Patent Publication Number: US-2015074417-A1

Title: Apparatus and method for access control of content in distributed environment network

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a Divisional of U.S. patent application Ser. No. 13/410,762 filed on Mar. 2, 2012, which claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2011-0018664, filed on Mar. 2, 2011, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field 
     The following description relates to an apparatus and a method for access control of content in a distributed environment network. 
     2. Description of Related Art 
     An access control of content based on an encryption technology may generally manage and control access authorization of the corresponding content based on whether a data encryption key (DEK) used for a content encryption is secured. A user securing the DEK may be considered to have read and access authorization in relation to the corresponding content. 
     Since a user having read and access authorization may previously secure the DEK or may generate the DEK, read and write authorizations may not be separately managed based on whether the DEK is secured. 
     Accordingly, an additional scheme for managing write authorization in a case of the access control of content based on an encryption technology may be desireable. 
     SUMMARY 
     In one general aspect, an apparatus for generating a key for access control of content in a distributed environment network is provided. The apparatus includes a first key distributor configured to generate first encrypted keys by encrypting a first key corresponding to a key for write authorization using each public key of members having write authorization among members included in an access control list including information of at least one user and information about access authorization and distribute the access control list and the first encrypted keys to the members having write authorization, and a second key distributor configured to generate second encrypted keys by encrypting a second key corresponding to a key for read authorization using the first key using each public key of members having read authorization among members included in the access control list and distribute the access control list and second encrypted keys to the members having read authorization. 
     The access control list may include identification information for identifying the access control list from other access control lists, information about a size of the access control list, information about a version of the access control list, information about an identification of each of members, information about access authorization of each of the members, information about a public key of each of the members, information about a signature of a generator generating the access control list, or any combination thereof. 
     The first key may be neither generated nor predicted using the second key. 
     The second key may be a result obtained by hashing the first key n times, the value of n being an integer greater than 0. 
     The first key distributor, the second key distributor, or any combination thereof may be implemented by a processor. 
     The apparatus may include a list generator to generate the access control list. 
     The apparatus may include a first key generator to generate the first key, and a second key generator to generate the second key. 
     In another aspect, an apparatus for generating content for an access control of content in a distributed environment network is provided. The apparatus includes a key decryption unit configured to secure a first key by decrypting a first encrypted key, encrypted by using a public key, using a secret key corresponding to the public key, an encryption key generator configured to generate an encryption key using a second key generated using the first key, a content encryption unit configured to generate an encrypted content by encrypting content using the encryption key, a signature generator configured to generate a signature using the first key, a content and a signature key in response to members included in an access control list having write authorization as a result of checking access authorization of the members, and a distributor configured to distribute the encrypted content and the signature through a network. 
     The encryption key generator may generate the encryption key using information of the content and the second key. 
     The first key may correspond to a key for write authorization and may be neither generated nor predicted using the second key. 
     The second key may correspond to a key for read authorization and may be a result obtained by hashing the first key n times, the value of n being an integer greater than 0. 
     The signature generator may generate the signature using a value obtained by hashing the first key m times, a value obtained by hashing the content, and the signature key, the distributor may distribute a value of the m in addition to the encrypted content and the signature and the value m may correspond to a random value less than n corresponding to a number of times the first key is hashed to generate the second key. 
     The signature generator may generate the signature using an algorithm having a one-way homomorphic characteristic. 
     The signature key may be generated based on a Rivest Shamir Adleman (RSA) encryption scheme. 
     In another aspect, an apparatus for verification of content for an access control of content in a distributed environment network is provided. The apparatus includes a receiver configured to receive an encrypted content, a signature of the encrypted content, and an access control list, and to receive a second encrypted key from a network in response to the apparatus being determined to have read authorization as a result of checking the access control list, a key decryption unit configured to secure a second key by decrypting the second encrypted key, encrypted by using a public key, using a secret key corresponding to the public key in response to the apparatus being determined to have read authorization as a result of checking the access control list, a signature verification unit configured to verify the signature using the second key and the encrypted content, a decryption key generator configured to generate a decryption key using the second key in response to the signature verification being successful, and a content decryption unit configured to decrypt the encrypted content using the decryption key. 
