JP2005197786A - Encryption cellular phone system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an encryption cellular phone system which is excellent in appearance confidentiality, can flexibly cope with a model change of a cellular phone, and in addition, is excellent in reliability. <P>SOLUTION: A cellular phone terminal in a figure is composed of a commercially available cellular phone 9 and a secret device positioned as a post-stage connection terminal of the cellular phone 9. The secret device is composed of a portable type secret device body 1 physically separated from the cellular phone 9, and a cellular phone set wired connection unit 2 directly connected to a receptacle 91 as the post-stage interface of the cellular phone 9. The body 1 communicates with the unit 2 by feeble radio. Since the body 1 exhibits an external appearance similar to that of a commercially available cellular phone, a third person recognizes it as the commercially available cellular phone. The cellular phone 9 with the unit 2 is put into a pocket or a bag of a caller. The caller makes a call by a microphone and a speaker of the body 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a mobile encryption telephone system that enables a secret call by encrypting sound collected by a microphone of a mobile phone using a secret talk device, and in particular, a portable type positioned as a rear connection terminal of a commercially available mobile phone. This is related to a mobile cryptographic telephone system in which the secret talk device is physically separated from the commercial mobile phone.

  FIG. 14 is a schematic diagram for explaining a conventional general cellular phone system. As shown in this figure, when an audio signal is transmitted as raw (plaintext) without being encrypted, it may be wiretapped at various points on the signal transmission path. Therefore, a secret call system that encrypts an audio signal and transmits it as an encryption that cannot be understood by others even if it is wiretapped has already been put into practical use. The secret call system is realized by providing a secret telephone device in a mobile phone terminal and encrypting and decrypting voice by the secret telephone device.

  Back number 2003-11-20 of Internet homepage Mainichi INTERACTIVE Mobile (URL: http://www.mainichi.co.jp/digital/mobile/archive/200311/20/2.html) The following article was published on the mobile cryptographic telephone system.

■ German manufacturer launches mobile phone that cannot be tapped
German mobile phone maker GSMK has recently released a mobile phone that can't be sniffed by encrypting the call. Calls can be made between mobile phones of the same type or with a personal computer with dedicated software installed, making it impossible for third parties to know the contents. It sells to users who handle important information, such as company tops, lawyers, and journalists.

  It is named “Cryptophone” and is sold through a subsidiary of the same name. The first product, GSMK Cryptophone 100, is based on a GSM mobile phone using Microsoft's Pocket PC 2002 OS for mobile phones. By instantly encrypting the voice and decrypting it on the receiving side, the eavesdropping is completely shut out. It also supports TCP / IP communication and can talk with a personal computer. PC software is available for download from the website.

  The company has released the source code of voice encryption software, allowing users to check their own security. The price is 3499 euros (about 455,000 yen) for one set, and 1899 euros (about 247,000 yen) for one set. In the future, we are considering commercializing embedded Linux, Symbian, and Palm OS platforms.

Several other manufacturers are developing mobile phones with encryption capabilities, but according to GSMK, cryptophones have been designed to prevent eavesdropping on investigators. On the other hand, security experts have pointed out that there are concerns about crimes.
[GSMK Cryptophone 100]
http://www.cryptophone.de/html/products_en.html [Non Patent Literature 1]
[Cryptophone]
http://www.cryptophone.de/

Mainichi INTERACTIVE The mobile article is as above. From the description of the product on the [GSMK Cryptophone 100] homepage, the encryption method of the mobile phone system can be summarized as follows.
(1) Exchange encryption keys using a 4096-bit DH (Diffie-Hellman) key exchange method.
(2) Provide an anti-tampering function by attaching an authenticator called SHA256.
(3) Voice messages are encrypted with AES encryption or Twofish encryption.
(4) The continuous cryptographic call time is 3 hours and 15 minutes, and the flat call time is 3 hours and 30 minutes.

  The function (2) used in the GSMK cryptophone 100 is not a new method but a basic VPN (virtual private network). Voice messages are encrypted with AES encryption or Twofish encryption. AES is the next generation encryption recommended by the US government, and Twofish is a widely used encryption in Europe, both of which are known encryption methods. .

