Patents by Inventor Hidema Tanaka

Hidema Tanaka has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 7499541
    Abstract: An object of the invention is to allow cipher strength evaluation when available resources such as the complexity and the number of plaintext available for decryption have conditions, and to allow comparison of cipher strength under given conditions. The invention combines the exhaustive search with an algebraic method, sets conditions for resources such as the complexity and the number of plaintext available for decryption beforehand, and utilizes the linear dependency of a decryption equation for use in decryption to optimize a decryption method as the maximum number of available plaintext is secured. Thus, it reduces the complexity and allows efficient search of solutions for the decryption equation.
    Type: Grant
    Filed: May 11, 2004
    Date of Patent: March 3, 2009
    Assignee: National Institute of Information and Communications Technology
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Yasuo Hatano
  • Patent number: 7460665
    Abstract: An object is to evaluate the strength in consideration of the relationship held between keys, to allow the detection of a weak key condition to lower the difficulty in decrypting ciphertext, and to detect a weak key based on the weak key condition. Based on the relationship between keys in a key schedule and based on estimated keys, a certain estimated extended key can be calculated by utilizing the relationship between the estimated extended key in the key schedule and an estimated extended key having been calculated, and cost information required for calculation is outputted to allow the verification of a weak key condition. A weak key can be detected based on the weak key condition, and the difficulty in decrypting ciphertext can be increased without modifying an encryption apparatus.
    Type: Grant
    Filed: January 21, 2004
    Date of Patent: December 2, 2008
    Assignee: National Institute of Information and Communications Technology
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Nobuyuki Sugio
  • Patent number: 7415616
    Abstract: A Feistel encryption apparatus having a plurality of steps of accepting unstirred text, stirring with an extended key, and calculating stirred text for encrypting plaintext step by step, the apparatus is allowed to utilize cryptanalysis conditions held at given predetermined steps, and decryption with higher order differences determined from stirred text at these steps is allowed. The invention can secure all the estimated extended keys including the last-step extended key to be right with a desired probability as well as it allows decryption by less complexity. The invention allows MISTY1 with six rounds without an FL function to be decrypted with 239 of selected plaintext and the complexity of 249 of an FO function. It also allows MISTY1 with seven rounds without the FL function to be decrypted with 239 of selected plaintext and the complexity of 2124 of the FO function.
    Type: Grant
    Filed: January 21, 2004
    Date of Patent: August 19, 2008
    Assignee: National Institute of Information and Communications Technology
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Yasuo Hatano
  • Patent number: 7340053
    Abstract: This invention intends to reduce the amount of calculation required by a cipher strength estimating device for estimating a ciphertext in collectively finding session keys for plural rounds of transformation. The cipher strength estimating device is configured to: first calculate one session key prospect presumed to be equivalent to a session key for use at a certain round of transformation in encryption which is calculated from a key; perform a decrypting operation with the session key prospect presumed to be true; calculating a session key prospect for the round immediately preceding the certain round based on the resulting text thereby calculating session keys for different rounds. This device enhances the possibility that plural true session keys are calculated faster.
    Type: Grant
    Filed: July 18, 2003
    Date of Patent: March 4, 2008
    Assignee: National Institute of Information and Communications Technology
    Inventors: Hidema Tanaka, Toshinobu Kaneko
  • Patent number: 7310421
    Abstract: An object is to enhance the difficulty in decrypting ciphertext. In order to do input into an encryption algorithm that receives plaintext to output ciphertext, a particular plaintext detector for detecting that the plaintext satisfying a predetermined condition is inputted, the particular plaintext detector includes: a receiving part for receiving the plaintext; a counter part for separating a predetermined part from a bit string forming the plaintext into a fixed part and a remaining part into a variable part, counting the inputted plaintext having a value of the fixed part included in a set of values of the fixed parts at every set of the values of the fixed parts formed of 1 or a plurality of the values of the fixed parts, and storing it as a separate count; and a detecting part for outputting a detection signal when at least one of the separate counts exceeds a predetermined number.
