Demonstration of Compression of Encrypted Data.

Daniel Schonberg - March 3, 2003

Updated - May 9, 2005

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In traditional systems offering secure and efficient communication over untrustworthy and resources constrained networks, incoming data is first compressed and then encrypted.  It has been important to operate in this order since existing compression systems would suffer performance losses otherwise.  Existing compression algorithms operate by exploiting redundancy in a source statistics.  Since encryption works by obfuscating source statistics (less then be susceptible to frequency counting attacks), existing compression algorithms are unable to operate on the encrypted data.  A block diagram of this is presented below.

In [1], the idea of reversing the order of these two operations was considered.  Surprisingly, they were able to show that swapping the order need not effect the performance of either the compression algorithm or the encryption algorithm.  When the encryption is a stream cipher (e.g. as a one time pad), then the same compression performance (to the entropy of the message source H(Message Source)) can be obtained and neither the information theoretic security [1]  nor complexity theory security [2] are effected.  A block diagram of the new proposed system is presented here.

Practical demonstrations of the compression of encrypted data is provided here.  Demo 1 presents a simple example.  For further depth, an example where the constraints of the system are strained is presented in Demo 2. 

References:

[1] M. Johnson, P. Ishwar, V. M. Prabhakaran, D. Schonberg, and K. Ramchandran, "On Compressing Encrypted Data," Signal Processing, IEEE Transactions on ,Volume: 52 , Issue: 10 , Oct. 2004, Pages 2992 - 3006. (pdf)

[2] M. Johnson, D. Wagner, and K. Ramchandran, "On Compressing Encrypted Data without the Encryption Key," Proceedings of The Theory of Cryptography Conference, (Cambridge, MA), February 2004. (pdf)

[3] P. Ishwar, V. M. Prabhakaran, and K. Ramchandran, "Compressing Encrypted Sources Using Side-Information Coding," Proceedings of the 2004 IEEE International Symposium on Information Theory (ISIT), Chicago, IL, June 2004. (ps)

[4] D. Schonberg, C. Yeo, S. C. Draper, and K. Ramchandran, "On Compression of Encrypted Images and Video Content," IEEE Transactions on Information Forensics and Security, Submitted for publication.

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This material is based upon work supported in part by the National Science Foundation under Grant No. 0325311.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.