     The apparatus may include a second key generator configured to generate the second key using a first key. The receiver may receive a first encrypted key from the network, and the key decryption unit may secure the first key by decrypting the first encrypted key using the secret key in response to the apparatus being determined to have write authorization as a result of checking the access control list. 
     The first key may correspond to a key for write authorization and may be neither generated nor predicted using the second key. 
     The second key may correspond to a key for read authorization and may be a result obtained by hashing the first key n times, the value of n being an integer greater than 0. 
     In another aspect, a method for an access control of content in an apparatus for generating a key of a distributed environment network is provided. The method includes generating a second key corresponding to a key for read authorization using a first key corresponding to a key for write authorization, generating first encrypted keys by encrypting the first key using each public key of members having write authorization among members included in an access control list including information of at least one user and information about access authorization, distributing the access control list and the first encrypted keys to the members having write authorization, generating second encrypted keys by encrypting the second key using each public key of members having read authorization among members included in the access control list, and distributing the access control list and the second encrypted keys to the members having read authorization. 
     In another aspect, a method for an access control of content in an apparatus for generating content of a distributed environment network is provided. The method includes requesting and receiving an access control list and a first encrypted key from a network, securing a first key corresponding to a key for write authorization by decrypting the first encrypted key, encrypted by using a public key, using a secret key corresponding to the public key in response to the apparatus being determined to have write authorization as a result of checking the access control list, generating an encryption key using information of a content and a second key corresponding to a key for read authorization using the first key, generating an encrypted content by encrypting content using the encryption key, generating a signature using the first key, the content, and a signature key, and distributing the encrypted content and the signature through the network. 
     The generating of the signature may include generating the signature using a value obtained by hashing the first key m times, a value obtained by hashing the content and the signature key, the distributing may include distributing a value of the m in addition to the encrypted content and the signature, and the value m may correspond to a random value less than n corresponding to a number of times the first key is hashed to generate the second key, the value of n being an integer greater than 0. 
     The generating of the signature may include generating the signature using an algorithm having a one-way homomorphic characteristic. 
     In another aspect, a method for an access control of content in an apparatus for verification of content of a distributed environment network is provided. The method includes checking access authorization of an encrypted content in an access control list to verify access requirements are satisfied, securing a second key corresponding to a key for read authorization in response to the encrypted content being determined to be accessible as a result of the verification, verifying a signature of the encrypted content using the second key and the encrypted content, generating a decryption key using the second key in response to the signature verification being successful, and decrypting the encrypted content using the decryption key. 
     The securing may include receiving a second encrypted key from the network in response to the apparatus being determined to have read authorization as a result of checking the access control list, and securing a second key by decrypting the second encrypted key, encrypted by using a public key, using a secret key corresponding to the public key. The securing may include receiving a first encrypted key from the network in response to the apparatus being determined to have write authorization as a result of checking the access control list, securing a first key by decrypting the first encrypted key, encrypted by using a public key, using a secret key corresponding to the public key, and generating the second key using the first key. 
     Other features and aspects may be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of an apparatus for generating a key for an access control of content in a distributed environment network. 
         FIG. 2  is a diagram illustrating an example of an apparatus for generating content for an access control of content in a distributed environment network. 
         FIG. 3  is a diagram illustrating an example of an apparatus for verification of content for an access control of content in a distributed environment network. 
         FIG. 4  is a flowchart illustrating an example of a process of generating an access control list for an access control of content and separately generating and distributing a key between write authorization and read authorization in an apparatus for generating a key in a distributed environment network. 
         FIG. 5  is a flowchart illustrating an example of a process of generating and distributing content for an access control of content in an apparatus for generating content in a distributed environment network. 
         FIG. 6  is a flowchart illustrating an example of a process of verifying content where access to content is controlled in an apparatus for verification of content in a distributed environment network. 
     
