Partial Image Encryption

Partial Image Encryption encrypts the huffman encoded high frequency coefficients in a jpg image file. The encryption is done in-place so the project can eventually be ported to a Windows kernel filter driver. Just encrypting the high level frequency coefficients serves to blur the image, but almost in an artistic way. The image contents are fully recognizable, but the details are pixelated or blurred. The general purpose of this program would be for securing images on the disk or in the cloud, available for searching but full resolution requiring a key to then access.

The high frequency coefficients are actually Huffman encoded. As such enough of them have to be spliced together in memory until a block is then available, encrypted, and then piece meal copied back in place.

Huffman encoding in jpg images uses control codes. The encryption can coincidentally produce a control code. Thus those are repeatedly encrypted until no control code, skipping preexisting control code runs.