WO2009067322A1

WO2009067322A1 - Method and apparatus for encrypting and decrypting encoded audio information

Info

Publication number: WO2009067322A1
Application number: PCT/US2008/081557
Authority: WO
Inventors: Jing Wang; John P. Belmonte; Samuel Chia
Original assignee: HU LIN (SUNNY); General Instrument Corp
Current assignee: HU LIN (SUNNY); Arris Technology Inc
Priority date: 2007-11-19
Filing date: 2008-10-29
Publication date: 2009-05-28
Anticipated expiration: 2010-05-19

Abstract

A method and apparatus for encrypting and decrypting audio information encodes audio to form encoded audio information, separates the encoded audio information into a class of sensitive encoded audio information and a class of insensitive encoded audio information, encrypts the insensitive encoded audio information to form encrypted encoded audio information, and transmit or write to memory the sensitive encoded audio information and the encrypted encoded audio information. Furthermore, an encoded audio information signal may be received or read from memory that includes encrypted insensitive encoded audio information and non-encrypted sensitive encoded audio information; the encrypted insensitive encoded audio information may be decrypted to form decrypted encoded audio information; the decrypted encoded audio information may be combined with the encoded sensitive audio information to form received or read encoded audio information; and the encoded audio information may be decoded to form received or playback audio.

Description

METHOD AND APPARATUS FOR ENCRYPTING AND DECRYPTING ENCODED AUDIO

INFORMATION

Field of the Disclosure

[0001] The present disclosure relates generally to encoded audio communications and more particularly to the encryption of audio communications.

Background

[0002] There exist systems in which digitally encoded audio signals are encrypted before transmission or storage in order to ensure privacy. Encryption has been used for such systems wherein the encoding technique that is used is lossy (for which myriad techniques have been developed over the last 15 years) and those in which the encoding technique is substantially not lossy (for example, the μlaw encoding used in legacy telephone systems). Due to the high value of radio spectrum and memory resources and the reduced cost of processing resources, many voice and music audio encoding schemes use compression techniques that are lossy. These compression techniques may be designed to correct for a certain amount of errors that may be expected for the type of channel through which the encoded signal is to be sent. In either situation (lossy or lossless audio encoding), and regardless of whether the encoding can correct for a certain amount of channel induced errors, if a receiving or playback device uses improper decryption, the audio rendered by the receiving or playback device is likely to be irritating and perhaps harmful to a listener, especially when it is unexpected. Improper decryption can mean either no decryption key is used, or an incorrect decryption key is used, or an incorrect decryption algorithm is used. This may not be an issue when the listener is an unauthorized listener, but when the listener is an authorized or an innocent bystanding listener, this effect may imbue the product that receives the audio with an undesirable characteristic. For example, an authorized listener may inadvertently select a wrong key from a set of keys the listener is authorized to use. In another example, a sender may only be able to conveniently send an encrypted audio transmission to a group who will all receive the audio, but certain members of the group may not be authorized to decrypt the audio. These situations are undesirable.

Brief Description of the Figures

[0003] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.

[0004] FIG. 1 is a block diagram of a portion of a communication system that comprises an audio transmitting device, an audio receiving device, and a channel.

[0005] FIG. 2, a composite diagram presents representations of some of the signals described above with reference to FIG. 1, in accordance with certain embodiments.

[0006] FIG. 3 is a flowchart that shows some steps of a method to uniquely encrypt encoded audio, in accordance with certain embodiments.

[0007] FIG. 4 is a flowchart that shows some steps of a method to decrypt a uniquely encrypted audio signal, in accordance with certain embodiments.

