Patent Publication Number: US-2002001388-A1

Title: High speed copy protection method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This application claims the benefit of Korean Application No. 2000-31028, filed Jun. 7, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       Field of the Invention  
       [0002] The present invention relates to a method of encrypting digital data, and more particularly, to a high speed copy protection method using a dual encryption key.  
       Description of the Related Art  
       [0003] Due to the speed of the Internet, electronic commerce, and the use of digital storage media (DSM), the number of applications in which encryption methods are being used is continually increasing. Examples of areas in which encryption methods are used include security, authentication, and copy protection. Two widely used encryption methods include a common key encryption method and a public key encryption method. The common key encryption method is a method of encrypting digital data using a 40-bit or 56-bit key, and the public key encryption method is a method of encrypting digital data using a 512-bit or 1024-bit key. Although increasing the size of the key used in encryption increases security, it also increases the amount of calculation required for encryption so as to dramatically decrease the processing speed of encryption.  
       [0004] Referring to FIG. 1, which is a block diagram of a conventional encryption apparatus, the encryption apparatus includes a sender  100  to encrypt a text  1  and providing a cipher text  5 , and a receiver  200  to receive a key  7  used in encrypting and decrypting the cipher text  5  and restoring the text  1 . Besides the sender  100  and the receiver  200 , an improved apparatus further includes (not shown) a third party for publicizing, updating, and/or distributing keys.  
       [0005] The sender  100  includes an encryptor  110  to encrypt the text  1  using an encryption key  7  and an authenticator  120  to obtain a safe transmission path  10  through which to transmit the encryption key  7 . The receiver  200  includes an authenticator  210  to obtain the safe transmission path  10  through which to receive the encryption key  7  used in encrypting and a decryptor  220  to decrypt the cipher text  5  using the transmitted encryption key  7 .  
       [0006] Referring to FIG. 2, which illustrates a flow chart of a conventional copy protection method, the sender  100  (or receiver  200 ) checks with the corresponding receiver  200  (or sender  100 ) whether it is okay to send (or receive). When the sender  100  checks with the receiver  200  whether it is okay to send (operation S 1 ), it is checked whether the receiver  200  is ready by the receiver&#39;s  200  response (operation S 2 ). Similarly, when the receiver  200  checks with the sender  100  whether it is okay to receive (operation S 3 ), it is checked whether the sender  100  is ready by the sender&#39;s  100  response (operation S 4 ).  
       [0007] When the receiver  200  is ready to receive (operation S 2 ) or the sender  100  is ready to send (operation S 4 ), the sender  100  authenticates the receiver  200  (operation S 5 ). In the operation S 5 , the sender  100  transmits a challenge for authentication to the receiver  200 . When the receiver transmits a response to the challenge for authentication to the sender  100 , the sender  100  compares the transmitted response and determines whether the response is authentic (operation S 6 ). In the operation S 6 , when the response is authentic, the receiver  200  authenticates the sender  100  (operation S 7 ). However, in the operation S 6 , when the response is not authentic, the authentication stops (operation S 8 ).  
       [0008] Similarly, when the receiver  200  transmits a challenge for authentication to the sender  100  and the sender  100  transmits a response to the challenge for authentication to the receiver  200  in the operation S 7 , the receiver  200  compares the transmitted response and determines whether the response is authentic (operation S 9 ). In the operation S 9 , when the response is authentic, an authentication key (not shown) is generated and the safe transmission path  10  is obtained (operation S 10 ). In the operation S 9 , when the response is not authentic, the authentication stops (operation S 11 ). The operations S 1  through S 11  generally comprise authentication operations.  
