Cryptographic Patents

© Brooke Clarke, N6GCE 2003 - 2005


Patent Classes

In this section when a title is a link it goes to the USPTO web page describing the top class.  There you can see the hierarchy of the classes, that are not so clear below.
When a class number is a link it takes you to a list of all patents in that class.  There are many more listed there than here.
327 - Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems
       164 - Generating rectangular (e.g., clock, etc.) or pulse waveform having random characteristic (e.g., random width, etc.)

380 Cryptography
    26 - Having mechanical control of signal encryption (e.g., cam) 119 pats
    27 - By perforated record  77 pats
    28 - Particular Algorithmic Function Encoding 636 pats
            29 - NBS/DES algorithm    257 pats
            30 - Public key   756 pats
    33 - Using plural paths or channels
    37 - Block/data stream enciphering 212 pats
    38 - Frequency shift or inversion 121 pats many speech scramblers here
        39 - Having plural band pass filters  95 pats
    40 - Having plural band pass filters 49 pats
    41 - Having quantizing and subsequent normalizing of signal (e.g., reentry telephone circuitry) 48 pats
    42 - Data stream/substitution enciphering  157 pats
    43 - Key sequence signal combined with data signal  255 pats
    45 - Multiple key level 162 pats
    46 - Nonlinear (e.g., pseudorandom)  487 pats
    47 - Plural generators  155 pats
    51 - Having production of printed copy (e.g., printer, typewriter)
    52 - Including particular structure or housing (e.g., display, keyboard)
    54 - By Modifying Optical Image (e.g., Transmissive Overlay) 322 pats
    55 - Having Production of Printed Copy (e.g., Cryptographic Printer or Typewriter)  161 pats
    56 - Selectively Movable Element having Code Characters  47 pats
            57 - Rotatable  54 pats
            58 - Characters on peripheral surface (e.g., cylinder section)  32 pats
    252 - Electrical Signal Masking  135 pats
            253 - By signal having discrete frequency component  50 pats
            254 - By signal having discrete step amplitude variation  33 pats
    255 - Communication System using Cryptography   169 pats
           260 - Symmetric key synchronization  125 pats
            262 - Transmitting a seed, sequence, or initial value  179 pats
            265 - Combining outputs of shift register  76 pats
            274 - Synchronization  100 pats
            275 - Speech scrambler detail  97 pats
            277 -
            284 -
400 Typewriting Machines
       89 - Key Reassignment
               90 - Electrically powered
708 Electrical Computers: Arithmetic Processing and Calculating
          100  Electrical Digital Calculating Computer
                  250 - Random number generation 289 patents

713 Electrical Computers and Digital Processing Systems: Support
       150 - Multiple Computer Communication using Cryptography 166 pats
               151 - Protection at a particular protocol layer  99 pats
               169 - Mutual entity authentication  147 pats
               171 - Having key exchange  215 pats
               181 - Message digest travels with message 142 pats

1800

253061 Aparatus for Preparing and Transmitting Secret Telegraphic Messages Jan 31 1832 A F & F B Johnson  178/92; 83/202; 178/4; 178/17R; 178/37; 380/26 - indentions on paper tape rather than printed characters.  Precursor topunched paper tape.  Little security since a skilled person could read the code.
420262 Mixer 366/247; 210/251; 210/466; 220/568; 222/192; 380/54 - beverage mixer
1210656 Aparatus for Coding and Decoding Jan 2, 1917 S M Kintner 380/26; 380/51; 400/77 - fixed subistution alphabet for teletype type machines
1244477 Telegraphy Oct 30, 1917 P.B. Delany 380/255; 178/98; 380/38 a public sounder with inverted singals to preventlistening to message
1310719 Secret Signaling System, G.S. Vernam, July 22, 1919, 380/33 ; 380/259; 380/26
Class 380/33 is for crypto systems that transmit the message using a plurality of paths, yet that's not how it works.  This is just a One Time Pad.
1312572 Secret Signaling System Aug 12 1919 380/43; 380/260 R D Parker - Morse code is broken up using a distributor
1320908 Ciphering and Decyphering Mechanism Nov 4, 1919 380/27 R. D. Parker - paper tape