[0008] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

[0009] The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

Detailed Description

[0010] In accordance with certain embodiments, two classes of bits are determined for the encoded audio generated by a particular encoding technique. The two classes are sensitive bits and insensitive bits. In general, the sensitive bits are a class of bits for which, when they are not altered before being decoded, will likely render audio that is not irritating or harmful to typical listeners even though all other bits (the class of insensitive bits) are all randomly altered before the audio is decoded. The sensitive bits are then transmitted or stored without being encrypted while the insensitive bits are encrypted for transmission or storage. As a result, if the decryption key is not used at the receiving or playback device, the audio is not irritating or harmful (i.e., it is benign as the term is used herein). The class separation is such that the audio is not intelligible when it is decoded without being decrypted

[0011] Referring to FIG. 1, a block diagram shows a portion of a communication system 100 that comprises an audio transmitting device 110, an audio receiving device 160, and a channel in accordance with certain embodiments. The audio transmitting device 110 comprises an audio source 115 that generates an audio signal that is coupled to an audio encoder that converts the audio signal to an encoded audio signal 121. The audio signal may be, for example, voice or music. The encoded audio signal 121 may be one that would be considered to be lossy compressed audio. For example, it could be generated by the vocoding portion of a 2400 bits per second LPC-10 vocoder, an MP3 audio coder, or the vocoding portion of an AMBE® half rate vocoder distributed by Digital Voice Systems, Inc. of Westford, Massachusetts, USA, just to cite a few of many possible examples. The encoded signal 121 is coupled to an encrytper 125 and a sensitive bits separator 130. The audio encrypter 125 encrypts at least the insensitive bits of the encoded audio and couples the resulting encrypted bits to the transmitter 135. The audio encrypter 125 may be the encryption portion of an AMBE® half rate vocoder, but embodiments using other techniques of encryption may provide the same benefits. The sensitive bits separator 130 conveys the sensitive bits to the transmitter 135 without encryption. The transmitter 135 may then insert the non-encrypted sensitive bits into a combined digital signal in place of encrypted sensitive bits that have been encrypted by the audio encrypter 125. The combined digital signal is used to modulate a transmitted signal 136 that propagates through a channel 155. The transmitted signal 136 may be a voltage conveyed by wires, or may be information transmitted by an electromagnetic field such as a light or radio beam.

[0012] The transmitted signal 136 is received by receiver 165 of audio receiving device 160, which demodulates the signal and may couple the demodulated signal 166 to decrypter 170 and sensitive bits separator 175. In accordance with certain embodiments the receiving device 160 comprises the decrypter 170, the sensitive bits separator 175, and audio decoder 180, and an audio sink 185. The decrypter 170 decrypts the demodulated signal 166 and couples the decrypted signal to audio decoder 180. The sensitive bits separator 175 couples the (non-decrypted) sensitive bits to the audio decoder 180, which may insert the sensitive bits into a combined digital signal which the audio decoder 180 may then decode, thereby generating an audio signal that may be coupled to an audio sink 185. The audio sink 185 may be, for example, a speaker or a memory. The audio decoder 180 has the capability to decode the type of encoding used by the audio encoder 120, and the decrypter 170 has the capability to decrypt the type of decryption used by the encrypter 125. Thus, in some embodiments, the audio decrypter 170 and audio decoder 180 may be portions of an AMBE® half rate vocoder. In accordance with certain embodiments an audio communication device or, more simply a communication device, may comprise either the audio transmitting device 110 or the audio receiving device 160, or both. A few examples of devices that may benefit from the improvements of certain of the embodiments described herein are personal communication devices that include cellular telephones and/or WiFi links, and walkie talkie radios. [0013] It will be appreciated that there are several ways to accomplish the separation of the sensitive bits from the insensitive bits, encrypt the insensitive bits, and provide a combined signal for modulating an output signal, without substantial alteration of the benefits provided. In one embodiment, the sensitive bits are identified and retained while the complete original set of encoded audio information is encrypted. Then the sensitive bits are used to replace the encrypted sensitive bits. The functions that perform these tasks may differ from those described above. For example, the replacement of the encrypted sensitive bits may be done in a function other than the transmitter 135, such as a separate assembly function, or by the sensitive bits separator 130. In another embodiment, the encrypter 125 performs the functions of sensitive bits separation and encryption simultaneously, for example by replacing the encrypting binary values of the sensitive bits by zeroes. In this embodiment, the encrypting values are used in an exclusive OR function with the bits to be encrypted in order to generate the encrypted bits from the encoded bit. By using a zero as an encrypting bit for each sensitive bit, the encoded bits are not encrypted. In yet another embodiment, the sensitive bits could be removed from the set of encoded bits and the encryption algorithm would be applied only to the insensitive bits. Then the sensitive bits could be inserted into the positions from which they were removed. For these other embodiments, as for the embodiment explained above, the actions could be performed by different functions in different embodiments. [0014] Although the embodiments described above with reference to FIG. 1 are what might be classified as audio communication embodiments, it will be appreciated that embodiments also exist in which the audio information is stored in memory and read from memory later for transmission or to be played back. In an embodiment in which the encoded, encrypted and non-encrypted audio portions are stored and played back, the device might be referred to as an audio entertainment device and the encryption may be used, for example, for privacy protection or as part of a digital rights management scheme. Examples of entertainment devices which may benefit from the improvements of certain of the embodiments described herein are personal music devices, such as an MP3 player. When the device is primarily used for storage and playback, the block diagram for the device could be the same as the block diagram of FIG. 1, with the channel 155 replaced by a memory, the transmitter 135 replaced by a memory write interface, and the receiver 165 replaced by a memory read interface. Then the system 100 becomes an electronic device that can be an audio entertainment device

