SYSTEM, METHOD, AND DEVICE FOR PLAYING BACK RECORDED AUDIO, VIDEO OR OTHER CONTENT FROM NON-VOLATILE MEMORY CARDS, COMPACT DISKS OR OTHER MEDIA

Abstract: A secure software package for original equipment manufacturers to run in electronic devices in order to access and dynamically decrypt encrypted audio video or other content from a memory storage device such as a memory card, optical or hard disk such that the user interface of the device need only send simple commands and the decrypted content is output.

Description: SYSTEM, METHOD, AND DEVICE FOR PLAYING BACK RECORDED AUDIO, VIDEO OR OTHER CONTENT FROM NON- VOLATILE MEMORY CARDS, COMPACT DISKS, OR OTHER MEDIA CROSS REFERENCE This application is related to and claims priority from U.S. Provisional Patent Application Serial No. 60/251,731 entitled "SECURE SOFTWARE SYSTEM FOR PLAYING BACK RECORDED AUDIO, VIDEO OR OTHER CONTENT FROM NON-VOLATILE MEMORY CARDS, COMPACT DISKS OR OTHER MEDIA" filed December 7, 2000, and is related to U.S. Application entitled "SYSTEM, METHOD, AND DEVICE FOR PLAYING BACK RECORDED AUDIO, VIDEO OR OTHER CONTENT FROM NON-VOLATILE MEMORY CARDS, COMPACT DISKS OR OTHER MEDIA," attorney docket number M-9913-1 US, filed concurrently on the same day as this application and having the same inventors as this application. These applications are hereby incorporated by this reference in their entirety. Source code is submitted on a compact disc according to 37 CFR 1.52 as an appendix containing the following files, each of which is hereby incorporated by this reference in its entirety: Sd_security\Sd_oem\Makefile, 11/05/01, 2KB; Sd_security\Sd_oem\Readme, 11/05/2001 , 3KB; Sd_security\Sd_oem\Sd_oem.c, 11/05/2001, 6KB; Sd_security\Sd_oem\Sd_oem.h, 11/05/2001, 1KB; Sd_security\Sd_oem\Sd_oern.inc, 11/05/2001 , 1KB; Sd_security\Sd_oem\Sdtypes.h, 11/05/2001, 3KB; Sd_security\Sd_oem\vssver.scc, 11/05/2001, 1KB; Sd_security\Security\Tstsampl\Dotest.c, 11/05/2001, 8KB; Sd_security\Security\Tstsampl\Makefile, 11/05/2001 , 4KB; Sd_security\Security\TstsamplVReadme, 11/05/2001, 3KB; Sd_security\Security\Tstsampι\Regress.c, 11/05/2001, 26 KB; Sd_security\Security\Tstsampl\Sdls.c, 11/05/2001, 10KB; Sd_security\Security\Tstsampl\Sdrm.c, 1 1/05/2001, 5KB; Sd_security\Security\Tstsampl\Securmmc.c, 1 1/05/2001, 6KB; Sd_security\Security\Tstsampl\Tstsampl.inc, 1 1/05/2001, 1KB; Sd_security\Security\Tstsampl\vssver.scc, 1 1/05/2001 , 1KB; Sd_security\Security\Err.h, 1 1/05/2001, 1KB; Sd_security\Security\Fsentry.c, 11/05/2001, 7KB; Sd_security\Security\keyInfo.h, 11/05/2001, 84KB; Sd_security\Security\Makefile, 11/05/2001 , 3KB; 11/05/2001, 4KB; Sd_security\Security\Scdrv.c, 11/05/2001, 29 KB; Sd_security\Security\Scdrv.h, 11/05/2001, 5KB; Sd_security\Security\Scfs.c, 1 1/05/2001, 13KB; Sd_security\Security\Scfs.h, 1 1/05/2001, 4KB; Sd_security\Security\Sdsec.h, 11/05/2001, 5KB; Sd_security\Security\Sdsys.c, 11/05/2001, 2KB; Sd_security\Security\Security.c, 11/05/2001, 64KB; Sd_security\Security\Smanager.c, 11/05/2001, 7KB; Sd_security\Security\Smanager.h, 11/05/2001 , 2KB; Sd_security\Security\Ssmapi.c, 11/05/2001, 3KB; Sd_security\Security\vssver.scc, 1 1/05/2001, lKB;Sdaudlib\HostFunc.c, 11/05/2001, 3KB; SdaudlibUnpoutp.c, 11/05/2001, 1KB; Sdaudlib\mssccprj.scc, 11/05/2001, 1KB; Sdaudlib\plmInfo.h, 11/05/2001, 16KB; Sdaudlib\Sd_plm.h, 11/05/2001, 5KB; Sdaudlib\Sd_tkm.h, 11/05/2001, 4KB; Sdaudlib\Sd_types.h, 11/05/2001, 2KB; Sdaudlib\Sdapi.h, 11/05/2001, 2KB; Sdaudlib\Sdaudapi.c, 11/05/2001, 91KB; Sdaudlib\Sdaudapi.h, 11/05/2001, 8KB; Sdaudlib\Sdaudlib.dsp, 11/05/2001, 4KB; Sdaudlib\Sdaudlib.dsw, 11/05/2001, 1KB; Sdaudlibwssver.scc, 11/05/2001, 1KB. BACKGROUND 1. Field of the invention This invention relates generally and specifically to secure playback of digital audio, video or other content from memory cards, compacts disks or other media. 2. Related art The potential of electronic distribution of copyrighted music over the Internet, by other communication systems or through retail kiosks, is being limited by concerns about unauthorized copying of the music. This is also the case for other audio, as well as video, content. The content is typically provided to the ultimate customer in encrypted form, and the customer records the encrypted content files onto some storage media, such as a personal computer memory, a memory of a portable playing device, a writable compact disk (CD) or a non- volatile memory card. Providers of the content would like to eliminate the possibility of unauthorized copying of the content but have to be satisfied with taking steps that minimize the amount of copying that occurs. This includes providing protection of the content on the recording media. The protection of content stored on non-volatile memory cards is described herein, as specific examples, but the same content protection techniques can be applied to compact disks or other recordable media. There are several commercially available non-volatile memory cards that are suitable for use as the content data storage media. One is the CompactFlash (CF) card, another is the MultiMediaCard (MMC), and yet another is the Secure Digital (SD) memory card that is closely related to the MMC card. All three, and others, are available in various storage capacities from SanDisk Corporation of Sunnyvale, California, assignee of the present application. The physical and electrical specifications for the MMC are given in "The MultiMediaCard System Specification" that is updated and published from time-to-time by the MultiMediaCard Association ("MMCA") of Cupertino, California. Versions 2.11 and 2.2 of that Specification, dated June 1999 and January 2000, respectively, are expressly incorporated herein by this reference. The MMC products are also described in a "MultiMediaCard Product Manual," Revision 2, dated April 2000, published by SanDisk corporation, which Manual is expressly incorporated herein by this reference. Certain aspects of the electrical operation of the MMC products are also described in co-pending patent applications of Thomas N. Toombs and Micky Holtzman, Serial Nos. 09/185,649 and 09/186,064, both filed November 4, 1998, and assigned to SanDisk Corporation. The physical card structure and a method of manufacturing it are described in U.S. patent no. 6,040,622, assigned to SanDisk Corporation. Both of these applications and patent are also expressly incorporated herein by this reference. The newer SD Card is similar to the MMC card, having the same in plan view. A primary difference between them is that the SD Card includes additional data contacts in order to enable faster data transfer between the card and a host. The other contacts of the SD Card are the same as those of the MMC card in order that sockets designed to accept the SD Card will also accept the MMC card. The electrical interface with the SD card is further made to be, for the most part, backward compatible with the MMC product described in version 2.11 of its specification referenced above, in order that few changes to the operation of the host need be made in order to accommodate both types of card. The electrical interface of the SD Card, and its operation, are described in co-pending patent application Serial No. 09/641,023, filed August 17, 2000, which application is incorporated herein in its entirety by this reference. SUMMARY OF THE INVENTION Encrypted content is difficult to access, and memory cards or compact disks with encrypted content each have specific structures that require specific commands and routines to access encrypted and unencrypted content. The software of the present invention is a simple solution that any original equipment manufacturer (OEM) can install and run on a myriad of different types of devices having a myriad of different types of microprocessors. These devices range from personal computers to portable devices to car stereos, and include any device from which one would like to access content that may be encrypted. The portable devices may be portable audio players or cell phones or portable organizers or generally any microprocessor controlled portable device. The storage media may be flash memory or any type of recordable disk. The devices may have a simple or powerful microprocessor with a small or large amount of memory. The software utilizes and requires only a small buffer for encryption purposes and is designed to run efficiently even in environments with limited processing power and memory. It can be run by any type of general purpose microprocessor, or special purpose microprocessors such as a DSP, or an ASIC. Additionally, computationally demanding portions of the software, such as the encryption and decryption (security) engine may be executed by the DSP, while other portions of the software may be executed by a another microprocessor or an ASIC. The software has audio, video and image interfaces to receive commands for each of the respective types of files. These interfaces can organize playback and recording, including managing playlists and other convenient features. Thus, whatever the device, it need only issue a command to an interface and the software will take care of reading or writing data from the secure media, and decoding and decompressing the data from any well known audio, video or image file formats within the audio video or image engines. The encryption and decryption takes place in an isolated module that is very difficult to access and thus isolated from any attempts from unauthorized persons wishing to access encryption keys in order to copy the files from the media or the device. Content is only decrypted in small portions, and a method of dynamic key generation and deletion minimizes exposure of decrypted keys. