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Claims  |
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I claim:
1. A computer system including a file transform mechanism, said system
comprising:
a) a file storage subsystem that provides for the storage of a file
composed of one or more blocks of data;
b) a memory providing for the storage of blocks of data in first and second
logical data areas within said memory;
c) a processor, including programming, providing for the execution of
instructions implementing a computer operating system in said first
logical data area and an application program in said second logical data
area, said processor being coupled to said file storage subsystem and said
memory to permit the transfer of a predetermined block of data between
said file storage subsystem and said memory, said processor including
i) a transform function, defined by the execution of instructions of said
computer operating system, for translating said predetermined block of
data between first and second data representations in said first logical
data area separately from another block of data;
ii) a request function, defined by the execution of instructions of said
application program, for selecting said predetermined block of data to be
operated on by the execution of instructions of said application program
in said second logical data area; and
iii) an interface function, defined by the execution of instructions of
said computer operating system and coupled to said transform function and
said request function, that controls the transfer of said predetermined
block of data between said file storage subsystem and said memory and
between said first and second logical data areas of said memory, said
interface function determining whether said predetermined block of data is
in said first or second data representations and wherein said interface
function, responsive to said request function, controls the transfer of
said predetermined block of data from said file storage subsystem to said
memory and from said first logical data area to said second logical data
area selectively through said transform function.
2. The computer system of claim 1 wherein said file storage subsystem
further stores authentication data with respect to said file, said
authentication data relating said first and second transform
representations of said data blocks of said file.
3. The computer system of claim 2 wherein said authentication data is
accessible by said interface function and used in determining whether said
predetermined block of data is in said first or second data
representation.
4. The computer system of claim 1, 2, or 3 wherein execution of said
transform function provides for the performance of at least one transform
from a set of transforms including encryption, compression, encoding,
translation and conversion.
5. A computer system including a file encryption mechanism, said system
comprising:
a) a file store providing for the storage of a file including one or more
blocks of data;
b) a memory store providing for the storage of blocks of data in first and
second logical data areas; and
c) a processor coupled to said memory store and said file store for
executing instructions implementing a computer operating system as stored
in said first logical data area and an application program as stored in
said second logical data area, said processor providing for the controlled
transfer of a predetermined block of data between said file store and said
data store means, said processor including:
i) an encryption routine, defined by the execution of instructions of said
computer operating system, for encrypting and decrypting said
predetermined block of data in said first logical data area separately
from another block of data;
ii) a request routine, defined by the execution of instructions of said
application program, for selecting said predetermined block of data to be
operated on by the execution of instructions of said application program
in said second logical data area; and
iii) a system interface routine, defined by the execution of instructions
of said computer operating system and responsive to said request routine,
that controls the transfer of said predetermined block of data between
said file store and said data store and between said first and second
logical data areas of said data store, said system interface routine
determining whether said predetermined block of data is encrypted as
stored by said file store, said system interface routine selectively
directing the transfer of said predetermined block of data between said
first and second logical data areas through said encryption routine.
6. The computer system of claim 5 wherein said file store further stores
file attribute data defining predetermined attributes of a corresponding
file stored by said file store, said file attribute data including a file
encryption attribute.
7. The computer system of claim 6 wherein said file attribute data is
accessible by said system interface routine and wherein said file
encryption attribute is used to determine whether said predetermined block
of data is encrypted.
