Patent Publication Number: US-8997214-B2

Title: Method and system for creating and accessing a secure storage area in a non-volatile memory card

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of and claims the benefit of priority from application Ser. No. 11/967,641, filed Dec. 31, 2007, entitled Method And System For Creating And Accessing A Secure Storage Area In A Non-Volatile Memory Card, and currently pending. Application Ser. No. 11/967,641 is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This application relates generally to the operation of non-volatile flash memory systems, and, more specifically, to a method and system for creating and accessing a secure storage area in a non-volatile memory card. 
     BACKGROUND 
     There are many commercially successful non-volatile memory products being used today, particularly in the form of small form factor cards, which employ flash EEPROM (Electrically Erasable and Programmable Read Only Memory) cells formed on one or more integrated circuit devices. Some of the commercially available card formats include Smart Cards, Subscriber Identity Module (SIM), and Removable User Identity Module (R-UIM) cards. These cards typically contain memory and a microcontroller (with associated logic memory and software). The data stored within a card is accessed via an interface that is controlled by a program and, in some cases, security hardware or software. 
     Typically, SIM cards and R-UIM cards are utilized in cellular telephones operating on Global System for Mobile communication (GSM) and Code Division Multiple Access (CDMA) networks, respectively. In these applications, SIM and R-UIM cards store limited amounts of information, such as encryption keys, subscriber identification values, and telephone contact lists. However, as the storage density of non-volatile memory has increased, more non-volatile memory may be contained within a storage card such as a SIM card. The additional storage may be utilized for a variety of advanced mobile services, such as storing Multimedia Messaging Service (MMS) object attachments, MP3 audio files, high-resolution images files, and video files, as well as providing full personal information management (PIM) functionality, such as e-mail contact lists and calendars. A Mobile Network Operator (MNO) may provide or sell digital content, such as video, picture, and audio files, which may be stored in the additional storage space of a high-capacity card. An example of a high-capacity SIM card is the SIM 5000™, a memory device from SanDisk Corporation of Milpitas, Calif. 
     The greater storage capacity of a high-capacity SIM card necessitates a faster interface to access the storage contents. The ISO 7816 interface utilized on a typical SIM card, or R-UIM card may be supplemented with an additional high speed interface, such as a Multimedia Card (MMC) interface, a Secure Digital (SD) interface, a Universal Serial Bus (USB), or a Serial Advanced Technology Attachment (SATA) interface, in order to access the storage space of high-capacity cards. The relatively slower ISO 7816 interface may still be utilized for backwards-compatibility purposes, or to control the storage accessible over the high-speed interface. An MNO may utilize the security features of a high-capacity SIM or R-UIM card to prevent copying of the content downloaded by or sold to a cellular telephone subscriber, or to prevent access to the content by unauthorized users or applications. 
     Some cellular telephones may access a SIM or R-UIM card over an ISO 7816 interface, but may not be capable of utilizing the additional storage space of high-capacity SIM or R-UIM card. Other cellular telephones may support additional storage by providing a receptacle for an additional non-volatile memory card, such as a CompactFlash (CF) card, a MultiMedia Card (MMC), a Secure Digital (SD) card, or a USB Flash Drive. However, an MNO may not be able to prevent copying or unauthorized access to content downloaded or sold to a cellular telephone subscriber that is stored on the additional card, because the additional card may not contain the security features of a high-capacity SIM or R-UIM card. 
     SUMMARY 
     In order to address these issues, there is a need for a method to limit access to digital content stored on one non-volatile memory device by utilizing security credentials calculated using a second non-volatile memory device. There is also a need for a system that can securely store and access digital content on one non-volatile memory device, using security credentials calculated using a second non-volatile memory device. 
     Thus, according to one embodiment, there is a method for creating a secure storage account to permit access to protected content in a non-volatile memory device. In this embodiment, an account identification value is calculated. A memory identification value is read from a first non-volatile memory device. The memory identification value and the account identification value are transmitted to a second non-volatile memory device. A credential is received from the second non-volatile memory device, where the credential is calculated using the memory identification value, the account identification value, and a formula. A command is transmitted to create a secure storage account in the first non-volatile memory device, where the command contains the credential and the account identification value. 
     In another embodiment, a method of accessing a secure storage account in a non-volatile memory device is provided. In this embodiment, an account identification value is calculated. A memory identification value is read from the first non-volatile memory device. The memory identification value and the account identification value are transmitted to a second non-volatile memory device. A credential is received from the second non-volatile memory device, where the credential is calculated using the memory identification value, the account identification value, and a formula. An account access sequence is performed. The account access sequence consists of transmitting a command containing the account identification value and a value based on the credential. 
     According to another embodiment, there is a secure storage system. In this embodiment, the storage system includes a first non-volatile memory device that contains a non-volatile memory adapted to store a memory identification value, and further adapted to limit access to a portion of the non-volatile memory using a credential. The storage system also contains a second non-volatile memory device adapted to compute the credential using the memory identification value. The storage system further includes a host adapted to associate the credential with the portion of the non-volatile memory within the first non-volatile memory device, and further adapted to use the credential to obtain read and write access permission to the limited access portion of the non-volatile memory within the first non-volatile memory device. 