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is an illustration of the devices used to read and write information on a secure media. FIG. 2 is a schematic diagram of a device used to access the secure media. FIG. 3 A is an abstract illustration of the layers of the secure media. FIG. 3B is an illustration of the physical and logical structure of the memory cells of the secure media. FIG. 3C is an illustration of the track structure and the component parts of a track. FIG. 4 is an illustration of a media key block (MKB) image broken into its component chunks. FIG. 5 is an illustration of a portion of the authentication and decryption process. FIG. 6 is an illustration of the authentication and encryption process. FIG. 7 is a schematic of the authentication key exchange process shown in FIG. 6. FIG. 8 A is a block diagram of the software of the present invention. FIG. 8B is a block diagram illustrating the modules of the software of the present invention. FIG. 8C is a flow chart overview of the pre-play and play process according to the present invention, with the related API modules/calls shown. FIG. 8D is an expanded flow chart of audio content initialization phase in FIG 8C. FIG. 8E is an illustration of information blocks created during the pre-play process 805 of FIG 8C. FIG. 9 is a flow chart overview of the playback of an audio track according to the present invention. FIG. 10 is a flow chart of the processing of an MKB image seen in FIG. 4, a step of FIG. 9. DETAILED DESCRIPTION OF THE INVENTION Encrypted content is difficult to access, and memory cards or compact disks with encrypted content each have specific structures that require specific commands and routines to access encrypted and unencrypted content. The software of the present invention is a simple solution that any original equipment manufacturer (OEM) can install and run on a myriad of different types of devices having a myriad of different types of microprocessors. These devices range from personal computers to portable devices to car stereos, and include any device from which one would like to access content that may be encrypted. The portable devices may be portable audio players or cell phones or portable organizers or generally any microprocessor controlled portable device. The storage media may be flash memory or any type of recordable disk. The devices may have a simple or powerful microprocessor with a small or large amount of memory. The software utilizes and requires only a small buffer for encryption purposes and is designed to run efficiently even in environments with limited processing power and memory. It can be run by any type of general purpose microprocessor, special purpose microprocessors such as a DSP, or an ASIC. Additionally, computationally demanding portions of the software, such as the encryption and decryption (security) engine may be executed by the DSP while other portions of the software may be executed by a another microprocessor or an ASIC. The source code referred to in the Cross Reference section forms a part of this application, and is hereby expressly incorporated in its entirety by this reference. With reference to Figure 1, an exemplary system is described in which content protection is applied to audio content such as music. A host computer device 11 may be a personal computer (PC), as shown, a kiosk located in a retail store to distribute music or other content, or the like. An SD memory card 13 is used in this example to store music. The card 13 is insertable into a utilization device, in this case a portable device (PD) 15 that operates from batteries to play the music or other audio content recorded on the card 13 through personal earphones. The music may be stored on the card 13 when inserted into the device 15 by connecting the device 15 to the host 11, such as through a computer universal serial bus (USB) connection 17. Alternatively, if the player device 15 is not provided with the capability of recording content onto the card 13, or if it is otherwise desirable, a card writer/reader 19 may be connected to the computer through a USB connection 21, and the card 13 inserted into it for recording music on the card. The card 13 is then removed from the writer/reader 19 and inserted into the portable device 15 to play the audio content recorded on the card. The host 11 is termed a licensed compliant module (LCM) when it includes the software necessary to write to and read from the card 13 content data in accordance with the security and authentication protocols of the 4C Entity and the SD Group. The electronic system within the example portable utilization device 15 is illustrated in Figure 2. Operably connected together through a bus 23 are a computing unit (MCU) 25, preferably with some non-volatile flash memory 25A, system memory 27, which is preferably a high speed random access memory (RAM), and interface circuits 29 for connecting with the memory card 13. The USB connection 17 is also optionally provided to the MCU 25. A digital signal processor (DSP) 31 is also included, when needed, for decompressing and/or decrypting content data, such as audio or video data, that is stored in a compressed and/or encrypted form. DSP 31 also has its own RAM memory 31 A included as part of the processor. DSP 31 may or may not be included. Furthermore, if a DSP processor is included, it may perform the functionality of MCU 25, and thus MCU 25 may therefore be eliminated. Read only memory (ROM) 32 can store part or all of the software of the invention. Software instructions and data in ROM 32 can be executed or read directly from ROM 32 or first shadowed into any RAM memory included in the circuitry of the device. Specifications for the protection of content on recordable media have been jointly established by Intel Corporation, International Business Machines Corporation, Matsushita Electric Industrial Co., Ltd. and Toshiba Corporation (4C Entity). Particularly relevant here are the following three publications of the 4C Entity, which are expressly incorporated herein by this reference: "Content Protection for Recordable Media Specification, Introduction and Common Cryptographic Elements," Revision 0.94, October, 2000, "Content Protection for Recordable Media Specification, SD Memory Card Book," Revision 0.95, May, 2001 , and "C2 Block Cipher Specification," Revision 0.9, January, 2000, and "Content Protection for Recordable MediaSpecification, DVD Book," Revision 0.95, May, 2001. Additional detailed specifications for implementing these 4C Entity specifications on SD memory cards have been established by Matsushita Electric Industrial Co., Ltd. (MEI), SanDisk Corporation and Toshiba Corporation (SD Group). Referring to Figure 3 A, a memory card 13 can be thought of as having four distinct layers. Such layers may also be present in other types of secure media. At its most basic level, data is stored in memory cells arranged in clusters on the physical layer 13d of memory card 13. The data is encrypted or secure if it is copyrighted material or otherwise worthy of encryption. Keys used to encrypt and decrypt the secure content are also encrypted and stored in a secure area of the physical layer. The software of the present invention runs within a device to allow the device to store and retrieve encrypted information without the manufacturer (OEM) having to program very specific instructions to access the memory cells containing encrypted data and keys. It contains methods of sending the encrypted data to the device, decrypting the data within the device, and decompressing and playing audio, video and image files upon requests from the device. In short, a device need only send a command such as "play track." The software will accept the command, retrieve the encrypted data stored in the memory cells, retrieve the encrypted keys, organize and decrypt the data, decompress and format it, and play the song back. Logical layer 13c contains the organizational structure for the memory cells and clusters of physical layer 13d. The two layers 13c and 13d contain and logically structure the memory of card 13. As card 13 is a secure card, security layer 13b controls and limits access to the secure data housed in the layers below. Application layer 13a is the part of memory card 13 that communicates with a device accessing the content stored in the card. It does this through a device interface or contacts 39. Memory card 13 preferably includes a controller that manages the operation of the card and functionality of the application layer 13 together with control of all layers 13a-d of the card. The physical and logical structure of a recording media, the SD card 13, according to the foregoing specifications, and corresponding to layers 13c and 13d of Figure 3 A, is illustrated in Figure 3B. The card includes an array of memory cells 33 and a memory controller 35. User data, commands and status signals are communicated between the controller 35 and the memory array 33 over a circuit 37. The controller 35 communicates with a host device connected to a socket in which the card is inserted through a series of electrical contacts 39 on the card. The memory cells of the array 33 are divided into the four non-overlapping areas of cells that are individually designated to store different types of data. A largest storage capacity area 41 is designated to store user data, in this case, encrypted audio, video or other data. The user data may or may not also include unencrypted data. A system area 43 of the memory stores a 64-bit media identifier (IDmedia) of the card manufacturer, and 16 media key blocks (MKB) provided