  As another conventional mobile cryptographic telephone device, the Internet homepage (URL: http://www.cellular.co.za/phones/siemens/archive/siemens_topsec_703_secure.htm [Non Patent Literature 2]) includes Siemens TopSec 703 There is a mobile encryption phone called Secure GSM Phone.

  The above-mentioned GSMK cryptophone 100 and Siemens TopSec 703 Secure GSM Phone encrypt the voice in the mobile phone on the transmitting side and encrypt the voice in the mobile phone on the receiving side. A decoding device).

  Japanese Patent Application Laid-Open No. 11-112492 [Patent Document 1] is a name of the invention of an encryption / decompression apparatus system, and there is a public key encryption / restoration method that allows only a receiver to restore a cipher with its own unique key. It is disclosed. Also in Patent Document 1, as in the two conventional mobile cryptographic telephone systems, the explanation is made on the assumption that the secret talk device is mounted inside the mobile phone.

JP-A-11-112492 http://www.cryptophone.de/html/products_en.html http://www.cellular.co.za/phones/siemens/archive/siemens_topsec_703_secure.htm

  In the conventional portable encryption telephone system described above, the secret talk device is built in the mobile phone. However, in the system in which the secret device is built in the mobile phone, it is necessary to update the secret device integrally whenever the mobile phone is updated. For example, when changing the communication company to join, if the communication standard of the communication company is different, it is necessary to change the mobile phone. Examples of communication standards include PDC, CDMA, PHS, and the like. PDC is adopted by NTT DoCoMo and J Phone (currently Vodafone) as Japan's original digital cellular phone standard. CDMA is a standard adopted by the AU group and is used in many countries and regions. PHS is used not only in Japan but also overseas as a simplified mobile phone standard. In addition, the technological progress of mobile phones is rapid, and the frequency of updates is actually quite high. Therefore, the method of incorporating the secret talk device in the mobile phone has a drawback that the selection of the mobile phone lacks flexibility.

  Therefore, a method of separating the secret talk device from the mobile phone can be considered. FIG. 13 shows a configuration example of a mobile phone terminal in which the secret talk device is separated from the mobile phone in this way. FIG. 2A shows a configuration in which the secret talk device 101 is directly connected to a receptacle which is a rear interface of the commercial mobile phone 9. FIG. 2B shows a configuration in which the plug 7 is connected to a receptacle which is a rear interface of the commercially available mobile phone 9, and the plug 7 is connected to the secret talk device 101 with a cable 35. This figure (C) has a configuration in which the secret talk device 100 is provided with a key panel unit 100a composed of a numeric keypad and a switch, a microphone 100b, and a speaker 100c, and the secret talk device 100 itself can make a call without the handset 102. Show. In each configuration of FIG. 13, the secret talk device is in a position as a rear connection terminal of the commercial mobile phone 9, and is connected to a receptacle which is a rear interface of the commercial mobile phone 9 by wire.

  The mobile cryptographic telephone system of FIG. 13 can flexibly cope with the mobile phone model change as compared with the system in which the secret device is built in the mobile phone. When there is a change in the receptacle, the plug and cable connected to the receptacle are connected. It is enough to change it. However, in the mobile cryptographic telephone system shown in FIGS. 13A and 13B, since it is possible for other people to see that the secret device 101 and the handset 102 are outside the mobile phone 9, a special call that is not a normal call can be made. It is known to others that it is doing, and lacks the confidentiality of the appearance of the secret call.

  In the mobile cryptographic telephone system of FIG. 13 (C), the appearance of the secret talk device 100 is the same as that of the portable phone, but since other people can see that the cable 37 extends from the secret talk device 100, it is not a special call that is not a normal call. The other person knows that he / she is making a call, and still lacks the confidentiality of the secret call.

  13B and 13C, the mobile phone 9 and the secret talk device 101 or 100 are connected by a cable 35 or 37. The number of cores of the cable connecting the mobile phone and the rear connection terminal is 16 for PDC, 18 for CDMA, and 12-16 according to the standard for PHS. As described above, since the number of cores is considerably large, the cable 35 or 37 and the collector are vulnerable to bending and external force, and there are many opportunities to apply various external forces in the portable device. The mobile cryptographic telephone system of C) lacks reliability.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a mobile cryptographic telephone system that has excellent appearance confidentiality, can flexibly cope with a model change of a mobile phone, and is excellent in reliability.

