Abstract:
A system and a method for electronic file transmission are proposed and applied to a network environment, whereby electronic files are encrypted and decrypted with hardware serial numbers of file reading devices that are authorized terminals for file uploading or downloading transmission. Since each hardware serial number is unique for a particular file reading device, thus for an encrypted file being transmitted to a destined file reading device, only which reading device can decrypt the encrypted file for file retrieval; other reading devices, who may get the transmitted file from the destined reading device, are incapable of proceeding file decryption for this particular file. Moreover, a decrypted or unencrypted file is necessarily encrypted similarly by means of a unique hardware serial number of a file reading device where the file is to be stored. This therefore effectively prevents unauthorized copying and propagation of electronic files or digital information from occurrence.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to systems and methods for electronic file transmission, and more particularly, to a system and a method for electronic file transmission that employ data encryption and decryption for preventing file transmission in a network.  
         BACKGROUND OF THE INVENTION  
         [0002]    In a current network system, it would be more preferable for allowing terminal users to obtain required digital information such as electronic books (e-books) through a safe and convenient transaction mechanism. Information providers e.g. publishers can accordingly establish information servers, in which digital information and electronic files are stored, and able to be retrieved and downloaded through Internet by the users in the use of digital electronic devices such as personal computers, personal digital assistants (PDA) or electronically readers.  
           [0003]    Referring to FIG. 1, a conventional system for digital information or e-book transmission is provided with an information server  11  to be connected to a personal computer  13  via Internet  12 .  
           [0004]    A digital information provider, such as a publisher, may set up a website  111  in the information server  11  for allowing a user to download an electronic file  113  from the website  111 , wherein the electronic file  113  can be an unencrypted file. In operation, after logging in the website  111 , the user needs to provide personal data and register for membership, so as to obtain reading software  112  for reading electronic files. With the reading software  112  being installed, the user can execute the reading software  112  for retrieving and downloading the electronic file  113  from the website  111  of the information server  11 .  
           [0005]    In particular, first, a user of the personal computer  13  requests for being linked to the information server  11 , and logs in the website  111  for membership registration. After becoming a member, the user downloads the reading software  112  for use in subsequent retrieval of digital information provided by the publisher. In order to retrieve a desired electronic file  113 , the user of the personal computer  13  needs to submit a file retrieval request to the website  111  of the information server  11 . After the website  111  authenticates the user is a registered member, it would provide the electronic file  113  through Internet  12  to the personal computer  13 , whereby the user can operate the reading software  112  and read the electronic file  113 . In the meantime, the electronic file  113  can be stored in a hard disk of the personal computer  13 , or in a floppy disk  131  or a compact disk  132 . However, it may occur that, for example, another personal computer  14  can obtain the electronic file  113  without being authorized by the publisher. A user of this personal computer  14  similarly logs in the website  111  of the information server  11 , and registers for downloading the reading software  112 . For retrieving the electronic file  113 , instead of accessing the website  111  via Internet  12 , the user of the personal computer  14  can get the electronic file  113  directly from the personal computer  13  by means of FTP (File Transfer Protocol), or download the electronic file  113  from the floppy disk  131  or compact disk  132 , whereby the electronic file  13  can then be read through the use of the reading software  112 . In this case, if the publisher desires to make profits from its members for file downloading, the user of the personal computer  14  who obtains the unauthorized electronic file  113  directly from the personal computer  13 , would not be charged.  
           [0006]    Referring to FIG. 2, another conventional transmission system for digital information or e-books is associated with an information server  15  to be connected to a personal computer  17  via Internet  16 .  
           [0007]    A website  151  set up in the information server  15  by a digital information provider, such as a publisher, allows a user of the personal computer  17  to retrieve required digital information e.g. an electronic file  153 , which electronic file  153  is encrypted with 128-bit encryption technique to become an encrypted file  154 . First, the user registers for membership in the website  151 , and is allowed to download reading software  152  for reading electronic files. With the reading software  152  being installed, the user can execute the reading software  152  that is used to directly download the encrypted file  154  through Internet  16  from the website  151  of the information server  15  and decrypt the downloaded encrypted file  154 , so as to allow the user to read the electronic file  153 . At the same time, the electronic file  153  obtained by decryption can be stored in a hard disk of the personal computer  17 , or in a floppy disk  171  or a compact disk  172 . However, similarly as above described, another personal computer  18  may obtain the electronic file  153  with no authorization from the publisher. Once the personal computer  18  registers in the website  151  and downloads the reading software  152 , a user of the personal computer  18  can get the electronic file  153  directly from the computer  17  in a FTP manner, or directly download the electronic file  153  from the floppy disk  171  or compact disk  172 . As such, without needing to access the website  151  for file retrieval or conduct file decryption, user of the personal computer  18  can simply read the unauthorized electronic file  153  by using the reading software  152 . In this case, the publisher would lose profits from the user of the personal computer  18  who illegally obtains the electronic file  153  from the personal computer  17 .  
