Abstract:
Since no control of accesses made by a computer as accesses to a storage apparatus is executed, the computer can be used illegally to steal and improperly change data stored in the storage apparatus. Thus, an access-control mechanism external to the computer is constructed to solve this problem. That is to say, the control of accesses is executed in the storage apparatus and a network apparatus for each program executed by the computer. In order to enhance the implementability of such control of accesses, the control is executed without extending a variety of protocols of communications among the computer, the network apparatus and the storage apparatus. By implementing the control of accesses in this way, a program other than programs specified in advance is not capable of making an access to data stored in the storage apparatus. Thus, even if the computer is used illegally, data stored in the storage apparatus can be prevented from being stolen and changed improperly.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to programs, a network apparatus, a storage apparatus as well as a computer system using the programs, the network apparatus and the storage apparatus. More particularly, the present invention relates to programs, a network apparatus, a storage apparatus and such a computer system, which are capable of assuring required high security.  
         BACKGROUND OF THE INVENTION  
         [0002]    In a storage apparatus directly connected to a computer, accesses to the storage apparatus are normally not controlled. Instead, an IO command issued by the computer directly connected to the storage apparatus is processed unconditionally. In a SAN (Storage Area Network) including one or more storage apparatus and one or more computers sharing the storage apparatus, accesses to the storage apparatus are controlled by including computers in set zones with and without access rights. However, an IO command received from a computer having an access right is processed unconditionally. Thus, since an IO command received from a computer having an access right is processed unconditionally in this way, data stored in a storage apparatus can be stolen by illegally using such a computer. If the worst comes to the worst, data stored in a storage apparatus may be changed improperly. There is a number of countermeasures for preventing a computer from being used illegally. However, those countermeasures are not necessarily perfect. For example, data can be encrypted so that the data cannot be decoded even if the data is stolen. If the encrypted data can be decrypted, nevertheless, the stolen data can be decoded.  
           [0003]    In addition to access control executed in a computer, access control executed in a storage apparatus is an effective means to prevent data from being stolen and changed improperly by using a computer illegally. Specially, in accordance with a method disclosed in Japanese Patent Laid-Open No. 2002-222110, control of accesses is executed in a storage apparatus for each application program making accesses to the storage apparatus. Thus, the security of data can be assured even if the user or a person in charge of computer management uses a computer illegally. In order to implement the access control disclosed in the document, however, a special OS is required. In addition, it is necessary to extend a protocol of communication between the computer and the storage apparatus.  
           [0004]    Thus, the present invention is provided as a means for solving a problem that data managed by a program is stolen, changed improperly or erased by using a computer illegally. In addition, the present invention provides a method for controlling accesses without changing a variety of programs and without requiring a special OS.  
         SUMMARY OF THE INVENTION  
         [0005]    In order to solve the problems described above, control of accesses to a storage apparatus is executed in the storage apparatus or a network apparatus for each program. In order to execute the control of accesses to a storage apparatus for each program, a program identifier is assigned to each program and delivered to the storage apparatus or the network apparatus along with an IO command issued by the program. On the basis of a program identifier, the storage apparatus or the network apparatus determines whether or not execution of the IO command received along with the program identifier is allowed. In order to be able to deliver a program identifier to the storage apparatus or the network apparatus without changing a protocol of communication between the computer and the storage apparatus or the network apparatus, the program identifier is embedded in a special value included in the IO command or an IO request made to generate the IO command. To put it concretely, a function f (x, y) is used to include the program identifier in the special value as an embedded program identifier. The function (x, y) is a function inputting two values x and y to generate one value, i. e., a new value including the embedded program identifier. In this case, x and y represent the program identifier and the special value respectively. In addition, an inverse function g (z) is also required as a function inversed to the function f (x, y). The inverse function g (z) is a function inputting 1 value z, i. e., the new value including the embedded program identifier, to obtain two values, i. e., the original special value and the original program identifier. In this way, a program identifier can be supplied to the storage apparatus or the network apparatus without changing the protocol of communication between the computer and the storage apparatus or the network apparatus.  
           [0006]    That is to say, a representative characteristic of the present invention is the use of the means described above to supply a program identifier to the storage apparatus and the network apparatus and to control accesses to the storage apparatus in the storage and network apparatus. In this specification, this technique of controlling accesses to the storage apparatus is referred to as a program-identifier method.  