    W.W. I 1914 - 1911

1920

1356546 Cyphering System Oct 26, 1920 380/47 L F Morehouse (AT&T)- Two 5 level paper tapes
1414496 Cryptographic Typewriter May 2 1922 P G G Beyer 380/51; 400/71; 400/184 - single rotor turns one step with each key press
1415106 Cyphering Device May 9 1922 380/27; 380/51; 380/267 L F Morehouse (AT&T) - improves on 1320908 by not encyphiring the control characters, makes for a legiable printout
1416765 Cyphering Device May 23 1922 380/27 G S Vernam (AT&T) - filed Jan 1920, paper tape
1426699  Cyphering Device Aug 22, 1922 380/27 R E Pierce (AT&T) - paper tape
1491358 Enciphering Machine April 22, 1924 380/27; 380/51; 400/73; 400/90 paper tape
1510441 Electric Coding Machine Sep 30, 1924 E. H. Hebern 380/51; 400/77
1516180 Secret Signaling System Employing Aparatus for Automatically Encyphering and Decyphering Messages Nov 18, 1924  380/27; 380/47 W. F. Friedman - paper tape
1522044 Secret Communication System June 6, 1925 R. Brown - speech frequency inversion 380/38
1522775  Secret Signaling System Employing Aparatus for Automatically Encyphering and Decyphering Messages Jan 13, 1925 380/27; 380/47 W. F. Friedman - paper tape
1523689 Coding and DEcoding Machine, S Hole, Jan 20, 1925, 380/55 ; 235/201ME; 400/181; 400/77
1533252 Coding and Decoding Machine H.A. Koch Apr 14, 1925 - pneumatic  380/51 ; 400/176
1540107 Apparatus for the Production of Cipher Documents especially for Telegraphic Dispatch AG Damm 380/52 ; 400/474; 400/77
1542567 Secret Signaling June 16, 1925 R.C. Mathes voice frequency subbands & multiple channels 380/34; 380/38
1633625 Sycercy System June 28 1927  380/28 (AT&T) - telephone scrambler using controlled distortion
1644239 Apparatus for Producing a Series of Signs Damm Oct 4, 1927 380/58
1683072 Electric Code Machine E. H. Hebern, Sep 4, 1928  380/52; 341/2; 380/58 (pre enigma)
1684028 Coding and Decoding Apparatus and Code Changing Device Therefore, S Hole, Sep 11, 1928, 380/26 ; 380/51; 400/182; 400/71
1724163  400/365; 181/201; 400/90; 400/689; 400/690 quiet electric typewriter
1726578 - Secret Telephone System - Sep 23, 1929 Harry Nyquist - add a time delay proportional to frequency to make unintelligable

1930

1744347 Coding Machine Kryha Jan 21, 1930 380/57 ; 380/58
1846105 Ciphering Aparatus Hagelin Feb 1932 380/55
1953918 Cryptographic System and Aparatus April 10, 1934 J.I. Bellamy 380/42 instead of a digraphic cipher, 4 letters are automatically used
1956384 Pocket Cryptographic Aparatus, April 24, 1934,  A. Gentet 380/56 -aka the Sphinx strip ciper device.
1984599 Educational Device Safar Dec 1934 434/228 ; 315/313; 340/332
2013671 Electrical System and Apparatus  for Transmitting Intelligence Sep 10, 1935
2028772 Cryptographic System Jan 28, 1936 Friedman 380/26 ; 380/51 - rotors
2056284 Signaling Means and Aparatus Oct 6, 1936 LeRoy A. MacColl 380/252; 178/63R; 178/69B; 307/106; 380/46 paper tape
2089603 Ciphering Machine Hagelin Aug 1937 380/55 ; 380/58; 400/162; 400/83; 400/88
2098956 Signaling System Dudley, Nov 16, 1937 380/36 ; 379/414; 704/205 - multiple circuit split frequency
2116683 Coding and Decoding Machine WS Lemmon  380/55 ; 400/373; 400/474; 400/477 -
2116731 Coding and Decoding MachineAR Noll  380/55 ; 400/474; 400/478; 400/479; 400/77
2125995 Ciphering Machine R.W. Doidge Aug 9, 1938 380/26
2139676 Cryptographic Apparatus Friedman Dec 1938 380/26 - Enigma like
2140424 Cryptographic Device Friedman Dec 13 1938 380/57 - 29 tooth gear meshing with 40 tooth gear
2151091 Signal Tansmission H.W. Dudley March 21, 1939 (filed 1935) 380/39; 84/701; 84/DIG11; 324/76.12; 324/76.29; 379/414; 704/205; 704/206; 704/209 - a vocoder used to compress speach to about 500 Hz bandwidth
2183248 Wave Translation, RR Riesz, Dec 12, 1939 381/61 ; 333/28R; 380/39; 472/64; 704/205 - also see 3012098

