Project/Area Number  10650361 
Research Category 
GrantinAid for Scientific Research (C)

Allocation Type  Singleyear Grants 
Section  一般 
Research Field 
情報通信工学

Research Institution  Osaka University 
Principal Investigator 
FUJIWARA Toru Graduate School of Engineering Science, Osaka University Professor, 基礎工学研究科, 教授 (70190098)

Project Period (FY) 
1998 – 1999

Project Status 
Completed(Fiscal Year 1999)

Budget Amount *help 
¥3,200,000 (Direct Cost : ¥3,200,000)
Fiscal Year 1999 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1998 : ¥2,200,000 (Direct Cost : ¥2,200,000)

Keywords  Information Security / Cryptography / Cryptographic Protocols / Database / Formal verification / Security / Unforgeability / Algorithm 
Research Abstract 
The purpose of this research is (1) to describe the unforgeability of data for cryptographic protocols,(2) determine classes for which the unforgeability is decidable, and (3) develop a system to verify the unforgeability. 1. Formal description : Operations provided in the protocol including the operations which enemy can execute are representer by functions. Data which the enemy can obtain are represented by terms. Relations between functions are described by axioms. Also, legal operation for obtaining the target data is represented by a term. 2. Decidable class : we obtained an sufficient condition under which the problem is decidable. 3. We developed an algorithm which works effectively for practical protocols. The problem is translated into the emptiness problem of a regular language. The number of edges from a state in the finite automata which accepts the language is not many. Using properties like this, we developed the algorithm. 4. The unforgeability problem can be applied to related problems, say the security of databases. For the illegal data access for a database, we formalize the decision problem for the security, and developed the decision algorithm.
