Ic Card for Encryption or Decryption Process and Encrypted Communication System and Encrypted Communication Method Using the Same

Abstract

It is possible to perform encrypted communication between members of a group while assuring a sufficient security compatible with a change of the members. An IC card having the same fixed code F(a) is distributed to all the staffs of company A. When communication is performed between a staff α and a staff β belonging to the same project group, α of the transmission side writes an arbitrary variable code V( 1 ) in the IC card ( 100 a ) so as to generate encryption key information K(a 1 ) according to F(a) and V( 1 ) in the IC card and encrypt data D 1 by using K(a 1 ). β of the reception side writes the variable code V( 1 ) received from a in the IC card ( 100 b ) so as to generate encryption key information K(a 1 ). By using this K(a 1 ), the encrypted data D 2 received is decrypted to obtain data D 3 . The fixed code F(a) is different for each of the companies and rewrite-disabled so as to assure security.

1 . An IC card, used for executing an encryption process or a decryption process using unique encryption key information, 
 said IC card comprising: a memory ( 110 ); a CPU ( 120 ) that executes predetermined processes based on data and programs stored in the memory; and an I/O unit ( 130 ) that performs transaction of information with the exterior;    a first storage location, a second storage location, and a third storage location being secured inside said memory;    a predetermined fixed code (F) being stored in advance in said first storage location (L 1 ) and arrangements being made so that said fixed code cannot be rewritten;    an arbitrary variable code (V) being enabled to be written from the exterior into said second storage location (L 2 ) and arrangements being made so that said variable code can be rewritten; and    there being stored in said memory, a key information generating program that performs a computation process based on a predetermined algorithm using the fixed code stored in said first storage location and the variable code stored in said second storage location to generate encryption key information (K) that is determined uniquely according to said two codes and stores the encryption key information in said third storage location (L 3 ), and an encryption and decryption program that executes the encryption process or the decryption process inside the IC card using the encryption key information stored in said third storage location.    
   
   
       2 . An IC card, used for executing an encryption process or a decryption process using unique encryption key information, 
 said IC card comprising: a memory ( 110 ); a CPU ( 120 ) that executes predetermined processes based on data and programs stored in the memory; and an I/O unit ( 130 ) that performs transaction of information with the exterior;    a first storage location, a second storage location, and a third storage location being secured inside said memory;    a predetermined fixed code (F) being stored in advance in said first storage location (L 1 ) and arrangements being made so that said fixed code cannot be rewritten;    an arbitrary variable code (V) being enabled to be written from the exterior into said second storage location (L 2 ) and arrangements being made so that said variable code can be rewritten; and    there being stored in said memory, a key information generating program that performs a computation process based on a predetermined algorithm using the fixed code stored in said first storage location and the variable code stored in said second storage location to generate encryption key information (K) that is determined uniquely according to said two codes and stores the encryption key information in said third storage location (L 3 ), and a key reading program that reads out the encryption key information stored in said third storage location or a portion of the encryption key information for execution of the encryption process or the decryption process outside the IC card.    
   
   
       3 . The IC card according to  claim 1 , wherein 
 the key information generating program has a function of generating an encryption key itself, which is used for encryption or decryption, as the encryption key information (K).    
   
   
       4 . The IC card according to  claim 1 , wherein 
 the key information generating program has a function of generating a key table, a portion of which is used as an encryption key for encryption or decryption, as the encryption key information (K).    
   
   
       5 . An encrypted communication system comprising: 
 a first IC card and a second IC card ( 100   a ), each being the IC card according to  claim 1  and both storing the same fixed code (F(a));    a transmission means that transmits encrypted text data encrypted using said first IC card; and    a reception means that receives said transmitted encrypted text data and provides the encrypted text data for decryption to said second IC card.    
   
   
       6 . An encrypted communication method comprising: 
 a preparation step of preparing a first IC card and a second IC card ( 100   a ), each being the IC card according to  claim 1  and both storing the same fixed code, and disposing said first IC card at a transmitter side and said second IC card at a receiver side;    an encryption step of performing, at said transmitter side, a process of writing a predetermined variable code (V( 1 )) into said first IC card to generate encryption key information (K(a 1 )) and using the generated encryption key information to encrypt transmission object data (D 1 );    a transmitting and communicating step of transmitting, from said transmitter side to said receiver side, said transmission object data (D 2 ) that has been encrypted and communicating, from said transmitter side to said receiver side, said variable code; and    a decryption step of performing, at said receiver side, a process of writing said variable code, which has been communicated, into said second IC card to make the encryption key information (K(a 1 )) be generated and using the generated encryption key information to decrypt said transmission object data that has been transmitted.