[0015] Referring FIG. 2, a composite diagram presents representations of some of the signals described above with reference to FIG. 1, in accordance with certain embodiments. A graph 205 having a horizontal time axis and vertical amplitude axis shows a portion of an audio signal 210 of the type that may be generated by the audio source 115 (FIG. 1). The duration of the portion of the audio signal 210 captured in the graph 205 is approximately 120 milliseconds in this example. For encoding, the audio encoder 120 (FIG. 1) analyzes frames 215-219 of the audio signal that have a predetermined duration that may typically be from 10 to 40 msec. In this example, 20 msec, frames are used. Each frame is analyzed and from the analysis a set of characteristic parameters is generated. (In some embodiments, the analysis of each frame may involve some amount of information obtained from preceding and/or succeeding frames.) The audio encoder 120 is shown in FIG. 2 as it generates the parametric bit set 221 generated for the frame 217 that includes the characteristic parameters. Also shown are portions 220, 222 of the parametric bit sets generated for frames 216 and 218. In some embodiments, the characteristic parameters may include such aspects of the frame of the audio signal as energy, pitch, relative frequency subband strength, and whether the frame is a voiced or unvoiced frame. Each characteristic parameter need not use the same quantity of bits within the parametric bit set to convey the information. In some embodiments, the audio encoder 120 generates a parametric bit set of 49 bits per frame of, of which five are used to characterize the average energy level of the audio signal during each frame. This group of five bits is represented in FIG. 2 by the group 230, which is hereafter called simply the energy parameter.

[0016] In accordance with certain embodiments that use an AMBE®-2000 series half rate vocoder, studies of the characteristic parameters have determined that several bits of the 5 bits in the energy are sensitive bits. When the encrypted, encoded voice information is transmitted in the unique manner described herein and the four most significant bits of these five are treated as sensitive bits, then a receiver that uses an improper decryption will render audio that is typically not irritating or harmful to a typical user. With reference to FIG. 2, bit 235 may be identified as the most significant bit and therefore bits 235-238 are the sensitive bits for this example. The respective four bits in each of the parametric bit sets for the audio signal 210 would likewise fall in to the class of sensitive bits. The rest of the bits in each parametric bit set, which are represented by the groups of bits 245, 250 and bit 239 of the energy parameter in parametric bit set 221, fall into the class of insensitive bits. In other embodiments, particularly those using different encoded techniques, more or fewer sensitive bits may be used, and it may be that the sensitive bits may be from other characteristic parameter or may be identified in some other manner (in embodiments that may not use characteristic parameters. Furthermore, when the receiver uses an improper decryption, the audio generated will still be unintelligible, even though it has some unencrypted bits. How the class of sensitive bits is determined is discussed further below.