8. A mechanism providing for transparent key based file protection in a
computer system including a processor, main memory and a mass storage
device, wherein the processor executes an operating system stored within
the main memory, wherein execution of the operating system establishes
kernel and application data spaces within the computer system, and wherein
the operating system includes a system call interface supporting a
plurality of operating system calls and a memory access routine executable
by the processor providing for the transfer of a block of data between the
kernel and application data spaces within the main memory and between the
main memory and a mass storage device that provides for the storage of a
file including one or more blocks of data, said mechanism comprising:
a) a key dependant data transformation routine provided in said kernel data
space, executable by the processor and coupleable to the memory access
routine, for selectively transforming a predetermined block of data of a
predetermined file between first and second data representations based on
a transformation key that is arbitrarily related to the data of said
predetermined block of data; and
b) an interface routine interposed between the system call interface and
the memory access routine within said kernel data space, said interface
routine being coupled to the memory access routine to control the transfer
of said predetermined block of data between the kernel and application
data spaces, said interface routine determining whether said predetermined
block of data is in said first or second data representation when stored
in said predetermined file, said interface routine selectively providing
for the transfer of said predetermined block of data between through said
key dependant data transformation routine whereby said predetermined block
of data is transformed between said first and second data representations
transparently with respect to an application executable in said
application data space.
9. The mechanism of claim 8 wherein the memory access routine includes a
plurality of memory access subroutines that provide for reading said
predetermined block of data from said predetermined file, writing said
predetermined block of data to said predetermined file, and establishing
file characterization attributes associated with said predetermined file,
wherein said interface routine includes a plurality of transformation
control subroutines that are associated respectively with said plurality
of memory access subroutines, and wherein each of said transformation
control subroutines may determine whether said predetermined block of data
is in said first or second data representation by examination of said file
characterization attributes associated with said predetermined file.
10. The mechanism of claim 9 wherein the file characterization attributes
associated with said predetermined file includes predetermined key
validation data, wherein a predetermined password is associated with a
predetermined application program executable in said application data
space, said interface routine including a data representation
transformation table established with respect to said predetermined
application program for use by said key dependant data transformation
routine, wherein the contents of said data representation transformation
table is data dependant on said predetermined password.
11. The mechanism of claim 10 wherein the operating system provides for
application programs to be executed within processes and wherein the
operating system includes a fork routine for instantiating a predetermined
child process related to a predetermined parent process within which said
predetermined application program is executed, said interface routine
including a fork subroutine that is associated with said fork routine, and
wherein said fork subroutine associates said data representation
transformation table with said predetermined child process, whereby said
predetermined child process transparently inherits said predetermined
password in connection with the instantiation of said predetermined child
process.
12. The mechanism of claim 8, 9, 10, or 11 wherein said key dependant data
transformation routine performs at least one transform from a set of
transforms including encryption, compression, encoding, translation and
conversion.
13. A key-based transparent file encryption system for use in a computer
system employing a processor for executing programs, a file system
providing for the storage of program and data files, a memory coupled to
the processor and providing for the storage of programs and data, and an
operating system including a program interface for receiving a plurality
of system call types and a plurality of system call subroutines that
implement the file oriented system calls, said key-based transparent file
encryption system comprising:
a) an encryption routine implementing a key based encryption algorithm
that, upon execution by the processor, provides for the encryption and
decryption of a predetermined file dependant on the value of a
predetermined encryption key; and
b) an interface module including a plurality of system call subroutine
wrappers interposed between the execution control path between the program
interface and the plurality of system call subroutines, said interface
module providing for the transfer of said predetermined file selectively
subject to the function of said encryption routine, said interface module
determining from predetermined attribute data provided with said
predetermined file whether said predetermined file will be in an encrypted
state as stored by the file system, said interface routine further
operating to authenticate a predetermined password against the attribute
data provided with said predetermined file where said predetermined
password is associated with a predetermined application program that
provides a data transfer system call to the program interface with respect
to said predetermined file, said interface module selecting said
encryption routine to encrypt or decrypt said predetermined file as
transferred between said predetermined application program and the file
system where said predetermined password is authenticated and where said
predetermined file is in an encrypted state as stored by the file system.
14. The key-based transparent file encryption system of claim 13 wherein
the encryption and decryption of said predetermined file by said
encryption routine is dependant on said predetermined password as an
encryption key.