           [0007]    The program-identifier method requires that the storage apparatus and the network apparatus be modified. In consequence, the possibility of implementability is lowered by as much as the changes made to the storage and network apparatus. In accordance with another characteristic of the present invention, an access control mechanisms already existing in the storage apparatus and the network apparatus are used. To put it in detail, in the network, network addresses are assigned to the computer and the storage apparatus to make it possible to execute control of accesses on the basis of the network addresses in the computer, the network apparatus and the storage apparatus. In actuality, a plurality of network addresses is assigned to the computer. In the computer, each network address is associated with a program identifier for identifying a program. The computer communicates with the storage apparatus by using a network address associated with a program identifier, transmitting an IO command to the storage apparatus. In the network apparatus and the storage apparatus, information indicating whether or not an access to the storage apparatus is allowed is set for each network address assigned to the computer. Thus, the storage apparatus and the network apparatus are capable of executing control of accesses to the storage apparatus by using a network address specified in each of the accesses. Since a network address associated with a program identifier in the computer is used, however, in essence, a program issuing an IO request executes the control of accesses to the storage apparatus. In this specification, the technique adopted by a program issuing an IO request to control accesses to the storage apparatus is referred to as a network-address conversion method.  
           [0008]    In the case of the network-address conversion method, a table associating a program identifier with a network address is included in the computer. If the table associating a program identifier with a network address is kept at the computer&#39;s internal location accessible to a user or a router, however, an unauthorized user hijacking the computer will be capable of illegally changing the contents of the table. Thus, the problem of the present invention cannot be solved. In order to solve the problem of illegal modification of the table associating a program identifier with a network address, the table is kept at the computer&#39;s internal location inaccessible to the user. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a conceptual diagram showing a program making an access to a protected logical volume;  
         [0010]    [0010]FIG. 2 shows a flowchart representing operations carried out by an address conversion module  104 ;  
         [0011]    [0011]FIG. 3 is a functional block diagram showing a computer system implemented by an embodiment of the present invention;  
         [0012]    [0012]FIG. 4 shows a flowchart representing operations carried out by an address inverse conversion module  306  of the embodiment;  
         [0013]    [0013]FIG. 5 is a diagram showing the data structure of a network-address table  308  employed in the embodiment;  
         [0014]    [0014]FIG. 6 is a functional block. diagram showing a computer system implemented by another embodiment of the present invention;  
         [0015]    [0015]FIG. 7 is a functional block diagram showing a computer system implemented by a further embodiment of the present invention;  
         [0016]    [0016]FIG. 8 shows a flowchart representing operations carried out by an accessibility determination unit  707  of the further embodiment;  
         [0017]    [0017]FIG. 9 is a diagram showing the data structure of an accessibility determination table  709  employed in the further embodiment;  
         [0018]    [0018]FIG. 10 is a functional block diagram showing a computer system implemented by a still further embodiment of the present invention;  
         [0019]    [0019]FIG. 11 shows a flowchart representing operations carried out by a communicatability determination unit  1007  of the still further embodiment; and  
         [0020]    [0020]FIG. 12 is a diagram showing the data structure of a communicatability determination table  1008  employed in the still further embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Preferred embodiments of the present invention are explained as follows.  
         [0022]    The description begins with an explanation of a function to embed a program identifier into a specific value to result in a new value and a function to fetch the original specific value and the program identifier from the new value including the program identifier embedded therein by the function to embed a program identifier. For the sake of simplicity, the function to embed a program identifier into a specific value to generate a new value is referred to as an identifier-embedding function f or simply as a function f. On the other hand, the function to fetch the original specific value and the program identifier from the new value including the program identifier embedded by the function f is referred to as an identifier-fetching function g or simply as an inverse function g. The function f can be any function as long as the function is capable of embedding a program identifier into a specific value. Likewise, the inverse function g can be any function as long as the function is capable of fetching the original specific value and the program identifier from the new value including the program identifier embedded by the function f. The function f is a function inputting two values and outputting one value. On the other hand, the inverse function g is a function inputting one value and outputting two values. If z is the output of f (x, y), g (z) outputs x and y. A conceivably simplest example of the function f is a function to concatenate a program identifier with a specific value on the high-order side of the specific value as high-order bits of a resulting new value. A conceivably simplest example of the inverse function g is a function to extract the high-order bits from the resulting new value to give the program identifier and the original specific value. The function f and the inverse function g can be applied to a case in which the real storage capacity of a logical volume is small so that high-order bits of the address are not used. Since types of the function f and the inverse function g have nothing to do with the embodiments described below, the following description does not specifically describe the types of the function f and the inverse function g.  