  The present invention provides the following means in order to solve the aforementioned problems.

(1) In a mobile cryptographic telephone system in which an encryption / decryption means is provided in a mobile phone terminal and a digital audio signal encrypted by the mobile phone terminal is communicated,
The mobile phone terminal is composed of a commercial mobile phone and a secret talking device positioned as a rear connection terminal of the commercial mobile phone,
The secret talk device includes a portable first device physically separated from the mobile phone, and a second device connected to the mobile phone terminal directly or via a cable in a wired manner. ,
The first device includes the numeric keypad, microphone, and speaker, is similar in appearance to a commercially available mobile phone, and includes the encryption / decryption means.
The first device and the second device communicate with a radio wave having a weak electric field strength, input the output of the encryption / decryption means to the commercial mobile phone, and for a later connection terminal of the commercial mobile phone A portable cryptographic telephone system, wherein an output is input to the encryption / decryption means.

(2) A first device that includes a numeric keypad, a microphone, and a speaker and that is similar in appearance to a commercially available mobile phone, and a second device that is connected to a rear interface of the commercially available mobile phone directly or via a cable in a wired manner And
The first and second devices respectively include first and second transmission / reception means for transmitting and receiving each other with radio waves having weak electric field strengths.
The first device generates encrypted voice data by performing digitization and encryption processing on a voice signal output from the microphone, and transmits the encrypted voice data by the first transmission / reception means. And performing decryption and analog processing on the encrypted audio data transmitted from the second transmitting / receiving means, generating an analog audio signal, and inputting the analog audio signal to the speaker;
The second device supplies the encrypted voice data output from the rear interface to the second transmission / reception means, and the encrypted voice data output from the second transmission / reception means to the rear interface. A mobile cryptographic telephone system characterized by supply.

  According to the above configuration, it is possible to provide a mobile cryptographic telephone system that has excellent appearance confidentiality, can flexibly cope with a model change of a mobile phone, and is excellent in reliability.

  Next, the portable encryption telephone system of the present invention will be described. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention. FIG. 2 is an external view showing the embodiment (A) of FIG. 1 and a modification (B) of the embodiment. FIG. 3 is a diagram for explaining the usefulness of the embodiment of FIG. FIG. 4 is a diagram showing the allowable electric field strength of the weak radio station according to the frequency. FIG. 5 is a diagram for explaining a disadvantage of the configuration in which the weak wireless communication path between the secret device main body and the mobile phone wired connection unit in the embodiment of FIG. 1 is changed to a cable. FIG. 6 is a diagram for conceptually explaining three services by a mobile phone. FIG. 7 is a diagram for explaining audio data encryption / decryption processing in the embodiment of FIG. FIG. 8 is a diagram for explaining a frame generation method in the embodiment of FIG. FIG. 9 is a diagram for explaining a mechanism for re-encoding audio data in the embodiment of FIG. FIG. 10 is a diagram for explaining two usage modes of the encryptor in the embodiment of FIG. FIG. 11 is a diagram for explaining a frame disassembling method in the embodiment of FIG. FIG. 12 is a diagram for explaining the safety of secret communication in the embodiment of FIG.

  The mobile cryptographic telephone system of the present invention includes an encryption / decryption means in a mobile phone terminal, and communicates a digital audio signal encrypted by the mobile phone terminal. In the embodiment of the present invention shown in FIG. 1, the mobile phone terminal includes a commercially available mobile phone 9 and a secret communication device positioned as a rear connection terminal of the commercially available mobile phone 9. The secret talk device includes a portable secret talk device main body 1 physically separated from the commercial mobile phone 9, and a mobile phone wired connection unit 2 directly connected to a receptacle 91 as a rear interface of the commercial mobile phone 9. It is equipped with. The mobile phone wired connection unit 2 includes a plug 24 at one end, and is connected to the receptacle 91 of the commercially available mobile phone 9 with the plug 24.