     In yet another embodiment, a host is provided. In this embodiment, the host contains a first communication interface adapted to communicate with a first non-volatile memory device, a second communication interface adapted to communicate with a second non-volatile memory device, and a processor in communication with the first and second communication interfaces. In this embodiment, the processor is configured to calculate an account identification value, and read a memory identification value from the first non-volatile memory device. The processor is also configured to transmit the memory identification value and the account identification value to the second non-volatile memory device, and receive a credential from the second non-volatile memory device, where the credential is calculated using the memory identification value, the account identification value, and a formula. In this embodiment, the processor is further configured to transmit a command to create a secure storage account in the first non-volatile memory device, where the command contains the credential and the account identification value. 
     According to yet another embodiment, a host is provided. In this embodiment, the host contains a first communication interface adapted to communicate with a first non-volatile memory device, a second communication interface adapted to communicate with a second non-volatile memory device, and a processor in communication with the first and second communication interfaces. In this embodiment, the processor is configured to calculate an account identification value, read a memory identification value from the first non-volatile memory device, and transmit the memory identification value and the account identification value to the second non-volatile memory device. The processor is also configured to receive a credential from the second non-volatile memory device, where the credential is calculated using the memory identification value, the account identification value, and a formula. In this embodiment, the processor is further configured to perform an account access sequence that involves transmitting a command containing the account identification value and a value based on the credential. 
     Other methods, systems, features, and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional methods, systems, features and advantages be included within this description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principle aspects of various embodiments of the system and method. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a diagram illustrating exemplary steps for accessing an account in a secure system. 
         FIG. 2A  is a diagram illustrating an exemplary secure storage system in accordance with an embodiment. 
         FIG. 2B  is a diagram illustrating an exemplary secure storage system in accordance with an embodiment. 
         FIG. 3  is a diagram illustrating exemplary steps for calculating an account identification value in a secure system in accordance with an embodiment. 
         FIG. 4  is a diagram illustrating exemplary steps for calculating a credential value in a secure system in accordance with an embodiment. 
         FIG. 5  is a diagram illustrating exemplary steps for creating a new storage account in a secure system in accordance with an embodiment. 
         FIG. 6  is a diagram illustrating exemplary situations for configuration and use of a secure storage system, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     An exemplary secure storage system may comprise a host, and a non-volatile memory device, such as a non-volatile memory card. The contents of a non-volatile memory card, such as files or storage partitions within the card, may be associated with a plurality of storage accounts. Each account may have its own account identification value, and each account may have a credential that may be utilized to control access to the account. One or more files, or a partition within a non-volatile memory card, may be associated with an account. 
     In order to access an existing file in the non-volatile memory card, or write a new file to a partition associated with an existing account, a host application may open or “log in” to the account.  FIG. 1  is a diagram illustrating exemplary steps for accessing an account in a secure system. In step  102 , a host calculates the account identification value corresponding to the account associated with the file or partition to be accessed. Control passes to step  104 , where a credential associated with the account is calculated. In step  106 , the host attempts to access the account utilizing the credential. Access may only be granted if the calculated credential is the correct value. A variety of algorithms may be utilized to verify the calculated credential. In one example, a credential acts as a password to the account. In this example, the credential is transmitted to the non-volatile memory card, and compared with a stored value at step  108 . If the values match, access to the account is granted, and control passes to step  110 . If the values do not match, access is denied, and control returns to step  102 . 
     In another example, the credential is an encryption or decryption key, and is used in a challenge/response algorithm. For example, the non-volatile memory card may encrypt a random value with a credential stored when the account was created, and may transmit the encrypted value to the host. The encrypted value is received by the host, and the host decrypts the encrypted random value with the calculated credential and returns the decrypted value to the non-volatile memory card. If the returned decrypted value does not match the original random value, access is denied, and control returns from step  108  to step  102 . If the values match, control passes to step  110 . At step  110 , the host application may read from and write to files associated with the account, or write new files to partitions of non-volatile memory storage associated with the account. The host may close the account at step  112 , and control returns to step  102 , where the host may initiate another account access. 
     The exemplary steps  100  for accessing an account in a secure system present several security challenges. If the credential in step  104  is calculated in the host, the formula utilized to calculate the credential may be compromised. Further, the credential may also be compromised if it is merely a constant value looked up in a table in the firmware or software. Moreover, if the calculated credential is not unique for every account, an application with access to one account may re-use a credential to gain unauthorized access to another account. 
     An account identification value that is unique to a pairing of host and non-volatile memory card may prevent files stored in a non-volatile memory card from being accessed by more than one host. If the calculation of an account identification value in step  102  does not produce a result unique to the host, a plurality of hosts utilizing the same software or firmware to calculate an account identification value may calculate the same account identification value in step  102 , and credential in step  104 , and thus, be capable of accessing the contents associated with an account in a non-volatile memory card. 
     A host such as a cellular telephone may be capable of calculating unique account identification and credential values. A cellular telephone in communication with a mobile network, such as Global System for Mobile communication (GSM) or Code Division Multiple Access (CDMA) networks, contains a SIM card or R-UIM card, respectively, that stores one more values that uniquely identify the subscriber or a subscriber&#39;s cellular telephone. Values that may identify a subscriber include an International Mobile Subscriber Identity (IMSI) value; another is a Mobile Subscriber Integrated Services Digital Network (MSISDN) value. Additionally, other MNO-defined values unique to a SIM or R-UIM card, such as a master seed value or a master key value, may be stored in the card, and some of these MNO-defined values may not be read from the card. Values such as the International Mobile Equipment Identity (IMEI) uniquely identify GSM-capable cellular telephones. In addition to providing secure non-volatile storage for parameters defined by a Mobile Network Operator (MNO), a SIM card or R-UIM card typically contains a microcontroller that executes programs that are also defined by an MNO and stored within the SIM or R-UIM card. 