15. The key-based transparent file encryption system of claim 14 wherein
said predetermined application executes within a predetermined process of
a plurality of processes executed by the processor under the control of
the operating system, wherein said predetermined process and a forked
process related as a child to said predetermined process is associated
with a predetermined data structure established in said interface module
in connection with the authentication of said predetermined password, and
wherein said predetermined data structure includes an encryption table
generated by said interface module based on said encryption key, said
interface module providing for the inheritance of an association with said
predetermined data structure by said forked process, whereby selective
transformations of file data between encrypted and decrypted states are
transparent to said predetermined application and any application executed
in said forked process.
16. The key-based transparent file encryption system of claim 13, 14 or 15
wherein respective instances of said predetermined attribute data are
attached to the files as stored by the file system that have been
encrypted by said interface module, and wherein said predetermined
attribute data includes an encrypted copy of a predetermined data string
that is used in authenticating said predetermined password and
predetermined flag data defining the encryption state of the attached file
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Claims |
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Description |
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Appendix I found on pages 43 through 76 of the specification as originally
filed is now filed microfiche appendix consisting of one microfiche with
36 frames.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related to computer based file service
extension systems and, in particular, to an extension system for at least
multi-tasking computer systems where a secure, block oriented file service
mechanism is employed transparently within the function of the operating
system.
2. Description of the Related Art
As communal access to and use of computer systems increases, there is an
increased demand for control over access rights to and transformation of
computer data on an individualized basis. Computer systems are continuing
to evolve toward and in the nature of multi-user systems, both directly
and indirectly through a heterogeneous architecture of single-user,
single-user multi-tasking and multi-user inter-networked systems
possessing a remote file sharing capability. Thus, there is increased
access capability to computer data maintained in a common logical file
system. Furthermore, the file state and transformation requirements of
varying data formats increases with the potentially greater number of
users and application programs that may access the computer data files.
Conventional operating system based file access and protection mechanisms
typically depend on file attribute and access list controls. These
mechanisms are, however, inadequate to provide a sufficient level and
transparency of security and control. In brief, attribute based controls
are typically used to define read, write and execute permissions
exercisable by the user, or file owner, a user group, or other, meaning
all. Access list controls rely on the existence and maintenance of a
predefined list of users that have been granted access rights to a file.
Unfortunately, at least the system administrator, or super user, and the
access list administrator are not preclusively bound by these permission
restrictions. Therefore, access to the data content of a file is not
secure against the super user or others who may inappropriately have or
gain super user status. An error in the use or function of an application
program that modifies the file attributes or control list also results in
a security failure.
Conventional file protection mechanisms, incorporated within broader
functioning application programs, generally provide for the encryption of
the entire data file. These dedicated protection mechanisms are completely
independent of file attribute and access list controls. There are,
however, a number of drawbacks to the use of such application based
protection mechanisms. Each such application program must entirely
implement a proprietary protection methodology, such as encryption to
ensure the security of the data files specifically associated with the
program. Consequently, there is a nearly universal data incompatibility
between such programs thereby precluding use or even simple access to
common data by different applications.
Use of a dedicated encryption program otherwise independent of any suite of
broad function application programs, i.e., an encryption utility program,
solves the data file incompatibility problem. However, such encryption
programs must generally be executed separately from and prior to the
execution of other application programs. Execution also typically results
in the restoration of a complete unencrypted data file within the logical
file system. Aside from the practical difficulties of dealing with
encrypted and decrypted versions of the same data file presumably closely
co-resident within the logical file system, the unencrypted data file is
no more secure than potentially obtained by conventional reliance on the
file attribute and access control mechanisms previously described.
Typically, the management of file attribute and access controls is
sufficiently tedious, particularly when considered in combination with the
separate need to execute and manage the encryption/decryption steps
separate from the execution of other application programs, that these
additional controls are not implemented. Consequently, the decrypted data
file obtained by use of an encryption utility program represents a
potentially greater security exposure.