  The secret device main body 1 includes a key switch unit 31 including a keypad and other switches, a microphone 32, and a speaker 33, and is similar in appearance to a general mobile phone, and includes an encryption transmission / reception unit 10. The encryption transmission / reception unit 10 includes encryption / decryption means and a transmission / reception unit. The encryption / decryption means includes an ADPCM 11, a compression unit 12, a frame generation / encryption unit 13, a serial communication interface 14, a frame disassembly / decryption unit 16, and an expansion unit 17. The transmission / reception unit is a weak wireless transmission / reception module 15. The key switch unit 31, the microphone 32, and the speaker 33 are connected to the ADPCM 11. The ADPCM 11 converts the analog audio signal output from the microphone 32 into a digital audio signal, and supplies the digital audio signal to the compression unit 12. The ADPCM 11 converts the digital audio signal output from the expansion unit 17 into an analog audio signal and inputs the analog audio signal to the speaker 33.

  As the ADPCM 11, the compression unit 12, and the decompression unit 17, for example, VP110 manufactured by VoicePump and AMBE-1000 manufactured by Digital Voice Systems, Inc. are known, such as http://www.voicepump.com, http: // www The specifications are shown at .dvsinc.com / products / a1000.htm or http://www.dvsinc.com/products.htm. Various commercially available products can also be used as the weak wireless transmitter / receiver module 14. For example, overseas manufacturers show various products at http://www.rfm.com/products/vwire.htm, and Japanese manufacturers also have http: // Various products are disclosed on www.itec-corp.co.jp/products/index.html. The serial communication interface 14 can be composed of many general-purpose products that are commercially available. The frame generation / encryption unit 13 and the frame disassembly / decryption unit 16 are a microprocessor, a RAM, a memory composed of CompactFlash (registered trademark), and a program mounted on these hardware. The operation will be described in detail later.

  The cellular phone wired connection unit 2 includes a weak wireless transmission / reception module 21, a cellular phone modem 23, and a plug 24. As the weak wireless transmission / reception module 21, the same module as the weak wireless transmission / reception module 15 can be used. As the cellular phone modem 23, for example, ML-7070 series (ML-7070-01, etc.) manufactured by Oki Electric Co., Ltd. can be used. Http://www.oki.com/jp/Home/JIS/New/OKI-News/2001 The specification is disclosed in /01/z2k89.html.

  2A shows the appearance of the embodiment of FIG. 1, and FIG. 2B shows a mobile phone in which the mobile phone wired connection portion 2 is connected to the receptacle of the commercial mobile phone 9 through the cable 20 and the plug 8. Shows the appearance of the terminal. The mobile phone terminal of FIG. 2B has a configuration obtained by modifying FIG. However, the configuration of FIG. 2B is the same as the configuration of FIG. 2A in that the mobile phone wired connection unit 2 is connected to the receptacle of the commercial mobile phone 9 by wire.

  FIG. 3 conceptually illustrates the usefulness of the embodiment of FIG. In this embodiment, the secret talk device main body 1 is wirelessly connected to the commercial mobile phone 9 via the mobile phone wired connection unit 2 and has the same appearance as a general commercial mobile phone. If the commercially available mobile phone 9 with the connection part 2 is stored in a pocket or a bag, the surrounding people recognize the secret device body 1 as a commercially available mobile phone. Therefore, the surrounding people do not realize that the phone call by the secret device main body 1 is a secret phone obtained by encrypting the voice signal, and thus the caller by the secret talk device main body 1 is not suspicious.

  FIG. 4 is a table (A) and a graph (B) showing the electric field strength of weak radio waves defined in Article 6 No. 1 of the Radio Law Enforcement Regulations as radio stations that do not require a license for each frequency range. This electric field strength is a value at a distance of 3 meters from the radio equipment. In the embodiment of FIG. 1, communication between the secret talk device main body 1 and the mobile phone wired connection unit 2 is performed with radio waves having electric field strength in the range shown in the figure, that is, a range that does not require a license. The commercially available mobile phone 9 with the mobile phone wired connection unit 2 is stored in a pocket of a caller (person who holds the secret device main body 1) or a hand bag. Therefore, the distance between the secret device main body 1 and the cellular phone wired connection unit 2 is usually within a few meters, and the secret talk device main body 1 and the cellular phone wired connection unit 2 with radio waves having an electric field strength within the range shown in FIG. Communication with is sufficient. However, the electric field strength of the weak radio wave used for communication between the secret talk device main body 1 and the cellular phone wired connection unit 2 may be arbitrarily selected within the range of the size allowed by the law and the like, and the value is inevitably large. Nor is it preferable. In short, assuming the distance between the secret device main body 1 and the mobile phone wired connection unit 2, the electric field strength is selected as a legal value that can be updated.