1939 - 1945 W.W. II

1940

2206590 Portable Transmissin System, Webb Jr., Jul 2, 1940 - simble speech inverter
2373890 Cipher Machine E. H. Hebern April 17, 1945 380/51; 400/77; 400/473; 400/474
2401402 Secret Communication System 380/28 - June 4, 1946 (RCA) - voice by using a record (or photographic image) as a key
2402182 Rotor  Jan 18, 1946  L. Rosen 380/26; 380/33; 380/58
2437255 Graphic Privacy System March 9 1948 J V L Hogan 380/54; 355/42; 355/52; 380/37; 380/243; 380/245
2247170 Ciphering Machine Hagelin June 1941 380/55 ; 400/162; 400/89
2265715 Cipher Aparatus H. S. Bacon Dec 9, 1941 380/27; 400/90
2411206 Electrical Signalling Method, Guanella, Nov 19, 1946 380/39 ; 380/38 - Original permuting sub bands, but they can have different bandwidths

1950

1950 - 1953 Korean conflict (aka Police Action)

2510338 Means of and Method for Scrambling Speech Signals, Guanella, Jun 6, 1950 380/39 - sub bands enchnced
2530579 Speech Inverter, L Koros, Nov 21, 1950  380/39 ; 332/153; 332/155
2629017 Speech Transmission System, Dahlbom, Feb 17, 1953 370/503 ; 327/418; 380/39 - uses VOCODER
2709218 Method and Means for Anti-Jamming in Radio, Gabrilovitch, May 24, 1955 455/45 ; 380/39; 455/1; 455/196.1; 455/48; 455/63.1
2765364 Keying Mechanism Hagelin Oct 1956 380/59 ; 380/55; 400/478; 400/89
2851794 Cryptographic Coding and Decoding Aparatus, B. C. W. Hagelin Sep 15, 1968 380/57 - Crypto AG CD-57
2855514 Gaseous Discharge R.F. Noise Source Oct , 1958 331/78; 313/633; 327/164; 327/601; 333/24R (up to 4.5 GHz)
2877565 Electrical Cryptograph, Friedman (M-325)  380/52
2896071 Security Communication System, July 21, 1959 380/39 ; 341/173; 380/260; 380/275 - synch signal embedded in message

1960

1961 - 1975 Vietnam era

3006081 Encoding Keying Device Nyberg Oct 31, 1961 380/59 ; 380/57
3046545  Rapid Correlation Echo Ranging System July 24, 1962 342/189; 342/195; 367/100; 370/521 - Pseudo Random Generator
3124748 Secret Signalling Systems Mar 10, 1964, 380/32 ; 380/34; 380/39 mixing voice bands with changing oscillator
3163809 Random Noise system for Vibration Testing Dec 29, 1964 318/132; 73/579; 327/164; 330/103; 330/126; 331/78 Pholtomultiplier generates noise and a lamp is used in the feedback circuit
3171089 Diode Random Noise Generator Feb 23, 1965 331/78; 327/164; 327/584 avalanche diode in reverse breakdown
3204035 - 370/208; 375/362 Orthonormal Pulse Multiplex Transmissions Systems 26 Nov 1962
3328526 Speech Privacy System Schroeder, Jun 27, 1967 380/39 ; 369/26.01; 455/39 - uses the sub band amplitudes to modulate the phase of that freq.  all the subbands are send at equal amplitude. see Dudley vocoder 2151091
3349882 Ciphering Machine Florin et al Oct 31, 1967 380/57 ; 400/162 - M209 like
3439279 - Synchronizing System for Ramdom Sequence Pulse Generators April 15, 1969

