We consider the problem of disseminating an update known to a set of servers to other servers in the system via a gossip protocol. Some of the servers can exhibit malicious behavior. We require that only the updates introduced by authorized clients are accepted by nonmalicious servers. Spurious updates, in particular those generated by compromised nodes, are not accepted by non-malicious servers. We take the approach of collective endorsement where each server endorses an accepted update by

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... uting a list of message authentication codes with symmetric keys allocated to it. We use a novel key allocation scheme that allocates a set of symmetric keys to each participating server to minimize the total number of keys. Our protocol is designed to minimize update diffusion time. In the absence of faulty nodes, its diffusion time is