    
    
     Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the systems, apparatuses and/or methods described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
     Examples relate to an apparatus for generating a key, an apparatus for generating content, and an apparatus for verification of content for separately controlling read authorization and write authorization with respect to content and a method thereof in a distributed environment network. 
       FIG. 1  includes an example of an apparatus for generating a key  100  for an access control of content in a distributed environment network. 
     Referring to  FIG. 1 , the apparatus for generating a key  100  may include a control unit  110 , a communication unit  120 , a storage unit  130 , a list generator  111 , a first key generator  112 , a second key generator  113 , a first key distributor  114 , and a second key distributor  115 . 
     The communication unit  120  may transmit and receive data through a wired and/or a wireless network. In this instance, the network may correspond to a content centric network (CCN) or a named data network (NDN). 
     The storage unit  130  may store an operating system, an application program, and data for controlling an operation of the apparatus for generating a key  100 . The storage unit  130  may store an access control list generated by the list generator  111 , a first key generated by the first key generator  112  and a second key generated by the second key generator  113 . 
     The access control list may includes information of at least one user and information relating to access authorization. 
     In this instance, the access control list may include identification information for identifying the access control list from other access control lists, information about a size of the access control list, information about a version of the access control list, information about an identification of each of the members, information about access authorization of each of the members, information about a public key of each of the members, information about a signature of a generator generating the access control list, or any combination thereof. 
     A structure of the access control list may be as shown in the following Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Structure 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Name 
                 Size 
                 Option Flag 
               
               
                   
                 Version (optional) 
                 Nonce (optional) 
                 Index (optional) 
               
               
                   
                 Principal[1] 
                 Principal[1]&#39;s rights 
                 Key Link[1] 
               
               
                   
                 * * * 
               
               
                   
                 Principal[n] 
                 Principal[n]&#39;s rights 
                 Key Link[n] 
               
            
           
           
               
               
            
               
                   
                 Signature 
               
               
                   
                   
               
            
           
         
       
     
     In Table 1, Name relates to identification information for identifying an access control list, Size relates to a number of Principals or a size of the access control list, Option Flag relates to identification information for identifying optional components, Version relates to a time stamp, Nonce relates to a random value for generating an encryption key, Index relates to information of a hash key, Principal[i] relates to identification information of a user or a user group, Principal[i]&#39;s rights relate to information about access authorization assigned to the Principal[i], Key Link[i] relates to identification information of a key assigned to the Principal[i] and Signature relates to a signature of a generator of the access control list. 
     The first key generator  112  may generate a first key. The first key may correspond to a key for write authorization. 
     The second key generator  113  may generate a second key. The second key may correspond to a key for read authorization using the first key. The second key generator  113  may be generated based on the following Equation 1. 
         K=H   n ( NK )  [Equation 1]
 