           [0008]    It can be found from the above that, although an electronic file is beforehand encrypted and transmitted in the form of an encrypted file to a personal computer, the encrypted file is decrypted back to the original electronic file by using reading software for file reading in the personal computer, and stored in the unencrypted form by a user of the personal computer. As a result, such an unencrypted electronic file can easily obtained and retrieved from the personal computer by other users who are also equipped with the same reading software for file reading. A publisher who provides the electronic file would be incapable of preventing digital information from being unauthorizedly copied and propagated. Therefore, how to build up a safe and fair transaction mechanism for digital information communication that can effectively prevent the rights and satisfy the requirements for both information providers and users, is a critical problem to solve.  
         SUMMARY OF THE INVENTION  
         [0009]    A primary objective of the present invention is to provide a system and a method for electronic file transmission, which are applied in a network environment, and encrypt an electronic file with a hardware serial number of a particular file reading device before file transmission. The encrypted electronic file is then transmitted through the network by virtue of PPTP (Point-to-Point Tunneling Protocol) to an authorized user of the file reading device by which the user can upload or download encrypted files. Since the transmitted electronic file is encrypted with the hardware serial number of the file reading device, the user can only uses the file reading device to download and decrypt the encrypted electronic file for file reading; afterwards, the decrypted electronic file is again similarly encrypted with the hardware serial number of the file reading device for file storage. Therefore, unauthorized file copying and propagation can be effectively prevented from occurrence.  
           [0010]    According to the foregoing and other objectives, the present invention proposes a system and a method for electronic file transmission, wherein electronic files are transmitted in the encryption form through a network. In particular, by virtue of file encryption/decryption, downloaded encrypted files can only decrypted and read by authorized receivers of file reading devices who request for file downloading; and the decrypted and read files are again encrypted by the file reading devices for file storage, so that electronic files or digital information can be prevented from being unauthorizedly copied and propagated.  
           [0011]    The electronic transmission system of the invention comprises a file processing center, a transmission network, and file reading devices. The file processing center is a digital information server for providing electronic files to be downloaded by the file reading devices, and storing uploaded files from the file reading devices. The transmission network, generally Internet or intranet, serves as a file transmission medium interposed between the file processing center and the file reading devices. The file reading devices serve as terminals for downloading or uploading electronic files, wherein each of the file reading devices is provided with a unique hardware serial number for use in encryption/decryption of electronic files, so that the encrypted electronic files cannot be decrypted by using other reading devices. During electronic file transmission, first, the file processing center records down the hardware serial numbers of the file reading devices.  
           [0012]    The file processing center includes an encryption/decryption module that is connected to at least one file reading device via the transmission network, whereby the file encryption/decryption module transmits its public key to the file reading device. When a file reading device requests for downloading an electronic file from the file processing center, the encryption/decryption module symmetrically encrypts the requested file with a hardware serial number of the file reading device, and then transmit the encrypted file to the file reading device via the transmission network. On the other hand, when a file reading device requests for uploading an electronic file to the file processing center, the encryption/decryption module can symmetrically decrypt the uploaded file by using a hardware serial number of the file reading device.  
           [0013]    Each file reading device having a retrieval/transmission module, obtains a public key from the file processing center via the transmission network. When the file reading device desires to upload an electronic file to the file processing center, first, the retrieval/transmission module uses its hardware serial number to symmetrically encrypt the electronic file, and then transmits the encrypted electronic file to the file processing center via the transmission network. On the other hand, when the file reading device downloads an electronic file from the file processing center, the retrieval/transmission module uses its hardware serial number to symmetrically decrypt the downloaded electronic file encrypted by the file processing center, so as to obtain the original unencrypted file for being displayed on a screen of the file reading device. Afterwards, if file storage is required, the retrieval/transmission module again use its hardware serial number to symmetrically encrypt the unencrypted file, and stores the encrypted file to a memory unit of the file reading device, or in a floppy disk or a compact disk.  
           [0014]    The electronic file transmission method of the invention comprises the following steps.  
           [0015]    The first step is to initiate registration. After connection between a file processing center and a file reading device is established via a transmission network, a public key of the file processing center can be transmitted to the file reading device. Then, the file reading device can use the public key to asymmetrically encrypt a hardware serial number thereof by means of a unidirectional function, and transmit the encrypted hardware serial number of the reading device to the file processing center via the transmission network. In response, the file processing center uses a private key thereof to asymmetrically decrypt the encrypted hardware serial number by using a unidirectional function, whereby the unencrypted hardware serial number of the file reading device is obtained and stored in a database of the file processing center.  
           [0016]    Next, for file unloading transmission, a retrieval/transmission module of the file reading device can use its hardware serial number to symmetrically encrypt an electronic file, and then upload the encrypted electronic file to the file processing center via the transmission network. Upon receiving the unloaded file from the file reading device, the file processing center searches in its database for a corresponding hardware serial number for the file reading device, and prompts an encryption/decryption module thereof to symmetrically decrypt the encrypted uploaded file for retrieving the original unencrypted file.  
           [0017]    Further, for file downloading transmission, when the file reading device requests for downloading an electronic file from the file processing center, the file processing center prompts its encryption/decryption module to symmetrically encrypt a requested electronic file with the hardware serial number of the file reading device, and then transmits the encrypted electronic file to the file reading device via the transmission network. Upon receiving the encrypted file from the file processing center, the retrieval/transmission module of the file reading device is prompted to symmetrically decrypt the encrypted file with the hardware serial number of the file reading device, so that the original unencrypted electronic file can be obtained and displayed on a screen of the file reading device. In the meantime, for file storage, the unencrypted file is again symmetrically encrypted with the hardware serial number by the retrieval/transmission module of the file reading device, and then stored in a memory unit of the file reading device, or in a floppy disk or a compact disk.  