1970

3610828 Privacy Communication Sysyem 380/260; 380/274; 380/275 Oct. 5, 1971
3614316  Secure Communication Sysyem Oct 17, 1971(filed 1964) Secretary of the Navy 380/47; 375/150; 380/34; 380/46
An improved secure communication system comprising: A first and a second pseudorandom noise generator, said generators having,espectively, a first and a second shift register, each register having N stages and having logical circuit means for randomly recirculating binary bits through the register for generating a random repeatable pattern of binary bits, A reset pulse source coupled to all stages of said first register to reset said first register to a predetermined starting binary number, A starting point switch matrix comprising N logical zero-one switches connected, respectively, between the stages of said second register and said reset pulse source, Means for feeding a binary information number to said switches to reset said second register to a starting point a predetermined number different from the starting binary number of said first register, Transmitting means for transmitting said pseudorandom noise generators outputs connected to the outputs of said pseudorandom noise generators; Receiving means for receiving said transmitting means transmissions, said receiving means having an output; Recycling storage means connected to the output of said receiving means for storing the receiving means output signals; A third pseudorandom noise generator identical in sequence to said first and second pseudorandom noise generators having an output and a reset input, said receiving means output connected to said reset input; A correlator having a first input connected to said storage means and a second input connected to said third pseudorandom noise generator output for generating a signal upon correlation of said storage means output and said third pseudorandom noise generator output, and; Timing means connected to said correlator for timing the interval between outputs thereof.  Relates to SONAR.
3618077  Walsh Function Generator - Nov 2, 1971
3639690 Digital Privacy System - Feb 1, 1972 Motorola
3651404 Voice Privacy Adapter - March 21, 1972 frequency inversion - Motorola 380/39 ; 332/168
3678204 - 177/15; 370/209 Signal Processing and Transmission by means of Walsh Functions 26 Oct 1970 ITT
3701143  Walsh Function Generator -
3723878 Voice Privacy Device, Miller, Mar 27, 1973 380/39 ; 380/275; 380/44 - additions to inverter
3742201 - 708/410 Transformer System for Orthogonal Digital Waveforms June 26, 1973
3746799  Method and Apparatus for Encoding and Decoding Analog Signals -
3749832 Binary Coded Signaland Ciphering and Deciphering Method and Systems Embodying Same July 31 1973  380/28; 341/95; 380/37
3766316 Frame Synchronization Detector -
3777064 Voice Privacy System, US Navy, Dec 4, 1973 380/39 - uses active RC low pass filters instead of LC or active LC filters.  uses "Weaver modulator"
3781472 -
3781473 -
3795864 - Methods and Apparatus for Generating Walsh Functions -
3798359 (Lucifer)Block Cipher Cryptographic System 380/37 ; 380/28; 380/29; 380/46
3808536 Communications Scrambler System 380/45; 375/141; 380/46; 380/47- A scrambler system in which amplitude zero-crossings in speech are encrypted at a transmitter by combination with a pseudo-random digital sequence, the reverse process occurring at the receiver. The amplitude envelope need not be encrypted, but if desired, can be encrypted by combination with a further pseudo-random digital sequence. A higher level of scrambling can be achieved in the transmitted signal by using the conjugate of the amplitude envelope.  With a sequence bit rate of about two kilobits per second, there is no increase in bandwidth requirements compared to the transmission of unscrambled speech. Thus standard transceivers can be employed, and pre-existing ones readily modified for scrambling and unscrambling.
3859515 - 708/410; 324/76.12; 324/76.21; 340/5.81; 382/121 Method and Apparatus for Signal Spectrum Analysis by Hadamard Transform Jan 7 1975 Burroughs
3886313 Voice security method and system Datotek, May 27, 1975 380/40 ; 341/181; 380/39
3893031 Synchronization System for Voice Privacy Unit filed Nov 8, 1972 granted July 1, 1975 Henry L. Majeau, Boeing Company, 380/274; 340/146.2; 380/44; 380/262; 380/275 - uses 3 tones for synchronization like the KY-57 - A system for synchronizing the operation of two or more voice privacy units. At least one otherwise "clear" tone is modulated by a statistically random signal known as a Barker word, this tone then being mixed with the audio signals and transmitted. The modulation is present for a very short time, the conclusion of the modulation initiating the operation of a code generator which scrambles the succeeding audio signals. The recognition of the reception of the modulated tone at the receiver initiates the operation of its code generator (at the conclusion of the modulation), thereby recovering the original plaintext speech.  This is a form of speech inversion
3909534 Voice privacy unit for intercommunication systems -
3920894 Pseudo-Random Parallel Word Generator
3934078
3936748
3936749
3937888
3944744 
3944745 
3962539 (DES) Product block cipher system for data security 380/29 ; 380/37; 713/150
3965296 
3965297 
3967067 Secret telephony Filed: Sep 24, 1941 Pat Date June 29, 1976 380/41; 380/40; 704/205 Part of the SIGSALY W.W. II Voice system
3968454
3976839
3979558
3983326
3983327
3984922
3985958 Secret telephony Filed: Dec 18, 1941 Pat: Oct 12, 1976 Part of the SIGSALY W.W. II Voice system
3991271 Voice security method and system - analog
3991273 Speech component coded multiplex carrier wave transmission Filed: October 4, 1943 Pat: Nov 9, 1976 Part of the SIGSALY W.W. II Voice system
3995115 Speech privacy system Bell Labs Nov 30, 1976 380/32 ; 380/275; 380/39; 704/205 Vocoder & removing fund freq
4013837 Voice security method and system - analog
4020285 Voice security method and system - analog
4052565 -
4079188 Multi-mode digital enciphering system
4115657 Random digital code generator - digital multiple registers with relativity prime lengths
4126761 Method of and means for processing an audio frequency signal to conceal intelligility -
4133973 Digital cryptographic system having synchronous and asynchronous capabilities
4133974 System for locally enciphering prime data - digital key generator using a register and addressable memory
4140873 Multi-mode digital enciphering system 
4145568 Method and apparatus for ciphering and deciphering messages 380/47; 380/44; 380/260; 380/277 Pat: March 20, 1979 Filed: October 6, 1964
4145569 Method and apparatus for synchronizing the ciphering and deciphering of binary-coded messages 380/262; 380/47 Pat: March 20, 1979 Filed: December 22, 1964
4149035 Method and apparatus for enciphering and deciphering audio information  -
4154006 Coding and decoding machine Wood; Chester C, May 15, 1979 380/57 ; 341/2 -
4156314 Rotors for a ciphering machine 380/26; 380/51; 439/43 Pat: May 29, 1979 Filed: February 21, 1944 Rosen; Leo 26 contacts
       not KL-7 and not used in any U.S. crypto machine
4157453 Cryptographic telegram transmission system 380/36 Pat: June 5, 1979 Filed: October 10, 1944 Rosen; Leo
4157454 Method and system for machine enciphering and deciphering June 5, 1979 380/37; 380/42; 380/45 (IBM) -
4166922 Multi-mode digital enciphering system with repeated priming sequences
4168395 Start/stop teleprinter scrambler 380/35; 380/43
4167700 Digital voice protection system and method -
4169212 Multi-mode digital enciphering system
4170714 Digital cryptographic system and testing thereof - digital data
4172968 Electrical system 380/43; 380/261; 380/275 digital voice encryption
4176316 Secure single sideband communication system using modulated noise subcarrier 380/34