         [0023]    [0023]FIG. 1 is a diagram showing a program  101  using the function f. Examples of the program  101  are an application program and middleware using a storage apparatus. Examples of such middleware are a database management system and a web server. The program  101  comprises a processing main module  102  and an IO-processing module  103  for inputting and outputting data from and to a storage apparatus. In the implementation of this patent, the IO-processing module  103  is provided with an address conversion module  104  for embedding a program identifier into an address by using the function f. In addition, the IO-processing module  103  has an IO-request issuance module  105  for issuing an IO request to an OS.  
         [0024]    When the processing main module  102  needs to input or output data from or to the storage apparatus, the processing main module  102  issues an IO request to the IO-processing module  103 . In the IO-processing module  103 , first of all, the IO request is received by the address conversion module  104 . FIG. 2 shows a flowchart representing operations carried out by the address conversion module  104 . The flowchart begins with a step  201  at which the address conversion module  104  first determines whether or not the IO request is an IO request issued to a protected logical volume existing in the storage apparatus. A protected logical volume is a logical volume subjected to control of accesses to the logical volume by execution of a program in accordance with the present invention. If the IO request is an IO request issued to a protected logical volume, the flow of the address conversion process goes on to a step  202  at which an original address included in the IO request and a program identifier set in the program  101  are used as inputs to the function f to generate a new address including an appended program identifier. The new address including an appended program identifier is then set as the original address included in the IO request. If the IO request is not an IO request issued to a protected logical volume, on the other hand, the execution of the address conversion process is ended without doing anything. The IO request generated by the IO-processing module  103  is issued from the IO-request issuance module  105  to the OS.  
         [0025]    [0025]FIG. 3 is a diagram showing a first embodiment. The first embodiment implements a computer system provided by the present invention as a computer system, which uses an access control function existing in a storage apparatus and adopts the network-address conversion method. The computer system shown in FIG. 3 comprises a computer  301 , a network apparatus  302  and a storage apparatus  303 . The computer  301  executes an OS  305  for managing programs and computer resources. Thus, the program  101  operates under the management executed by the OS  305 . The program  101  is the program described earlier by referring to FIG. 1. That is to say, the program  101  may need to carry out IO operations to input and output data from and to the storage apparatus  303 . If an IO request for the IO operation is an IO request issued to a protected logical volume existing in the storage apparatus  303 , the original address specified in the IO request is converted into a new address with an identifier appended thereto to generate a new IO request to be actually issued to the storage apparatus  303 . The new address with an identifier appended thereto is an address specified in the IO request as an address, which now includes a program identifier assigned to the program  101 . In the embodiment, the computer  301  and the OS  305  are not limited to a special computer and a special OS respectively. A TCP/IP (Transmission Control Protocol/Internet Protocol) network or a SAN (Storage Area Network) can each be used as an optimum network connecting the computer  301  to the storage apparatus  303 . The network apparatus  302  is a network apparatus having a type suitable for the network. If a TCP/IP network is used, the network apparatus  302  is a hub, a switch, a router and/or a gateway. If a SAN is used, on the other hand, the network apparatus  302  is an FC (Fibre Channel) switch. The storage apparatus  303  is dependent on the type of the network. If a TCP/IP network is used, the storage apparatus  303  is a disk apparatus conforming to NAS (Network Attached Storage) specifications or an iSCSI (Internet Small Computer System Interface). If a SAN is used, on the other hand, the storage apparatus  303  is a storage apparatus conforming to FC specifications. An example of the storage apparatus  303  conforming to FC specifications is a RAID (Redundant Array of Independent Disks) apparatus. The storage apparatus  303  provides a logical volume  311  to the computer  301 . A logical volume  311  is a disk space made available to a computer. The logical volume  311  includes the so-called logical device and the so-called logical unit.  