  FIG. 5 is a diagram conceptually showing a case where the communication path between the secret talk device main body 1 and the mobile phone wired connection unit 2 is changed from wireless to wired, and the wired is realized by an 18-core cable 6. As described above with reference to FIG. 13, the number of cores of the cable connecting the mobile phone and the rear connection terminal is 16 for PDC, 18 for CDMA, and 12-16 for PHS. If the main unit 1 and the mobile phone wired connection unit 2 are connected by a wired cable 6, the required number of cores of the cable 6 is still 16 for PDC, 18 for CDMA, and 12-16 for PHS. It is. The disadvantage of the configuration in which both portable devices are connected by a cable is as described with reference to FIG. In the embodiment of the present invention shown in FIG. 1, since the communication path between the secret talk device main body 1 and the mobile phone wired connection unit 2 is configured with weak radio, the secret talk device main body 1 can be moved easily, In addition to excellent convenience, there is no risk of failure such as poor contact between the cable and the plug or between the plug and the receptacle, and the reliability is excellent.

  FIG. 6 conceptually shows three communication services in the digital cellular phone system. As shown in FIGS. (A), (B), and (C), the three communication services are a voice service, a digital data communication service, and a packet communication service, and each mobile phone company provides at least these three services. providing. A normal call is performed using a voice service, and mail transmission / reception and Internet access are performed using a packet communication service (for example, I-mode). When using the digital data communication service, a mobile phone terminal is configured in which a rear connection terminal 90 is connected to a receptacle 91 as a rear interface of the mobile phone 9 via a cable 93, and communication is performed by this mobile phone terminal. (In FIG. 6B, illustration of the plug connected to the receptacle 91 is omitted). In the digital data communication service, the output data of the rear connection terminal 90 is transmitted to the rear connection terminal in the mobile phone terminal having the same configuration on the other party and transmitted from the rear connection terminal on the other party. Is received by the rear connection terminal 90. FIG. 6B illustrates a configuration in which a commercially available mobile phone 9a provided with a computer 104a as the rear connection terminal 90 and a commercially available mobile phone 9b provided with the computer 104b as the rear connection terminal 90 are illustrated. is there.

  The secret telephone (secret communication) performed in the embodiment of FIG. 1 is performed by the digital data communication service of FIG. By using the digital data communication service of FIG. 6B instead of the voice service of FIG. 6A for voice communication, the following advantages arise.

(1) A portable secret device (the secret device main body 1 in FIG. 1) physically separated from the mobile phone can be provided as a rear connection terminal of the mobile phone, and as a result, the hardware and software of the mobile phone. An independent mobile phone terminal can be realized.
(2) Since advanced digital audio compression technology can be introduced, miniaturization is facilitated, and the implementation of a portable cryptographic telephone terminal is facilitated.
(3) When the portable secret device (the secret device main body 1 in FIG. 1) physically separated from the cellular phone is lost, there is a possibility that another person impersonates the legitimate owner and misuses the secret device. However, by setting the unique number of the mobile phone corresponding to the secret device in the password of the secret device in advance, the secret device can be prevented from communicating with a mobile phone other than the mobile phone having the unique number. So you can prevent abuse in the previous term.
(4) It becomes easy to introduce advanced encryption technology in the computer network field such as the Internet.
(5) Key exchange scheme Diffie-Hellman, public key scheme RSA, etc. can be easily introduced.

  Next, frame generation, encryption, decryption, and frame disassembly in the frame generation / encryption unit 13 and frame disassembly / decryption unit 16 in the embodiment of FIG. 1 will be described with reference to FIGS. . Data processing such as frame generation, encryption, decryption, and frame disassembly is performed by a computer program that operates on the microprocessor of the frame generation / encryption unit 13 and the frame disassembly / decryption unit 16.