     Therefore, a unique account identification value or credential may be calculated utilizing IMSI, MSISDN, or similar values stored in a SIM card or R-UIM card, or alternatively, an IMEI value of a cellular telephone. Further, the formula utilized to calculate one or both values may be executed within the SIM card or R-UIM card to prevent the formula from being compromised, or to keep the formula under the control of the MNO. In one embodiment, the formula used to calculate the credential is stored and executed in the SIM card, and the formula utilized to calculate the account identification value is stored and executed in the host. 
     A typical SIM or R-UIM card contains a limited amount of storage, typically for the storage of subscriber identification values, and telephone contact lists. A product which incorporates high capacity non-volatile storage and the security features of a SIM card or R-UIM card under MNO control is sometimes referred to as a high-capacity SIM card. An example of a high-capacity SIM card is the SIM 5000™, a memory device from SanDisk Corporation of Milpitas, Calif. High-speed SIM cards may support the relatively slower ISO 7816 interface for backwards-compatibility with the existing SIM card receptacle on cellular telephones. Some high-capacity SIM cards may require a high-speed interface, such as a USB, SATA, MMC, or SD interface, in order to access the additional storage space. The SIM card receptacle found on some cellular telephones does not support accessing a high-speed SIM card over an additional, high-speed interface. Many cellular telephones, however, may support high speed access to a high-capacity non-volatile memory card in an additional card receptacle separate from the SIM or R-UIM card receptacle. 
     Therefore, a system may utilize the security features of a second volatile memory device such as a SIM or R-UIM card, to control access to a first non-volatile memory, such as a high-capacity non-volatile memory card.  FIG. 2A  is a diagram illustrating an exemplary secure storage system in accordance with an embodiment. An exemplary system  250  comprises a host  252  and two non-volatile memory devices  254  and  256 . The host  252  comprises a processor  260 . The processor  260  may be configured to communicate with a first non-volatile memory device  256  through a first communications interface  266 . The processor  260  may be further configured to communicate with a second non-volatile memory device  254  through a second communications interface  264 . The host  252  may be a personal computer, a notebook computer, a personal digital assistant (PDA), a data communication device, a digital camera, a cellular telephone, a portable audio player, an automobile sound system, or other similar types of equipment. In one embodiment, the host  252  and two non-volatile memory devices  254  and  256  are contained within the same enclosure, and one or both non-volatile memory devices  254  and  256  may not be removed from the enclosure. 
     In another embodiment, shown in  FIG. 2B , the host is a cellular telephone  202 , and the non-volatile memory devices are a SIM card  204 , and a non-volatile memory card  206 . The SIM card  204 , and a non-volatile memory card  206  may be inserted into receptacles in the cellular telephone  202 , and the cellular telephone may communicate with both cards. In another embodiment, the host  202  and non-volatile memory devices  204 ,  206  are contained in the same enclosure as the host, and the non-volatile memory devices are not removable. 
     An exemplary non-volatile memory card  206  may contain a plurality of accounts. Each account may be associated with a plurality of stored files, or storage partitions, in a non-volatile memory card  206 . Each account may be identified by a unique account identification value. Each account may also be associated with a credential, which may be utilized with various security methods to limit access to the account. For example, in order to access the files or partitions in a non-volatile memory card  206 , a host application may open or “log in” to the account. In one embodiment, the non-volatile memory card  206  with these features is a TrustedFlash™ memory device from SanDisk Corporation of Milpitas, Calif. In other embodiments, other types of non-volatile memory devices may be utilized in accordance with the system and method. For example, other types of memory devices may secure part of all of the storage space utilizing accounts associated with files or partitions, and credentials used in authentication procedures to access an account. 
     Referring back to  FIG. 1 , in order to gain access to an account in a non-volatile memory card  206 , an account identification value is calculated in step  102 , and a credential is calculated in step  104 .  FIG. 2B  also shows an exemplary flow of data between the cellular telephone  202 , the SIM card  204 , and the non-volatile memory card  206 , when performing the steps  100  to gain access to an account in the non-volatile memory card  206 . The cellular telephone  202  may read a card identification value, also referred to as a memory identification value, which may uniquely identify a single non-volatile memory card  206  or which may be associated with a group of cards. The cellular telephone  202  may also read an MNO identification value from the SIM card  204 . In one embodiment, the MNO identification value is an International Mobile Subscriber Identity (IMSI) value or similar value that uniquely identifies one subscriber or one cellular telephone. In another embodiment, the MNO identification value is the Mobile Country Code (MCC) and the Mobile Network Code (MNC) fields of the IMSI value, or any value which may uniquely identify the MNO. The cellular telephone  202  may use the MNO identification value or the card identification value to calculate an account identification value. The cellular telephone  202  may pass the calculated account identification value, and the card identification value read from the non-volatile memory card  206 , to the SIM card  204 . The SIM card  204  may utilize these values, and may also use an MNO identification value stored within the SIM card  204 , to calculate a credential. The MNO identification value utilized to calculate the credential may preferably be the same MNO value utilized to calculate the account identification value. However, in other embodiments, different MNO identification values may be utilized to calculate the account identification value and the corresponding credential. The cellular telephone  202  receives the calculated credential from the SIM card  204 , and may use the account identification value and credential to gain access to an account in the non-volatile memory card  206 , using a secure authorization procedure such as a challenge/response algorithm. 
