Compression of Encrypted Data

Mark Johnson
(Professors Kannan Ramchandran and David A. Wagner)
Microsoft and Philips

When a data source is to be transmitted across an insecure, bandwidth-constrained channel, the standard solution is to first compress the data and then encrypt it. We examine the problem of reversing the order of these steps, first encrypting and then compressing. Such a scheme could be used in a scenario where the data generator and the compressor are not co-located, and the link between them is vulnerable to eavesdropping.

We encrypt a binary data sequence by forming the mod-2 sum with a pseudo-random binary key. Because the decoder will also have access to the same key, we can compress the encrypted data using distributed source coding principles. The DISCUS framework [1] provides a constructive method for generating codes that approach the Slepian-Wolf bound. By modifying the DISCUS decoding procedure, we should be able to incorporate more complex encryption algorithms into our scheme.

Figure 1: Secure compression framework

S. S. Pradhan and K. Ramchandran, "Distributed Source Coding Using Syndromes (DISCUS): Design and Construction," Proc. Data Compression Conference, Snowbird, UT, March 1999.

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