International Business Machines Corporation

Ran Canetti

Amir Herzberg

A mechanism which secures the communication and computation between processors in an insecure distributed environment implements efficient 'compilers' for a protocol between processors. The protocol is one that assures some input-output relation when executed by processors which are not all trusted but with secret and authenticated communication links between every two processors. This protocol is transformed by a compiler into a protocol that guarantees essentially the same input-output relations in the presence of (the same type of) insecure processors and insecure communication links. Additionally, a method maintains secret values for a sequence of periods, each secret value being shared by two or more processors for one or several periods, where the processors are connected by a communication network. Another mechanism establishes different cryptographic keys established for each period of communication. Essentially, the effect of exposures is contained to the period in which they occur, or to a minimal number of following periods, and the effect of exposures is contained to the processors exposed. At each period a processor is called nonfaulty if the adversary does not control it. A processor is called secure at a given period if it is non-faulty and also has a secret key, unknown to the adversary.

Secure communication and computation in an insecure environment

A method is provided which allows a set of servers to maintain a set of keys, shared with a client, in the presence of mobile eavesdroppers that occasionally break into servers and learn the entire contents of their memories. Static and dynamic schemes maintain secret keys common to the user and each of several servers in the presence of a mobile, transient adversary that occasionally breaks into servers in order to gather information on the users' secret keys. The schemes use periodic 'refreshments' of every user's private keys. In each round the servers involve in a computation in which each server computes a new private key to be shared with the user, in a way that allows the user to keep track of the changing keys without any communication with the servers. The schemes are very efficient. In particular, a user has to interact only with one server in order to obtain a session key. The user may choose the server with whom it wants to interact. The method may be used to securely generate random numbers (i.e., using the keys as random numbers).

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Tel Aviv, Israel

Ran Canetti