## 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

- [1]
- S. S. Pradhan and K. Ramchandran, "Distributed Source Coding Using
Syndromes (DISCUS): Design and Construction,"
*Proc. Data
Compression Conference,* Snowbird, UT, March 1999.

More information (http://basics.eecs.berkeley.edu/) or

Send mail to the author : (mjohnson@eecs.berkeley.edu)

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