Utilizing a key for enciphering and deciphering that is modified during enciphering and deciphering

An enciphering method, comprising the steps of:

• enciphering data using a cryptographic key;
• generating a first key;
• generating a second key which is changed at a predetermined timing while the data are enciphered;
• and
• producing the cryptographic key using the first key and the second key.

A deciphering apparatus, comprising:

• receiving means for receiving enciphered data;
• deciphering means for deciphering the received data using a cryptographic key;
• first generating means for generating a first key;
• second generating means for generating a second key which is changed at a predetermined timing while the data is deciphered;
• and
• producing means for producing the cryptographic key using the first key and the second key.

A deciphering method, comprising the steps of:

• receiving enciphered data;
• deciphering the received data using a cryptographic key;
• generating a first key;
• generating a second key which is changed at a predetermined timing while the data is deciphered;
• and
• producing the cryptographic key using the first key and the second key.

An information processing system, comprising:

• a plurality information processing apparatus connected to each other by a bus;
• said information processing apparatus including first information processing apparatus each having a function whose change is not open to a user, and second information processing apparatus each having a function whose change is open to a user;
• each of said first information processing apparatus including:
• first receiving means for receiving enciphered data;
• first deciphering means for deciphering the data received by said first receiving means using a cryptographic key;
• first generating means for generating a first key;
• second generating means for generating a second key which is changed at a predetermined timing while the data is deciphered;
• and
• first producing means for producing the cryptographic key using the first key generated by said first generating means and the second key generated by said second generating means;
• each of said second information processing apparatus including:
• second receiving means for receiving enciphered data;
• third generating means for generating the first key;
• fourth generating means for generating the second key which is changed at a predetermined timing while the data is deciphered;
• second producing means for producing a first cryptographic key using one of the first key generated by said third generating means and the second key generated by said fourth generating means;
• third producing means for producing a second cryptographic key using the other of the first key generated by said third generating means and the second key generated by said fourth means;
• second deciphering means for deciphering the enciphered data received by said receiving means using the first cryptographic key;
• and
• third deciphering means for further deciphering the data deciphered by said second deciphering means using the second cryptographic key.

An information processing method for an information processing system composed of a plurality information processing apparatus connected to each other by a bus, said information processing apparatus including first information processing apparatus each having a function whose change is not open to a user, and second information processing apparatus each having a function whose change is open to a user, comprising the steps performed by each of said first information processing apparatus of:

• receiving enciphered data;
• deciphering the data received in the receiving step using a cryptographic key;
• generating a first key;
• generating a second key which is changed at a predetermined timing while the data is deciphered;
• and
• producing the cryptographic key using the first key generated in the first generating step and the second key generated in the second generating step;
• and
• the steps performed by each of said second information processing apparatus of:
• receiving enciphered data;
• generating the first key;
• generating the second key which is changed at a predetermined timing while the data is deciphered;
• producing a first cryptographic key using one of the first key and the second key;
• producing a second cryptographic key using the other of the first key and the second key;
• deciphering the enciphered data received in the receiving step using the first cryptographic key;
• and
• deciphering the deciphered data further using the second cryptographic key.

An information processing apparatus, comprising:

• receiving means for receiving data transmitted thereto through a bus;
• producing means composed of a software program for producing a first cryptographic key and a second cryptographic key which is changed at a predetermined timing while the data is deciphered from the data received by said receiving means;
• first deciphering means for deciphering the enciphered data received by said receiving means using one of the first cryptographic key and the second cryptographic key produced by said producing means;
• and
• second deciphering means for deciphering and processing the data deciphered by said first deciphering means further using the other of the first cryptographic key and the second cryptographic key produced by said producing means.

An information processing method, comprising the steps of:

• receiving data transmitted thereto through a bus;
• producing, from the received data, a first cryptographic key and a second cryptographic key which is changed at a predetermined timing while the data is deciphered;
• deciphering the received enciphered data using one of the first cryptographic key and the second cryptographic key;
• and
• deciphering the deciphered data further using the other of the first cryptographic key and the second cryptographic key.