         [0026]    The program  101  issues an IO request to the OS  305 . Normally, the OS  305  puts IO requests received from a plurality of processes in the program  101  in a buffer. Each of the IO requests is eventually output as an IO command to the storage apparatus  303  from a device driver, which is provided for each IO device including the storage apparatus  303 , or a microprogram embedded in the board of the computer  301 . An IO-command issuance module  307  represents the device driver, the microprogram or the like. In the present invention, an IO request is supplied to the IO-command issuance module  307  by way of an address inverse conversion module  306 . FIG. 4 shows a flowchart representing operations carried out by the address inverse conversion module  306 .  
         [0027]    The flowchart begins with a step  401  to determine whether or not the IO request is an IO request issued to a protected logical volume. If the IO request is not an IO request issued to a protected logical volume, the execution of the address inverse conversion process is ended without doing anything. If the IO request is an IO request issued to a protected logical volume, on the other hand, the flow of the process goes on to a step  402  at which an address specified in the IO request is used as an input of the inverse function g to generate an original address and a program identifier. Then, at the next step  403 , a network-address table  308  is searched for a network address associated with the generated program identifier and a logical-volume identifier represented by the original address. FIG. 5 is a diagram showing the data structure of the network-address table  308 . Each row of the network-address table  308  shows a logical-volume identifier, a program identifier and a network address. Symbol * represents any identifier in addition to identifiers each set as a concrete symbol on the column on which symbol * appears. Typical data of the network-address table  308  shown in FIG. 5 indicates that a program with a program identifier of  001  is allowed to communicate with logical volume LV 1  by using an IO request specifying a network address of aaa. In addition, a program with a program identifier of  002  is allowed to communicate with any logical volumes besides LV 1  and LV 2  by using an IO request specifying a network address of bbb. Furthermore, a program with any program identifier in addition to  001  and  002  is allowed to communicate with logical volume LV 2  by using an IO request specifying a network address of ccc. Moreover, a row showing a logical-volume identifier of * and a program identifier of * is always provided in the network-address table  308  as a pattern representing each request for an IO access to an inaccessible protected logical volume. Since an IO request corresponding to this pattern is always a rejected IO request, the network address included on the row showing this pattern is set as at a value with which a communication with the storage apparatus  303  cannot be carried out. In the typical data of the network-address table  308  shown in FIG. 5, the network address included on the row showing this pattern is set at ddd. After a network address is obtained, the flow of the address inverse conversion process goes on to a step  404  at which the network address obtained from the network-address table  308  is used in an IO command as the network address of the computer  301  and the original address generated by the inverse function g is used in an IO command as a substitute for the address specified in the IO request. Finally, the execution of the address inverse conversion process is ended.  
         [0028]    The IO request output by the address inverse conversion module  306  is supplied to the IO-command issuance module  307 . A communication with the storage apparatus  303  is carried out through the use of an IO command specifying the network address of the computer  301 . To be more specific, the IO command is transmitted to the storage apparatus  303 .  
         [0029]    In the storage apparatus  303 , when an IO command making a request for a connection is received, a communicatability determination unit  309  examines the network address specified in the IO command to determine whether or not the storage apparatus  303  is allowed to carry out a communication with the computer  301  identified by the network address as the originator of the request. If the network address in the IO command is set at a value by which a communication with the storage apparatus  303  is not allowed, the storage apparatus  303  does not accept the IO command, generating an error. If the network address in the IO command is set at a value by which a communication with the storage apparatus  303  is allowed, on the other hand, the storage apparatus  303  accepts the IO command. In this case, the communicatability determination unit  309  passes on the IO command to an IO-command-processing unit  310  for processing the IO command.  
         [0030]    The first embodiment comprises one computer  301 , one network apparatus  302  and one storage apparatus  303 . However, the principle of a multi-unit computer system comprising a plurality of computers  301 , a plurality of network apparatus  302  and a plurality of storage apparatus  303  is all but the same as the first embodiment. Thus, a special explanation of such a multi-unit computer system is not required.  