       [0009] When the safe transmission path  10  is obtained in the operation S 10 , a text  1  is encrypted by an encryption key  7 , and a cipher text  5  is transmitted (operation  12 ). The encryption key  7  used in encrypting the text  1  is also encrypted by the authentication key (not shown) generated in the operation S 10  and transmitted through the safe transmission path  10  (operation S 13 ). The cipher text  5 , which is transmitted through a normal, unsafe transmission path, is decrypted by the encryption key  7  transmitted through the safe transmission path  10 , and the text  1  is restored (operation S 14 ).  
       [0010] The method of encrypting the cipher text  5  illustrated in FIG. 2, is the common key encryption method, and an identical encryption key  7  is used in encrypting and decrypting. The transmission path includes a safe transmission path  10  to transmit an encryption key  7 , and a normal path used for transmitting encrypted data. On the assumption that decryption cannot be performed without using the encryption key  7 , the cipher text  5  is transmitted via the normal path (i.e. an unsafe transmission path), and the normal path is designated as a public path such as an Internet network, or a telephone network, a wireless network, or an area network such as a LAN, WAN, MAN, etc. Further, it is understood that the normal path could include storing the cipher text  5  on a medium and sending the medium by mail.  
       [0011] The most common transmission method for safely transmitting the encryption key  7  used in encrypting is a specific encryption method, and the safe transmission path  10  obtained by authentication is used in the specific encryption method. That is, another encryption method other than that used in encryption of a document is used in the operation S 13  of FIG. 2 using the safe transmission path  10  obtained by the authentication. Also, an encryption method, in which a larger authentication key than the encryption key  7  is used, is mainly used. Here, as the size of the authentication key increases, security is increased, but the processing speed is reduced.  
       [0012] Specifically, the sender  100  transmits the encryption key  7  to the receiver  200  via the safe transmission path  10  (operation S 13  of FIG. 2). A text  1  to be transmitted is encrypted by the common key encryption method using the encryption key  7  (operation S 12  of FIG. 2). Here, since a 40-bit or 56-bit encryption key  7  is mainly used in the common key encryption method, security is decreased, and processing speed is increased. Thus, the common key encryption method is useful for a large amount of data processing. The encrypted cipher text  5  is transmitted to the receiver  200  via an unsafe normal path or a public network or path. The receiver  200  receives the encryption key  7  from the authenticated safe transmission path  10  and decrypts the cipher text  5  and obtains the encryption key  5 , and the cipher text  5  processed by the common key encryption method is decrypted using the encryption key  7 , and the text  1  is restored.  
       [0013] Since the same encryption key  7  is used in encrypting and decrypting, the method is referred to as a common key (or symmetric key) encryption method. Another method in which a different key is used in encryption and decryption is referred to as a public key (or asymmetric key) encryption method. Usually, in the common key encryption method, the size of the key is small and the encryption method is simple in comparison with the public key encryption method. Thus, the security is relatively low, and its processing speed is relatively high. In the public key encryption method, the size of the key is generally large, processing speed is low, and security is relatively high. Thus, the public key encryption method is used in the operation of authentication for obtaining the safe transmission path  10  (operations S 5  through S 10  of FIG. 2), and the common key encryption method is used in the operation of data processing for encrypting a text (operations S 12  through S 14  of FIG. 2).  
       [0014] However, due to the spread of high-performance computers, the security of the encryption methods is being threatened. That is, a personal computer (PC) having improved calculation ability can access the cipher text  5 , which is sent through the unsafe public network, without the encryption key  7 . Since the size of the encryption key  7  is small and simple, and repetitive tasks are often performed in using the encryption key  7 , the encryption key  7  used in the encryption can be found and decryption is possible without using the encryption key  7 .  
       [0015] As such, the conventional common key encryption method using the current common encryption key  7  of the size of 40 bits or 56 bits would no longer be used. However, for non-computers, such as information household electric appliances which have a low operation ability, while their security can be increased using the encryption method in which an encryption key  7  having a size greater than 128 bits is used, this increased security is impractical due to the reduced processing speed in these appliances to perform their functions. Further, it is more difficult to introduce the public key encryption method in which an encryption key having a size greater than 512 bits is used. However, while high security like that used in electronic commerce should be available for the information household electric appliances, the current encryption methods can not satisfy both the need for security and the need for speed.  