           [0018]    The system and method for electronic file transmission of the invention, is characterized of encrypting and decrypting electronic files with particular hardware serial numbers of file reading devices that are authorized terminals for file uploading or downloading transmission. Since each hardware serial number is unique for a particular file reading device, thus for an encrypted electronic file being transmitted to a destined file reading device, only which file reading device can decrypt the encrypted file for file retrieval; in other words, other file reading devices, who may get the transmitted file from the destined file reading device, are incapable of proceeding file decryption for this particular file. Moreover, in respect of file storage, a decrypted or unencrypted file is necessarily encrypted similarly by means of a unique hardware serial number of a file reading device where the file is to be stored. This therefore can effectively prevent unauthorized copying and propagation of electronic files or digital information from occurrence. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:  
         [0020]    [0020]FIG. 1 (PRIOR ART) is a schematic diagram showing basic architecture of a conventional electronic file transmission system;  
         [0021]    [0021]FIG. 2 (PRIOR ART) is a schematic diagram showing basic architecture of another conventional electronic file transmission system;  
         [0022]    [0022]FIG. 3 is a systematic block diagram showing hardware configuration of a preferred embodiment of an electronic file transmission system of the invention;  
         [0023]    [0023]FIG. 4 is a systematic block diagram showing hardware configuration of another preferred embodiment of an electronic file transmission system of the invention;  
         [0024]    [0024]FIG. 5 is a schematic diagram showing data flow directions in the electronic file transmission system of FIG. 3;  
         [0025]    [0025]FIG. 6 is a flowchart showing the steps involved in an electronic file transmission method by using an electronic file transmission system of the invention;  
         [0026]    [0026]FIG. 7 is a flowchart showing the procedures involved in a step for initiating registration of FIG. 6;  
         [0027]    [0027]FIG. 8 is a flowchart showing the procedures involved in a step for transmitting electronic files of FIG. 6;  
         [0028]    [0028]FIG. 9 is a flowchart showing the steps involved in an electronic file transmission method by using the electronic file transmission system of FIG. 3; and  
         [0029]    [0029]FIG. 10 is a flowchart showing the steps involved in an electronic file transmission method by using the electronic file transmission system of FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    [0030]FIG. 3 illustrates hardware configuration of a preferred embodiment of an electronic file transmission system of the present invention. As shown in the drawing, the electronic file transmission system  2  includes a file processing center  3 , a transmission network  4 , and file reading devices  5 ,  6  for reading electronic files. The file processing center  3  is a digital information server for providing electronic files to be downloaded by the file reading devices  5 ,  6 , and storing uploaded files from the file reading devices  5 ,  6 . The transmission network  4 , generally Internet or intranet, serves as a file transmission medium interposed between the file processing center  3  and the file reading devices  5 ,  6 . The file reading devices  5 ,  6 , such as personal computers, personal digital assistants or e-book readers, serve as terminals for downloading or uploading electronic files, wherein each of the file reading devices  5 ,  6  is provided with a unique hardware serial number S 52 , S 62  for use in encryption/decryption of electronic files, so that the encrypted electronic files cannot be decrypted by using other reading devices.  
         [0031]    The file processing center  3  includes an encryption/decryption module  31  that is connected to the file reading devices  5 ,  6  via the transmission network  4 , whereby a public key (Key 32 ) of the encryption/decryption module  31  is transmitted to the file reading devices  5 ,  6 , respectively. Retrieval/transmission modules  51 ,  61  of the file reading devices  5 ,  6  use the public keys (Key 32 ) to encrypt their hardware serial numbers S 52 , S 62  by means of asymmetrically unidirectional function encryption (this encryption method is customarily designated as Ea), which encrypted hardware serial numbers S 52 , S 62  are transmitted to the file processing center  3  via the transmission network  4 . In receipt of transmitted data, the encryption/decryption module  31  of the file processing center  3  uses its private key (Key 33 ) to decrypt the encrypted hardware serial numbers S 52 , S 62 , and stores the unencrypted hardware serial numbers S 52 , S 62  into a database  34  thereof.  
         [0032]    For uploading information or files to the file processing center  3 , the retrieval/transmission modules  51 ,  61  of the file reading devices  5 ,  6  encrypt electronic files with their hardware serial numbers S 52 , S 62  by using symmetrical encryption methods (Es), and then transmit the encrypted electronic files to the file processing center  3  via the transmission network  4 . On the other hard, encrypted electronic files downloaded from the file processing center  3  are decrypted by the retrieval/transmission modules  51 ,  61  with the hardware serial numbers S 52 , S 62  in operation of symmetrical decryption (Ds) methods. The decrypted electronic files are displayed on screens  53 ,  63  of the file reading devices  53 ,  63 , respectively. Afterwards, for file storage, the decrypted electronic files are again encrypted with the hardware serial numbers S 52 , S 62  by the retrieval/transmission modules  51 ,  61 , and the encrypted electronic files are stored in memory units  54 ,  64  of the file reading devices  5 ,  6 , or in floppy disks  55 ,  65  or compact disks  56 ,  66 .  
