism comprising an identically punched tape to that used in transmission and automatic stepping means therefor, means under the joint control of said receiving means and said decoding mechanism for reproducing speech-defining currents similar to those existent at the transmitting station, and means to reproduce speech currents under control of said reproduced speech-defining currents.

17. In a system of secret transmission of speech in which the speech waves are analyzed into low frequency currents in individual circuits representative in relative current strengths of the frequency energy distribution of speech from instant to instant, means also deriving from the speech the voice fundamental frequency and means to translate such derived frequency into a current of varying strength corresponding to variation in such fundamental frequency means to translate different magnitudes of said last current into respective indications in respectively different circuits, means to transmit to a distant receiving point energy variations characteristic of said low frequency currents in each of said individual circuits and of said indications in said different circuits, means at the receiving point to generate waves of a fundamental frequency under control of and corresponding to said respective indications, together with harmonics thereof, and means to control the generated waves in accordance with said low frequency currents in said individual circuits to reconstruct simulations of speech waves in intelligible form.

18. A system according to claim 17, including means to increase the secrecy of transmission comprising means to combine code signals with said low frequency currents and said indications before transmission and means to supply duplicate code signals at the distant receiving point for canceling the effect of the code signals introduced before transmission.