Automatic or transparent file security systems have been proposed, such as
the one disclosed in U.S. Pat. No. 5,007,082, issued to Cummins, on Apr.
9, 1991. There, an encryption mechanism is implemented through the
addition of a hardware specific software based control routine at the
basic input/output (I/O) system (BIOS) level of an operating system. This
routine provides for the simple selective re-vectoring of the lowest level
file transfer BIOS functions, specifically the floppy diskette access
operations, through a file encryption routine. The entire file is
automatically encrypted or decrypted when written or read from the
diskette. In addition, a global "decryption flag," is stored uniquely in
the computer memory and not with the diskette files. This flag is utilized
to specify whether a specific diskette is to be treated as an encrypted or
ordinary data file store quite independent of the specific files stored on
the diskette. Where data is to be transferred to or from an encrypted
diskette store, the data is encrypted within the memory of the computer
system at the lowest level of the operating system and then only for the
duration of the actual data transfer. Cummins specifically teaches that
all in-memory data buffers need to store the data file in an unencrypted
state in order to ensure operational compatibility with all potentially
executing application programs.
A number of obvious vulnerabilities to the secure function of the Cummins
mechanism exist. The revectoring approach is vulnerable to simple
restoration of the original vectors, thereby bypassing the encryption
control routine. Unencrypted diskette data files can then be freely
prepared.
The use of a global flag signifying continuing use of the encryption
control routine also provides a single, simple point for disabling the
function of the encryption routine. Reliance on this flag is not specific
to any specific user or file but rather to an entire computer system. Once
modified, the security of the entire system is breached irrespective of
any specific user or file.
Further, the maintenance of all data buffers within the computer system in
an unencrypted state, except briefly in performing a physical data
transfer, results in the computer memory image being inherently insecure.
Finally, the Cummins system is described solely with respect to diskette
based data file protection. The data protection mechanism provides
protection for data files only if removed from a computer system on
transportable media. The disclosed mechanism is therefore clearly not
applicable to freely internetworked systems, but rather only for
physically separate, and physically secured single user systems.
Conventionally, file state and transformation requirements for data files
are preserved as an integral part of the data files. As such, the relevant
state defining information is largely usable only by the application that
created the data file. Other applications must be specifically compatible
with another application's file format or provide, typically through
execution of a separate program, a conversion between file formats. All of
the disadvantages discussed above, related to encryption and multiple
instances of a given file, attach here as well.
SUMMARY OF THE INVENTION
Accordingly, a general purpose of the present invention is therefore to
provide a file extension system, such as a secure file encryption system,
transparently within an environment of multi-user and inter-networked
computer operating systems.
This is achieved in the present invention by a computer system including a
file extension mechanism, a file storage subsystem for storing a file
composed of one or more blocks of data, a data storage subsystem for
storing blocks of data in first and second logical data areas and a
processor for executing instructions implementing a computer operating
system in the first logical data area and an application program in the
second logical data area. The processor is coupled to the file storage
subsystem and the data storage subsystem for transferring a predetermined
block of data between the file storage subsystem and the data storage
subsystem. The processor includes (1) a file extension mechanism, defined
within the operating system, for transforming the predetermined block of
data in the first logical data area separately from any other block of
data; (2) a request mechanism defined by the application program, for
selecting the predetermined block of data to be operated on; and (3) an
interface that controls the transfer of the predetermined block of data
between the file storage subsystem and the data storage subsystem and
between the first and second logical data areas. The interface can
determine whether the predetermined block of data is transformed. The
interface controls the transfer of the predetermined block of data from
the file storage subsystem to the data storage subsystem and between the
first and second logical data areas, transforming the data as required.
Thus, an advantage of the present invention is that a file extension
mechanism, providing a secure file encryption mechanism, for example, is
established within the function of a computer operating system.