         [0031]    [0031]FIG. 6 is a diagram showing a second embodiment. The second embodiment implements a computer system provided by the present invention as a computer system, which uses an access control function existing in a storage apparatus and adopts the network-address conversion method. The configuration of the computer  301  as well as internal operations of the address inverse conversion module  306 , the IO-command issuance module  307  and the IO-command-processing unit  310  are identical with those of the first embodiment shown in FIG. 3. Thus, elements of the second embodiment, that are identical with their counterparts in the first embodiment shown in FIG. 3, are denoted by the same reference numerals assigned to the counterparts. The second embodiment is different from the first embodiment in that, in the case of the second embodiment, the communicatability determination unit  609  is provided in the network apparatus  602  so that the network apparatus  602  is capable of executing control of accesses to the storage apparatus  303 .  
         [0032]    Like the first embodiment, the second embodiment comprises one computer  301 , one network apparatus  602  and one storage apparatus  303 . However, the principle of a multi-unit computer system comprising a plurality of computers  301 , a plurality of network apparatus  602  and a plurality of storage apparatus  303  is all but the same as the second embodiment. Thus, a special explanation of such a multi-unit computer system is not required.  
         [0033]    [0033]FIG. 7 is a diagram showing a third embodiment. The third embodiment implements a computer system provided by the present invention as a computer system, which uses an access control function existing in a storage apparatus and adopts the program-identifier method. Since the configuration of the third embodiment is identical with the first embodiment, most explanation of the third embodiment is omitted except for differences between the two embodiments.  
         [0034]    In a computer  701 , a program  704  issues an IO request specifying an address including a program identifier embedded therein. An IO-command issuance module  706  included in an OS  705  issues an IO command for the IO request to a storage apparatus  703 . In the storage apparatus  703 , the IO command received from the computer  701  is supplied to an IO-command-processing unit  708  by way of an accessibility determination unit  707 . The IO-command-processing unit  708  carries out operations to input and output data from and to a logical volume  710  in accordance with the IO command.  
         [0035]    On the basis of the program identifier included in the IO command, the accessibility determination unit  707  determines whether or not processing of the IO command is allowed. FIG. 8 shows a flowchart representing operations carried out by the accessibility determination unit  707 . The flowchart begins with a step  801  to determine whether or not the IO command is a command issued to a protected logical volume. If the IO command is not a command issued to a protected logical volume, the IO command is passed on to the IO-command-processing unit  708  without carrying out any operation on the IO command. If the IO command is a command issued to a protected logical volume, on the other hand, the flow of the processing goes on to a step  802  at which the address specified in the IO command is used as the input to the inverse function g for generating an original address and a program identifier. Then, at the next step  803 , an accessibility determination table  709  is searched for a row showing the program identifier and a logical volume identifier represented by the original address. Then, at the next step  804 , the search result is used as a basis for determining whether or not the program  704  issuing the IO command has the right of making an access to the logical volume. FIG. 9 is a diagram showing an example of the data structure of the accessibility determination table  709 . In accordance with the typical accessibility determination table  709  shown in FIG. 9, a program  704  identified by a program identifier of  001  or  002  has the right of making accesses to logical volume LV 1 , a program  704  identified by a program identifier of  001  has the right of making accesses to logical volume LV 2  and a program  704  identified by a program identifier of  003  has the right of making accesses to logical volume LV 3 . If the program  704  issuing the IO command has an access right, the flow of the processing goes on to a step  805  at which the original address generated by the inverse function g is used as a substitute for the address specified in the IO command. Finally, the execution of the processing is ended. If the program  704  issuing the IO command does not have an access right, on the other hand, the flow of the processing goes on to a step  806  at which an error code is returned without passing on the IO command to the IO-command-processing unit  708  before the execution of the processing is ended.  
         [0036]    Like the first embodiment, the third embodiment comprises one computer  701 , one network apparatus  702  and one storage apparatus  703 . However, the principle of a multi-unit computer system comprising a plurality of computers  701 , a plurality of network apparatus  702  and a plurality of storage apparatus  703  is all but the same as the third embodiment. Thus, a special explanation of such a multi-unit computer system is not required.  
         [0037]    [0037]FIG. 10 is a diagram showing a fourth embodiment. The fourth embodiment implements a computer system provided by the present invention as a computer system, which uses an access control function existing in a storage apparatus and adopts the program-identifier method. Since the configuration of the fourth embodiment is identical with the first embodiment, most explanation of the fourth embodiment is omitted except for differences between the two embodiments.  
