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

• US 6,307,940 B1
• Filed: 06/25/1998
• Issued: 10/23/2001
• Est. Priority Date: 06/25/1997
• Status: Expired due to Term

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Yamamoto, Takahisa, Iwamura, Keiichi
• Primary Examiner(s): Hayes, Gail
• Assistant Examiner(s): Seal, James
• Application Number:
  US09/104,279
• Time in Patent Office: 1,216 Days
• Field of Search: 380/277, 380/45, 380/44
• US Class Current: 380/277
• CPC Class Codes: H04L 2209/125 Parallelization or pipelining, e.g. for accelerating processing of cryptographic operations
• CPC Class Codes: H04L 9/0662 with particular pseudorandom sequence generator

Abstract

In a cryptosystem which performs encryption/deciphering of communication text using k bits of cryptographically secure pseudo-random numbers as the block cipher key thereof, the block cipher key is updated each time j=k/m bits of new pseudo-random numbers are generated, with the j·m=k bits of pseudo-random numbers created by combining the j·(m−1) bits within the k bits of the present key and the newly generated j bits, serving as a new key, thereby shortening the updating cycle and improving the safety. Also, by sending the number of times of generation of pseudo-random numbers along with the encrypted communication text from the sending side, and by the receiving side using from the sequentially generated pseudo-random numbers, pseudo-random numbers generated after the received number of times of generation as the new key, deciphering can be performed regardless of the order to reception, in the event that a plurality of cipher texts are sequentially sent while updating the encryption key.

Claims

1. 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 a common key secretly shared with a receiver;

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

encrypting and transmitting the communication text using the updated encryption key.

2. 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.

3. 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.

4. A communication terminal device according to claim 3, wherein said means for creating a new encryption key further comprises a shift register which shifts an input of an output of said means for generating pseudo-random numbers.

5. A communication terminal device according to claim 3, wherein said means for creating a new encryption key further comprises an addressable register with output of said means for generating pseudo-random numbers as input thereof.

6. A communication terminal device according to claim 3, wherein said means for creating a new encryption key further comprises a plurality of ROMs with output of said means for generating pseudo-random numbers as input thereof, and computing means for performing a logical operation of an output of said plurality of ROMs.

7. 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.

8. A communication terminal device according to claim 7, wherein said means for creating a new encryption key further comprises a shift register which shifts an input of an output of said means for generating pseudo-random numbers.

9. A communication terminal device according to claim 7, wherein said means for creating a new encryption key further comprises an addressable register with output of said means for generating pseudo-random numbers as input thereof.

10. A communication terminal device according to claim 7, wherein said means for creating a new encryption key further comprises a plurality of ROMs with output of said device for generating pseudo-random numbers as input thereof, and computing means for performing a logical operation of an output of said plurality of ROMs.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. A communication network according to claim 16, wherein said second generating means further comprises:

second counting means for counting a number of times pseudo-random numbers are generated by said second generating means;

count number storing means for storing the number of times counted by the counting means received by the receiving means; and

means for judging whether or not the number of times counted by said second counting means is equal to the number of times stored by said count number storing means.

18. A communication network according to claim 16, wherein said transmitting terminal further comprises a recording medium for storing said number of times counted by said counting means, wherein said recording medium is removable from said transmitting terminal.

19. A communication network according to claim 18, wherein said recording medium further holds a value of an internal variable of said first generating means, and further comprises means for setting a value of an internal variable stored within said recording medium by said first generating means.