[0017] Referring to FIG. 3, a flowchart shows some steps of a unique method 300 used to encrypt encoded audio, in accordance with certain embodiments. At step 305 the classes of sensitive and the insensitive encoded audio information are identified, in some embodiments by experimental techniques. These experimental techniques may range from being quite objective to being somewhat subjective. In certain embodiments, the experimental techniques typically involve an iterative approach in which a small group of bits is selected from the parametric set of bits as a candidate group of sensitive bits and an encoded audio segment is encrypted, except for the sensitive bits, and is decoded without being decrypted. A level of irritation may be determined for the decoded audio segment and is used to either a) select a new candidate group of sensitive bits or b) to stop the iteration and use the current candidate group of sensitive bits as a selected group of sensitive bits when the irritation is below an acceptable level, or in other words, when the audio of the decoded audio segment is benign. The audio segment may be one of a plurality of audio segments that are tested for each candidate group of sensitive bits. The plurality of audio segments may be chosen from a full set of benign audio segments that represents a full range of expected audio to be encoded, encrypted, and transmitted or stored by an audio device. The plurality of audio segments may be chosen as those audio segments that are determined to be irritating when no sensitive bits are identified and the audio segments are decoded without being decrypted. The experimental technique may involve verifying for the full set of audio segments that the audio that is decoded without decryption is benign. The experimental technique may further involve verifying that when an encoded audio segment is encrypted, but for the sensitive bits, that the decoded audio remains unintelligible. Generally speaking, when a group of the sensitive bits is a small fraction of the parametric set of bits (i.e., less than 10%), the audio will not become intelligible. In certain embodiments the level of irritation may be established using human listeners that participate in a mean opinion scoring (MOS) test. In more analytical approaches, the audio irritation level may be numerically related to an average energy level. It will be appreciated that the characteristic parameter or parameters from which the sensitive bits are selected using a chosen experimental technique will depend upon the encoding method being used to encode the audio. When the encoding method being used to encode the audio is one that generates an energy parameter then it is likely that choosing sensitive bits from the energy parameter will result quickly in the determination of a set of sensitive bits that results in decoded audio that is benign. In accordance with the embodiments described herein above, when the encoder is an AMBE® encoder, a choice of the four most significant bits of the five bits of the energy parameter in the 49 bits of the parametric sets of bits generated by the AMBE® encoder. When the group of sensitive bits has been determined by experimentation they may be identified as a first class of encoded audio information, the sensitive encoded audio information. The other bits in the parametric set of bits are then identifiable as a second class of encoded audio information, the insensitive encoded audio information.

[0018] After the classes of sensitive and insensitive encoded audio information have been identified, an audio device may be designed that includes a method that comprises the remaining steps of method 300. At step 310 an audio segment is captured that is to be encoded, encrypted, and transmitted or stored by the audio device. The audio segments are then encoded at step 315 (by the encoding technique used for the selection of the sensitive bits) to form encoded audio information. At step 320 the encoded audio information is separated into a class of sensitive coded audio information and a class of insensitive coded audio information. The classes of insensitive and sensitive encoded audio information are characterized by a) being mutually exclusive portions of the encoded audio information and b) by forming audio noise that is benign to humans when i) the audio that is used to form the encoded audio information is benign audio and ii) the encrypted in sensitive encoded audio information is improperly decrypted and combined with the sensitive encoded audio information. The terms "forming audio noise" used in characterization b) above are meant to convey that the resulting audio is unintelligible. The terms "improperly decrypted" used in characterization b) above means one of i) not decrypting, ii) decrypting with an incorrect decryption key, an decrypting with an incorrect algorithm. An incorrect algorithm includes one that may use the correct operations but has wrong parameters. It will be appreciated that when the captured audio is expected to be voice, the audio device may employ a vocoder that generates encoded audio information on a frame by frame basis, and the insensitive audio information and the sensitive audio information may comprise mutually exclusive subsets of each encoded audio frame. In other embodiments, such as those for encoding the music, frames may not necessarily be used. In certain embodiments the transmitting of the sensitive encoded audio information and the encrypted encoded audio information may be performed in a manner compatible with the set of specifications identified as 3GPP TS Version 8 released by the 3GPP committee in 1999. In certain embodiments the class of sensitive encoded audio comprises at least the most significant bit of each energy parameter that may be included in the encoded audio information.

