Reversibility improved data hiding in encrypted images

• The proposed method is completely reversible. That is to say, no error happens in data extraction and image recovery step.
• The PSNR of decrypted image containing the embedded data is much higher for large payloads.
• The extraction and decryption processes are completely independent, which is much more applicable in applications.

A novel reversible data hiding technique in encrypted images is presented in this paper. Instead of embedding data in encrypted images directly, some pixels are estimated before encryption so that additional data can be embedded in the estimating errors. A benchmark encryption algorithm (e.g. AES) is applied to the rest pixels of the image and a special encryption scheme is designed to encrypt the estimating errors. Without the encryption key, one cannot get access to the original image. However, provided with the data hiding key only, he can embed in or extract from the encrypted image additional data without knowledge about the original image. Moreover, the data extraction and image recovery are free of errors for all images. Experiments demonstrate the feasibility and efficiency of the proposed method, especially in aspect of embedding rate versus Peak Signal-to-Noise Ratio (PSNR).