  FIG. 7 is a diagram illustrating the concept of encryption and decryption of audio data in the frame generation / encryption unit 13 and the frame disassembly / decryption unit 16. FIG. 6A schematically illustrates a plaintext data stream of 25 bytes per frame received from the compression unit 12 and 34 frames per second, and FIG. 5B illustrates a frame generation / encryption unit 13 on the transmission side. (C) schematically shows the decryption process in the frame disassembly / decryption unit 16 on the receiving side. The encryption device 50 is a common key encryption device shown in FIG. The frame generation / encryption unit 13 receives plaintext audio data from the compression unit 12, performs re-encoding processing on the plaintext audio data, generates re-encoded audio data, and generates 23-byte re-encoded audio data. A 1-byte delimiter and a 1-byte authenticator are added to generate a 25-byte plaintext frame, and the 23-byte re-encoded audio data in each plaintext frame is encrypted, and the encrypted frame ( (Encryption frame) is generated, and a data stream including the encryption frame is output to the serial communication interface 14.

  FIG. 8 shows frame generation processing in the frame generation / encryption unit 13. One frame is composed of a 1-byte frame delimiter, 23-byte re-encoded audio data, and a 1-byte authenticator. The 23-byte re-encoded audio data in FIG. 8A is data generated by processing the audio data obtained from the compression unit 12 by the method shown in FIG. As shown in FIG. 8B, a 1-byte frame delimiter is added to the head of the 23-byte re-encoded audio data. In the frame delimiter (which may be simply abbreviated as “delimiter”), the first bit of the byte is always “1” as shown in FIG. On the other hand, the first bit of each byte in the re-encoded audio data is always “0”. Therefore, a byte whose first bit value is “1” is recognized as a delimiter, and frames can be divided. The authenticator is 1-byte data output from the encryptor 50 when 23-byte re-encoded audio data is input to the encryptor 50 by the method of FIG. 10C, and the 23-byte re-encoded audio data. Appended to the end of Thus, the 25-byte plaintext frame shown in FIG. The 23-byte re-encoded audio data in the 25-byte plain text frame is input to the encryptor 50 by the method shown in FIG. 10B, converted into encrypted re-encoded audio data, and thus 25 bytes shown in FIG. 8C. Encryption frames are constructed.

  FIG. 9 is a diagram for explaining a re-encoding mechanism. The purpose of re-encoding is to redistribute the code space of the audio data and avoid collisions with delimiters. The data stream of the audio data before conversion shown in FIG. 9 (A) is the audio data obtained from the compression unit 12 and is divided into 7-bit units, and “0” is added to the head of each 7-bit. A new data stream is generated with 8 bits (1 byte). The data stream of the audio | voice data (recoded audio | voice data) after conversion is shown. The first bit of all bytes of the new data stream is “0”, and “1” is not possible. That is, each byte of all the encoded audio data is gathered to a value of 0 to 127 by the above processing. Therefore, if a byte (character string or the like) having a leading bit of “1” is inserted into a new data stream, the inserted bytes (character string or the like) are 128 to 255, and thus function as a delimiter. FIG. 9C shows a data stream in which a 1-byte delimiter “11111111” is inserted into the data stream of FIG.

  FIG. 10 is a diagram for explaining how to use the common key encryptor 50 built in the frame generation / encryption unit 13 and the frame disassembly / decryption unit 16. The common key is also called an encryption key. As shown in FIG. 10A, the common key encryptor 50 (which may be simply abbreviated as “encryptor”) has the plaintext (Plain Data) and the encryption key (key) as inputs. Outputs encryption data. The encryptor 50 can be used as shown in FIGS. 5B and 5C by selecting input data. “1 byte fixed data” in FIG. 10C is fixed 1 byte data stored in advance in the frame generation / encryption unit 13 and is the same data in one secret communication system as a whole. With the method shown in FIG. 10C, for one re-encoded audio data, only one 1-byte authenticator corresponding to the re-encoded audio data is generated.

  FIG. 11 shows a frame disassembly method performed by the frame disassembly / decoding unit 16 in FIG. The frame disassembly / decoding unit 16 recognizes the head of each frame with a delimiter, cuts out the frame, and decodes the encrypted re-encoded audio data in the frame. The frame disassembly / decoding unit 16 generates an authenticator for the decoded re-encoded audio data by the method of FIG. 10C and compares it with the received authenticator. If the authentications match, it is determined that the data has been correctly received, reverse-recoded (8 bits → 7 bits) speech processing is performed, reverse-recoded speech data is output to the decompressor 17, and further converted to analog by the ADPCM11. Then, an analog audio signal is sent to the speaker 33 and uttered. If the authenticators do not match, it is determined that there has been a transmission error or tampering with the communication path, the frame is discarded, and the immediately preceding frame is used for speech.