by the 4C Entity, each MKB having a maximum size of 4k bytes, all being pre-recorded by the card manufacturer. One of the 16 MKBs is specified for use with audio user data, another for use with video user data, another for use of image data, and so on. The system area 43 is a write-protected area that is accessible for reading from outside of the card. A hidden area 45 carries 16 pre-recorded media unique keys (Kmu) corresponding to the 16 distinct media key blocks (MKB) stored in the system area 43. The hidden area 45 is a write-protected area that is accessible only by the memory card itself. A protected area 47 is a read/write area that is accessible only after a successful explicit mutual authentication has occurred. Randomly picked title keys (Kt) and copy control information (CCI) are stored in the protected area 47 in an encrypted form. Each piece (file) of content stored in the user data area 41 is encrypted with a unique title key that is also stored in an encrypted form in the protected area 47. The title keys and CCI stored in the protected area 47 are concatenated and encrypted together by the media unique key, which is unique for each memory card and stored in its hidden area 45. The file system of the user data area 41 is typically an ordinary FAT file system. The FAT system describes what memory clusters make up what tracks and the various sub-components of the tracks. Audio or video tracks within user data area 41 may comprise multiple files as illustrated in Figure 3C. Audio files are referred to as audio objects (AOB's) and picture files are referred to a picture objects (POB's). A track may comprise both. Track 300, for example is composed of AOB 304 and AOB 308, and track 302 is composed of AOB 306 and the last track xxx is composed of AOB xxx and POB xxx. Each AOB or POB is also broken down into sub components. AOB 304 is shown broken down into AOB blocks 312, which are further broken down into AOB elements 316 with header 318. Each element may be stored in one or more memory clusters of memory card 13. AOB elements are divided into the lowest component level, AOB frames 320. Depending on the encoding and compression of the content, each two seconds may comprise a varying number of frames. A time search table (TMSRT) has information about the number of frames and data size which corresponds to "every two seconds" of playback. This information is used when an audio or video track and the component AOB's elements and frames are accessed for fast forward and rewind. Also, as will be discussed later with regard to Figures 9 and 10, at title key (Kt) is an a decrypted state only for the time it takes to access this "every two seconds" of content, although anywhere from less than one to ten seconds of content may be decrypted at a time. For further detail, please refer to the CPRM Specification, SD Memory Card Book, which was previously incorporated by reference. The media key block (MKB), as stored in the system area 43 of the card memory, contains a sequence of contiguous records, one such record being illustrated in Figure 4. The entire MKB image 49 is 64 Kbytes. It is broken into 128 chunks of 512 bytes, and chunk 1, which contains all or part of they first record, and is labeled MKB chunk 50 in the figure, is enlarged to show its component parts. Chunk 50 may also contain multiple records. A first field 51 contains the record type, a second field 53 the total length of the record, and the remaining field 55 the key itself. The data in the record type and length fields 51 and 53 are not encrypted. Each record of the MKB is a multiple of 4 bytes in total length. As illustrated by a block 57 of Figure 5, the MKB key records are decrypted by device keys stored in the portable device (PD), licensed compliant module (LCM) or other device that utilizes a memory card for reading or programming content data stored on it. Device keys Kdl , Kd2, Kd3 ... are written into a memory of the utilization device, such as non-volatile flash memory within the MCU 25 of the portable audio player of Figure 2, by the manufacturer of the device. The device keys are provided to device manufacturers by the 4C Entity, and are maintained in confidence. The number of device keys which are stored in a given utilization device depends upon the type of the device. The utilization device (PD, LCM or other device) which performs the processing of Figure 5 calculates the media key Km as part of the decryption of block 57, which is discussed in further detail with regard to Figures 9 and 10. Each record (Figure 4) of the MKB read from the system area of an inserted memory card is usually processed in this manner. After processing of the MKB is completed, the most recently calculated Km value is taken as the secret media key output of the block 57. This media key Km and the media identifier IDmedia are combined by use of a C2 one-way function, as indicated by a block 59 of Figure 5, to produce the media unique key Kmu. Additional details of this processing may be had by reference to the 4C Entity publications referenced previously. Figure 6 illustrates all of the authentication and encryption processing that takes place when either recording audio content onto, or playing audio content from, a memory card 13 having the memory space allocation of Figure 3. Processing that takes place in a personal computer or other LCM 63 is illustrated for recording audio or other content onto the card 13. Similarly, the processing of a portable audio or other utilization device 65 is shown for reading the recorded content from the card 13. Included in both is the processing described with respect to Figure 5, the processing blocks 57 and 59 being part of the utilization device 65 and corresponding processing blocks 57' and 59' being part of the content recording system 63. As part of recording content, an arbitrarily assigned title key Kt is input at a line 67 for use by an encryption module 69 to encrypt one file (piece) of audio or other content input at line 71. The encrypted file is then stored in the user data area 41 of the memory card 13. In order to make the title key available for decrypting the recorded content, an encrypted version of the title key (Kt) is stored in the protected card memory area 47, as previously described. An encrypted version of the title key (Kt) is also stored in either system memory 27, RAM memory 25 A of MCU 25, or RAM memory 31 A of DSP 31. Storing the encrypted title key (Kt) in a memory of the device eliminates the need to access protected card memory area 47. This is significant because it saves considerable time and processing capacity in comparison to accessing the protected area 47 for each read. This will be discussed later with regard to Figure 9. The title key Kt and copy control information CCI are encrypted by a series of encryption modules 75, 77 and 79 in the LCM 63, and a module 81 on the memory card 61. The media unique key Kmu is used by the module 77. An authentication key exchange (AKE) module 83 combines the media unique keys Kmu as calculated by the module 59' and stored in the hidden area 45 of the card 61, to generate a session key Ks that is used by each of the modules 79 and 81. In order for the utilization device 65 to decrypt the recorded encrypted content, corresponding modules, indicated with the same reference numbers but with a prime (') added, are utilized to perform an inverse of the encryption process. Figure 7 illustrates a technique for accessing the protected area 47 of a memory card, utilizing an authentication and key exchange (AKE) challenge-response protocol between a card and some LCM or utilization device. When this authentication is successful, the card and the other module or device share a secure common session key Ks. Additional details of the forgoing processing and protocols may be had by reference to the 4C Entity publications previously identified. Figures 8A and 8B illustrate an embodiment of a software system designed to run in a portable device or LCM in order to access information encrypted with the aforementioned processes. The SanDisk software, SW 100, is a complete turn-key software solution that enables OEM music players and recorders to readily support secure media including the secure digital (SD) memory card. SW 100 shown within portable device 15 in order to access SD card 13. SW 100 may also be installed in any licensed compliant module such as a personal computer. As seen in Figure 8A, at its highest level, SW100 receives calls from device 15, particularly a user interface of device 15, retrieves encrypted content from the Secure Digital card 13, and returns decrypted content to the device. Thus only simple calls are required to execute many complicated processes. The complicated processes of retrieving encrypted content stored in memory locations of card 13, and then subsequently decrypting and formatting the content are handled by SW 100. Performing accesses to the authentication area of the SD Memory Card requires using secret device keys that OEMs must license from the 4C Entity, as mentioned previously. Protecting these key values and restricting their exposure within SDK SW 100 software layers is one of the central considerations in the software design. Isolation of these keys (and other resultant values such as session keys) within a single internal module while enabling a secure media such as the SD memory card device driver to perform operations dependent on these values is achieved in a robust and secure interface methodology. Once again, the SD memory card is used to illustrate the invention; however, the invention can be used on any secure media such as