     The variables utilized by the system  200  to calculate the account identification value and credential may differ depending on the type of secure account being accessed. The secure accounts may be broadly categorized into downloaded content accounts, and preloaded content accounts. 
     A downloaded content account may be associated with the digital content downloaded by the host  202  and stored on the non-volatile memory card  206 . In one embodiment, the host  202  is a cellular telephone, and the content may be downloaded through a connection established with an MNO, or an internet connection established through a wired or wireless connection. It may be desirable to limit access to the downloaded content to an individual subscriber of a mobile network, or to any subscriber of a particular mobile network. In one embodiment, an MNO may limit access by programming a cellular telephone  202  to calculate an account identification value utilizing a unique value associated with one subscriber, such as an International Mobile Subscriber Identity (IMSI) value or similar value that uniquely identifies one subscriber. Such a value may be stored in the SIM card  204 . In this embodiment, because the account identification value is calculated a utilizing the a unique value associated with one subscriber, the content stored in the non-volatile memory card  206  and associated with that account identification value may only be accessed by a host  202  in communication with that particular subscriber&#39;s SIM card  204 . 
     In another embodiment, an MNO may limit access to downloaded content by creating a downloaded content account with an account identification value based on a unique value associated with the MNO, such as a value formed from the Mobile Country Code (MCC) and the Mobile Network Code (MNC) fields of the IMSI value. The MCC and MNC mobile network identification values may also be stored in the SIM card  204 , and may uniquely identify a subscriber&#39;s MNO. In this embodiment, because the account identification value is calculated utilizing a unique value associated with the network of one MNO, the content stored in the non-volatile memory card  206  and associated with that account identification value may be accessed by a host  202  in communication with any SIM card  204  associated with that particular MNO. In this way, subscriber of a mobile network may replace a SIM card  204  and old host  202  with a new host  202  and SIM card  204  from the same MNO, and still be able to access content downloaded and stored on the non-volatile memory card  206  by the old host. In another example, the content stored in the non-volatile memory card  206  and associated with an account identification value derived from a mobile network identification value may be accessible from the cellular telephone hosts of two or more subscribers of the same MNO. 
     As shown above, two removable components of the system  200  of  FIG. 2B  are used to implement the account access steps  100  of  FIG. 1 . A new system  200  may be formed for each combination or pairing of a SIM card  204  and a non-volatile memory card  206 . While the SIM card  204  and the non-volatile memory card  206  may be physically separable from the system  200 , the downloaded content in non-volatile memory card  206  may only be accessible in a system  200  that utilizes a particular SIM card  204 . In this way, the SIM card  204  and the non-volatile memory card  206  can be said to be bound to one another. Binding may also refer to the process of creating accounts in the non-volatile memory card  206  using account identification values and credentials calculated with unique or special values in stored in the SIM card  204 . These accounts may be associated with content downloaded and stored in the non-volatile memory card  206 . The type of binding depends on the values utilized to calculate the account identification value and credential value. If the values utilized are unique to a SIM, such as an IMSI or a MSISDN value, the binding may be referred to as SIM binding. If the values utilized are unique to a cell phone, such as an IMEI value, the binding may be referred to as cellular telephone binding or handset binding. If the values utilized are unique to an MNO, such as a value formed from the Mobile Country Code (MCC) and the Mobile Network Code (MNC) fields of the IMSI value, the binding may be referred to as MNO binding. 
     In another embodiment, an MNO or content provider may not desire to restrict access to downloaded content to a particular subscriber or cellular telephone, or to subscribers of a particular network. In this embodiment, the downloaded content is not bound to a particular SIM card, to a particular cellular telephone, or to a particular MNO. The account identification values utilized may be predetermined or static values, such as the ASCII value corresponding to the string “download,” or values associated with a particular content provider, such as “download_MNO.” The account identification value may also be computed utilizing one or more card identification values stored within the non-volatile memory card  206 , which may uniquely identify a single non-volatile memory card  206 , or which may be associated with a group of cards. 
     In this embodiment, a value associated with a subscriber&#39;s IMSI value or a cellular telephone IMEI value may not be utilized to calculate the account identification and credential values for the downloaded content account. If the subscriber&#39;s IMSI value or cellular telephone IMEI value is not utilized, a downloaded content account may be accessible in a number of hosts  202  utilizing SIM cards  204  with different IMSI values. Instead, the account identification value of a downloaded content account may be a fixed value or may be based on a value stored within the non-volatile memory card  206  containing the account. The credential may be calculated utilizing the calculated account identification value or the value stored within the non-volatile memory card  206 . A non-volatile memory card  206  containing downloaded content accounts created utilizing these input variables may be accessed by a variety of systems  200  utilizing the correct formula or program to calculate the credential and account identification value, and is not dependent on a unique subscriber identification value stored in the SIM card  204 , or a unique hardware identification value associated with a host  202 . 