Another advantage of the present invention is that the function of the file
extension mechanism can be securely and transparently embedded in the
operating system and specifically at the highest control level while
maintaining full compatibility with conventional multi-tasking and/or
multi-user operating system process inheritance mechanisms.
A further advantage of the present invention is that the file extension
mechanism, in implementing the encryption algorithm is fast, provides an
inherently substantial degree of file security, is easily maintained by
authorized users for their encrypted files, imposes little additional
processing overhead for accessing both encrypted and unencrypted files,
and may be flexibly tailored to selectively permit additional ordinary
users access to the encrypted files of another.
Yet another advantage of the present invention is that the file extension
mechanism operates in implementing transformation operations on block
level portions of a file, thereby inherently limiting the existence of
untransformed portions of a file within the computer system to the minimum
portion of the file required by a user application.
Still another advantage of the present invention is that, while block
portions of a transformed file may be temporarily maintained in an
operating system buffer pool for operating system and hardware efficiency
reasons, such blocks are preserved there in a transformed state, thereby
globally precluding a security exposure due to snooping of a memory image
for untransformed blocks.
A still further advantage of the present invention is that file system
maintenance where both transformed and untransformed files exist is
essentially unaltered. A transparent method of identifying transformed
files fully consistent with existing conventional multi-tasking and
multi-user file privilege attribute mechanisms is used.
Yet still another advantage of the present invention is that the
transformation operation is generally consistent with conventional file
security and operating system implementation paradigms, thereby being
generally portable to a wide variety of multi-tasking and multi-user
computer operating systems.
A yet still further advantage of the present invention is that the file
extension mechanisms implementing encryption, provides a secure
cost-effective file protection mechanism that is specifically independent
of any particular computer system hardware.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other advantages and features of the present invention will
become better understood upon consideration of the following detailed
description of the invention when considered in connection with the
accompanying drawings, in which like reference numerals designate like
parts throughout the figures thereof, and wherein:
FIG. 1 is a representative drawing of a computer system according to the
present invention;
FIG. 2 is a schematic diagram of the logical data space and control
structures utilized in a preferred implementation of the present
invention;
FIG. 3 is a schematic diagram representing the interception of select
system calls in accordance with a preferred embodiment of the present
invention;
FIG. 4a is a representative depiction of the generation of an encryption
control table entry;
FIG. 4b is a representative depiction of the relation between a user
procedure control table, kernel process control table and encryption
control table in accordance with a preferred embodiment of the present
invention;
FIG. 4c is a representative depiction of the encryption process in
accordance with a preferred embodiment of the present invention;
FIG. 4d is a representative depiction of the decryption process in
accordance with a preferred embodiment of the present invention;
FIG. 5a is a schematic diagram illustrating the control flow in support of
a modified read operation in accordance with a preferred embodiment of the
present invention; and
FIG. 5b is a schematic diagram illustrating the control flow in support of
a modified chmod operation in accordance with a preferred embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for a system of file transformations
particularly suited for use in advanced computer operating systems. While
the preferred embodiment of the present invention, and the following
description thereof, are specific in detail to an encryption transform
performed using the Unix.RTM. (trademark owner not known) operating
system, persons of average or ordinary skill in the art will readily
appreciate the ready extension of the principles of the present invention
to other transforms, including code set conversion, compression, and
translation, as well as encryption, and to other operating systems,
including Windows-3.1 and Windows-NT by Microsoft, Inc., Redmond, Wash.,
System 7 by Apple Computer, Inc., Cupertino, Calif. VMS by Digital
Equipment Corporation, San Jose, Calif. OS/2 by International Business
Machines, Inc., Armonk, N.Y., and the many specific variants of the Unix
Operating System such as provided by the Santa Cruz Operation, Inc. Santa
Cruz, Calif. (SCO Unix), International Business Machines, Inc. Armonk,
N.Y. (AIX), and Novell, Inc. Provo, Utah (UnixWare).
