Efficient robust storage using secret tokens

We present algorithms that reduce the time complexity and improve the scalability of robust storage for unauthenticated data. Robust storage ensures progress under every condition (wait-freedom) and never returns an outdated value (regularity) nor a forged value (Byzantine fault tolerance). The algorithms use secret tokens, which are values randomly selected by the clients and attached to the data written into the storage. Tokens are secret because they cannot be predicted by the attacker before they are used, and thus revealed, by the clients. Our algorithms do not rely on unproven cryptographic assumptions as algorithms based on self-verifying data. They are optimally-resilient, and ensure that reads complete in two communication rounds if readers do not write into the storage, or in one communication round otherwise. © 2009 Springer-Verlag Berlin Heidelberg