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Abstract
When it is desired to transmit redundant data over an insecure and bandwidth-constrained channel, it is customary to first compress the data and then encrypt it. In this paper, they investigated the novelty of reversing the order of these steps, i.e., first encrypting and then compressing, without compromising either the compression efficiency or the information-theoretic security. Although counterintuitive, they showed surprisingly that, through the use of coding with side information principles, this reversal of order is indeed possible in some settings of interest without loss of either optimal coding efficiency or perfect secrecy. They showed that in certain scenarios our scheme requires no more randomness in the encryption key than the conventional system where compression precedes encryption. In addition to proving the theoretical feasibility of this reversal of operations, they also described a system which implements compression of encrypted data. Consider the problem of transmitting redundant data over an insecure, bandwidthconstrained communications channel. It is desirable to both compress and encrypt the data. The traditional way to do this is to first compress the data to strip it of its redundancy followed by encryption of the compressed bit stream. The source is first compressed to its entropy rate using a standard source coder. Then, the compressed source is encrypted using one of the many widely available encryption technologies. At the receiver, decryption is performed first, followed by decompression.