     In Equation 1, K relates to the second key for read authorization, NK relates to the first key for write authorization, H( ) relates to a hash function, and H n ( ) relates to performing a hash n times. N may be an integer greater than zero. 
     The first key may be neither generated nor predicted using the second key. 
     The first key distributor  114  may generate first encrypted keys by encrypting the first key using each public key of members having write authorization. The members having write authorization may be included in the access control list. The first key distributor  114  may distribute the access control list and the first encrypted keys to the members having write authorization. 
     The second key distributor  115  may generate second encrypted keys by encrypting the second key using each public key of members having read authorization. The members having read authorization may be included in the access control list. The second key distributor  115  may distribute the access control list and second encrypted keys to the members having read authorization. 
     The control unit  110  may control an overall operation of the apparatus for generating a key  100 . The control unit  110  may function as the list generator  111 , the first key generator  112 , the second key generator  113 , the first key distributor  114 , and the second key distributor  115 . The control unit  110 , the list generator  111 , the first key generator  112 , the second key generator  113 , the first key distributor  114 , and the second key distributor  115  are separately illustrated to separately describe each function. Furthermore, the control unit  110  may include at least one processor to function as an entire or a portion of the list generator  111 , the first key generator  112 , the second key generator  113 , the first key distributor  114 , and the second key distributor  115 . 
     In response to authorization of a user included in the access control list being changed or deleted, the apparatus for generating a key  100  may newly generate and distribute a first key and a second key. In this instance, a user whose authorization is deleted may not use content generated after deletion of authorization. As another aspect, content generated and distributed before deletion of authorization of the user may be continued to be used by the user. 
     In response to a new user being added to the access control list, the apparatus for generating a key  100  may newly encrypt and distribute a key corresponding to authorization assigned to the added user. The key corresponding to authorization assigned to the added user may be encrypted and distributed using a public key of the added user. 
       FIG. 2  includes an example of an apparatus for generating content  200  for an access control of content in a distributed environment network. 
     Referring to  FIG. 2 , the apparatus for generating content  200  may include a control unit  210 , a communication unit  220 , a storage unit  230 , a receiver  211 , a key decryption unit  212 , a second key generator  213 , a content generator  214 , an encryption key generator  215 , a content encryption unit  216 , a signature generator  217 , and a distributor  218 . 
     The communication unit  220  may transmit and receive data through a wired and/or wireless network. In this instance, the network may correspond to a CCN or an NDN. 
     The storage unit  230  may store an operating system, an application program, and data for controlling an overall operation of the apparatus for generating content  200 . The storage unit  230  may store an access control list received through the receiver  211 , a first key decrypted by the key decryption unit  212  and a second generated by the second key generator  213 . 
     The receiver  211  may request and receive an access control list from a network. The receiver  211  may request and receive a first encrypted key from the network. 
     The key decryption unit  212  may secure a first key corresponding to a key for write authorization by decrypting the first encrypted key using a secret key corresponding to the public key. The first encrypted key may be encrypted by using a public key. 
     The second key generator  213  may generate a second key. The second key may be generated using the first key and may correspond to a key for read authorization. 
     The content generator  214  may generate content. 
     The encryption key generator  215  may generate an encryption key. The encryption key may be generated using the second key. In another example, the encryption key may be generated using information of the content and the second key. In this instance, the encryption key generator  215  may generate the encryption key based on the following Equation 2. 
         DEK=KGF ( K ,Content Inform)  [Equation 2]
 
     In Equation 2, DEK relates to an encryption key, KGF( ) relates to a function for generating an encryption key, K relates to the second key for read authorization, and Content Inform relates to information of content. 
     The content encryption unit  216  may encrypt content using the encryption key to generate an encrypted content. 
     In response to members included in the access control list having write authorization as a result of checking access authorization of the members included in the access control list, the signature generator  217  may generate a signature using the first key, the content, a signature key, or any combination thereof. In this instance, the signature generator  217  may generate the signature using an algorithm which has a one-way homomorphic characteristic. As another aspect, the signature generator  217  may generate the signature based on the following Equation 3. 
       Sig=Signature( F ( H   m ( NK ), H ( C )),signature key)  [Equation 3]
 
     In Equation 3, Signature( ) relates to a function for generating a signature, F( ) relates to a function which has a one-way homomorphic characteristic, C relates to an encrypted content, NK relates to the first key, m relates to a random value less than n corresponding to a parameter used for generating the second key and n relates to a number of times the first key is hashed to generate the second key and may be an integer greater than 0. 
     In response to a Rivest Shamir Adleman (RSA) encryption scheme being used, the signature generator  217  may generate a signature key based on Equation 4. 
       Sig=( H   m ( NK*h )) d   [Equation 4]
 
     In Equation 4, h relates to H(C), C relates to an encrypted content, H( ) relates to a function having a one-way homomorphic characteristic, d relates to a signature key, NK relates to the first key, m relates to a random value less than n corresponding to a parameter used for generating the second key, n relates to a number of times the first key is hashed to generate the second key, and H m  ( ) relates to performing a hash m times. 
     Depending on the one-way homomorphic characteristic of H( ) in Equation 4, the following Equation 5 may be satisfied. 
       ( H   m ( NK*h )) d =( H   m ( NK )· H   m ( h )) d   [Equation 5]
 
