More on master keys for group sharing☆

In this article, we propose a two-phase encryption algorithm for data base systems. The system, a record-oriented cryptosystem, allows the encryption and decryption of fields within a record by means of writing and reading subkeys of fields. In addition, we develop two algorithms for cryptographic relational algebra in data base systems. Two simple methods of solving the key management problem in the subkey scheme are presented.

A cryptographic implementation is proposed for access control in a situation where users and information items are classified into security classes organized as a rooted tree, with the most privileged security class at the root. Each user stores a single key of fixed size corresponding to the user's security class. Keys for security classes in the subtree below the user's security class are generated from this key by iterative application of one-way functions. New security classes can be defined without altering existing keys. The scheme proposed here is based on conventional cryptosystems (as opposed to public key cryptosystems).

Keyless cryptography is a technique in which the basis of security is the anonymity of the sender. We describe a protocol that fits the technique to realistic communication environments, and extend the security and the range of applications of the technique.