An encoder calculates an entropy of at least a portion of a signal and
encodes the signal with the calculated entropy. A decoder decodes the
signal in order to recover the encoded entropy. The decoder may also
determine an entropy of the signal and may compare the entropy that it
determines to the decoded entropy. The decoder detects
compression/decompression based upon results from the comparison, and/or
the decoder prevents use of a device based upon results from the
comparison.