Compcrypt–Lightweight ANS-Based Compression and Encryption

Abstract

Compression is widely used in Internet applications to save communication time, bandwidth and storage. Recently invented by Jarek Duda asymmetric numeral system (ANS) offers an improved efficiency and a close to optimal compression. The ANS algorithm has been deployed by major IT companies such as Facebook, Google and Apple. Compression by itself does not provide any security (such as confidentiality or authentication of transmitted data). An obvious solution to this problem is an encryption of compressed bitstream. However, it requires two algorithms: one for compression and the other for encryption.In this work, we investigate natural properties of ANS that allow to incorporate authenticated encryption using as little cryptography as possible. We target low-level security communication and storage such as transmission of data from IoT devices/sensors. In particular, we propose three solutions for joint compression and encryption (compcrypt). The solutions offer different tradeoffs between security and efficiency assuming a slight compression deterioration. All of them use a pseudorandom bit generator (PRBG) based on lightweight stream ciphers. The first solution is close to original ANS and applies state jumps controlled by PRBG. The second one employs two copies of ANS, where compression is switched between the copies. The switch is controlled by a PRBG bit. The third compcrypt modifies the encoding function of ANS depending on PRBG bits. Security and efficiency of the proposed compcrypt algorithms are evaluated. The first compcrypt is the most efficient with a slight loss of compression quality. The second one consumes more storage but the loss of compression quality is negligible. The last compcrypt offers the best security but is the least efficient.

A Review of the Asymmetric Numeral System and Its Applications to Digital Images

“…There are cases where low-level security may be workable with the aid of other control mechanisms. For example, the distribution of art collections and the verification of medical images are under particular management rules, which is quite different from the communications scenario among IoT sensors or devices considered in [34]. We believe that ANS might still provide a useful jointly compressing and encrypting function for those applications.…”

“…According to the distributions of the source symbols and methods of realization, there are three variants of ANS [1][2][3][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] (follow the chronological sequence of publication dates):…”

“…It is well known that the probability of getting a successful frame synchronization is negligible even for short sequences of symbols and decreases exponentially with the number of compressed symbols. However, as analyzed in [34], plain ANS could only support applications with low-level security requirements. In the same writeup, Seyit Camtepe et al investigated the natural properties of ANS, allowing incorporation with authenticated encryption using as little cryptography as possible.…”

“…The third algorithm deploys encoding function evolution to enhance the obtained security level. The contributions of [34] boomed up the applicability of ANS in joint compression and encryption a lot.…”

“…As mentioned in [34], though, the randomness of the pure Avalanche effect-based encryption scheme is not enough to deal with high-level security applications. There are cases where low-level security may be workable with the aid of other control mechanisms.…”