         [0033]    [0033]FIG. 4 illustrates hardware configuration of another preferred embodiment of an electronic file transmission system of the invention. As shown in the drawing, the electronic file transmission system  7  includes a file processing center  71 , a transmission network  72 , and file reading devices  73 ,  74 . The file processing center  71  is a digital information server for providing electronic files to be downloaded by the file reading devices  73 ,  74 , and storing uploaded files from the file reading devices  73 ,  74 . The transmission network  72 , generally Internet or intranet, serves as a file transmission medium interposed between the file processing center  71  and the file reading devices  73 ,  74 . The file reading devices  73 ,  74 , such as personal computers, personal digital assistants or e-book readers, serve as terminals for downloading or uploading electronic files, wherein each of the file reading devices  73 ,  74  is provided with a unique hardware serial number S 735 , S 745  for use in encryption/decryption of electronic files, so that the encrypted electronic files cannot be decrypted by using other reading devices.  
         [0034]    The file processing center  71  includes a processor  711 , a memory  712 , a data storage medium  713  containing an encryption/decryption program  714 , and a database  717 . The processor  711  can be a microprocessor or a central processing unit, and may execute the encryption/decryption program  714  to function as the foregoing encryption/decryption module  31 . The data storage medium  713  can be a hard disk, a floppy disk, a compact disk, an EPROM (erasable programmable read-only memory), an EEPROM (electrically erasable programmable read-only memory) or a flash ROM (read-only memory). As the file processing center  71  is connected to the file reading devices  73 ,  74  via the transmission network  72 , its public key (Key 715 ) can be transmitted to the file reading devices  73 ,  74 , respectively. Retrieval/transmission programs  734 ,  744  of the file reading devices  73 ,  74  use the public keys (Key 715 ) to encrypt their hardware serial numbers S 735 , S 745  by means of asymmetrically unidirectional function encryption (Ea), which encrypted hardware serial numbers S 735 , S 745  are transmitted to the file processing center  71  via the transmission network  72 . Thereafter, in operation of the encryption/decryption program  714 , the processor  711  cooperating with the memory  712  uses a private key (Key 716 ) of the file processing center  71  to decrypt the encrypted hardware serial numbers S 735 , S 745 , and stores the unencrypted hardware serial numbers S 735 , S 745  into the database  717 .  
         [0035]    Each of the file reading devices  73 ,  74  has a processor  731 ,  741 , a memory  732 ,  742 , a data storage medium  733 ,  743 , and a screen  736  or  746 . The data storage media  733 ,  734  each contains a retrieval/transmission program  734 ,  744 , and can be a hard disk, a floppy disk, a compact disk, an EPROM, an EEPROM or a flash ROM. The processors  731 ,  741  each can be a microprocessor or a central processing unit, and may execute the retrieval/transmission program  734 ,  744  to function as the foregoing retrieval/transmission module  31 . For uploading information or files to the file processing center  71 , the processors  731 ,  741  can operate the retrieval/transmission programs  734 ,  744  and cooperate with the memories  732 ,  742  for encrypting electronic files with the hardware serial numbers S 735 , S 745  by using symmetrical encryption (Es) methods, and then transmit the encrypted electronic files to the file processing center  71  via the transmission network  72 . On the other hard, in operation of the retrieval/transmission programs  734 ,  744 , the processors  731 ,  741  cooperating with the memories  732 ,  742  can decrypt encrypted electronic files downloaded from the file processing center  71  with the hardware serial numbers S 735 , S 745  in operation of symmetrical decryption (Ds) methods. The decrypted electronic files are displayed on the screens  736 ,  746  of the file reading devices  73 ,  74 , respectively. Afterwards, for file storage, the decrypted electronic files are again similarly encrypted with the hardware serial numbers S 735 , S 745  by the processors  731 ,  741 , and the encrypted electronic files are stored in the storage media  733 ,  743  of the file reading devices  73 ,  74 .  
         [0036]    [0036]FIG. 5 is a schematic diagram showing data flow directions in the electronic file transmission system  2  of FIG. 3. As shown in the drawing, the file processing center  3  and the reading devices  5 ,  6  of the electronic file transmission system  2  are interconnected via the transmission network  4 , wherein transmission of the public key (Key 32 ) of the file processing center  3  to the file reading device  5  is customarily indicated by a data flow direction A 1  of the public key (Key 32 ), and also transmission of the public key (Key 32 ) to the file reading device  6  is customarily indicated by a data flow direction A 2  of the public key (Key 32 ). After the file reading devices  5 ,  6  receive the public keys (Key 32 ), the retrieval/transmission modules  51 ,  61  use the public keys (Key 32 ) to encrypt the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  by means of asymmetrically unidirectional function encryption (Ea-5, Ea-6), which encrypted data Ea-5(S 52 ), Ea-6(S 62 ) are then transmitted to the file processing center  3 ; wherein Ea-5(S 52 ) transmission from the file reading device  5  to the file processing center  3  is customarily indicated by a data flow direction of A 3 , and Ea-6(S 62 ) transmission from the file reading device  6  to the file processing center  3  is indicated by a data flow direction of A 4 .  