     A preloaded content account may be associated with digital content stored on the non-volatile memory card  206  before a user attempts to operate the card within a system, such as the system  200 . In one example, a non-volatile memory card  206  is sold or provided to the user with content, such as mp3 audio files, picture files, or video files, already stored or preloaded onto the card. A plurality of preloaded accounts may be utilized, corresponding to different content providers. The account identification values may be predetermined or static values, such as the ASCII value corresponding to the string “preload,” or values associated with a particular content provider, such as “preload_MNO.” The account identification value may also be computed utilizing one or more card identification values stored within the non-volatile memory card  206 , which may uniquely identify a single non-volatile memory card  206 , or which may be associated with a group of cards, such as a group of cards sold with the same preload content account or accounts. 
     In this embodiment, a value associated with a subscriber&#39;s IMSI value or a cellular telephone IMEI value may not be utilized to calculate the account identification and credential values for the preloaded content account, because the preloaded content accounts on the non-volatile memory card  206  are created before the card is operated within the system  200  containing the subscriber&#39;s SIM card  204 . If the subscriber&#39;s IMSI value or cellular telephone IMEI value is not utilized, a preloaded content account may be accessible in a number of hosts  202  utilizing SIM cards  204  with different IMSI values. Instead, the account identification value of a preloaded content account may be a fixed value or may be based on a value stored within the non-volatile memory card  206  containing the account. The credential may be calculated utilizing the calculated account identification value or the value stored within the non-volatile memory card  206 . By utilizing these input variables, a non-volatile memory card  206  containing preloaded content accounts may be accessed by a variety of systems  200  utilizing the correct formula or program to calculate the credential and account identification value, and is not dependent on a unique subscriber identification value stored in the SIM card  204 , or a unique hardware identification value associated with a host  202 . 
     Therefore, depending on whether preloaded content is being accessed, or downloaded content is being stored or accessed, the variables utilized to calculate the account identification value and credential may differ. When preloaded content is accessed, SIM binding, handset binding, or MNO binding may not be performed, and therefore, the MNO identification values are not utilized to calculate account identification values or credential values. When downloaded content is being stored or accessed, SIM binding, handset binding, or MNO binding may preferably be performed, and MNO identification values such as IMEI, IMSI, or MSISDN values may be utilized to calculate account identification values or credential values. However, in other embodiments, SIM binding, handset binding, and MNO binding are not used when creating accounts and credentials for downloaded content. Thus, the account identification value calculation in step  102  of  FIG. 1  and the credential calculation in step  104  of  FIG. 1  require further elaboration, when applied in the system  200  of  FIG. 2B . 
     Referring briefly back to  FIG. 1 , in order to read a file from or write a new file to the secure storage within the non-volatile memory card  206 , an account identification value may be calculated in step  102  in order to access an existing account, or create a new account. The system  200  comprising a SIM card  204 , a non-volatile memory card  206 , and host  202  may be utilized to calculate an account identification value in step  102 .  FIG. 3  is a diagram illustrating exemplary steps for calculating an account identification value in a secure system in accordance with an embodiment. At step  302 , the host determines whether the account to be opened is bound to a SIM card, an MNO, or a particular cellular telephone. Such binding may be utilized for downloaded content. If SIM binding, MNO binding, or cell phone binding is utilized, control passes to step  310 , where the host reads an MNO identification value from the SIM card. Depending on the degree of binding between the SIM card and the non-volatile memory card, the identification value may be a value unique to a single subscriber, such as an IMSI value or MSISDN value, a value unique to a cellular telephone, such as an IMEI value, or a value unique to a particular MNO, such as value formed by the combination of the Mobile Country Code (MCC) and the Mobile Network Code (MNC) fields of the IMSI value. Control passes to step  312 , where the host calculates the account identification value utilizing the MNO value read from the SIM card. 
     For preloaded content, and some types of downloaded content, an account may be created without SIM binding, MNO binding, or cell phone binding. If the host is opening this type of account, then control passes from step  302  to step  320 , where an identification value is read from the non-volatile memory card. The card identification value may uniquely identify a single non-volatile memory card, or the value may be associated with a group of cards, such as a group of cards sold or distributed with the same preloaded content. A predetermined or static value may also be determined by the host, such the ASCII value of the string “preload,” “download,” “preload_MNO,” or “download_MNO,” where “MNO” identifies a content provider. Control passes to step  322 , where an account identification value is formed, using either the predetermined or static value, a value calculated from the card identification value, or a combination or concatenation of the two. For example, if the static value is “preload,” and the value calculated from the card identification value is 1234, then the combination or concatenation may be the ASCII value of the string “preload — 1234.” 
     In one embodiment, the host, such as a cellular telephone, may calculate the account identification value utilizing the steps  300 . In another embodiment, the host may pass the input parameters, such as the static value, and the card identification value, to the SIM card, and trigger the SIM card to perform the account identification value calculation. In this embodiment, the SIM card may utilize the MNO identification value within the SIM card, without passing it to and from the host. In this embodiment, the MNO identification value utilized may be a value not readable from the SIM card by the host, such as a MNO-defined master seed value or a MNO-defined master key value. The SIM card may return the calculated account identification value to the host once the calculation is complete. 
