Masahiro Mambo


Research topics:

Information Security and Cryptology

We study several topics on information security, in particular, construction and evaluation of communication and authentication protocols.

Study of secure communication protocols:

Constructing secure protocols in communication networks is a complicated task because electronic data can easily be copied. Furthermore, there are protocols which themselves are difficult to construct. For instance in election schemes, votes being tallied must be kept secret and frauds of attackers and participants prevented. Meanwhile, such protocols are inevitable in our society and some of them are necessary for communication networks. Today, much more activities are played in communication networks than before. It is highly likely that such a tendency continues for at least a few decades. Then we will not be able to avoid to implement secure protocols and to solve problems related to them. In such a highly computer-oriented society, anonymity might be one of the biggest concerns. As enlightened by the key escrow debate, a well-equipped computer system has a capability to violate user privacy. Therefore, we study different types of protocols from the aspects of protecting user rights and privacy.

Authentication:

Authentication is the act of verifying messages or identifying users, promising the faithfulness of the messages or users. Outside of communication networks, authentication is performed with the use of inimitable physical objects such as handwritten signatures and credit cards. The former verifies the correctness of messages and the latter the identity of users. An electronic alternative to the physical object is desired for use in communication networks. A promising alternative to the handwritten signature is provided by digital signature schemes. Basically, digital signature imitates handwritten signature or seal. So, many different functionalities should be added into digital signatures. For example, in a proxy signature scheme, one can give other the power to sign message for him, without giving his secret. Moreover, if possible, we should find a new property originated from digital information. On the other hand, a promising alternative to the credit card is provided by zero-knowledge interactive proof systems (ZKIP). ZKIP provides very high security. Then other properties, e.g. computational work and communicated bits, should also achieve the high level. We study secure, fast and flexible authentication methods in general, including ZKIP.

Security criteria, database access control and protocol verification:

Security criteria are standards which promise a certain level of security to communication systems that follow them. They recommend actual algorithms or provide guidelines. The more events security criteria cover, the more reliable they become. We create new security criteria which cover many possible events. Subjects related to security criteria are database access control and protocol verification. We study access models and protocol verification methods which can deal with a change of time.

Publications:

  1. Communication Protocols with Untraceability of Sender and Receiver, Masahiro Mambo, Hirotsugu Kinoshita, Shigeo Tsujii, Trans. of IEICE, Vol.J74-D-I, No.7, pp.429-434 (1991). [in Japanese]
  2. A Secure Broadcast Communication Method with Short Messages, Masahiro Mambo, Akinori Nishikawa, Eiji Okamoto and Shigeo Tsujii, Trans. of IEICE, Fundamentals, Vol.E77-A, No.8, pp. 1319-1327 (1993).
  3. Proxy Signatures: Delegation of the Power to Sign Messages, Masahiro Mambo, Keisuke Usuda and Eiji Okamoto, IEICE Trans. on Fundamentals, Vol.E79-A, No.9, pp.1338-1354 (1996).
  4. How to Utilize the Transformability of Digital Signatures for Solving the Oracle Problem, Masahiro Mambo, Koichi Sakurai and Eiji Okamoto, Advances in Cryptology -- Asiacrypt'96, Lecture Notes in Computer Science 1163, Springer-Verlag, pp.322-333 (1996).
  5. Proxy Cryptosystem: Delegation of the Power to Decrypt Cihpertexts, Masahiro Mambo and Eiji Okamoto, IEICE Trans. on Fundamentals, Vol.E80-A, No.1 pp.54-63(1997).