A detailed evaluation of format-compliant encryption methods for JPEG XR-compressed images

Abstract

JPEG XR is the most recent still image coding standard, and custom security features for this format are required for fast adoption of the standard. Format-compliant encryption schemes are important for many application scenarios but need to be highly customised to a specific recent format like JPEG XR. This paper proposes, discusses, and evaluates a set of format-compliant encryption methods for the JPEG XR standard: coefficient scan order permutation, sign bit encryption, transform-based encryption, random level shift encryption, index-based VLC encryption, and encrypting entire frequency bands are considered. All algorithms are thoroughly evaluated by discussing possible compression impact, by assessing visual security and cryptographic security, and by discussing applicability in real-world scenarios. Most techniques are found to be insecure and, in a cryptographic sense, have a limited range of applicability and cannot be applied to JPEG XR bitstreams in an efficient manner. Encrypting entire frequency bands is identified to be a good solution in case a weaker form of format compliance can be accepted.

To See or Not To See: Determining the Recognition Threshold of Encrypted Images

“…A Note on the Encryption: To describe the three encryption methods, [2,3,4], used would only clutter the paper without giving any new insight. It should suffice that the encryption strength ranges from a relatively high quality to a non recognizable quality, illustrated in Fig.…”

“…There are numerous SEnc encryption schemes, e.g., [1,2,3,4], and an important assessment is always that of quality and recognizability. It has been pointed out, [5], that the quality assessment is problematic since quality metrics are not usually built for such low quality material.…”

Visual Security Evaluation Based on SIFT Object Recognition

“…to alter the value of the DC coefficients by adding or subtracting random numbers which are derived from a key. To increase the impact of the encryption method on visual security we have recently suggested to apply RLS to all coefficients of a transform block, not only to its DC coefficient [1].…”

“…In JPEG XR the coefficients are grouped into three frequency bands, the DC-, the Lowpass-(LP) and Highpass (HP) band. In the experiment only the coefficients of the LP and HP band are subject to the permutation process [1]. Swapping of coefficients across frequency bands is not carried out.…”

“…In order to be able to discuss the exact notion of visual security, we need to distinguish distinct application scenarios of media encryption schemes [1]:…”