     The one-way homomorphic characteristic may have the following three characteristics. 
     First, even though F(X) may be easily evaluated for a given X, X may be difficult to be evaluated from F(X). F(X) may have the one-way homomorphic characteristic. 
     Secondly, F(A*B)=F(A)·F(B). 
     Thirdly, F(X) −1  may be difficult to be evaluated. 
     The distributor  218  may distribute the encrypted content and the signature through the network. 
     The control unit  210  may control an operation of the apparatus for generating content  200 . The control unit  210  may function as the receiver  211 , the key decryption unit  212 , the second key generator  213 , the content generator  214 , the encryption key generator  215 , the content encryption unit  216 , the signature generator  217  and the distributor  218 . The control unit  210 , the receiver  211 , the key decryption unit  212 , the second key generator  213 , the content generator  214 , the encryption key generator  215 , the content encryption unit  216 , the signature generator  217  and the distributor  218  are separately illustrated to separately describe each function. Thus, the control unit  210  may include at least one processor to function as an entire or a portion of the receiver  211 , the key decryption unit  212 , the second key generator  213 , the content generator  214 , the encryption key generator  215 , the content encryption unit  216 , the signature generator  217 , and the distributor  218 . 
       FIG. 3  includes an example of an apparatus for verification of content  300  for an access control of content in a distributed environment network. 
     Referring to  FIG. 3 , the apparatus for verification of content  300  may include a control unit  310 , a communication unit  320 , a storage unit  330 , a receiver  311 , a key decryption unit  312 , a decryption key generator  313 , a second key generator  314 , a signature verification unit  315 , and a content decryption unit  316 . 
     The communication unit  320  may transmit and receive data through a wired and/or wireless network. In this instance, the network may correspond to a CCN or an NDN. 
     The storage unit  330  may store an operating system, an application program and data for storage for controlling an overall operation of the apparatus for verification of content  300 . The storage unit  330  may store an access control list, a first key and a second key. 
     The receiver  311  may receive an encrypted content, a signature of the encrypted content and an access control list. That is, in response to the receiver  311  being determined to have write authorization as a result of verification of the access control list, the receiver  311  may receive a first encrypted key from the network. Further, in response to the receiver  311  being determined to have read authorization as a result of verification of the access control list, the receiver  311  may receive a second encrypted key from the network. 
     In response to the receiver  311  receiving the first encrypted key or the second encrypted key, the key decryption unit  312  may decrypt the first encrypted key or the second encrypted key using a secret key. The secret key may correspond to a public key. 
     The second key generator  314  may generate the second key. The second key may correspond to a key for read authorization using the first key. In this instance, the second key may be generated based on Equation 1. 
     The signature verification unit  315  may verify a signature using the second key and the encrypted content. The signature verification unit  315  may perform verification based on the following Equation 6. 
       Verify(Sig, n,m,K,H ( C ),signature verification key)  [Equation 6]
 
     In Equation 6, Verify( ) relates to a function for verifying a signature, Sig relates to a signature, K relates to the second key corresponding to a key for read authorization, H( ) relates to a hash function, m relates to a random value less than n corresponding to a to parameter used for generating the second key, and n relates to a number of times the first key is hashed to generate the second key. The value of n may be an integer greater than 0. 
     In response to the signature generator  217  generating a signature key using a Rivest Shamir Adleman (RSA) encryption scheme such as Equation 4, the signature verification unit  315  may verify a signature based on the following Equation 7. 
         A =Sig e =(( H   m ( NK*h )) d ) e   =H   m ( NK*h )= H   m ( NK )· H   m ( h )
 
         A′=H   n-m ( A )= H   n ( NK )· H   n ( h )
 
         B=K·H   n ( h ) 
       If  A′=B ,Sig is valid 
       If  A′≠B ,Sig is invalid  [Equation 7]
 