CDs or other secure memory that may be in a card or even in a remotely located storage device. Figure 8B illustrates the layered structure of SW 100 in more detail. Audio interface 105, video interface 110, and imaging interface 115 are the points of communication to the device. These interfaces provide a single point of communication for the device and generally receive simple commands from the device so that the device does not have to get involved with the intricacies of getting encrypted data from a secure media, then decrypting and processing the data. All of these complex processes are handled by SW 100. Interfaces 105, 110, and 115 also manage the arrangement of playback such as managing playlists and the correlation of images such as that of an artist with the songs of the artist or the various playlists. Application programming interface (API) 130A resides within command dispatcher (CD) 130. CD 130 and API 130A receive commands from interfaces 105, 110, and 1 15, relay information to the interfaces, and organize all of the processes that take place in the SW 100 - the processes of device 15 related to the playback and recording of content stored on the secure media, with all of the requisite encryption, decryption, and compression algorithms. SD audio engine (SDAE) 140, SD video engine (SDVE) 150, and SD image engine (SDIE) 160 respectively process audio, video, and image content residing on the secure media, upon receipt of instructions from CD 130. This means SDAE 140 can process any of the well known formats for audio, such as AAC, WMA, and MP3. Likewise, SDVE 150 can process any of the well known formats for video clips such as Windows media files or real networks files MPEGs or any other well known type of video files. Finally, SDIE 160 can process any well known type of image files such as TIF, GIF, JPEG, bitmaps, etc. Each interface has a secure API (SAPI) and a non-secure API (NSAPI). The content processed may or may not be encrypted. Encrypted content is accessed through SAPIs 140A, 150A, and 160A. These SAPIs communicate with SanDisk security manager (SSM) 180. All commands having to do with secure content are channeled through SSM 180. Secure digital security engine (SDSE) 175, which will be described later in further detail, handles all encryption and decryption processes. Keys used to authenticate the media and decrypt the content are contained within and handled exclusively by SDSE 175. Unencrypted content residing on the card is accessed through NSAPI 140B, 150B, and 160B. These NSAPIs communicate with a non-secure file interface (NSFI) 170 in order to access unencrypted content on the media. In order to read or write data in the storage media, NSFI 170 and SDSE 175 communicate with device driver 190. Device driver 190 in the example of the SD card manages and drives signals to and from the device interface 39's contacts of the SD card 13. Device driver 190 will be tailored to the specific type of device interface 39 of various devices or media. In the case of a memory card device, driver 190 manages and drives signals to and from contacts located on device 15. In the case of optical media, device driver 190 may manage and drive signals from various hardware components including an optical pick-up unit. Alternatively, in the case of a hard disk drive (hdd), device driver 190 will manage and drive the required hdd signals. Device driver 190 contains a secure device driver interface (SDDI) 190A, and a non-secure device driver interface (NSDDI) 190B. SDDI 190A and NSDDI 190B are isolated from each other within device driver 190. SDDI 190A communicates exclusively with SDSE 175, while NSDDI 190B communicates exclusively with NSFI 170. Device keys and other values central to the SD-Audio security scheme are housed within one restricted security software module, SD security engine (SDSE) 175. All manipulation of these values is solely restricted to this module. Values are never passed in or out to software layers above SDSE 175. All requests for the security services involving these keys are controlled and monitored by SSM 180 that shields this security module. Beneath the security module, the SD Memory Card device driver 190 carries out security accesses. Requests for these driver services are made via a private driver security interface, secure device driver interface (SDDI) 190A, that is only known to the security module. SDSE 175 uses this interface.190A to perform special security commands such as Get Media Key Block (MKB). Non- secure device driver interface (NSDDI) 190B also utilizes device driver 190 to access any unencrypted files in user area 41 of card 13. The security of SW100 architecture resides in the security of its keys. Secret "soft keys" are not stored in temporary secure areas for a long period of time, since this increases the possibility of compromising the keys and thus the encrypted content. SW 100 utilizes a scheme within SDSE 175 of dynamically generating the needed keys (or "soft keys") and deleting them when there is no immediate need for those specific keys. Operation of SW 100 is now described in more detail. SW 100, in particular, command dispatcher 130/ API 130A have a number of API routines that can be called upon to perform a certain function. Although there are many routines, only 22 of the routines are accessed externally by device 15. These routines are accessed by calls, which are also referred to as commands. In order to retrieve the content in memory card (or other media) 13, the device need only send one of the 22 calls and the content will be retrieved, decrypted if necessary, and decoded. In the case of audio, for example, the device need only send the "play" call, and the music will start. The following listed APIs allow applications to interface to device compliant with the Secure Digital (SD) standard. Although implementation of the invention is illustrated with the SD standard, the present invention can be used with many different standards. Table 1 -API Routines/Calls The principle API routines which can be called by device 15 will now be described in detail. Reference will be made to Figures 8A-8E. As can be seen in Figure 8C, there is a pre-play process 805 and a play process 810. The blocks of Figure 8E are created during the processes of Figure 8C. The related API modules are executed when called upon by the user interface of device 15. In the case of audio playback, calls to the modules are sent by the user interface of device 15 to the audio interface 105 as seen in Figure 8B. The primary calls/modules that carry out the functionality listed in the flowchart are indicated on the right. Many of these modules execute other internally and externally accessed modules, and the list is not meant to be exhaustive, but is meant to be a reference to the software code on compact disc that was previously incorporated by reference and forms a part of this application. For further detail please refer to the software code. The device is first powered up in step 803, after which the pre-play process 805 commences. The pre-play process has two major phases: a power up initialization phase 805.10, and an audio content initialization phase 805.20. Audio content initialization phase will be described in further detail with regard to Figure 8D. Generally speaking, in pre-play process 805 the device and media are initialized and certain information from the media is read from the media and stored in a buffer of a RAM memory of device 15. As seen previously in Figure 2 this RAM memory may either be system memory 27, RAM memory 31 A of DSP 31 , or RAM memory 25A of MCU 25. In step 805A SW 100 will get the drive number of the media. In some applications there may be more than one memory card or disk being accessed by device 15. In this step it will get all the drive numbers in order that content on each of the drives can be properly accessed. This is accomplished with API routine SdlnitAudioSystem, and can either be called upon by device 15 or can be internally called by SW 100 as part of a pre-play routine. SW 100 will then initialize SSM 180 and SDSE 175 within SW 100. This is necessary before any encrypted keys and content from the media can be processed. SW 100 will also initialize the playlist and track manager in card 13. In step 805B, SW 100 will initialize and verify the media. In the case of the SD card illustrated here, the MKB process of Figures 5-7 will be performed. This MKB process can also be executed during step 805 A, and if previously executed it will not be executed again in step 805B. For further detail of this process please see Figures 5-7 and the 4C documents incorporated earlier. This process will also be discussed in greater detail with regard to Figure 10. In step 805B, media information values will be copied from the card 13 and stored in locations of media information block 850 of Figure 8E in a RAM memory of device 13. This is accomplished with API routine SdMountAudio, and can either be called upon by device 15 or can be internally called by SW 100 as part of a pre-play routine. Thus values for playlist general information (pTGInfo), the validity number of the media (SanDisk), the drive number (drivenum), the security system of the media (security) and the mounting status of the media (mounted) will be filled in their respective locations. These locations can then be subsequently read from the RAM of device 15 when called upon by any number of API calls without having to read them from card 13. After the power-up initialization 805.10 is completed, audio content initialization 805.20 commences. Generally speaking, during audio content initialization 805.20, information