Communication network for encrypting/deciphering communication text while updating encryption key, a communication terminal thereof, and a communication method thereof

A communication method for receiving and deciphering an encrypted communication text, said communication method comprising the steps of:

• a receiver sequentially generating pseudo-random numbers based on a common key secretly shared with a sender;
• creating a new encryption key each time a newly-created first certain amount of pseudo-random numbers are generated by removing the first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers, and updating the encryption key;
• and
• deciphering the encrypted communication text using the updated encryption key.

A communication terminal device, comprising:

• transmitting means for encrypting and transmitting a communication text using an encryption key;
• means for a sender sequentially generating pseudo-random numbers based on a common key secretly shared with a receiver;
• means for creating a new encryption key each time a newly-created first certain amount of pseudo-random numbers are generated by said means for generating pseudo-random numbers by removing the newly-created first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers;
• and
• means for updating the encryption key used by said transmitting means each time a new encryption key is created by said means for creating a new encryption key.

A communication terminal device, comprising:

• receiving means for receiving and deciphering an encrypted communication text;
• means for a receiver sequentially generating pseudo-random numbers based on a common key secretly shared with a sender;
• means for creating a new encryption key each time a newly-created first certain amount of pseudo-random numbers are generated by said means for generating pseudo-random numbers by removing the newly-created first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers;
• and
• means for updating the encryption key used by said receiving means each time a new encryption key is created by said means for creating a new encryption key.

A communication method for encrypting and transmitting a communication text, said communication method comprising the steps of:

• a sender sequentially generating pseudo-random numbers based on sequentially updated internal variables with a common key secretly shared with a receiver as an initial value;
• updating an encryption key by generating a new encryption key each time a newly-created first certain amount of pseudo-random numbers are generated by removing the first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers;
• encrypting and sending the communication text using the updated encryption key;
• and
• storing the internal variables at an end of transmission as internal variables for subsequent communication with said receiver.

A communication method for receiving and deciphering an encrypted communication text, said communication method comprising the steps of:

• a receiver sequentially generating pseudo-random numbers based on sequentially updated internal variables with a common key secretly shared with a sender as an initial value;
• updating an encryption key by generating a new encryption key each time a newly-created first certain amount of pseudo-random numbers are generated by removing the first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers;
• deciphering the encrypted communication text using the updated encryption key;
• and
• storing the internal variables at an end of transmission as internal variables for subsequent communication with said sender.

A communication terminal device, comprising:

• transmitting means for encrypting and sending a communication text using an encryption key;
• means for a sender sequentially generating pseudo-random numbers based on sequentially updated internal variables with a common key secretly shared with a receiver as an initial value;
• means for creating a new encryption key each time a newly-created first certain amount of pseudo-random numbers are generated by said means for sequentially generating pseudo-random number by removing the first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers;
• means for updating the encryption key used by said transmitting means each time a new encryption key is created by said means for creating a new encryption key;
• and
• means for storing the internal variables, at an end of transmission by said transmitting means, as internal variables for subsequent communication with said receiver.

A communication terminal device, comprising:

• receiving means for receiving and deciphering an encrypted communication text using an encryption key;
• means for a receiver sequentially generating pseudo-random numbers based on sequentially updated internal variables with a common key secretly shared with a sender as an initial value;
• means for creating a new encryption key each time a first certain amount of pseudo-random numbers are generated by said means for sequentially generating pseudo-random numbers by removing the first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers;
• means for updating the encryption key used by said receiving means each time a new encryption key is created by said means for creating a new encryption key;
• and
• means for storing the internal variables, at an end of reception by said receiving means, as internal variables for subsequent communication with said sender.

A communication method for encrypting and transmitting a communication text, said communication method comprising the steps of:

• a transmitting terminal performing the steps of:
• sequentially generating pseudo-random numbers based on a common key secretly shared with a receiving terminal;
• counting a number of times pseudo-random numbers are generated;
• creating a new encryption key each time a first certain amount of pseudo-random numbers are generated by removing the first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers, and updating the encryption key;
• encrypting the communication text using the updated encryption key;
• and
• transmitting the encrypted communication text with a number of times pseudo-random numbers are generated prior to the encryption of the communication text;
• and
• a receiving terminal performing the steps of:
• receiving the encrypted communication text and the number of times the pseudo-random numbers are generated preceding the encryption of the communication text;
• sequentially generating pseudo-random numbers based on a common key secretly shared with the transmitting terminal and the number of times the pseudo-random numbers generated are received;
• creating a new encryption key after the number of times the pseudo-random numbers generated in the generating step of the receiving terminal equals the received number of times that the pseudo-random numbers are generated, the new encryption key being generated by removing a first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amount of pseudo-random numbers, and updating the encryption key;
• and
• deciphering the encrypted communication text using the updated encryption key.

A communication network connecting a transmitting terminal and a receiving terminal, said communication network comprising:

• a transmitting terminal, comprising:
• means for encrypting a communication text using an encryption key;
• first generating means for sequentially generating pseudo-random numbers based on a common key secretly shared with a receiving terminal;
• counting means for counting a number of times pseudo-random numbers are generated by said first generating means;
• first creating means for creating a new encryption key each time a first certain amount of pseudo-random numbers are generated by said first generating means by removing the first certain amount of an oldest pseudo-random numbers from a second certain amount of previously-created pseudo-random numbers and adding the first certain amount of pseudo-random numbers;
• first updating means for updating the encryption key used by said encrypting means each time a new encryption key is created by said first creating means;
• and
• means for transmitting the communication text encrypted by said encrypting means, together with the number of times counted by said counting means preceding the encryption means encrypting the communication text;
• and
• a receiving terminal, comprising:
• means for receiving the encrypted communication text and the number of times the pseudo-random numbers are counted by the counting means preceding the encryption of the communication text;
• means for deciphering the encrypted communication text using an encryption key;
• second generating means for sequentially generating pseudo-random numbers based on a common key secretly shared with the transmitting terminal and the number of times counted by the counting means received by the receiving means;
• second creating means for creating a new encryption key after the number of times the pseudo-random numbers generated by said second generating means equals the received number of times counted by the counting means, the new encryption key being generated by removing a first certain amount of an oldest pseudo-random numbers from a previously-created second certain amount of pseudo-random numbers and adding the newly-created first certain amoun of pseudo-random numbers;
• and
• second updating means for updating the encryption key used by said receiving terminal each time a new encryption key is created by said second creating means.