[0019] At step 325, the insensitive encoded audio information is encrypted to form encrypted encoded audio information. In accordance with certain embodiments the encryption of the insensitive encoded information is accomplished using a one to one bit transformation. In these embodiments the sensitive encoded information may also be allowed to be encrypted, after which the encrypted sensitive bits may be replaced with the (original) non-encrypted sensitive bits. In other embodiments, the classes of bits may be separated and the insensitive bits encrypted separately. The two portions of the audio information may then be transmitted or stored separately and recovered accordingly. At step 330 the sensitive encoded audio information and the encrypted encoded audio information are either transmitted or stored, or both. The sensitive encoded audio information is transmitted without encryption. [0020] Referring to FIG. 4, a flowchart shows some steps of a method 400 used to decrypt an encrypted audio signal, in accordance with certain embodiments. At step 405 an encoded audio information signal is received or read from memory that comprises encrypted insensitive encoded audio information and non-encrypted sensitive encoded audio information. The classes of insensitive and sensitive encoded audio information are characterized as described above with reference to step 320 (FIG. 3). The encrypted insensitive encoded audio information is decrypted at step 410 to form the decrypted encoded audio information. At step 415, the decrypted encoded audio information is combined with the encoded sensitive audio information to form received or playback encoded audio information. At step 420 the received encoded audio information is decoded to form received or playback audio. The received or playback audio may then be stored or presented to a user.

[0021] In the above description, there are instances where the information which is written or read from memory is described as a signal, an audio signal, an encrypted audio signal, a digital signal, etc. It will be appreciated that the signal could be alternatively described as a file for the purposes of reading and writing to memory It will be further appreciated that in some instances, the transmitted (and received) signal may be referred to herein as an encrypted signal, and that in such instances what is meant is a signal (or file) that is encrypted according to the unique encryption technique described herein, in which the sensitive bits are actually not encrypted. [0022] In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

[0023] Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," "has", "having," "includes", "including," "contains", "containing" or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises ...a", "has ...a", "includes ...a", "contains ...a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms "a" and "an" are defined as one or more unless explicitly stated otherwise herein. The terms "substantially", "essentially", "approximately", "about" or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art unless otherwise described. The term "coupled" as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is "configured" in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0024] It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or "processing devices") such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the methods and/or apparatuses described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.

[0025] Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.

[0026] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may lie in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

Claims

ClaimsWe claim:

1. A method comprising: encoding audio to form encoded audio information; separating the encoded audio information into a class of sensitive encoded audio information and a class of insensitive encoded audio information; encrypting the insensitive encoded audio information to form encrypted encoded audio information; and performing at least one of transmitting and storing the sensitive encoded audio information and the encrypted encoded audio information, wherein the sensitive encoded audio information is correspondingly transmitted and stored without encryption.

2. The method according to claim 1, wherein the classes of insensitive and sensitive encoded audio information are characterized by a) being mutually exclusive portions of the encoded audio information and b) by forming audio noise that is benign to humans when i) the audio that is used to form the encoded audio information is benign audio and ii) the encrypted insensitive encoded audio information is improperly decrypted and combined with the sensitive encoded audio information.

3. The method according to claim 2, wherein improper decryption means at least one of a) not decrypting, b) decrypting with an incorrect decryption key, and decrypting with an incorrect decryption algorithm.

4. The method according to claim 1, wherein the encoded audio information comprises a plurality of encoded audio frames, and the insensitive audio information and sensitive audio information comprise mutually exclusive subsets of each encoded audio frame.

5. The method according to claim 1, wherein the class of sensitive encoded audio comprises at least one most significant bit of each energy parameter of the encoded audio information.

