KYUDAI NEWS KYUSHU UNIVERSITY CAMPUS MAGAZINE Spring 2013 No.24

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Future ProspectsThis result is not just a new world record of cryptanalysis, it also means the acquisition of valuable data that forms a technical foundation on which to estimate selection of secure encryption technology or the appropriate timing to exchange a key length. We will continue to move forward on research that pushes the boundary of the secure use of cryptography.New AchievementsAs for a security evaluation of cryptographies, we succeeded with the cryptanalysis of the pairing-based cryptography of 278 digits (923 bits) by using 21 personal computers (252 cores) in 148.2 days. The cryptanalysis is the equivalent to spoofing the authority of the information system administrator. As a result, for the first time in the world we proved that the cryptography of the parameter was vulnerable and could be broken in a realistic amount of time. This was an extremely challenging problem as it required several hundred times computational power compared with the previous world record of 204 digits (676 bits). We were able to overcome this problem by making good use of various new technologies, that is, a technique optimizing parameter setting that uses computer algebra, a two dimensional search algorithm extended from the linear search, and by using our efficient programing techniques to calculate a solution of an equation from a huge number of data, as well as the parallel programming technology that maximizes computer power.*1 Pairing-based cryptography : A next-generation cryptography (proposed in 2001) based on a map called pairing, which offers many useful functionalities that could not be achieved by previous public-key cryptography. The security of pairing-based cryptography is based on the intractability of discrete logarithm problem (DLP). DLP is a problem to compute d such that a = gd for given g and a*2 Identity-based encryption : A type of public-key encryption in which the public key of a user is some unique information about the identity of the user (e.g. a user's email address). It does not require authentication of public keys unlike former public-key cryptosystems. *3 Keyword searchable encryption : An encryption scheme which enables searching keywords on encrypted data. *4 Functional encryption : An encryption scheme where an author of a document can specify access control info in a predicate logic using attributes and embed it into an encrypted document.*5 Public-key cryptography : A cryptographic system requiring two separate keys, one to encrypt the plaintext, and one to decrypt the ciphertext. One of these keys is public and the other is kept private. Introduced by Diffie and Hellman in 1976. RSA and Elliptic curve cryptography (ECC) are typical examples.Glossary and Notes12Kyudai News No.24 NICT and Fujitsu Laboratories Record Cryptanalysis of CryptographyNext-Generation CryptographyFig.1 World records of cryptanalysesFig.2 The security comparison of conventional and new cryptographic technology

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