     Referring briefly back to  FIG. 1 , in order to read a file from or write a new file to the secure storage within the non-volatile memory card  206 , a credential may be calculated in step  104  in order to access an existing account, or create a new account. The system  200  comprising a SIM card  204 , a non-volatile memory card  206 , and a host  202  may be utilized to calculate a credential in step  104 .  FIG. 4  is a diagram illustrating exemplary steps for calculating a credential value in a secure system in accordance with an embodiment. In step  402 , an account identification value is calculated. The account identification value may be calculated utilizing the steps  300  shown in  FIG. 3 . Control passes to step  404 , where an identification value is read from the non-volatile memory card. The card identification value may uniquely identify a single non-volatile memory card, or the value may be associated with a group of cards. In step  406 , the card identification value and the account identification value are transmitted to the SIM card. At step  408 , the type of credential calculation requested is dependent on whether the secure account to be accessed is bound to a SIM card, an MNO, or a particular cell phone. Such binding may be utilized for downloaded content. 
     If SIM binding, MNO binding, or cell phone binding is utilized, then control passes to step  412 , where the host requests that the SIM card calculates a credential utilizing the account identification value, card identification value, and an identification value stored within the SIM card, such as an IMSI, MSISDN, IMEI, or the combined MCC/MNC value. The selection of the SIM card identification value may depend on or correspond to the value selected in order to calculate the account identification value in step  312  of  FIG. 3 . For example, for subscriber or SIM binding, if the account identification value is calculated using the IMSI value, the corresponding credential for that account may be calculated utilizing the same IMSI value. In another example, for MNO binding, if the account identification value is calculated using or the combined MCC/MNC value, the corresponding credential for that account may be calculated utilizing the same combined MCC/MNC value. Control then passes to step  414 , the host receives the calculated credential from the SIM card. 
     For preloaded content, and some types of downloaded content, an account and corresponding credential may be created without SIM binding, MNO binding, or cell phone binding. If the host is determining a credential to open this type of account, then control passes from step  408  to step  410 , where the host requests that the SIM card calculates a credential utilizing the account identification value and the card identification value. At step  414 , the host receives the calculated credential from the SIM card. 
     Referring briefly back to  FIG. 1 , the exemplary steps  100  assumed that an account is already established in the non-volatile memory card to be accessed. This may not always be the case. When a new file is being written to a non-volatile memory card, it may be necessary to create an account to associate with the file to be written. Similarly, when a new non-volatile memory card is being initialized, such as when a host first interacts with a particular non-volatile memory card, the host may determine which accounts already exist, and which accounts should be created. For example, a downloaded content account may have an account identification value calculated using a unique value associated with a subscriber&#39;s SIM card, such as the IMSI number stored within the SIM card  204  of  FIG. 2B . Therefore, when a non-volatile memory card  206  is first introduced to the system  200 , the host  202  may create a downloaded content account that is bound with the system  200 , or more specifically, with identification values in the SIM card  204 , in order to download and store files to the non-volatile memory card  206 . 
     A host, such as host  202  in  FIG. 2B , may determine whether an account should be created by generating an account identification value and attempting to access an account with that account identification value in the non-volatile memory card  206 . If the access fails, then the host  202  may create a new account utilizing the calculated account identification value.  FIG. 5  is a diagram illustrating exemplary steps for creating a new storage account in a secure system in accordance with an embodiment. In step  502 , a host calculates the account identification value corresponding to an account to be created, or corresponding to an account associated with a file to be stored. Referring briefly back to  FIG. 3 , the account identification value may be calculated utilizing the exemplary steps  300 . Control passes to step  504 , where a credential associated with the account is calculated. Referring briefly back to  FIG. 4 , the credential may be calculated utilizing the exemplary steps  400 . 
     In step  506 , the host attempts to access the account utilizing the calculated credential and the calculated account identification value. In response, the non-volatile memory card may return a successful result and open the account. Therefore, the account exists, and control returns from step  508  to step  512 , where the opened account is closed, and then returns back to step  502 . Alternatively, the non-volatile memory card may indicate that the account does not exist, or may instead indicate that the account access failed, in which case, the host may assume that the account does not exist. In this case control passes from step  508  to step  510 . In step  510 , the host may create a new account on the non-volatile memory card utilizing the calculated account identification value and the calculated credential. The account creation process may include a series of commands and responses, such as transmitting the account identification value and credential from the host to the non-volatile memory card, and may further include a separate authorization procedure. 
     Multiple downloaded content accounts may be created on a single non-volatile memory card, where each downloaded content account has an account identification value based on a different SIM card ISMI. For example, a first host  202  and first SIM card  204  may be used to download and store content into a non-volatile memory card  206 . The account identification value associated with the first created downloaded content account may be based on a value unique a subscriber, such as an ISMI value in the first SIM card  204 . The same non-volatile memory card may be used to store content downloaded using a second host  202  and second SIM card  204 . The account identification value associated with the second created downloaded content account may be based on the different ISMI value stored in the second SIM card  204 . In this way, multiple downloaded accounts may be co-exist on a single non-volatile memory card  206 . 