       SUMMARY OF THE INVENTION  
       [0016] To solve the above and other problems, it is an object of the present invention to provide a high speed copy protection method in which a dual key encryption method is implemented.  
       [0017] It is another object of the present invention to provide a high speed copy protection method of encrypting a first region of a text using a first encryption key to increase security, and encrypting a second region of the text using a second encryption key for high speed processing.  
       [0018] Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
       [0019] Accordingly, to achieve the above and other objects, there is provided a copy protection method to prevent unauthorized copying of digital data during digital data transmission between a sender and a receiver according to an embodiment of the present invention that comprises encrypting a first region of a text containing a second encryption key using a first encryption key, encrypting a second region of the text using the second encryption key to generate a cipher text, and transmitting the cipher text.  
       [0020] According to an aspect of the present invention, the copy protection method further comprises transmitting the first encryption key, region segmentation information for segmenting the text into the first region and the second region, and information related to the second encryption key through a safe transmission path.  
       [0021] According to another aspect of the present invention, the copy protection method further comprises decrypting the first region of the cipher text using the first encryption key and the region segmentation information transmitted through the safe transmission path, extracting the second encryption key from the decrypted first region using the information related to the second encryption key transmitted through the safe transmission path, and decrypting the second region of the cipher text and restoring the text using the extracted second encryption key. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022] The above and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings in which:  
     [0023]FIG. 1 is a block diagram of a conventional encryption system;  
     [0024]FIG. 2 is a flow chart of a conventional copy protection method;  
     [0025]FIG. 3 is a schematic diagram illustrating a high speed copy protection method according to an embodiment of the present invention; and  
     [0026]FIG. 4 is a flow chart of the high speed copy protection method according an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0027] Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
     [0028] Referring to FIG. 3, a sender  100  extracts data which are at a specific position within a text  1000  to be encrypted, as a second encryption key  3000 . The position of the second encryption key data (i.e., the data used to form the second encryption key  3000 ) can be varied or fixed. The size of the second encryption key  3000  may or may not be the same as that in a conventional common key encryption method. The sender  100  may be a multipurpose or specific purpose computer, a server, of an information appliance.  
     [0029] Meanwhile, where a common key encryption method is used in an embodiment of the present invention, the size of a first encryption key  2000  is larger than that in the conventional common key encryption method. In the case of using a public key encryption method according to another embodiment of the present invention, the size of the first encryption key  2000  may be the same as that in the conventional public key encryption method.  
     [0030] A predetermined region A of the text  1000  is encrypted using the first encryption key  2000 . During encryption of the predetermined region A, the predetermined region A (hereinafter referred to as a “first region A”) must include data to be extracted as the second encryption key  3000 . The other region of the text  1000  is referred to as a second region B. The size of the first region A and the second region B can be varied, but the size and the segmentation region of respective encryption keys (first and second encryption keys  2000  and  3000 ) between the sender  100  and a receiver  200  must be the same.  
     [0031] That is, the first region A and the second region B are predetermined, and the first region A is encrypted as the first encryption key  2000  after the second encryption key  3000  is extracted from the first region A. Next, the second region B is encrypted using the second encryption key  3000 . Subsequently, a safe transmission path  10  of FIG. 1 is obtained, and the first encryption key  2000  is transmitted to the receiver  200  via the safe transmission path  10  of FIG. 1. A cipher text  1500  can be transmitted through a normal unsecured path.  
     [0032] As described above, the text data  1000  can be therefore encrypted, with the first encryption key  2000  used in the encryption being the same, but where the second encryption key  3000  extracted from the first region A is different.  