    Type: Grant
    Filed: October 6, 2003
    Date of Patent: December 18, 2007
    Assignee: National Institute of Information and Communications Technology
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Nobuyuki Sugio
  • Publication number: 20050257069
    Abstract: An object of the invention is to allow cipher strength evaluation when available resources such as the complexity and the number of plaintext available for decryption have conditions, and to allow comparison of cipher strength under given conditions. The invention combines the exhaustive search with an algebraic method, sets conditions for resources such as the complexity and the number of plaintext available for decryption beforehand, and utilizes the linear dependency of a decryption equation for use in decryption to optimize a decryption method as the maximum number of available plaintext is secured. Thus, it reduces the complexity and allows efficient search of solutions for the decryption equation.
    Type: Application
    Filed: May 11, 2004
    Publication date: November 17, 2005
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Yasuo Hatano
  • Publication number: 20050157879
    Abstract: An object is to evaluate the strength in consideration of the relationship held between keys, to allow the detection of a weak key condition to lower the difficulty in decrypting ciphertext, and to detect a weak key based on the weak key condition. Based on the relationship between keys in a key schedule and based on estimated keys, a certain estimated extended key can be calculated by utilizing the relationship between the estimated extended key in the key schedule and an estimated extended key having been calculated, and cost information required for calculation is outputted to allow the verification of a weak key condition. A weak key can be detected based on the weak key condition, and the difficulty in decrypting ciphertext can be increased without modifying an encryption apparatus.
    Type: Application
    Filed: January 21, 2004
    Publication date: July 21, 2005
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Nobuyuki Sugio
  • Publication number: 20050160262
    Abstract: A Feistel encryption apparatus having a plurality of steps of accepting unstirred text, stirring with an extended key, and calculating stirred text for encrypting plaintext step by step, the apparatus is allowed to utilize cryptanalysis conditions held at given predetermined steps, and decryption with higher order differences determined from stirred text at these steps is allowed. The invention can secure all the estimated extended keys including the last-step extended key to be right with a desired probability as well as it allows decryption by less complexity. The invention allows MISTY1 with six rounds without an FL function to be decrypted with 239 of selected plaintext and the complexity of 249 of an FO function. It also allows MISTY1 with seven rounds without the FL function to be decrypted with 239 of selected plaintext and the complexity of 2124 of the FO function.
    Type: Application
    Filed: January 21, 2004
    Publication date: July 21, 2005
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Yasuo Hatano
  • Publication number: 20050117742
    Abstract: This invention intends to reduce the amount of calculation required by a cipher strength estimating device for estimating a ciphertext in collectively finding session keys for plural rounds of transformation. The cipher strength estimating device is configured to: first calculate one session key prospect presumed to be equivalent to a session key for use at a certain round of transformation in encryption which is calculated from a key; perform a decrypting operation with the session key prospect presumed to be true; calculating a session key prospect for the round immediately preceding the certain round based on the resulting text thereby calculating session keys for different rounds. This device enhances the possibility that plural true session keys are calculated faster.
    Type: Application
    Filed: July 18, 2003
    Publication date: June 2, 2005
    Inventors: Hidema Tanaka, Toshinobu Kaneko
  • Publication number: 20050074117
    Abstract: An object is to enhance the difficulty in decrypting ciphertext. In order to do input into an encryption algorithm that receives plaintext to output ciphertext, a particular plaintext detector for detecting that the plaintext satisfying a predetermined condition is inputted, the particular plaintext detector includes: a receiving part for receiving the plaintext; a counter part for separating a predetermined part from a bit string forming the plaintext into a fixed part and a remaining part into a variable part, counting the inputted plaintext having a value of the fixed part included in a set of values of the fixed parts at every set of the values of the fixed parts formed of 1 or a plurality of the values of the fixed parts, and storing it as a separate count; and a detecting part for outputting a detection signal when at least one of the separate counts exceeds a predetermined number.
    Type: Application
    Filed: October 6, 2003
    Publication date: April 7, 2005
    Inventors: Hidema Tanaka, Toshinobu Kaneko, Nobuyuki Sugio