specifying location and sequencing of the encrypted audio content of an individual track and multiple audio tracks (playlists) are copied from the card (or other media) 13 into a small buffer in a RAM of device 15. This information, shown in blocks in Fig. 8E, is thus quickly and easily accessible within the device and does not need to be constantly read from or updated to card 13 during the subsequent play process 810. Referring to Figure 8D, the audio content initialization phase 805.20 will be described in more detail. This phase creates a number of structures that act as a local roadmap or directory to the encrypted content on memory card (or other media) 13. In step 805C, device 15 calls API module SdGetPlayListCount. This call, and all of the following calls, are generally sent from the software of a user interface of device 15 to one of the interface modules of SW100. In this illustration of audio playback the call is sent from the user interface to audio interface 105. In the case of video playback, the call would be sent to video interface 110 and in the case of image reproduction, the call would be sent to imaging interface 115. The call is then relayed to command dispatcher 130 which contains the API modules within API 130A. In step 805D, SdGetPlayListCount will fill in the values for the Playlist Info block 860 by copying the information from card 13 into a RAM memory of device 15. It will select the appropriate authorized drive(s) by referring to media info block 850. The total number of playlists for all authorized drives will be copied into a RAM of device 15. In step 805E, device 15 calls API module SdGetPlaylist. In step 805F, SdGetPlaylist will fill in the values for the playlist info block 860 by copying the information from card 13 into a RAM memory of device 15. It will select the appropriate authorized drive where the playlist info resides by referring to media info block 850. The total playback time of the selected or default playlist in milliseconds (pListTime), the number of tracks in the playlist (tracksInPlist), the index number corresponding to the current playlist (index), the playlist name string length (Length), and the playlist name (pListName) will be filled into their respective locations of Playlist Info block 860. In step 805G device 15 calls API module SdGetTracklnfo. In step 805H, SdGetTracklnfo will fill in the values for the track information block 870 by copying the information from card 13 into a RAM of device 15. It will select the appropriate authorized drive where the playlist info resides by referring to media info block 850. It will select the tracks within each playlist by referring to the Playlist info block 860. The total track time (trackTime) in milli-seconds including the related track units ("TKI's") in the track, the total track size in bytes (bytesize), including the related TKI's, the number of TKI's in the track (tkisInTrack), the track number (tracknum), the index corresponding the current track (index), and the track information from the media (trklnformation) will be filled into their respective locations. In step 8051 device 15 calls API module SdOpenTrack. In step 805 J, SdOpenTrack fills in some of the values for the Track Gen Info block 880 by copying the information from card 13 into a RAM of device 15. It will select the appropriate drive by referring to media info block 850, and it will select the tracks within the appropriate playlists and tracks by referring to Playlist Info block 860 and Track Info block 870, the total playback time of the playlist in milliseconds (pListTime), the current playlist number (plistnum), the track number to be played (tracknum), the first AOB block for the track (firstAOB), and the current AOB being decrypted (current AOB). In step 805K SdOpenTrack fills Track Index Info block 875 by copying the information from card 13 into a RAM of device 15. It will select the authorized drive where the playlist info resides by referring to media info block 850 and playlist info block 860, and it will select the proper tracks within the proper playlists by referring to Playlist info block 860 and Track Info block 870. After Track info block 870 is created, in step 805L, SdOpenTrack will fill in the remaining values of Track General Info Block 880 by copying the information from card 13 into a RAM of device 15. The following values will be filled into their respective locations of block 880: a verification number for the media (SanDisk), an operation command (CMD), the audio format such as MP3, AAC, or WMA (audioformat), the codec sampling frequency (sampfreq), the application attribute, e.g., music, book image, etc. (appAtrib), the size of the audio object in bytes (size AOB), the last AOB block for the track(lastAOB), the total number of AOB's for the track (countAOB), the current position of sync position in AOB (syncword) also known as the header, the seek position within the AOB(seekposAOB), the elapsed time of the track in milliseconds (trkElapsedTime), the total play time of the track in milliseconds (trkTotalTime), the total track size in bytes including related TKI's (bytesize), the playtime of each element in milliseconds (elementplaytime), the forward seek time (fwTime), the time to the next track (fwNext), the number of the tracks in the playlist (tracksInPlist), the size of the current element (elementsize), the offset within the current element (element offset), the current elements in the AOB (currentelement), the total number of elements n the AOB (totalelements), and the file handle of the AOB (fdAOB). In a different embodiment of the invention, step 805 J will completely fill the values of Track General Info block 880 and step 805K will be eliminated. Track Index Info block 875 is a subset of Track Gen Info block 880 and is designed to save space and processing time. It is meant to be referred to by the user interface of device 15 in the event that it is just browsing the information. Once the user interface has selected a particular track for playback, Track Gen info block 880 will be filled, including the subset of information contained in block 875. SdOpenTrack and can either be called upon by device 15 or can be internally called by SW 100 as part of a pre-play routine Having the blocks and the information of the blocks contained in a memory of the device is an advantage because if there is any failure in the playback process, it is not necessary to reset the media, i.e., perform steps 805A or 805B of power up initialization 805.10. Also, it should normally not be necessary to read the information needed for playback from card 13. The information in the blocks can be used to access the next content (audio, video etc.) frame because the information in the blocks 850, 860, 870, 875, and 880 is used as a pointer to the content contained in the next frame. The blocks of Figure 8E detail the location within memory card 13 of the files, elements and frames that make up and audio or video track are located within memory card 13, as was earlier described with regard to Figure 3C. The pre-play process of step 805 can be triggered by a number of calls (the numbers in parenthesis indicate the call in Table 1). As seen in Figure 8C, the external calls that will trigger audio content initialization 805.20 are: SdOpenTrack, SdGetPlayhstCount, SdGetPlaylist, and SdGetTracklnfo. SdOpenTrack (10) is internally called by SdNextTrack (12), SdStopPlay (13), and SdResetPlaylist (16). API modules SdGetPlayhstCount, SdGetPlaylist, and SdGetTracklnfo can also be called internally by SdOpenTrack. Generally, it will be called upon by device 15 for such device functions as displaying the track time, rewinding, fast forwarding, changing playlists, changing graphic user interface displays, or deleting tracks. Once the pre-play process 805 is complete, the play process 810 can commence. In play process 810, calls that will initiate, stop, or pause playback of 'one or more audio or video tracks are received by the audio interface 105, video interface 110, or imaging interface 115 of Figure 8B in step 810A. These calls can be seen in Figure 8C next to play process 810 and are SdPlayTrack, SdNextTrack, SdStopPlay, SdPauseTrack, SdResumeTrack, SdResetPlayList, SdForward, SdAddTKItoPLM, SdDelTKItoPLM, SdDelTKItoTMG, SdConvertMP3ToSAl, and SdConvertAACToSAl . Regardless of how many API modules are executed, either internally or when called upon by the device, two primary modules will always be required in order to play an audio track. These modules are SdOpenTrack (10) and SdPlayTrack (1 1). SdOpenTrack (10) and SdPlayTrack (11) will read the information in Track General Info block 880 in order to access the encrypted content in the memory locations of clusters of memory card 13. SdOpenTrack (10) is internally called by SdNextTrack (12), SdStopPlay ( 13), and SdResetPlaylist (16). Generally, it will be called upon by device 15 for such device functions as displaying the track time, rewinding, fast forwarding, changing playlists, changing graphic user interface displays, or deleting tracks. SdPlayTrack (11) is the core API that plays the music or video track. It is generally used by a device when the user wants to play the current track, the next track, or when he wants to rewind or fast forward within a track. It is called upon by other API's such as SdNextTrack (12) SdResumeTrack (15) and SdForward (17). SdPlayTrack finds the AOB for the selected track, checks the audio format (MP3, AAC, or WMA etc.) and decodes the track. Referring to Figure 8B, 9, and 10, playback of an encrypted track, step 810B of Figure 8C, will now be described. If encrypted content