  FIG. 12 conceptually shows the security of secret communication in the embodiment of FIG. Since voice data is encrypted everywhere in one secret communication system, even if communication is intercepted, since the intercepted data can only be heard as noise, the voice data is not decrypted.

It is a figure which shows the structure of embodiment of this invention. It is an external view which shows embodiment (A) of FIG. 1 and the modification (B) of the embodiment. It is a figure explaining the usefulness of embodiment of FIG. It is a figure which shows the allowable electric field strength of a weak radio station according to a frequency. It is a figure explaining the disadvantage of the structure which changes the weak radio | wireless communication path of the secret talk apparatus main body and mobile telephone wired connection part in embodiment of FIG. 1 into a cable. It is a figure which illustrates notionally three services by a mobile telephone. It is a figure explaining the encryption / decryption process of the audio | voice data in embodiment of FIG. It is a figure explaining the production | generation method of the flame | frame in embodiment of FIG. It is a figure explaining the mechanism of the re-encoding of the audio | voice data in embodiment of FIG. It is a figure explaining two usage modes of the encryption device in embodiment of FIG. It is a figure explaining the dismantling method of the frame in embodiment of FIG. It is a figure explaining the safety | security of the secret communication in embodiment of FIG. It is an external view which shows the example of a structure which provides a secrecy apparatus separately from a commercially available mobile telephone, and connects a commercially available mobile telephone and a secret talk device by wire. It is a figure explaining the confidential maintenance difficulty of communication in the mobile telephone system which communicates by the audio | voice signal which is not encrypted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Secret device main body 2 Mobile telephone wired connection part 6 Cable 7,8 Plug 9,9a, 9b Commercial mobile telephone 10 Encryption transmission / reception part 11 ADPCM
12 compression unit 13 frame generation / encryption unit 14 serial communication interface 15 weak wireless transmission / reception module 16 frame disassembly / decryption unit 17 expansion unit 20 plug 21 weak wireless transmission / reception module 23 mobile phone modem 24 plug 31 key switch unit ( Numeric keypad and switch)
32 Microphone 33 Speaker 35, 37 Cable 50 Encryptor 90 Rear connection terminal 91 Receptacle 92 Plug 93 Cable 100, 101 Secret talk device 100a Key switch part (keypad and key)
100b Microphone 100c Speaker 102 Handset 104a, 104b Computer 105a, 105b Adapter 191 Base station 201, 202 Mobile phone network 203 Relay station

Claims (2)

In a cellular phone system comprising a mobile phone terminal with encryption / decryption means for communicating digital audio signals encrypted by the mobile phone terminal,
The mobile phone terminal is composed of a commercial mobile phone and a secret talking device positioned as a rear connection terminal of the commercial mobile phone,
The secret talk device includes a portable first device physically separated from the mobile phone, and a second device connected to the mobile phone terminal directly or via a cable in a wired manner. ,
The first device includes the numeric keypad, microphone, and speaker, is similar in appearance to a commercially available mobile phone, and includes the encryption / decryption means.
The first device and the second device communicate with a radio wave having a weak electric field strength, input the output of the encryption / decryption means to the commercial mobile phone, and for a later connection terminal of the commercial mobile phone A portable cryptographic telephone system, wherein an output is input to the encryption / decryption means. A first device that includes a numeric keypad, a microphone, and a speaker, and that is similar in appearance to a commercially available mobile phone, and a second device that is connected to a rear interface of the commercially available mobile phone directly or via a cable in a wired manner ,
The first and second devices respectively include first and second transmission / reception means for transmitting and receiving each other with radio waves having weak electric field strengths.
The first device generates encrypted voice data by performing digitization and encryption processing on a voice signal output from the microphone, and transmits the encrypted voice data by the first transmission / reception means. And performing decryption and analog processing on the encrypted audio data transmitted from the second transmitting / receiving means, generating an analog audio signal, and inputting the analog audio signal to the speaker;
The second device supplies the encrypted voice data output from the rear interface to the second transmission / reception means, and the encrypted voice data output from the second transmission / reception means to the rear interface. A mobile cryptographic telephone system characterized by supply.

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