Accordingly, the detailed description of the preferred embodiments provided
here is not to be taken as limiting the applicability of the present
invention to any specific transform, operating system or computer system
architecture, but rather the present invention is intended to be
applicable to all transform and operating systems, as executed on
corresponding computer systems, within the scope of the appended claims.
The Unix operating system is widely known and understood in terms of the
operating principles and related control structures of the operating
system. An excellent treatment of these concepts is provided in "The
Design of Unix Operating System," by Maurice J. Bach, Prentice-Hall, Inc.,
1986, and is expressly incorporated herein by reference. A significant
design feature of the Unix operating systems is the ability to extend the
operating system to accommodate selected sets of new and existing
peripheral devices through the addition of corresponding kernel resident
device drivers. A standard device driver interface generally as supported
by the Unix operating system is described in "Device Driver Writer's
Guide," available from the Santa Cruz Operation, Inc., 400 Encinal Street,
Santa Cruz, Calif. 95061, and is also expressly incorporated herein by
reference.
Referring now to FIG. 1, there is shown a computer system 10 suitable for
implementation of the present invention through the execution of an
operating system and application programs. In the preferred embodiments of
the present invention, the operating system is an implementation of the
Unix operating system. A central processing unit ("CPU") 12 executes the
operating system and any number of application programs. The CPU 12 is
connected via a bus 14 to a main memory unit 16, a disk controller unit
18, and other peripheral devices generally indicated by the reference
numeral 20.
The main memory 16 provides an addressable memory space to the CPU 12 for
the storage of application programs and data and of the operating system
and related data. As generally depicted in FIG. 1, the main memory 16 is
logically managed as a combination of user space and kernel space. When
the CPU 12 is executing program code in user space, the process within
which such execution is occurring then exists in user mode. Where the
process is executing in kernel space, then execution is in kernel mode.
Within the kernel space, a buffer pool, or buffer cache, is maintained by
the operating system. This buffer pool represents a temporary buffer cache
for data transferred via the disk controller 18 from a secondary memory
such as a disk drive 22.
Referring now to FIG. 2, a schematic diagram of the logical user and kernel
mode spaces is shown. The application program 26 executes in user mode.
Operating system calls 30 are issued by the application program to gain
access to operating system resources. These calls are directed through a
system call interface substantially existing within the kernel data space,
though presenting an application program interface (API) accessible from
user space. Typically this interface is implemented through a system call
trap mechanism 32 that permits the user mode system call to initiate a
mode switch to a kernel mode of operation within the same processes
context. This mode switch may be delayed subject to the operation of the
process scheduler of the operating system. When the mode switch completes,
the process, now in kernel mode, is processed through the trap handler
routine 32 that may be part of the system call interface. As a
consequence, a call is placed against a system entry, or sysent, table 34.
The structure of the system entry table is provided in Table I.
TABLE I
______________________________________
Structure of the System-Entry Table
From <sys/systm.h>
______________________________________
extern struct sysent {
char sy.sub.-- narg;
/* total number of arguments */
char sy.sub.-- setjmp;
/* 1 if systrap( ) should
not setjmp( ) */
int (*sy.sub.-- call) ( ) ;
/* handler */
} syset [ ];
extern int nsysent;
/* number of valid entries
in sysent */
______________________________________
The sysent table 34 functions as a dispatch table with each entry in the
table corresponding to a different function supported by the operating
system. Of particular relevance to the encryption transform embodiment of
the present invention, the sysent table 34 includes entries for the open,
create, read, write, chmod, fork, statf, seek, exit and ioctl system call
procedures generally represented as procedures 36. As is evident from each
entry in the sysent table, the system call address of each of the system
call procedures is maintained in a respective entry ((*sy.sub.-- call)())
within the sysent table 34.