is desired, then commands are issued to/from device 15 and SW 100 which require the OEM's 4C-licensed device keys to be used. All processing of these keys is solely limited to the SDSE 175 module which is housed beneath the SSM 180. If non secure or non-encrypted content is requested, NSFI 170 and NSAPI's 140B, 150B, and 160B and NSDD 190B will access the content. When SSM 180 receives a request for security services, it carries it out by passing the command request packet to the process_security function within SDSE 175. Key values are never contained within the request packets or exposed at software layers above SDSE 175. When needed internally by SDSE 175, device keys are retrieved via a function call into an OEM-supplied library. The library of SDSE 175, security.lib, contains the following APIs designed to reduce the time that a decrypted key resides in the secure area of the system: 1)SEC_AKEAPI; 2) SEC_ENC_TKEY API; 3) SEC_DEC_TKEY API; 4) SEC_GETCCI API; 5) SEC PDATECCI API. The functionality and the structure of SW 100 are described in the text of this application and more specifically, the functionality of APIs 1-5 above are shown within the flowchart of FIG. 9. The APIs are shown next to the corresponding functions that they implement. Further detail of the implementation of these APIs, as well as all of SW 100, can be seen in the source code that is submitted in an appendix of this application. Once obtained, the device key is combined with the Media Key Block (MKB) from the SD Memory Card to form the "media key." This value is kept within SDSE 175 for use in processing subsequent requests. Note, however, the "unique media key" (Kmu) is never retained inside SDSE 175. This value, which forms the basis for all security accesses, is always calculated on a real-time basis (and never cached) as an extra security precaution. Detailed description of the processing of the keys within SDSE 175 follows. The encryption process is in general terms designed to stop unauthorized copying of the content located on the secure media. There are many aspects of the invention that achieve this. First, an entire file, for example, a song, is never decrypted at once and stored into memory where it may be vulnerable. The portable device allocates a buffer and SDSE 175 reads chunks of encrypted content at a time, decrypts it, and then writes over the same buffer over and over again until the end of the file. As was seen in Figures 6 and 7, the media unique key (Kmu) and title key (Kt) are the keys finally used to decrypt the content. There are many ways to protect the title key. One is to store the keys in a very secure area of device 15, another is to read the title key from the protected area 47 of card 13 each time the encrypted buffer is read and decrypted. Figure 9 is a flow chart depicting the preferred method. Returning to Figure 9, in step 205, an MKB image, which, as seen in Figure 4, is 64 kilobytes, is read to process the media key (Km), as seen in Figure 6, to yield the media unique key (Kmu). This step is further detailed in Figure 10 which will be described later. After mutual authentication of the device and the media is complete in step 205, the AKE process is undergone to yield a session key (Ks) that can only be used during that session (as long as the device is turned on or is in an active state) in step 210. The AKE process can be seen by referring once again to Figure 6. In step 213, the media unique key (Kmu) is deleted. In step 215, the session key (Ks) is used to decrypt the doubly encrypted title key E(E(Kt)) stored in protected area 47 of memory card 13. The result is a singly encrypted title key (E(Kt)). In step 220, this encrypted title key (E(Kt)) is stored in a memory of the device 15. The (E(Kt)) may be stored in system memory 27, RAM memory 25 A of MCU 25, or RAM memory 31 A of DSP 31. The title key Kt is specific for each title, referred to as a track in the realm of audio and on Figure 9 used to illustrate the invention. Each track may be made of multiple files, for example, in the case of a long classical song. For large video clips, a title may comprise many files. Thus, for all subsequent reading and decryption of the encrypted content of the track, the title key need not be retrieved from the memory card because it is stored in a local memory, and precious time and computing resources can be saved, while at the same time, the title key remains encrypted for security purposes. In step 225, a portion of the track is played back. This portion may be in any of the files that comprise the track. In step 225a, the media unique key (Kmu) is calculated once again. In step 225b, the encrypted title key stored in local memory is decrypted. Then, in step 225c, the title key is used to decrypt the content from the buffer of device 15 containing content from the user area 41 of card memory card 13. Immediately after the buffer is decrypted, the title key is deleted in step 225d and the media unique key is deleted in step 225e. The order of steps 225d and 225e is not important, but it is important that both keys are only exposed for the time it takes to read a portion of the track. This portion may be anywhere from a fraction of a second of playback (decrypted, decompressed, and decoded) content, audio or otherwise, to about ten seconds. Preferably it is two seconds. The time it takes to read the portion is dependent on many factors including the processing speed and the buffer size of the device. As discussed previously, SW 100 can be executed by either the MCU 25 or DSP 31 and stored in any of the memory 27, 25 A, 31A or 32 of device 15, thus, the processing times can vary. This is repeated until all portions of the track are read as seen in step 230. Once all portions have been read the system can move on to the next track, as shown in step 235, if playback is to continue. This may be the case, for example, if the user has chosen to play an entire playlist. When the all portions of track have been read and the reading of the next track is to commence, the process will begin again at step 215 and will retrieve the next doubly encrypted title key from the protected area 47 of card 13. This is generally the case if the user has set the device in motion to play an entire playlist that includes multiple tracks. If the session is closed (i.e., device 15 has been turned on or off), then a new session key will have to be generated and the process will initiate at step 210. If memory card is removed or freshly inserted, the device and media will have to be re-authenticated and the process will begin again at step 205 in order to read a track. Figure 10 describes the operation of processing the Media Key Block, step 205 of Figure 9 described above. As was seen in Figure 4, an MKB image 49 is 64 Kbytes in length. Reading the entire image 49 at once to calculate the MKB would be inefficient, requiring a large RAM and long processing times. The present system reduces RAM requirements and decreases processing time. The MKB image 49 is divided into chunks 1 through 128. Each chunk is 512 bytes and may contain one of four different types of records of the MKB: the verify media key record (VMKR) known as 0x81 ; the calculate media key record (CMKR) known as 0x01 ; the conditionally calculate media key record (CCMKR) known as 0x82; or the end media key record (EMKR) known as 0x02. These records are described in the Content Protection for Recordable Media (CPRM) Specification of the 4C Entity, referenced above. In this example, the chunk length and the buffer length are the same. However, the buffer length and chunk length can both range from 256 bytes to 4096 bytes. Each record is examined to perform specific operations based on the record type and certain data will be saved for later to obtain the Media Key. The record length is added to the total length of the buffer offset every time a record is identified. The chunk number is calculated by dividing the total length with the chunk length. The chunk number is the index to the Media Key Block of a selected chunk data. The remainder of the total length is the offset to the selected chunk data. The row and column are used to figure out where the encrypted media key and the conditional encrypted media key are. Those encrypted keys are saved and the decryption C2 cipher in Electronic Codebook Mode algorithm is performed to obtain the Media Key. This Media Key is then verified for a correct final Media Key (Km) . The number of reads, T, required per MKB chunk for obtaining the Media Key (Km) from the MKB associated with the number of records is shown below: Number of Records < T < (Number of records * 2) T: Number of times required for accessing MKB chunks Each record has different length and data values. The information of each record can be obtained within two reads. Since there are four records, between 4 and 8 reads will be necessary to process the MKB chunk and obtain the records. Therefore, the number of reads, T, are: 4 < T < 8 Suppose that it takes N ms to access 512-byte of MKB data. It will take (128*N)ms to access an entire 64K MKB image to obtain the Media Key from the first method. It only takes, from the second method, (8*N)ms, as the worst case scenario, to obtain the Media Key. Thus, there is a considerable time saved using this scheme. On the average, to obtain the Media Key (Km), the number of reads would be in the range of 4 to 6, and the time necessary would be proportionately less than shown above. Step 205 of Figure 9, expanded here in Figure 10, is performed until a final media key is produced in step 205.75 or the media is rejected in step 205.80. Not all of the 128 