     In Equation 7, Sig relates to a signature, NK relates to the first key, K relates to the second key corresponding to a key for read authorization, h relates to H(C), C relates to an encrypted content, H( ) relates to a hash function which has a one-way homomorphic characteristic, d relates to a signature key, e relates to a signature verification key, m relates to a random value less than n corresponding to a parameter used for generating the second key, and n relates to a number of times the first key is hashed to generate the second key. 
     The value of n may be an integer greater than 0. 
     In response to the RSA encryption scheme such as Equation 4 being used, the signature verification unit  315  may calculate A′ using a received signature, calculate B using K and the received encrypted content, and determine whether the verification is successful by comparing A′ to B. K may correspond to the second key of the signature verification unit  315 . 
     A signature scheme using the signature generator  217  and the signature verification unit  315  may be satisfactory for security, for the reasons discussed below. Since a user having read authorization may have information of K=H n (NK) and m&lt;n, H m (NK) used for generating Sig may not be evaluated using information of K due to a one-way homomorphic characteristic. Even though Sig e =H(NK) me ×H(C) is secured in a verification operation, a signature key k of a user having write authorization may be used to secure H m (NK). Thus, a valid signature may not be generated without collaboration from the user having write authorization. 
     In response to the signature verification succeeding, the decryption key generator  313  may generate a decryption key based on the second key. In another aspect, the decryption key generator  313  may generate the decryption key using information of content and the second key. The generation of the decryption key may be based on the same scheme as the encryption key generator  215 . The decryption key generator  313  may use the encryption key generated based on Equation 2 as the decryption key. 
     The content decryption unit  316  may use the decryption key to decrypt the encrypted content. 
     The control unit  310  may control an overall operation of the apparatus for verification of content  300 . The control unit  310  may function as the key decryption unit  312 , the decryption key generator  313 , the second key generator  314 , the signature verification unit  315 , and the content decryption unit  316 . The control unit  310 , the key decryption unit  312 , the decryption key generator  313 , the second key generator  314 , the signature verification unit  315 , and the content decryption unit  316  are separately illustrated to describe the function of each. Thus, the control unit  310  may include at least one processor configured to function as an entire or a portion of the key decryption unit  312 , the decryption key generator  313 , the second key generator  314 , the signature verification unit  315 , and the content decryption unit  316 . 
     Hereinafter, an example of a method for an access control of content in a distributed environment network will be described with reference to  FIG. 4  through  FIG. 6 . 
       FIG. 4  illustrates an example of a process for generating an access control list for an access control of content and separately generating and distributing a key between write authorization and read authorization in an apparatus for generating a key  100  in a distributed environment network. 
     Referring to  FIG. 4 , in operation  410 , the apparatus for generating a key  100  may generate an access control list. The access control list may include information of at least one user and information about access authorization. 
     In operation  412 , the apparatus for generating a key  100  may generate a first key. The first key may correspond to a key for write authorization. 
     In operation  414 , the apparatus for generating a key  100  may generate a second key. The second key may correspond to a key for read authorization using the first key. 
     In operation  416 , the apparatus for generating a key  100  may encrypt the first key using each public key of members having write authorization among members to generate first encrypted keys. The members having write authorization among members may be included in the access control list. 
     In operation  418 , the apparatus for generating a key  100  may distribute the access control list and the generated first encrypted keys to the members having write authorization. 
     In operation  420 , the apparatus for generating a key  100  may encrypt the second key using each public key of members having read authorization among members to generate second encrypted keys. The members having read authorization among members may be included in the access control list. 
     In operation  422 , the apparatus for generating a key  100  may distribute the access control list and the second encrypted keys to the members having read authorization. 
       FIG. 5  illustrates an example of a process for generating and distributing content for an access control of content in an apparatus for generating content  200  in a distributed environment network. 
     Referring to  FIG. 5 , in operation  510 , the apparatus for generating content  200  may generate content. 
     In operation  512 , the apparatus for generating content  200  may request and receive an access control list and a first encrypted key from a network. 
     In operation  514 , the apparatus for generating content  200  may verify whether the apparatus for generating content  200  has write authorization by checking access authorization of members based on the access control list. 
