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How to Forget a Secret
In STACS 99, Lecture Notes in Computer Science 1563, pp. 500-509, Springer Verlag, 1999.
We uncover a new class of attacks that can potentially affect any cryptographic protocol. The attack is performed by an adversary that at some point has access to physical memory of a participant, including all its previous states.
In order to protect protocols from such attacks, we introduce a cryptographic primitive that we call erasable memory. Using this primitive, it is possible to implement the essential cryptographic action of forgetting a secret. We show how to use a small erasable memory in order to transform a large non-erasable memory into a large and erasable memory. In practice, this shows how to turn any type of storage device into a storage device that can selectively forget. Moreover, the transformation can be performed using the minimal assumption of the existence of any one-way function, and can be implemented using any block cipher, in which case it is quite efficient. We conclude by suggesting some concrete implementations of small amounts of erasable memory.
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