chunks need to be read, and not all of the 512 bytes per chunk need to be read in order to calculate the media key. Processing MKB data is an operation that requires requesting a chunk of data at a time, pointing to the desired location within that specific chunk and computing the obtained values. Not all MKB data is needed. The algorithm depicted in Figure 10 will provide a mathematical calculation to figure out exactly what chunk of MKB data is needed, what record should be processed and where the encrypted data is located. In step 205.5, the buffer pointer is set to the data buffer and the buffer offset is cleared. Next, in step 205.10, the chunk number is checked to see if it is equal to or larger than the maximum chunk number. If it is, an error will be returned in step 205.15. If it is not, the chunk number will be incremented and new data will be loaded into the buffer in step 205.20. Then the buffer offset will be updated in step 205.25. Thus, the pointer can be set to the correct location (the chunk number plus offset). In step 205.30, the buffer pointer is set to the buffer offset. In step 205.40 the buffer is read starting at the offset where the pointer is located. The system will then determine what type of record it is reading. As seen in step 205.40, the system will first check what type of record is being read, and what record length is associated with that record. The actions that will follow differ depending upon the record type and length. The record length of each record will be used to determine where the buffer pointer should be located in reading the subsequent record. This is reflected by steps 205.49, updating the buffer offset and setting the buffer pointer at the new offset. If the record is a CMKR as shown in step 205.42, then the system updates the buffer chunk number and offset to the correct MKB location where the encrypted media key (Km)is located in step 205.49. Each card has 16 MKBs. Thus, the system will get the offset where the encrypted media key is, go to the specific MKB chunk number, allocate buffer (16 blocks x 512 bytes), and go to the offset within each block to read the encrypted media key. Then the system uses a device key (Kd) supplied from device 15 to decrypt (calculate) the media key in step 205.50. Once the media key has been calculated the next step is to verify the media key. If the record is a VMKR as evaluated in step 205.44, the media key that was previously calculated, either on the first attempt in step 205.50, or in a subsequent attempt in step 205.65, will be compared to a reference media key (Km) in step 205.55. In order to do this, reference media key will first be stored locally. If the key is the same a pass will be returned, which in hex is DEADBEEF, and the system will not need to conditionally calculate the media key. In order to figure out where to start reading the next record, the record length of the VMKR is used to move the buffer pointer to the next record. If it is not the same it then it will be calculated again when a CCMKR record is read in step 205.46. When this record is read, the media key will be calculated once again in step 205.65 after the buffer point has been set to read at the updated buffer offset in step 205.49, and then it will be subsequently verified when the next VMKR is read. The maximum number of times the CCMKR is calculated may be set by the system and preferably one. The first calculation takes place when a CMKR is found. If it is successfully calculated, as determined during the verification process initiated when a VMKR is found, then there will be no need to conditionally calculate the media key (Km). If the verification is unsuccessful then when a CCMKR is found the media key (Km) will be recalculated and re-verified. This means that there are two chances to calculate the media key. Finally, if the record is an EMKR as evaluated in step 205.48, then in step 205.75 the system will verify that at the end of the record a valid media key (Km) is present, and in step 205.75 the final media key (Km) will be produced, after the buffer pointer is set at a the proper offset for this type of record in step 205.49. If, however, a valid media key is not returned in step 205.70, the media will be rejected in step 205.80. If the final media key is returned in step 205.70, the processing will continue at step 210 of Figure 9, as shown by step 205.85. Thus the MKB process is complete. Functions within SDSE 175 perform security accesses such as Get MKB by using a secure device driver interface (SDDI) 190A to device driver 190. This same device driver, SDDI 190A also makes use of functions within SDSE 175 which it can call directly. For example, prior to issuing a read of the authentication area, SDDI 190a must first call the sec_ake function within SDSE 175. The sec ake function will in turn call back into SDDI 190A. This "dual calling relationship" which facilitates the isolation of the device key within SDSE 175 is unique to SW 100s implementation of the SD- Audio standards. Since SDSE 175 handles all key-oriented processing, and these values are needed when certain SD commands are received by the audio interface 105, video interface 110, or image interface 115, the device driver must make use of functions within SDSE 175 which it can call directly. When carrying out the functions, SDSE module 175 must in turn call back into the device driver 190's private security interface, SDDI 190A. This "dual calling relationship" allows interwoven requests between SDSE 175 and device driver 190, thus enabling key values to be isolated within the security module. The SDSE 175 software layer invokes security device driver services via the private interface by initiating a security driver request packet and calling the security driver interface entry point passing a request packet pointer. In order to clarify the appended source code which has been incorporated by reference, the following tables are provided. The request packet (defined in sdapi.h) consists of a data type SSMSERVE which is defined as follows: Table 2 Command index (INT 16 opCode) holds the command for the service being requested. Supported commands include: Table 3 Security device driver service requests are issued from the SDSE 175module. For example, the Generate Challenge 1 function sends challenge 1 as follows: Table 4 - Generate Challenge 1 Because all key manipulation is confined to SDSE 175, SSDI 190A must rely on SDSE 175 functions to perform Authentication Key Exchange (AKE) or for decrypting data that has been transferred across the bus (note that all data sent across the bus is first encrypted using the "session key" which is generated from each AKE.) When performing the AKE, SDSE 175 must send commands to the SD Memory Card 13, thus, it must in turn call into SDDI 190A. This calling relationship is outlined in the diagram of Figure 7 which depicts the steps necessary to process a read of the authentication area. Notice that the sec ake function within the SDSE 175, when called by the security SDDI 190A, performs four calls back into the security device driver via the private driver interface. These four requests consist of: SDDRV SETCHALGE, SDDRV GETCHALGE, SDDRV_SETRESP, and SDDRV_GETRESP. This enables the security module to carry out the requisite set challenge/get challenge, set response/get response steps seen in Figure 7. The resultant session key is stored within the security module. This is used to decrypt data when the security device driver calls into the SDSE 175's bus decrypt function to get information from SDDI 190A. The system and method of the present invention are advantageous over prior techniques in many ways. The present invention provides a turnkey solution for original equipment manufacturers to access encrypted content without having to have any knowledge of the memory structure of the storage media. The decryption process by itself is very complex. Futhermore, simply reading and writing to a memory card or compact disk is complex in and of itself. All a manufacturer needs to do is send a simple command such as "play" or "next track" and return the decrypted content from whatever the memory device happens to be. Device keys and resultant session keys are manipulated in a very isolated and protected software layer. These are never exposed in upper layers. Even the lower device driver layer is not given direct access to the keys. Device keys are retrieved from an OEM-supplied library when generating the media key. This key is retained within the security engine, but the media unique key (K mu ) which is the heart of the security scheme is never stored. A private interface to the security engine enables the security engine to gain low-level access to the memory card while keeping the exposure of all security-related keys (e.g., device keys, media keys, session keys) confined within the security engine. A "dual calling relationship" allows the security engine and the security device driver to make interwoven use of each other's services. While particular embodiments of the present invention and their advantages have been shown and described, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended Claims. For example, although usage of an SD memory card has been shown to illustrate the functioning of the invention, the invention can be used on any media having encrypted content. It can also be utilized by any type of device. Furthermore, encrypted content can be decrypted from any type of memory device, whether it be fixed or removable, and whether it be solid state or rotating. The content is not limited to audio or video, but can be any content worthy of encryption.