     In operation  516 , the apparatus for generating content  200  may decrypt the first encrypted key to secure a first key corresponding to a key for write authorization using a secret key in response to the apparatus for generating content  200  being determined to have write authorization as a result of the verification in operation  514 . The first encrypted key may be encrypted using a public key. The secret key may correspond to the public key. 
     In operation  518 , the apparatus for generating content  200  may generate a second key corresponding to a key for read authorization using the first key. 
     In operation  520 , the apparatus for generating content  200  may generate an encryption key using information of the content and the second key. 
     In operation  522 , the apparatus for generating content  200  may encrypt content using the encryption key to generate an encrypted content. 
     In operation  524 , the apparatus for generating content  200  may generate a signature using a value. The value may be obtained by hashing the first key m times, a value obtained by hashing the content, and the signature key. In this instance, the value m may correspond to a random value less than n corresponding to a number of times the first key is hashed to generate the second key. The value n may be an integer greater than 0. 
     In operation  526 , the apparatus for generating content  200  may distribute the encrypted content, the signature, and the value m through the network. 
       FIG. 6  includes an example of a process for verifying content where access to content is controlled in an apparatus for verification of content in a distributed environment network. 
     Referring to  FIG. 6 , in operation  610 , an apparatus for verification of content  300  may receive an encrypted content and a signature of the encrypted content. 
     In operation  612 , the apparatus for verification of content  300  may receive an access control list from a network. 
     In operation  614 , the apparatus for verification of content  300  may check access authorization of the encrypted content in the access control list to verify satisfaction of access requirements. 
     In operation  616 , the apparatus for verification of content  300  may secure a second key in response to the encrypted content being determined to be accessible as a result of the verification in operation  614 . The second key may correspond to a key for read authorization. 
     In operation  616 , the apparatus for verification of content  300  may receive a second encrypted key from the network in response to the apparatus for verification of content  300  being determined to have read authorization as a result of checking the access control list. The apparatus for verification of content  300  may decrypt the second encrypted key to secure a second key using a secret key. The second encrypted key may be encrypted by using a public key. The secret key may correspond to the public key. 
     In operation  616 , the apparatus for verification of content  300  may receive a first encrypted key from the network in response to the apparatus for verification of content  300  being determined to have write authorization as a result of checking the access control list, secure a first key by decrypting the first encrypted key using a secret key, and generate the second key using the first key. The first encrypted key may be encrypted by using a public key. The secret key may correspond to the public key. 
     In operation  618 , the apparatus for verification of content  300  may verify the signature using the second key and the encrypted content, and check whether the signature verification is successful. 
     In operation  620 , the apparatus for verification of content  300  may generate a decryption key using the second key in response to the signature verification being determined to succeed as a result of the verification in operation  618 . In this instance, the decryption key may be identical to the decryption key generated by the apparatus for generating content  200 . 
     In operation  622 , the apparatus for verification of content  300  may decrypt the encrypted content using the decryption key. 
     Program instructions to perform a method described herein, or one or more operations thereof, may be recorded, stored, or fixed in one or more computer-readable storage media. The program instructions may be implemented by a computer. For example, the computer may cause a processor to execute the program instructions. The media may include, alone or in combination with the program instructions, data files, data structures, and the like. Examples of computer-readable media include magnetic media, such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVDs; magneto-optical media, such as optical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. Examples of program instructions include machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The program instructions, that is, software, may be distributed over network coupled computer systems so that the software is stored and executed in a distributed fashion. For example, the software and data may be stored by one or more computer readable recording mediums. Also, functional programs, codes, and code segments for accomplishing the example embodiments disclosed herein can be easily construed by programmers skilled in the art to which the embodiments pertain based on and using the flow diagrams and block diagrams of the figures and their corresponding descriptions as provided herein. Also, the described unit to perform an operation or a method may be hardware, software, or some combination of hardware and software. For example, the unit may be a software package running on a computer or the computer on which that software is running. 
     A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.