language: en

[Abstract apearing in Procedings of the 27th ACM Symposium on the Theory of Computing,]

May195.

Incremental Cryptography and Application to Virus Protection

Mihir Bellare Oded Goldreich Shafi Goldwasser

Abstract The goal of incremental cryptography is to design cryptographic algorithms with the property that having applied the algorithm to a document, it is possible to quickly update the result of the algorithm for a modified document, rather than having to re-compute it from scratch. In settings where cryptographic algorithms such as encryption or signatures are frequently applied to changing documents, dramatic efficiency improvements can be achieved. One such setting is the use of authentication tags for virus protection. We consider documents that can be modified by powerful (and realistic) document modification operations such as insertion and deletion of character-strings (or equivalently cut and paste of text). We provide efficient incremental signature and message authentication schemes supporting the above document modification operations. They meet a strong notion of tamper-proof security which is appropriate for the virus protection setting. We initiate a study of incremental encryption, providing definitions as well as solutions. Finally, we raise the novel issue of "privacy" of incremental authentication schemes.

[Abstract to appear in Proceedings of the 27th ACM Symposium on the Theory of Computing, May 1995.]

1 Introduction