         [0038]    In a computer  1001 , a program  1004  issues an IO request specifying an address including a program identifier embedded therein. An IO-command issuance module  1006  included in an OS  1005  issues an IO command for the IO request to a storage apparatus  1003  by way of a network apparatus  1002 . The network apparatus  1002  has a communicatability determination unit  1007  for controlling packets flowing through a network.  
         [0039]    The communicatability determination unit  1007  examines a packet to determine whether or not the packet can be transmitted to the transmission destination of the packet. FIG. 11 shows a flowchart representing operations carried out by the communicatability determination unit  1007 . The flowchart begins with a step  1101  at which the communicatability determination unit  1007  fetches an IO command from a packet conveying the IO command. Then, at the next step  1102 , the IO command is examined to determine whether or not the IO command is a command issued to a protected logical volume. If the IO command is not a command issued to a protected logical volume, the packet is transmitted without carrying out any operation on the packet. If the IO command is a command issued to a protected logical volume, on the other hand, the flow of the processing goes on to a step  1103  at which the address specified in the IO command is used as the input to the inverse function g for generating an original address and a program identifier. Then, at the next step  1104 , a communicatability determination table  1008  is searched for a row showing the program identifier, the identifier of a logical volume and the identifier of a storage apparatus. The identifier of a logical volume and the identifier of a storage apparatus are represented by the original address. Then, at the next step  1105 , the search result is used as a basis for determining whether or not a communication requested by the IO command can be carried out. FIG. 12 is a diagram showing an example of the data structure of the communicatability determination table  1008 . In accordance with the typical communicatability determination table  1008  shown in FIG. 12, a program  1104  identified by a program identifier of  001  or  002  has the right of making accesses to logical volume LV 1  existing in a storage apparatus  1003  identified by a storage identifier of ST 1 , a program  1004  identified by a program identifier of  001  has the right of making accesses to logical volume LV 1  existing in a storage apparatus  1003  identified by a storage identifier of ST 2  and a program  1004  identified by a program identifier of  003  has the right of making accesses to logical volume LV 2  existing in a storage apparatus  1003  identified by a storage identifier of ST 2 . If the program  1004  issuing the IO command has an access right, the flow of the processing goes on to a step  1106  at which the original address generated by the inverse function g is used as a substitute for the address specified in the IO command, and the packet including the IO command is transmitted to the storage apparatus  1003 . Finally, the execution of the processing is ended. If the program  1004  issuing the IO command does not have an access right, on the other hand, the flow of the processing goes on to a step  1107  at which an error code is returned to the computer  1001  and the packet including the IO command is discarded before the execution of the processing is ended.  
         [0040]    Like the first embodiment, the fourth embodiment comprises one computer  1001 , one network apparatus  1002  and one storage apparatus  1003 . However, the principle of a multi-unit computer system comprising a plurality of computers  1001 , a plurality of network apparatus  1002  and a plurality of storage apparatus  1003  is all but the same as the fourth embodiment. Thus, a special explanation of such a multi-unit computer system is not required.  
         [0041]    In either case of the  4  embodiments described above, any program running on the OS is assumed to be the program  101  explained by referring to FIG. 1. Even if a program, which issues an IO request specifying an address including no program identifier embedded therein to a protected logical volume, runs on the OS, however, the program will not raise a problem. This is because, if such a program issues such an IO request to a protected logical volume, in the address inverse conversion module  306  employed the first embodiment and the address inversion conversion module  306  employed in the second embodiment generate an incorrect program identifier associated with such a network address that a result of searching an address conversion table (the network-address table  308 ) will indicate an unallowable communication. In the case of the third embodiment, on the other hand, the accessibility determination unit  707  generates an incorrect program identifier corresponding to an inaccessibility in the accessibility determination table  709 . Likewise, in the case of the fourth embodiment, the communicatability determination unit  1007  generates an incorrect program identifier corresponding to an unallowable communication in the communicatability determination table  1008 .  
         [0042]    With the present invention, a program other than the program set in advance as a program having the right of making accesses to a protected logical volume is not allowed to make an access to the logical volume. Thus, if a computer is used illegally, data accessed by the computer cannot be directly used. As a result, data can be prevented from being stolen and changed improperly.