Claims: CLAIMS 1. A software program to be utilized in an audio or video device by the original equipment manufacturer of the device, the device for playback of encrypted audio or video content residing on a memory card, the software program configured to: receive commands including a playback command from a user interface of the device; decrypt encrypted audio or video content from the memory card such that the original equipment manufacturer need only send the playback command from the user interface of the device to the software program and the decrypted audio or video will be played back. 2. The software program of claim 1 wherein the software program is further configured to: copy location information of the encrypted content into a memory of the audio video device; access the location information from the memory of the audio video device; locate the encrypted content within the memory card with the accessed location information. 3. The software program of claim 1 wherein decrypting the audio or video content comprises: copying one or more encrypted keys from a protected area of the memory card into a memory buffer of the device; copying encrypted audio or video content from the memory card into a memory buffer of the device; decrypting one or more of the copied encrypted keys; decrypting the copied encrypted audio or video content with the one or more decrypted keys. 4. " The software program of claim 3 further comprising immediately deleting the one or more decrypted keys after decrypting the audio or video content. 5. The software program of claim 4 wherein about less than one to ten seconds of content is decrypted at a time with the one or more decrypted keys before the one or more decrypted keys are deleted. 6. The software program of claim 4, wherein about two seconds of content is decrypted at a time with the one or more decrypted keys before the one or more keys are deleted. 7. The software program of claim 1 wherein decrypting the audio or video content comprises: (a) calculating a media unique key; and thereafter (b) decrypting a title key stored in the memory of the device with the media unique key; and thereafter (c) decrypting a group of frames; and thereafter (d) deleting the decrypted title key; (e) deleting the media unique key; and (f) repeating (a) through (e) until the entire track is completed. 8. A portable device having a microprocessor, random access memory and a software program executed by the microprocessor, the device configured to: receive a group of commands including a playback command from a user interface of the portable device; retrieve encrypted data residing in a removable storage media upon receiving the command; store the encrypted data in a memory of the device; decrypt the data; and output decrypted audio or video content such that the device only need send a command from the group of commands from the user interface to the software program in order to output the decrypted audio or video content. 9. The portable device of claim 8, wherein about two seconds of encrypted data is stored in the memory of the device, and subsequently decrypted before being deleted. 10. The portable device of claim 8, wherein the removable storage media is a solid state memory card. 11. The portable device of claim 8, wherein the removable storage media is an optical disc. 12. The portable device of claim 8, wherein the software of the device is further configured to decompress and decode audio content in either the AAC, MP3 or WMA format. 13. The portable device of claim 8, wherein the software of the device is further configured to: copy playlist information and track information from the removable storage media into a memory of the device, and locate the encrypted data to be retrieved based on the playlist and track information within the memory of the device. 14. The portable device of claim 13 wherein the track information comprises for each track: the number of audio objects comprised by the track; the first audio object comprised by the track; the last audio object comprised by the track; the current audio object being decrypted; and the offset of the current audio object. 15. The portable device of claim 14 wherein the track information further comprises: the size of the track in bytes; the total playback time of the track; the elapsed time of the track the current element number within the audio object; current element of the track to be played; the offset of the current element; the total number of elements in the audio object. 16. A method of playing encrypted audio or video content stored in a secure media with a device, the method comprising: a pre-play process comprising: copying one or more groups of information regarding the tracks to be played back in to a memory of the device; a play process comprising: receiving one more commands from a user interface to initiate playback; accessing the one or more groups of information from the memory of device; copying encrypted content from the secure media into a memory of the device according to a sequence based upon information of the one or more groups of information copied into the ram memory; decrypting the encrypted information from the secure media in a sequence based up on the information of the one or more groups of information. 17. The method of claim 16 wherein approximately less than one to five seconds of the encrypted content is copied and decrypted at a time. 18. The method of claim 16 wherein the one or more groups of information comprise playlist and track information. 19. The method of claim 16 wherein the one or more groups of information specify which playlist is to be played, which track within the playlist is to be played. 20. The method of claim 19 wherein the one or more groups of information further comprises which audio object within the track is to be played, and where the audio object is located within the secure media. 21. The method of claim 20 wherein the one or more groups of information further comprises which element within the audio object is to be played, and which frame within the element is to be played. 22. The method of claim 16 wherein the pre-play process further comprises authorizing the secure media. 23. A system enabling a portable device to access encrypted music on a memory storage device comprising: one or more application programming interfaces configured to: receive a plurality of commands from a user interface of the portable device; and send commands to an isolated security engine, the isolated security engine configured to: receive commands from the application programming interface; copy encrypted keys and encrypted content from the memory storage device to a memory of the portable device; decrypt the keys; decrypt the content using the decrypted keys; and thereafter delete the decrypted keys. 24. A method for allowing a device having a processor and random access memory to easily access encrypted data from a memory card with a group of commands, the method comprising: retrieving playlist information from the memory card and storing the information in the random access memory of the device; retrieving track information from the memory card and storing the track information into the random access memory of the device; receiving a command selected from the group of commands from the device, the command accessing both of the playlist information, and track information from the random access memory; executing the command by retrieving the encrypted data stored within the memory card and decrypting the data based on the accessed information. 25. The method of claim 24 wherein the playlist information comprises: the name of a playlist; the playlist name string length; the playback time of the playlist; the tracks comprised by the playlist; and the index corresponding to the playlist. 26. The method of claim 24 wherein the track information comprises: a track number; an index corresponding to the track number; a number of track units in the track; and the playback time of the track. 27. The method of claim 24 wherein the track information comprises: a format type of a track; a sampling frequency of the track; the size of the track in bytes; and the current track being decrypted. 28. The method of claim 27 wherein the general track information further comprises: the number of audio objects comprised by the track; the first audio object comprised by the track; the last audio object comprised by the track; the current audio object being decrypted; and the offset of the current audio object. 29. The method of claim 27 wherein decrypting the data comprises: copying one or more encrypted keys from a protected area of the memory card into a memory buffer of the device; copying encrypted audio or video content from the memory card into a memory buffer of the device; decrypting one or more of the copied encrypted keys; decrypting the copied encrypted audio or video content with the one or more decrypted keys. 30. The method of claim 27 wherein decrypting the data comprises: (a) calculating a media unique key; and thereafter (b) decrypting a title key stored in the memory of the device with the media unique key; and thereafter (c) decrypting a group of frames; and thereafter (d) deleting the decrypted title key; (e) deleting the media unique key; and (f) repeating (a) through (e) until the entire track is completed. 31. A software system that enables a device to access content on a secure medium comprising: one or more user interface modules for receiving commands from the device; an applications programming interface for receiving the commands from the user interface module(s) and managing the retrieval and storage of both encrypted and non encrypted content from the secure medium; a security engine for decrypting the encrypted content and encrypted keys sent from the secure medium to memory of the device, the decrypted keys used to decrypt the encrypted content, and wherein one or more of the keys are contained in a first encrypted data segment, and encrypted content is contained in a second encrypted data segment, and the security engine buffers and decrypts a portion of the first data segment, buffers and decrypts the second data segment, and thereafter deletes the decrypted one or more keys before decrypting the, such that decrypted keys are in a decrypted state for the time it takes to decrypt less than one to about five seconds of content. 32. The software system of claim 31 , wherein the key is in a decrypted state for the time it takes to decrypt and process about two seconds of content. 33. The software system of claim 32, wherein the content is encoded in the form of AAC, MP3 or WMA. 34. The software system of claim 31 , wherein the portion of the first data segment buffered and decrypted is about 512 bytes.

Inventors: CHANG ROBERT C, QAWAMI BAHMAN, SABET-SHARGHI FARSHID, CHANG, ROBERT, C., QAWAMI, BAHMAN, SABET-SHARGHI, FARSHID
Applicants: SANDISK CORP, SANDISK CORPORATION
Application year: 2001
Main classification: G11B20
IPC codes: G06F12, G06F21, G06K17, G09C1, G10L19, G11B20, H04L9, H04N5