     [0033] The receiver  200  decrypts the first region A using the first encryption key  2000  transmitted through the safe transmission path  10  of FIG. 1, extracts the second encryption key  3000  from the decrypted first region A, and decrypts the second region B to then obtain the text  1000 . The receiver  200  may be a multipurpose or specific purpose computer, a server, of an information appliance.  
     [0034] The safe transmission path  10  of FIG. 1 is obtained through authentication. Here, information on the segmentation of each region (such as a starting address of the second region B or the size of the first region A), the size of the first and second encryption keys  2000  and  3000  according to the receiver&#39;s operation ability, the position of the second encryption key  3000 , and information on encryption of each region A and B can be shared.  
     [0035] Thus, more variable and safer encryption can be realized, where the encryption uses a high speed copy protection method according to the present invention that can be applied to a conventional encryption apparatus as shown in FIG. 1. Whereas the conventional encryption apparatus transmits only the encryption key  7  for encrypting the text  1  via the safe transmission path  10 , using the encryption method according to the present invention, the first encryption key  2000  is used to encrypt the first region A of the text  1000 , the second encryption key information (the size and position of the second encryption key  3000  used to encrypt the second region B), and the region segmentation information are transmitted via the safe transmission path  10 . Here, the first region A containing the second encryption key  3000  is smaller than the second region B, and the size of the first encryption key  2000  is larger than that of the second encryption key.  
     [0036] Referring to FIG. 4, the safe transmission path  10  is obtained in operation  101  using a conventional authorization procedure as shown in operations S 1  through S 11  of FIG. 2. After authentication (operation S 101 ), the second encryption key  3000  is extracted from the first region A of the text  1000  (operation S 102 ). The first region A is encrypted using the first encryption key  2000  (operation S 103 ). The second region B of the text  1000  is encrypted using the second encryption key  3000  and the cipher text  1500  is transmitted (operation S 104 ). The first encryption key  2000  is transmitted through the safe transmission path  10  of FIG. 1 (operation S 105 ), as is the region segmentation information and the second encryption key information (size and position) (operation S 106 ). It is understood that the method shown in FIG. 4 can be performed by a computer program embedded on a computer readable medium.  
     [0037] Meanwhile, the receiver  200  decrypts the first region A of the cipher text  1500  using the received first encryption key  2000  and the region segmentation information (operation S 107 ). The second encryption key  3000  is extracted from the decrypted first region A of the cipher text  1500  using the received second encryption key information (size and position) (operation S 108 ). The second region B of the cipher text  1500  is decrypted using the extracted second encryption key  3000  (operation S 109 ).  
     [0038] Accordingly, the present invention uses the first encryption key, which is larger than that in the conventional common key encryption method or the first encryption key used in the public key encryption method, to encrypt the first region of the text containing the second encryption key, thereby enhancing its security. The second encryption key, which is smaller than the first encryption key used in the common key encryption method, is used in the second region of the text. As a result, a large amount of data requiring high speed processing are processed using the key of the common key encryption method, and part of the cipher text is processed using the large common key or the key of the public key encryption method such that speed and security can be simultaneously satisfied.  
     [0039] While not shown, it is understood that security could be additionally enhanced by using additional keys could be extracted from the text. For instance, a third key could be extracted from the second or first portion of the text in order to encrypt a third portion of the text.  
     [0040] Accordingly, since the present invention uses a first encryption key larger than that in the conventional method and decrypts most of the data using the small second encryption key, its security is increased without requiring an increased operation ability and processing time.  
     [0041] As described above, the present invention increases and improves security and speed using dual encryption keys. The present invention securely transmits only a part of the transmitted key, compared with conventional encryption methods for copy protection, which also increases security. Further, the present invention encrypts part of the text using the second encryption key. Thus, the first encryption key is sufficient for the second encryption key to be transmitted through a safe transmission path, and the second encryption key, which is one of the dual keys, is always varied. As a result, encryption keys which are varied according to each transmission unit are transmitted, which further enhances security.  
     [0042] Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.