     Referring briefly back to  FIG. 1 , until this point, it has been assumed that the formula used to calculate the credential in the exemplary steps  100  is already stored in the SIM card  204  of  FIG. 2B . This may not always be the case. For example, a SIM card  204  in the system  200  may be replaced with a SIM card without a formula. In another example, an MNO may provide a cellular telephone  202  with a SIM card  204  that does not contain the formula. When a non-volatile memory card  206  is inserted into the host  202 , the host  202  may determine whether the SIM card  204  contains the formula required to compute a credential for account creation or access. If the host  202  determines that the SIM card  204  does not contain the formula, the host  202  may obtain the formula and store it in the SIM card  204 . 
     In one embodiment, the host  202  contacts a server, receives the formula from the server, and stores the formula in the SIM  204 . The server may verify that host  202  has permission to receive the formula. Additionally, the host may verify the downloaded formula, and verify that the downloaded formula has been transmitted from a trusted source. In one embodiment, the host  202  is a cellular telephone, and the server request and formula download are over the air (OTA) transmissions of secure short messages (SSM). The downloaded formula may be encrypted. The host  202  may decrypt the received formula before storing in the SIM card  204 . Alternatively, the microcontroller in the SIM card  204  may decrypt the formula before storage or use within the SIM card  204 . 
     In another embodiment, the formula may be stored in the non-volatile memory card  206 . The host  202  may read the formula from the non-volatile memory card  206 , and store it in the SIM card  204 . Depending on the embodiment, there are several methods of securing the formula stored in the non-volatile memory card  206 , and each method may be used individually or in combination with other methods. In one embodiment, the formula stored in the non-volatile memory card  206  is encrypted. The host  202  may decrypt the formula read from the non-volatile memory card  206  before storing it in the SIM card  204 . Alternatively, the microcontroller in the SIM card  204  may decrypt the formula before storage or use within the SIM card  204 . In another embodiment, the formula is stored in a protected partition in the non-volatile memory card  206 . The host  202  may calculate an account identification value and credential in order to access the partition and formula, utilizing the exemplary steps  100  of  FIG. 1 . In this embodiment, the account identification value may be a static value, and the calculated credential may be calculated without using the formula stored in the non-volatile memory card  206 . A protected partition may also be referred to as a hidden partition, because a protected partition may not be visible to or accessible by a host file system, and a host application may trigger a security authorization routine such as the exemplary steps  100  in order to access the partition. 
     If the SIM card  204  is also utilized to calculate the account identification value, similar methods may be used to retrieve an additional program from a server or from the non-volatile memory card  206 . 
     Referring back to  FIG. 2B , where a system utilizes one non-volatile memory  204  to at least partially control access to storage within a second non-volatile memory  206 , there are a variety of configuration and usage scenarios introduced by the fact that the two non-volatile memories  204 ,  206  may be individually separable from each other and the system  200 . For example, a non-volatile memory card  206  may be preloaded with content and associated accounts, or may have not have any accounts established in the card. In another example, a SIM card  204  may not have the formula or program required to calculate the account identification value, or the credential.  FIG. 6  is a diagram illustrating exemplary situations for configuration and use of a secure storage system, in accordance with an embodiment. The exemplary situations may be divided into a setup phase  600 , where the system is configured, and an execution phase  650 , where the system is used to read and write content. 
     The chart corresponding to the setup phase  600  shows various initial configurations a system, such as system  200  of  FIG. 2B . In a first initial configuration, the SIM card  204  contains the formula or program needed to calculate the credential and possibly the account identification value, and the preloaded content accounts are already created in the non-volatile memory card  206 . This situation may occur when an MNO provides a system  200  to a subscriber containing a pre-configured SIM card  204  and a non-volatile memory card  206  with preloaded content. In this situation, no additional configuration is required, and the system is configured to access the preloaded content. 
     In a second initial configuration, the SIM card  204  does not contain the formula or program needed to calculate the credential and possibly the account identification value, and the preloaded content accounts are already created in the non-volatile memory card  206 . This situation may occur when an MNO provides the cellular telephone  202  and the SIM card  204 , and the subscriber purchases or obtains a non-volatile memory card  206  with preloaded content, and installs the non-volatile memory card  206  into the cellular telephone  202 . In this situation, the formula or program may be downloaded from a server, or retrieved from the non-volatile memory card  206 , and installed in the SIM card  204 . The system is then configured to access the preloaded content. 
     In the first or second situation, if a subscriber later decides to download and store content to the non-volatile memory card  206 , a downloaded content account may be created utilizing the steps  300  in  FIG. 3 , and the account may be accessed to store downloaded content using the steps  100  of  FIG. 1 . Thus, preloaded content accounts and downloaded content accounts may co-exist on the same non-volatile memory card  206 . 
     In a third initial configuration, the SIM card  204  contains the formula or program needed to calculate the credential and possibly the account identification value, and the non-volatile memory card  206  does not contain an account to associate downloaded content with. This situation may occur when an MNO provides the cellular telephone  202  and the SIM card  204 , and the subscriber purchases or obtains a non-volatile memory card  206 , and installs the non-volatile memory card  206  into the cellular telephone  202 . In this situation, a downloaded content account may be created utilizing the steps  300  in  FIG. 3 , and the account may be accessed to store downloaded content using the steps  100  of  FIG. 1 . 
