Simple and Secure Image Encryption

Image Encryption is a wide area of research. Encryption basically deals with converting data or information from its original form to some other form that hides the information in it. The protection of image data from unauthorized access is important. Encryption is employed to increase the data security. The Encrypted Image is secure from any kind cryptanalysis. In the proposed work, the image to be encrypted is decomposed into 8X8 blocks, these blocks are transformed from the spatial domain to frequency domain by the DCT , Then, only selected DCT coefficients i.e the DCT coefficients correlated to the higher frequencies of the image block are encrypted. For encryption the DCT coefficients are xored with pseudorandom bit, Pseudorandom bit is generated by Non-Linear Shiftback Register. The bits generated by Non- Linear Shiftback Register cannot be predicted so cryptanalysis becomes difficult. To enhance the security further the unencrypted DCT coefficients are shuffled, since some information may also be stored in DCT coefficient correlating to lower frequency, While encrypting selected DCT coefficients alone will provide complete perceptual encryption, it would be possible for an attacker to gain information about the image from the other coefficients, especially in images that have a lot of edges.