The Unix operating system utilizes a file oriented paradigm in providing
operating system services. Consequently, the open, create, read, write,
seek, stat and close system call procedures permit logical operation
relative to a wide variety of logical data entities, including
directories, files, and pipes, for example, that are treated as files
referenceable via directories. In turn, directories are maintained on disk
as standard files containing specifically structured data. This directory
file data includes a pointer to a disk based structure of disk inode
entries. Each inode entry stores specifically relevant information
describing, among other things, the protection mode, owner, user group and
size of a particular data file. A summary of an inode entry, as stored on
disk, is provided in Table II.
TABLE II
______________________________________
Structure of a Disk Inode
From <sys/ino.h>
______________________________________
struct dinode
ushort di.sub.-- mode;
/* protection mode, file type */
short di.sub.-- nlink;
/* number links to file */
ushort di.sub.-- uid;
/* owner's user id */
ushort di.sub.-- gid;
/* owner's group id */
off.sub.-- t di.sub.-- size;
/* number bytes in file */
. . .
};
______________________________________
The open and create system call procedures cause the creation of "in-core"
inodes in an inode table for each file opened or created. The in-core
inode of a file contains much of information held in the disk inode
structure. The statf system call procedure can be used to return a
structure containing the disk inode mode information.
The chmod system call procedure is provided specifically to change the
protection mode of disk files. The inode structure maintains a binary
coded entry (di.sub.-- mode) defining the file type and protection mode of
the disk file. The three least significant octal digits of the mode
specify the existent read, write, and execute permissions of the file for
the file owner (0x00), the owner's group (00x0), and other (000x), where x
represents any octal digit. Another octal digit of the mode entry (x000)
is utilized to store additional permissions related information. The
remaining bits of the mode are used to define the file type or are
reserved. The chmod system call procedure takes, as an argument, a binary
representation of the file protection mode (xxxx) and appropriately
modifies the mode value stored by the disk inode corresponding to the
referenced file.
In accordance with the present invention, a transformed file is identified
by the presence of an enode data structure appended to a corresponding
regular file. As will be discussed in greater detail below, this trailing
enode structure includes data defining the transform applied to the file.
A specific pre-existing file mode may also be used to indicate the
transformed state of a corresponding regular file. In an alternate
embodiment of the present invention the selected mode is octal xx0x, where
x is any octal digit. This represents an otherwise unlikely file mode
since the group permission is defined as without conventional read, write
or execute access to the file. Any other mode bit or bit pattern could be
used where the same can be seen to have no other significant use. Any
logically permitted mode bit or pattern can be used to define, for
example, the encryption state of the corresponding regular file consistent
with the present invention. Consequently, incompatibilities that might
arise either from a redefinition of the mode bits with existing programs
that rely on the existing exclusive definition of the mode bits is
avoided. Further, as a logically permitted mode, the existing chmod
utility program will readily accept and apply the mode value to the
corresponding file inode.
The seek system call procedure is provided to position the file access
pointer within, typically, a file. Subsequent read and write file accesses
are performed relative to this pointer. The create and open system call
procedures initialize the file access pointer to zero.
The fork system call procedure is utilized to create a new process within
the control of the operating system. This child process is a logical copy
of the parent process. All processes are managed by the operating system
through the use of a process table within the kernel space of the
operating system. A summary of a process table entry, stored as an element
of a process table linked list, is provided in Table III.
TABLE III
______________________________________
Structure of the Process Table
From <sys/proc.h>
______________________________________
typedef struct proc {
char p.sub.-- stat;
/* status of process */
. . .
ushort p.sub.-- uid;
/* real user id */
ushort p.sub.-- suid;
/* saved uid from exec */
int p.sub.-- sid;
/* POSIX session id num */
short p.sub.-- pgrp;
/* proc grp leader name */
short p.sub.-- pid;
/* unique process id*/
short p.sub.-- ppid;
/* process id of parent*/
ushort p.sub.-- sgid;
/* saved gid from exec */
sigset.sub.-- t
p.sub.-- sig;
/* signals pe | | |
