On Forward-Secure Storage

Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4117)


We study a problem of secure data storage in a recently introduced Limited Communication Model. We propose a new cryptographic primitive that we call a Forward-Secure Storage (FSS). This primitive is a special kind of an encryption scheme, which produces huge (5 GB, say) ciphertexts, even from small plaintexts, and has the following non-standard security property. Suppose an adversary gets access to a ciphertext C = E(K,M) and he is allowed to compute any function h of C, with the restriction that |h(C)| ≪|C| (say: |h(C)| = 1 GB). We require that h(C) should give the adversary no information about M, even if he later learns K.

A practical application of this concept is as follows. Suppose a ciphertext C is stored on a machine on which an adversary can install a virus. In many cases it is completely infeasible for the virus to retrieve 1 GB of data from the infected machine. So if the adversary (at some point later) learns K, then M remains secret.

We provide a formal definition of the FSS, propose some FSS schemes, and show that FSS can be composed sequentially in a secure way. We also show connections of the FSS to the theory of compressibility of NP-instances (recently developed by Harnik and Naor).


Encryption Scheme Random Oracle Security Parameter Random String Pseudorandom Generator 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2006

Authors and Affiliations

  1. 1.Institute of InformaticsWarsaw University 
  2. 2.Institute for Informatics and TelematicsCNR Pisa 

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