1980

       Berlin Wall 1961 - 1989

4183088 Random number generator 708/250; 331/78
4184117 Communication security method and system 380/34; 380/35; 455/46
4185166 Multi-mode digital enciphering system - digital: off line, asynchronous or synchronous data
4185928 Printer for electric coding machines 380/55
4188580 - Secure communication system-  380/254; 375/145
4195202 Voice privacy system with amplitude masking -
4200770 - (Public Key) Cryptographic apparatus and method April 29, 1980 380/30; 380/44; 380/285; 713/169; 713/171
4217469 - Coding and decoding apparatus for the protection of communication secrecy 380/27; 380/36 time delay
4218582 (Trapdoor flawed)Public key cryptographic apparatus and method 380/30 ; 713/168; 713/170
4229817 Portable electronic cryptographic device - alpha numeric digital keypad & display
4232194 Voice encryption system, Adams, Nov 4, 1980 380/28 ; 380/257; 380/275; 380/39; 704/205 - using DSP methods to provide more sub bands
4244053 Privacy communication method and system -
4268720 Scrambler speech transmission and synchronization system -
4276652 Secure communication system with improved frequency-hopping arrangement - variable BFO
4278840 Dynamic frequency and time voice encryption system and method - analog
4309569 (tree authentication) Method of providing digital signatures 713/177 ; 340/5.8; 713/180; 902/2; 902/5
4316055 - Stream/block cipher crytographic system February 16, 1982 380/37; 380/43; 380/45
4341925 - Random digital encryption secure communication system - combine two PR code streams
4349695 Recipient and message authentication method and system - two way pass & CRC at end
4351982 RSA Public-key data encryption system having large random prime number generating microprocessor or the like September 28, 1982 380/30; 380/282; 380/285 (Racal-Miglo Datacryptor64)
4386233 Crytographic key notarization methods and apparatus 380/281 ; 380/280; 380/45; 713/155; 713/180; 902/2; 902/5
4392021 Secure facsimile transmission system using time-delay modulation - FAX
4405829 (RSA) Cryptographic communications system and method Sep 20, 1983 380/30; 380/255; 713/150; 713/151 (Racal-Miglo Datacryptor64)
4424414 Exponentiation cryptographic apparatus and method 380/30 ; 380/285; 380/44; 713/171
4433211 Privacy communication system employing time/frequency transformation
4434322 Coded data transmission system Feb 28, 1984 380/43; 380/44; 380/265 (Racal-Miglo Datacryptor64)
4567600 Method and apparatus for maintaining the privacy of digital messages conveyed by public transmission 713/174 ; 380/278; 380/285; 380/33
4625076 (ESIGN signatures) Signed document transmission system 713/176 ; 380/30; 713/180
4633036 (Prime 3 Gen)Method and apparatus for use in public-key data encryption system 380/30 ; 380/277; 902/2
4748668 Method, apparatus and article for identification and signature 380/30 ; 380/28
4754482 Method and apparatus for synchronizing encrypting and decrypting systems June 28, 1988 713/181; 380/262; 714/798
4850017 Controlled use of cryptographic keys via generating station established control values 380/280 ; 380/281; 380/45; 380/47
4850019 Data randomization equipment 380/29 ; 380/33; 380/37; 380/46
4856063 No-overhead synchronization for cryptographic systems August 8, 1989 380/262- Datotek

