Abstract: We propose a multi user information theoretically secure scheme. Our scheme allows any two parties in a multi user system to exchange messages securely using encryption, and to sign messages. Our scheme achieves a significant saving in the number of total keys in the system and in the keys each user must store. The encryption, and signing algorithms proposed in the scheme are as efficient as possible. Our scheme is designed so that it is possible to easily and efficiently revoke and add membership of new users into the system. It is also designed so that authentication and security against man in the middle attacks can be added at low cost. In addition, we introduce a novel and efficient way to use steganography for key replenishment.

Abstract: We propose an encryption scheme which uses steganography. The encryption algorithm encrypts messages by embedding them in a data stream in such a way that an adversary cannot get information about the messages. Since the embedding is the only computation requires this scheme is optimal in computational efficiency. However, since the size of the data stream is large, this scheme is most beneficial when the cost of bandwidth is less expensive than the cost of computation. The scheme embeds the message as specified by a pseudo random generator. Therefore, the scheme's security is based on a new weak assumption base on the pseudo random generator which we introduce.