         [0037]    After the file processing center  3  receives encrypted data Ea-5(S 52 ), Ea-6(S 62 ), the encryption/decryption module  31  decrypts the received encrypted data Ea-5(S 52 ), Ea-6(S 62 ) with the private key (Key 33 ) of the file processing center  3  by means of asymmetrically unidirectional function decryption (Da-5, Da-6), which decryption operates as Da-5(Ea-5(S 52 ))=S 52  and Da-6(Ea-6(S 62 ))=S 62 , so that the unencrypted hardware serial number S 52 , S 62  of the file reading device  5 ,  6  are obtained and them stored in the database  34 .  
         [0038]    In a file uploading process to the file processing center  3 , the retrieval/transmission modules  51 ,  61  of the file reading devices  5 ,  6  firstly encrypt electronic files m, n with the hardware serial numbers S 52 , S 62  by using symmetrical encryption (Es-5, Es-6) methods, and then transmit the encrypted files Es-5(m), Es-6(n) to the file processing center  3  via the transmission network  4 . File Es-5(m) transmission from the reading file device  5  to the file processing center  3  via the transmission network  4  is indicated by a data flow direction of A 5 ; file Es-6(n) transmission from the file reading device  6  to the file processing center  3  via the transmission network  4  is indicated by a data flow direction of A 6 .  
         [0039]    Upon receiving the encrypted file Es-5(m), Es-6(n) from the file reading devices  5 ,  6 , the file processing center  3  searches in the database  34  for the hardware serial numbers S 52 , S 62  corresponding to the file reading devices  5 ,  6 . Then, the encryption/decryption module  31  is prompted to decrypt the encrypted files Es-5(m), Es-6(n) with the searched hardware serial numbers S 52 , S 62  by using symmetrical decryption (Ds-5, Ds-6) methods, which decryption operates as Ds-5(Es-5(m))=m, Ds-6(Es-6(n))=n, so that contents of the file m, n can be obtained.  
         [0040]    In a file downloading process, firstly, the encryption/decryption module  31  of the file processing center  3  use the hardware serial numbers S 52 , S 62  as encryption keys (KeyS 52 , KeyS 62 ) in response to the file reading devices  5 ,  6  that request for file downloading, so as to encrypt electronic files p, q by using symmetrical encryption (Es-5, Es-6) methods, allowing the encrypted files Es-5(p), Es-6(q) to be respectively transmitted to the file reading devices  5 ,  6  via the transmission network  4 . File Es-5(p) transmission from the file processing center  3  to the file reading device  5  via the transmission network  4  is indicated by a data flow direction of A 7 ; file Es-6(q) transmission from the file processing center  3  to the file reading device  6  via the transmission network  4  is indicated by a data flow direction of A 8 .  
         [0041]    Upon receiving the encrypted files Es-5(p), Es-6(q), the retrieval/transmission modules  51 ,  61  of the file reading devices  5 ,  6  decrypt the encrypted files Es-5(p), Es-6(q) with the hardware serial numbers S 52 , S 62  by using symmetrical decryption (Ds-5, Ds-6) methods, which decryption operates as Ds-5(Es-5(p))=p, Ds-6(Es-6(q))=q, allowing the obtained unencrypted files p, q to be displayed on the screens  53 ,  63  of the file reading devices  5 ,  6 . For file storage, the retrieval/transmission modules  51 ,  61  again use the hardware serial numbers S 52 , S 62  as encryption keys (KeyS 52 , KeyS 62 ) to encrypt the files p, q in operation of symmetrical encryption (Es-5, Es-6) methods, so as to store the encrypted files Es-5(p), Es-6(q) in the memory units  54 ,  64  of the file reading devices  5 ,  6 , or in the floppy disks  55 ,  65  or the compact disks  56 ,  66 . It should be noted that, unencrypted files cannot be stored in these memory units, floppy disks or compact disks.  
         [0042]    Even though a user of the file reading device  6  obtains an encrypted file Es-5(p) from the file reading device  5  though FTP via the transmission network  4 , or directly from the floppy disk  55  or compact disk  56 , the retrieval/transmission module  61  of the file reading device  6  is not capable of decrypting the encrypted file Es-5(p), since the hardware serial number S 62  of the reading device  6  and symmetrical decryption (Ds-6) are not in operational compliance with decryption of the encrypted file Es-5(p) that is encrypted by the hardware serial number S 52  of the file reading device  5 . Similarly, the retrieval/transmission module  51  of the file reading device  5  having the hardware serial number S 52 , is also not allowed to decrypt an encrypted file Es-6(q) from the file reading device  6 .  
         [0043]    In conclusion from the above described, by using the electronic file transmission system  2  of the invention, transmitted electronic files are encrypted to be uploaded as encrypted files Es-5(m), Es-6(n) to the file processing center  3 , or to be downloaded as encrypted files Es-5(p), Es-6(q) by the file reading devices  5 ,  6 . For example, since the encrypted files Es-5(p), Es-6(q) are encrypted with hardware serial numbers S 52 , S 62  by symmetrical encryption (Es-5, Es-6) methods respectively, only the file reading devices  5 ,  6  having the hardware serial numbers S 52 , S 62  can accordingly operate symmetrical decryption (Ds-5, Ds-6) methods for decrypting the downloaded encrypted files Es-5(p), Es-6(q) and retrieving contents of electronic files p, q. Also, for file storage, the unencrypted electronic files p, q are again similarly encrypted to become encrypted files Es-5(p), Es-6(q) for storage. This therefore assures that only authorized users or receivers can decrypt and retrieve transmitted electronic files, whereby unauthorized copying and propagation of electronic files can be prevented from occurrence.  
