Digital image scrambling for image coding systems

An image encryption system comprising

• an encryption buffer, and
• at least one encryption subsystem operating on transform data stored in the encryption buffer, the encryption subsystem selected from the group of subsystems consisting of:
• a sign bit scrambler that accepts a space-frequency transform coefficient map having signed coefficients, and scrambles the sign bits of the coefficients;
• a block shuffler that accepts a space-frequency transform coefficient map and shuffles two-dimensional coefficient blocks to pseudorandom locations in the map;
• a block rotator that accepts a space-frequency transform coefficient map and rotates two-dimensional coefficient blocks to pseudorandom orientations;
• and
• a coefficient shuffler that accepts a space-frequency transform coefficient map and shuffles coefficients from a two-dimensional group of coefficients from a spatial frequency subband to pseudorandom locations within the group.

An encrypted-image decryption system comprising

• a decryption buffer, and
• at least one decryption subsystem operating on encrypted transform data stored in the decryption buffer, the decryption subsystem selected from the group of subsystems consisting of:
• a sign bit descrambler that accepts a space-frequency transform coefficient map and/or a motion vector array having encrypted sign bits, and applies a decryption key to the encrypted sign bits to recreate the original sign bits;
• a block deshuffler that accepts a space-frequency transform coefficient map having shuffled two-dimensional coefficient blocks, and applies a decryption key to the coefficient block pattern to restore the blocks to their original locations;
• a block derotator that accepts a space-frequency transform coefficient map having rotated two-dimensional coefficient blocks, and applies a decryption key to the coefficient block pattern to restore the blocks to their original orientations;
• and
• a coefficient deshuffler that accepts a space-frequency transform coefficient map having a shuffled two-dimensional group of coefficients from a spatial frequency subband, and applies a decryption key to the coefficient pattern to restore the coefficients in the group to their original locations.