6. The method according to claim 5, wherein the class of sensitive encoded audio comprises the 4 most significant bits of each energy parameter of encoded audio information generated by an AMBE® half rate vocoder distributed by Digital Voice Systems, Inc. of Westford, Massachusetts, USA.

7. The method according to claim 6, wherein the transmitting of the sensitive encoded audio information and the encrypted encoded audio information is performed in a manner compatible with a set of specifications identified as 3GPP TS Version 8 released by the 3GPP committee in 1999.

8. The method according to claim 1, wherein the method is performed in an audio device.

9. The method according to claim 1, further comprising: identifying by experimentation the classes of sensitive and insensitive encoded audio information using samples of benign audio of a type anticipated to be candidates for audio encoding.

10. A method comprising: performing at least one of receiving or playing an encoded audio information signal comprising encrypted insensitive encoded audio information and non-encrypted sensitive encoded audio information; decrypting the encrypted insensitive encoded audio information to form decrypted encoded audio information; combining the decrypted encoded audio information with the encoded sensitive audio information to form at least one of received or playback encoded audio information; decoding the received encoded audio information to form at least one of received and playback audio.

11. The method according to claim 10, wherein the insensitive and sensitive encoded audio information are characterized by a) being mutually exclusive portions of the encoded audio information and b) by forming audio noise that is a benign to humans when i) audio that was used to form the encoded audio information was benign audio and ii) the encrypted insensitive encoded audio information is improperly decrypted and combined with the sensitive encoded audio information.

12. An apparatus comprising: an audio encoder that encodes audio to form encoded audio information; a sensitive bits separator that separates the encoded audio information into a class of sensitive encoded audio information and a class of insensitive encoded audio information; an encrypter that encrypts the insensitive encoded audio information to form encrypted encoded audio information; and at least one of a transmitter that transmits and a memory that stores the sensitive encoded audio information and the encrypted encoded audio information, wherein the sensitive encoded audio information is correspondingly transmitted and stored without encryption.

13. The apparatus according to claim 12, wherein the classes of insensitive and sensitive encoded audio information are characterized by a) being mutually exclusive portions of the encoded audio information and b) by forming audio noise that is benign to humans when i) the audio that is used to form the encoded audio information is benign audio and ii) the encrypted insensitive encoded audio information is improperly decrypted and combined with the sensitive encoded audio information.

14. The apparatus according to claim 13, wherein improper decryption means at least one of a) not decrypting, b) decrypting with an incorrect decryption key, and decrypting with an incorrect decrypting algorithm.

15. The apparatus according to claim 12, wherein the class of sensitive encoded audio comprises at least one most significant bit of each energy parameter of the encoded audio information.

16. The apparatus according to claim 15, wherein the class of sensitive encoded audio comprises the 4 most significant bits of each energy parameter of encoded audio information generated by an AMBE® half rate vocoder distributed by Digital Voice Systems, Inc. of Westford, Massachusetts, USA.

17. The apparatus according to claim 16, wherein the transmitting of the sensitive encoded audio information and the encrypted encoded audio information is performed in a manner compatible with a set of specifications identified as 3GPP TS Version 8 released by the 3GPP committee in 1999.

18. The apparatus according to claim 12, wherein the apparatus is performed in an audio device.

19. An apparatus comprising: a receiver that receives an encoded audio information signal comprising encrypted insensitive encoded audio information and non-encrypted sensitive encoded audio information; a decrypter that decrypts the encrypted insensitive encoded audio information to form decrypted encoded audio information; an audio decoder that combines the decrypted encoded audio information with the encoded sensitive audio information to form received encoded audio information and decodes the received encoded audio information to form received audio.

20. The apparatus according to claim 19, wherein the insensitive and sensitive encoded audio information are characterized by a) being mutually exclusive portions of the encoded audio information and b) by forming audio noise that is a benign to humans when i) audio that was used to form the encoded audio information was benign audio and ii) the encrypted insensitive encoded audio information is improperly decrypted and combined with the sensitive encoded audio information.