         [0044]    [0044]FIG. 6 is a flowchart showing the steps involved in an electronic file transmission method by using an electronic file transmission system of the invention. As shown in the drawing, first in step  21  for initiating registration, allowing a file processing center  3  to obtain hardware serial numbers S 52 , S 62  of file reading devices  5 ,  6 . Thereafter, step  22  is proceeded.  
         [0045]    In step  22  for transmitting electronic files between the file processing center  3  and the file reading devices  5 ,  6 , wherein retrieval/transmission modules  51 ,  61  of the file reading devices  5 ,  6  can encrypt electronic files with the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  by using symmetrical encryption (Es-5, Es-6) methods, or decrypt encrypted electronic files with the hardware serial numbers S 52 , S 62  in operation of symmetrical decryption method (Ds-5, Ds-6). Thereafter, step  23  is proceeded.  
         [0046]    In step  23 , electronic file transmission ends.  
         [0047]    [0047]FIG. 7 is a flowchart showing the procedures involved in a step for initiating registration of FIG. 6. As shown in the drawing, first in step  211 , the file processing center  3  of the electronic file transmission system  2 , is connected to the file reading devices  5 ,  6  via a transmission network  4 , allowing a public key (Key 32 ) of the file processing center  3  to be transmitted to the file reading devices  5 ,  6 , respectively. Thereafter, step  212  is proceeded. In step  212 , upon receiving the public keys (Key 32 ), the file reading devices  5 ,  6  operate the retrieval/transmission modules  51 ,  61  and the public keys (Key 32 ) to encrypt the hardware serial numbers S 52 , S 62  thereof by means of asymmetrically unidirectional function encryption (Ea-5, Ea-6), whereby encrypted data Ea-5(S 52 ), Ea-6(S 62 ) are transmitted to the file processing center  3 . Thereafter, step  213  is proceeded. In step  213 , after the file processing center  3  receives the encrypted data Ea-5(S 52 ), Ea-6(S 62 ), an encryption/decryption module  31  thereof is prompted to decrypt the encrypted data Ea-5(S 52 ), Ea-6(S 62 ) with its private key (Key 33 ) by means of asymmetrically unidirectional function decryption (Da-5, Da-6), which decryption operates as Da-5(Ea-5(S 52 ))=S 52 , Da-6(Ea-6(S 62 ))=S 62 , so that the unencrypted hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  are obtained and stored in a database  34  of the file processing center  3 .  
         [0048]    [0048]FIG. 8 is a flowchart showing the procedures involved in a step for transmitting electronic files of FIG. 6. As shown the drawing, first in step  221 , it is to determine if the file reading devices  5 ,  6  request for file downloading from the file processing center  3  or for file uploading to the file processing center  3 . If file downloading is requested, then step  222  is proceeded; if file uploading is requested, then step  226  is proceeded.  
         [0049]    In step  222  for downloading electronic files, the file processing center  3  prompts the encryption/decryption module  31  to encrypt electronic files p, q with the hardware serial numbers S 52 , S 62  as encryption keys (KeyS 52 , KeyS 62 ) stored in the database  34  by using symmetrical encryption (Es-5, Es-6) methods, whereby encrypted files Es-5(p), Es-6(q) are transmitted to the file reading devices  5 ,  6  via the transmission network  4 . Thereafter, step  223  is proceeded.  
         [0050]    In step  223 , the retrieval/transmission modules  51 ,  61  of the file reading devices  5 ,  6  decrypt the encrypted files Es-5(p), Es-6(q) with the hardware serial numbers S 52 , S 62  in operation of symmetrical decryption (Ds-5, Ds-6) methods, which decryption proceeds as Ds-5(Es-5(p))=p, Ds-6(Es-6(q))=q, so that the electronic files p, q are obtained and then displayed on screens  53 ,  63  of the file reading devices  5 ,  6 . Thereafter, step  224  is proceeded.  
         [0051]    In step  224 , if file storage is required, the unencrypted files p, q are again encrypted with the hardware serial numbers S 52 , S 62  as encryption keys (KeyS 52 , KeyS 62 ) by the retrieval/transmission modules  51 ,  61  in operation of symmetrical encryption (Es-5, Es-6) methods, thereby allowing encrypted files Es-5(p), Es-6(q) to be stored in memory units  54 ,  64  of the file reading devices  5 ,  6 , or in floppy disks  55 ,  65  or compact disks  56 ,  66 . Thereafter, step  225  is proceeded.  
         [0052]    In step  225 , it is to determine if the file reading devices  5 ,  6  continue the file uploading or downloading transmission. If file transmission is continued, then the step  221  is return; or else, step  228  is proceeded for ending the file transmission.  
         [0053]    In step  226  for uploading electronic files, the retrieval/transmission modules  51 ,  61  encrypt electronic files m, n with the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  by using symmetrical encryption (Es-5, Es-6) methods, whereby encrypted files Es-5(m), Es-6(n) are transmitted to the file processing center  3  via the transmission network  4 . Thereafter, step  227  is proceeded.  