     In a fourth initial configuration, the SIM card  204  does not contain the formula or program needed to calculate the credential and possibly the account identification value, and the non-volatile memory card  206  does not contain an account to associate downloaded content with. This situation may occur when an MNO provides the cellular telephone  202  and the SIM card  204 , and the subscriber purchases or obtains a non-volatile memory card  206 , and installs the non-volatile memory card  206  into the cellular telephone  202 . In this situation, the formula or program may be downloaded from a server, or retrieved from the non-volatile memory card  206 , and installed in the SIM card  204 . Once the formula or program is installed, a downloaded content account may be created utilizing the steps  300  in  FIG. 3 , and the account may be accessed to store downloaded content using the steps  100  of  FIG. 1 . 
     Once a system  200  of  FIG. 2B  is configured to access content, the setup phase  600  is complete, and the execution phase begins, where the exemplary steps  100  of  FIG. 1  may be executed to access or store content in the non-volatile memory card  206  of the system  200 . The calculation of the account identification value in step  102  of  FIG. 1  may be performed according to steps  300  of  FIG. 3 . Further, the calculation of the credential in step  104  of  FIG. 1  may be performed according to the steps  400  of  FIG. 4 . The steps  300   FIG. 3  and the steps  400  of  FIG. 4  show that different input variables may be utilized to calculate the account identification value and the credential, respectively, depending on whether preloaded content or downloaded content is being accessed in the non-volatile memory  206 . The chart corresponding to the execution phase  650  of  FIG. 6  summarizes the differences. 
     In Situation A of the chart for the execution phase  650 , the cellular telephone  202  attempts to access preloaded content, or store and access downloaded content associated with an account created without SIM binding, cellular telephone binding, or MNO binging, on the non-volatile memory card  206 . In this situation, a card identification value from the non-volatile memory card  206 , or a static value, may be utilized to compute an account identification value. The calculated account identification value and a card identification value from the non-volatile memory card  206  may be utilized to calculate the credential. The calculated credential and the calculated account identification value may be used to access the preloaded content account in the non-volatile memory card according to the remaining steps  106 - 112  of  FIG. 1 . 
     In Situation B of the chart for the execution phase  650 , the cellular telephone  202  attempts to download and store content to the non-volatile memory card  206 , or access downloaded content already stored in the non-volatile memory card  206 , where the downloaded content is associated with an account created with SIM binding, cellular telephone binding, or MNO binding. In this situation, an MNO identification value from the SIM card  204  may be utilized to compute an account identification value. Depending on the degree of binding between the SIM card  204  and the non-volatile memory card  206 , the identification value may be a value unique to a single subscriber, such as an IMSI value or MSISDN value, a value unique to a cellular telephone, such as an IMEI value, or a value unique to a particular MNO, such as value formed by the combination of the Mobile Country Code (MCC) and the Mobile Network Code (MNC) fields of the IMSI value. The calculated account identification value, a card identification value from the non-volatile memory card  206 , and the MNO identification value may be utilized to calculate the credential. The calculated credential and the calculated account identification value may be used to access the downloaded content account according to the remaining steps  106 - 112  of  FIG. 1 . 
     Thus, non-volatile memory  206  in exemplary system  200  may be accessed according to the security protocol steps  100  of  FIG. 1 . The calculation of the account identification value in step  102 , and the calculation of the associated security credential in step  104 , may be further secured by utilizing a second non-volatile memory device, such as a SIM card  204 , to provide input variables and perform some of all of the calculation of the values. Specifically, in some cases, a SIM card  204  may provide unique identification values in order to calculate the account identification value according to steps  300  of  FIG. 3 . Additionally, the SIM card  204  may provide unique identification values, and may also be used to calculate the credential value according to steps  400  of  FIG. 4 . Utilizing the exemplary steps  100 ,  300 , and  400  of  FIGS. 1 ,  3 , and  4 , an MNO may bind selected downloaded content with an individual subscriber, an individual cellular telephone, or an individual MNO. Alternatively, downloaded content may be stored in accounts created without binding to an individual subscriber, an individual cellular telephone, or individual MNO. Depending on the type of binding utilized, an MNO may restrict access to and copying of downloaded content by unauthorized users. Additionally, an MNO may support a system  200  that may access preloaded content securely stored on mass produced non-volatile memory cards  206 , and may control access to that preloaded content provided on a non-volatile memory card  206 . 
     While the system  200  in  FIG. 2B  utilizes a SIM card  204 , various other embodiments may not be limited to this configuration. For example, a high-capacity SIM card, such as the SIM 5000™, a memory device from SanDisk Corporation of Milpitas, Calif., may be utilized in place of the SIM card  204 . In this system  200 , the high-capacity SIM card may perform the functions associated with the SIM card  204 , such as calculating the credentials or account identification value utilized for account access, or storing unique subscriber, equipment, and MNO identification values. The additional storage within the high-capacity SIM card may augment or supplement the total amount of secure storage available to the user of the system  200 . 
     Further, while other aspects of the systems and methods may have been described with respect to the use of Subscriber Identity Module (SIM) cards and identification values associated with SIM cards and GSM networks, these embodiments may not be so limited. Embodiments in accordance with various principles of the present invention may also be implemented in systems that utilize other card formats, such as high-capacity SIM cards, Smart Cards, or R-UIM cards. Moreover, although various principles of the invention have been described with respect to various exemplary embodiments, it will be understood that the invention is entitled to protection within the full scope of the appended claims.