Efficient encryption of compressed color images

An efficient, secure color image coder based on color set partitioning in hierarchical trees (C-SPIHT) compression and partial encryption is presented. Confidentiality of the image data is achieved by encrypting only the significance bits of individual wavelet coefficients for K iterations of the C-SPIHT algorithm. The use of a stream cipher and the encryption of a small number of bits keeps computational demands at a minimum and makes the technique suitable for hardware implementation. By varying K, the level of confidentiality vs. processing overhead can be controlled. It was found that using K = 2 achieved an adequate level of security for test images coded at 0.8 bpp, resulting in an average of only 0.33% of the coded image being encrypted.