         [0054]    In step  227 , upon receiving the encrypted files Es-5(m), Es-6(n), the file processing center  3  searches in the database  34  for the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  who upload the electronic files, and then prompts the encryption/decryption module  31  to decrypt the encrypted files Es-5(m), Es-6(n) with the hardware serial numbers S 52 , S 62  by using symmetrical encryption (Ds-5, Ds-6) methods, which decryption operates as Ds-5(Es-5(m))=m, Ds-6(Es-6(n))=n, so that the unencrypted files m, n are obtained. Thereafter, the step  225  is returned.  
         [0055]    In step  228 , file uploading or downloading transmission between the file reading devices  5 ,  6  and the file processing center  3  is stopped.  
         [0056]    [0056]FIG. 9 is a flowchart showing the steps involved in an electronic file transmission method by using the electronic file transmission system of FIG. 3. As shown in the drawing, first in step  311 , a file processing center  3  of the electronic file transmission system  2  is connected to file reading devices  5 ,  6  via a transmission network  4 , thereby allowing a public key (Key 32 ) of the file processing center  3  to be transmitted to the file reading devices  5 ,  6 , respectively. Thereafter, step  312  is proceeded.  
         [0057]    In step  312 , upon receiving the public keys (Key 32 ), the file reading devices  5 ,  6  adopt retrieval/transmission modules  51 ,  61  thereof and the public keys (Key 32 ) to encrypt their hardware serial numbers S 52 , S 62  by means of asymmetrically unidirectional function encryption (Ea-5, Ea-6), whereby encrypted data Ea-5(S 52 ), Ea-6(S 62 ) are transmitted to the file processing center  3 . Thereafter, step  313  is proceeded.  
         [0058]    In step  313 , after the file processing center  3  receives the encrypted data Ea-5(S 52 ), Ea-6(S 62 ), an encryption/decryption module  31  thereof is prompted to decrypt the encrypted data Ea-5(S 52 ), Ea-6(S 62 ) with its private key (Key 33 ) by means of asymmetrically unidirectional function decryption (Da-5, Da-6), which decryption operates as Da-5(Ea-5(S 52 ))=S 52 , Da-6(Ea-6(S 62 ))=S 62 , so that the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  are obtained and then stored in a database  34  of the file processing center  3 . Thereafter, step  314  is proceeded.  
         [0059]    In step  314  for downloading electronic files, the file processing center  3  prompts its encryption/decryption module  31  to encrypt electronic files p, q with the hardware serial numbers S 52 , S 62  as encryption keys (KeyS 52 , KeyS 62 ) stored in the database  34  by using symmetrical encryption (Es-5, Es-6) methods, allowing encrypted files Es-5(p), Es-6(q) to be transmitted via the transmission network  4  to the file reading devices  5 ,  6  who request for file downloading, respectively. Thereafter, step  315  is proceeded.  
         [0060]    In step  315 , upon receiving the encrypted files Es-5(p), Es-6(q), the file reading devices  5 ,  6  prompt the retrieval/transmission modules  51 ,  61  to decrypt the encrypted files Es-5(p), Es-6(q) with their hardware serial numbers S 52 , S 62  in operation of symmetrical decryption (Ds-5, Ds-6) methods, which decryption proceeds as Ds-5(Es-5(p))=p, Ds-6(Es-6(q))=q, whereby the unencrypted files p, q are obtained and then displayed on screens  53 ,  63  of the file reading devices  5 ,  6 . Thereafter, step  316  is proceeded.  
         [0061]    In step  316 , if file storage is required, the unencrypted files p, q are again encrypted with the hardware serial numbers S 52 , S 62  as encryption keys (KeyS 52 , KeyS 62 ) by the retrieval/transmission modules  51 ,  61  in operation of symmetrical encryption (Es-5, Es-6) methods, thereby allowing encrypted files Es-5(p), Es-6(q) to be stored in memory units  54 ,  56  of the file reading devices  5 ,  6 , or in floppy disks  55 ,  65  or compact disks  56 ,  66 . Thereafter, step  317  is proceeded.  
         [0062]    In step  317  for uploading electronic files, the retrieval/transmission modules  51 ,  61  encrypt electronic files m, n with the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  by using symmetrical encryption (Es-5, Es-6) methods, whereby encrypted files Es-5(m), Es-6(n) are transmitted to the file processing center  3  via the transmission network  4 . Thereafter, step  318  is proceeded.  
         [0063]    In step  318 , upon receiving the encrypted files Es-5(m), Es-6(n), the file processing center  3  searches in the database  34  for the hardware serial numbers S 52 , S 62  of the file reading devices  5 ,  6  who upload the electronic files, and then prompts the encryption/decryption module  31  to decrypt the encrypted files Es-5(m), Es-6(n) with the hardware serial numbers S 52 , S 62  by using symmetrical encryption (Ds-5, Ds-6) methods, which decryption operates as Ds-5(Es-5(m))=m, Ds-6(Es-6(n))=n, so that the unencrypted files m, n are obtained. Thereafter, step  319  is proceeded.  
         [0064]    In step  319 , file uploading or downloading transmission between the file reading devices  5 ,  6  and the file processing center  3  is stopped.  