1990

4881264 Digital signature system and method based on a conventional encryption function 713/177 ; 380/28; 713/180
4893339 Secure communication system January 9, 1990
4908861 Data authentication using modification detection codes based on a public one way encryption function 713/187 ; 340/5.8; 380/29; 380/30; 726/2
4956863 Cryptographic method and apparatus for public key exchange with authentication 380/30 ; 380/285; 380/44; 380/47; 713/169; 713/171
4995082 Method for identifying subscribers and for generating and verifying electronic signatures in a data exchange system 713/169 ; 380/30; 380/46; 705/67; 713/180
5003597 Method and apparatus for data encryption 380/37 ; 380/28; 380/29
5003599 In-band framing method and apparatus
5016274 On-line/off-line digital signing 705/66 ; 235/379; 235/380; 340/5.4; 380/29; 380/30; 713/180
5140634 Method and apparatus for authenticating accreditations and for authenticating and signing messages 713/180 ; 235/382; 380/30; 705/67; 713/172
5146498 Remote key manipulations for over-the-air re-keying - based on modifying the current stored ket to make the new one
5214703 Device for the conversion of a digital block and use of same 380/37 ; 380/28; 380/42
5222136 Encrypted communication system 380/266; 380/29; 380/43; 380/284
5231668 Digital signature algorithm 380/28 ; 380/30
5237611 Encryption/decryption apparatus with non-accessible table of keys 380/284; 380/30; 380/44; 380/45; 380/243; 713/181; 713/194
5276737 Fair cryptosystems and methods of use 380/30 ; 380/286
5278907Analog scrambling with continuous synchronization - Audio Samples -
5299262 Method for exponentiating in cryptographic systems 380/28 ; 380/30; 713/168; 713/174; 713/180
5301247 Method for ensuring secure communications 380/43; 380/46; 380/47; 380/277; 380/284
5305384 Apparatus, system and method for transmitting secure signals over narrow spaced channels -300 Hz to 3200 Hz spaced 11.4 kHz
5311176  Method and apparatus for generating Walsh codes -
5363376 Method and apparatus for synchronizing timing among radio ports in wireless communications systems
5428686 - Secure communication system having long-term keying variable -  NSA patent about mixing a key held in the scrambler with a key sent over the air.
5455861 Secure telecommunications - using encryptation only over part of the comm path
5528693 Method and apparatus for voice encryption in a communications system
5787180 Method of connecting a scrambler or encryption device to a hand-held portable cellular telephone - mike and spkr connections
5822430 System for encoding encryption/decryption information into IFF challenges Oct 13, 1998 380/260; 342/45; 380/274; 380/277
5852803 Apparatus, System and Method for Recording and/or Retrieving Audio Information Dec 22, 1998 704/270; 704/272 (talking label)

2000

6097812 Cryptographic system Friedman Aug 1, 2000 380/26 ; 341/50; 341/90; 341/91; 380/287; 380/52; 380/56; 380/57; 380/59
6130946 Cryptographs Friedman Oct 10, 2000 380/26 ; 341/50; 341/90; 341/91; 380/287; 380/52; 380/56; 380/57; 380/59
6175625 Control circuits for electric coding machines 380/26 ; 341/50; 341/90; 341/91; 380/287; 380/52; 380/56; 380/57; 380/59

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