Chaos-based partial encryption of SPIHT coded color images

• We find six bit types obtained by Color-SPIHT (CSPIHT) by modifying the bit values.
• We analyze the effects of various bit types and find the most important one.
• Each important bit encrypted by PWLCM diffuses to the subsequent encryption bits.
• Extensive experiments and analysis are done in order to verify the encryption effect.
• The scheme has less computational amount and scalability property of the encoder.

An embedded partial encryption technique of compressed color images based on chaos is proposed. Modifying the bit values of different types which are obtained by Color-SPIHT (CSPIHT) compression algorithm leads to varying degradation degree of retrieved images. This signifies that the six bit types have various contributions to decoding. As long as the most important bits that have the greatest contribution are encrypted, we can ensure no information leaking out and minimal computation. The piecewise linear chaotic map (PWLCM) is appropriate for generating random number sequence used in proposed cryptosystem for its perfect ergodicity and confusion. Thorough performance and security analysis as regards to diverse evaluation metrics ascertains that the scheme has less computational amount than 0.49%, resists against common cryptanalytic attacks, and preserves the scalability property of the encoder.