         [0065]    [0065]FIG. 10 is a flowchart showing the steps involved in an electronic file transmission method by using the electronic file transmission system of FIG. 4. As shown in the drawing, first in step  411 , a file processing center  71  of the electronic file transmission system  7  is connected to file reading devices  73 ,  74  via a transmission network  72 , thereby allowing a public key (Key 715 ) of the file processing center  71  to be transmitted to the file reading devices  73 ,  74 , respectively. Thereafter, step  412  is proceeded.  
         [0066]    In step  412 , upon receiving the public keys (Key 715 ), processors  731 ,  741  of the file reading devices  73 ,  74  execute retrieval/transmission programs  734 ,  744  and cooperate with memories  732 ,  742 , so as to encrypt their hardware serial numbers S 735 , S 745  with the public keys (Key 715 ) by means of asymmetrically unidirectional function encryption (Ea-5, Ea-6), whereby encrypted data Ea-5(S 735 ), Ea-6(S 745 ) are transmitted to the file processing center  71  via the transmission network  72 . Thereafter, step  413  is proceeded.  
         [0067]    In step  413 , after the file processing center  71  receives the encrypted data Ea-5(S 735 ), Ea-6(S 745 ), a processor  711  thereof executes an encryption/decryption program  714  and cooperates with a memory  712 , so as to decrypt the encrypted data Ea-5(S 735 ), Ea-6(S 745 ) with its private key (Key 33 ) by means of asymmetrically unidirectional function decryption (Da-5, Da-6), which decryption operates as Da-5(Ea-5(S 735 ))=S 735 , Da-6(Ea-6(S 745 ))=S 745 , thereby allowing the hardware serial numbers S 735 , S 745  to be obtained and then stored in a database  717  of the file processing center  71 . Thereafter, step  414  is proceeded.  
         [0068]    In step  414  for uploading electronic files, the processors  731 ,  741  execute the retrieval/transmission programs  734 ,  744  and cooperate with the memories  732 ,  742 , so as to encrypt electronic files m, n with the hardware serial numbers S 735 , S 745  of the file reading devices  73 ,  74  by using symmetrical encryption (Es-5, Es-6) methods, whereby encrypted files Es-5(m), Es-6(n) are transmitted to the file processing center  71  via the transmission network  72 . Thereafter, step  415  is proceeded.  
         [0069]    In step  415 , upon receiving the encrypted files Es-5(m), Es-6(n), the file processing center  71  searches in the database  717  for the hardware serial numbers S 735 , S 745  of the file reading devices  73 ,  74  who upload the electronic files, and then executes the encryption/decryption program  714  and cooperates with the memory  712 , so as to decrypt the encrypted files Es-5(m), Es-6(n) with the hardware serial numbers S 735 , S 745  by using symmetrical encryption (Ds-5, Ds-6) methods, which decryption operates as Ds-5(Es-5(m))=m, Ds-6(Es-6(n))=n, so that the unencrypted files m, n are obtained. Thereafter, step  416  is proceeded.  
         [0070]    In step  416  for downloading electronic files, the processor  711  of the file processing center  71  executes the encryption/decryption program  714  and cooperates with the memory  712 , so as to encrypt electronic files p, q with the hardware serial numbers S 735 , S 745  as encryption keys (KeyS 735 , KeyS 745 ) stored in the database  717  by using symmetrical encryption (Es-5, Es-6) methods, allowing encrypted files Es-5(p), Es-6(q) to be transmitted via the transmission network  72  to the file reading devices  73 ,  74  who request for file downloading, respectively. Thereafter, step  417  is proceeded.  
         [0071]    In step  417 , upon receiving the encrypted files Es-5(p), Es-6(q), the processors  731 ,  741  of the file reading devices  73 ,  74  execute the retrieval/transmission programs  734 ,  744  and cooperate with the memories  732 ,  742 , so as to decrypt the encrypted files Es-5(p), Es-6(q) with their hardware serial numbers S 735 , S 745  in operation of symmetrical decryption (Ds-5, Ds-6) methods, which decryption proceeds as Ds-5(Es-5(p))=p, Ds-6(Es-6(q))=q, whereby the unencrypted files p, q are obtained and then displayed on screens  736 ,  746  of the file reading devices  73 ,  74 . Thereafter, step  418  is proceeded.  
         [0072]    In step  418 , if file storage is required, the unencrypted files p, q are again encrypted with the hardware serial numbers S 735 , S 745  as encryption keys (KeyS 735 , KeyS 745 ) in operation of symmetrical encryption (Es-5, Es-6) methods by the processors  731 ,  741  in cooperation with the memories  732 ,  742 , whereby encrypted files Es-5(p), Es-6(q) can be stored in data storage media  733 ,  743  of the file reading devices  73 ,  74 . Thereafter, step  419  is proceeded.  
         [0073]    In step  419 , file uploading or downloading transmission between the file reading devices  73 ,  74  and the file processing center  71  is stopped.  
         [0074]    In conclusion, the system and method for electronic file transmission of the invention provide significant advantages. For example, by virtue of file encryption and decryption, encrypted files downloaded from a file processing center can be decrypted and read only by authorized receivers of file reading devices who request for file downloading. And, the decrypted and read files are again encrypted by the file reading devices for file storage, wherein storage unencrypted files is not permitted in the file reading devices. This therefore can effectively prevent electronic files or digital information from being unauthorizedly copied and propagated.  
         [0075]    The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.